SJ23 Tech Tip E01, (Updated 2021-08-10) Bob Schimmel


Power up with Solar Energy - Generating, Regulating & Storing Electricity.

     SECTION 1 - GENERATE POWER - Panel Types, Panel Location, Rigid Panels, Hail Protection for Rigid Panels, Temp Panel, Flexible Panel.
     SECTION 2 - REGULATE POWER - Charge Controllers, PWM Controller, MPPT Controller, RFI & Damaging Voltage Spikes.
     SECTION 3 - STORE POWER - Battery, Dual Batteries, Discharge Protection.
The bottom line.

(To distribute & use electricity, go to Tech Tip E02). 

CAUTION - It is important to note that this is a floating ground system with no connection for shore power.  However, once the outboard leg touches water it should be considered a grounded system since the negative of the battery is connected to the frame of the outboard.  This must be taken into consideration when refuelling at a fuel dock or tied to a marina dock equipped with AC power.

The nice thing about a solar panel is that it can charge a battery without noise or smelly fumes, so it's definitely the environmental thing to do.  However, it still requires oil to make a panel, but let's set that aside for now.  The general idea here is to make Panache self sufficient for electrical power since there is no dock power on any dock in Alberta and the run time of my outboard is not sufficient to maintain the battery.  So .......

There are three main components of a solar charging system; the solar panel, a solar charge controller and the RV battery to store the juice and operate appliances from.  If the components are sized correctly to match the electrical load then you can expect a five year service life from the battery as opposed to two or three years.  It's not uncommon to extend the battery life 50%.  If the hardware and wiring is installed and configured correctly you can expect very low maintenance with dependable power.  However, all systems require occasional maintenance; wash the panel, clean the battery top, check the electrolyte, torque & lube the electrical connections once a year, and monitor the battery charging voltage/current regularly.  The last one verifies the overall system health if you know how much maintenance current your system requires.  You'll learn this with experience. 


SOLAR PANEL TYPES - As of the early 1990s there were two types of solar panels, monocrystalline (rigid) or amorphous (rigid or flexible).  Back then a solar panel was about 10-15% efficient in converting sunlight to electricity.  By 2016 the efficiency was up to 21%.  Some of the more expensive type are constructed with a bypass diode around each cell to be shade tolerant.  If a cell is shaded (not generating voltage) then the power from the illuminated cells (generating voltage) bypass the shaded cell via a diode.  In other words, with one cell switched off the output voltage drops only slightly because the rest keep generating, resulting in more power generated during a day.  Perfect for a sailboat installation with lines casting a moving shadow over the panel.  On a panel that is not equipped with bypass diodes, the output voltage typically drops to half the illuminated voltage.

A monocrystalline solar panel generates the most output power, making it the technology of choice for a boat.  This panel derives its name from the fact that wafer thin slices of black crystals are attached to a sheet in squares.  During panel assembly the crystals are wired together manually and sandwiched between sheets of tempered glass, Lexan or laminated flexible sheet material.  This panel is expensive since it is labour intensive to construct but retains its output performance for life and is therefore the most cost effective.

A polycrystalline solar panel is less efficient than a monocrystalline but costs less.  They are light blue in colour.

An amorphous silicon solar panel (thin film) consists of a thin coating of brown silicon 'painted' on the back of tempered glass or Lexan.  The silicon coating is applied in narrow ribbons for maximum coverage.  The coating is then protected by a backing sheet and sealed at the perimeter with a hermetic sealant and rigid moulding.  If the seal at the perimeter of the two sheets breaks, the wiring corrodes and the panel will soon fail.  They are the least expensive panel to manufacture, being machine produced but loose their emission with time and so has a limited life span.  Its OK to install on a sailboat provided you can add hail protection.

A rigid panel is very delicate so don't ever step on it as it will break, rendering it useless as you pollute the air with obscenities.  Oh well, you can always take it apart to find out what makes it tick!  A flexible panel on the other hand, is very robust as it can usually be stepped on, doesn't leak and can conform to the shape of the deck.  For all out durability you can't match a flexible panel but you pay extra for this robust construction.  At one time all flexible panels were amorphous silicone.  Now monocrystalline flexible panels incorporate very tiny cut crystals, small enough to survive the bending radius of the panel.  This way you have the best of both worlds, flex, strength, power output with long life.  They are the best choice for a sailboat.   TOP

SOLAR PANEL LOCATION - There are several parts to a successful installation:

  1. The very first criteria is that the panel MUST fit in the desired location.  Too big is definitely out of the question.
  2. The mechanical mounting MUST work in all weather conditions.
  3. The desired location should receive lots of exposure to the sun, regardless of which way the boat is pointed.  This is important since even the shadow from a line across the panel will reduce the output power by ~40%, unless its a shade tolerant panel
  4. The panel should be installed away from foot traffic, unless its a flexible panel rated for occasional foot traffic.  Unused deck space is scarce on a sailboat which is where a flexible panel excels.  Besides being strong enough to step on, they can usually withstand hail.
  5. Multiple panels create redundancy.  A panel on either side of the deck generally ensures that at least one of them provides charging current.  Half the charging current is better than none. 
  6. A small panel is easier to install than a large panel.
  7. A panel installed on a dodger, bimini or arch can charge a battery very quickly due to the excellent exposure and can operate cooler.  It can also provide shade for the carbon based life forms below it!  A flexible panel can be secured up there by lacing, zippers, snaps or sometimes sewn to the cloth.  This makes it easy to live with.

If your boat doesn't have a dodger, bimini or arch then the least interfering permanent location on a SJ23 is on the pushpit as shown below.  I rejected this for Panache due to the gusty winds in the anchorage.  My criteria is that the solar panels have to stand up to whatever weather blows through an exposed anchorage, be easy to remove or tilt, survive hail and lastly work while sailing.  But I don't see these two having a problem with their panel and they look like they're having a good time?  The hardware to install a panel on the pushpit has greatly improved over the years so its worth considering again.  All the following installations require creativity to run the wires.

  1. ON TOP OF THE SLIDING HATCH A solar panel in this location is clear of most deck work.  Long ago I made it a practice to NOT step on the sliding hatch so installed a rigid panel here.  A second panel was added to increase the charging current from .5A to 1A.  At least one of the two panels receives sunlight most of the time.  They charge while sailing; an important consideration if you intend to operate an electric autopilot for any length of time.  This configuration gave me sufficient power at the time and I no longer concerned myself with battery drain.  Shown below are the panels mounted on the original wood feet glued to the hatch with Sikaflex.  The panels are at a slight slope so most of the dust washes off.  Every once in a while I gave them a wipe.  They are easy to store for end of season by removing the black center strip.  My next version will be a flexible panel I can step on.
  2. CLIPPED TO THE PUSHPIT - I like this spot more and more everyday because the panel is out of the way.  I'm considering it for a third panel on Panache.  A friend has two articulating panels on his pushpit and I'm envious of the charging performance. 
  3. MOUNTED ON THE PUSHPIT - Here is another SJ23 with a pushpit mounted solar panel.
  4. ABOVE THE COCKPIT ON AN ARCH, BIMINI OR DODGER - I like these locations because you get both shade and power from the panel while under way.  No moving parts, an extra hand hold, a place to hang things, clip the back of an awning to, mount cockpit lights and best of all, out of the way.  Problem is, its a lot of work to build an arch.
  5. SOME TEMPORARY LOCATIONS; These locations work well when the boat is stationary in a slip as you have the option of choosing one that is illuminated.  Failing this, a small articulating panel is beneficial as it is can be pointed to the sun for maximum illumination.  Watch your ammeter as you rotate the panel and lock it at maximum current.  This is very useful to recharge a low battery at anchor. 
    1. Hang from the companionway drop boards.
    2. Hang from a lifeline.
    3. Hang from the pushpit.
    4. Hang from a cabin grab rail. 
    5. Rest against the cockpit backrest.
    6. Lay on the cockpit sole.

Solar panel installations I have seen but rejected for Panache.

  1. ON THE FORWARD HATCH - Probably the least interfering location on a SJ23, but I consider covering the acrylic hatch sacrilegious.  After all, you may as well use a piece of plywood for a hatch and never look at the stars from the forward berth!  I did make a concession for a Nicro vent though as I definitely need ventilation and I can look around it! 
  2. ON THE DECK JUST FORWARD OF THE SLIDING HATCHThis spot is fairly well illuminated and is out of the way when sailing.  With a thin panel the sliding hatch can pass over it.  While you could install a window in the hatch to pass light and restore some output power when the hatch is open Gene doesn't recommend it since it would weaken the sliding hatch too much.    TOP

Over the years I have "experimented" with the following locations.

  1. ON THE DECK BEHIND THE MAST (Panache version 1, 2002) Panache's original single rigid solar panel was installed in a wood frame mounted flat on the deck behind the mast.  This spot is mostly out of the way when sailing but is often shaded by the mast.  When the boat pitched a lot I quickly discovered it was in the way for reefing or covering the mainsail. 
  2. ON THE SLIDING HATCH (Panache version 2, 2003) - With the addition of my mechanical boom vang the shadow over the panel reduced the output power too much so I moved it to the top of the sliding hatch where it received good illumination and was out of the way of foot traffic.  It worked OK but was soon replaced with version 3 to double the output. 

    TWO RIGID SOLAR PANELS on the SLIDING HATCH (Panache version 3, 2003).
    (regulated by several types of linear regulators and finally a Morningstar SG4 PWM controller).

    The two rigid solar panels on Panache's sliding hatch were mounted on wood feet glued to the hatch.  The panels were connected to the boat wire harness below each panel and wired in parallel under the center support.  The wire harness went through a sealed hole at the center of the hatch, then to the aft starboard corner where 2' of slack cable was loosely secured with a nylon cable strap.  From there it was plugged into the boat wiring harness at the top of the companionway. 

    Fig 1 - Solar panel wood mounting brackets showing electrical connectors for each panel.  This was prior to installing hail guard covers.

    Fig 2 - Power cable tightens to almost straight when hatch is fully open.

    Fig 3 - With the hatch closed the power cable hangs in a loop.  This loop is never in the way, despite what it looks like. 

    The 2' of slack cable accommodates the movement of the sliding hatch.  When the hatch is closed the loop hangs at the aft end of the cabin where it is out of the way.  When the hatch is open the cable is stretched straight along the underside of the hatch, also out of the way.  All the wiring is connectorized to remove the solar panels for winter storage or to service the sliding hatch.  To comply to standards, the panel positive output is the female side of the connector.  I haven't figured out a simpler, more effective technique and it hasn't failed, yet.  TOP


HAIL PROTECTION:  Our lake gets some very nasty thunder storms with golf ball size hail in early to mid summer and I didn't relish the prospect of loosing another panel to those icy demons.   I held off installing hail protection for many years, thinking that overheating or filtering light would reduce the charging performance.  It was time to do something about this problem. 
A panel will heat up with exposure to the sun.  As the temperature increases the output power is reduced at about .258 %/0C.  The output of a panel is rated at 250C (770F) which will drop about 20% at 300C (900F).  Heat is one of the greatest killers of electronics.  For that reason there should be an air gap behind the panel to cool it or install it against a cooling heat sink.  If the panel is installed at a slope it is self cleaning in the rain, self cooling in the sun and can achieve maximum output.  The slope can also prevent water from creeping into the edge of a rigid panel, corroding the internal wiring.
  These are the major reasons why I did not install a hail cover over the panels for so many years.  Then my experiment proved the Lexan cover did not reduce the light and there was only a slight temperature increase.  So..... 

NEW MOUNTS & HAIL PROTECTION for RIGID PANELS (Panache version 4, 2010)
(regulated by a Morningstar SG4 PWM controller)

I fabricated 2 removable Lexan covers for the rigid solar panels.  While there are solar panels today that a person can step on and withstand hail, the mounting hardware for my rigid panels was in place so I saw little point in replacing them.  The previous wood corner posts were replaced with the slightly taller UHMW posts shown below.  The solar panels fit in the bottom slot and the 1/8" thick Lexan sheet fits in the top slot.  If I had a C&C machine these posts would have been constructed as one piece, but since I didn't, I made them in layers.  Each layer was cut to exact dimensions, then stacked to make the corner posts you see here.  The top of each post was capped with an aluminum plate (2" square with a corner cut out) to squeeze the layers together uniformly.  This technique worked very well.  Each post is through bolted to the hatch and sealed to the top with butyl rubber.  To secure the Lexan sheet at the middle support I stacked an aluminum spacer (slightly thicker than the Lexan) and an aluminum cap on top of the middle support to create an upper slot.  This last part was amazingly simple and effective.  The Lexan has withstood all winds and hail. 

The outside corner of the solar panel fits in the lower slot of each post and the center rests in the slot of the middle support.

Solar panels in place ready for the aluminum cap to go over the middle support. 
Note the use of flat head screws on the corner posts so they are smooth on top.
The Lexan cover fits in the upper slot of each post.
Lexan covers snapped in place to protect the solar panels. 

The fabrication was done, the hardware was installed and the panels produced power again.  And none too soon because another hail storm was only a few hours away.  Time to get off the boat.  I'm happy to report that the protective Lexan covers stand up to the hail and can be snapped into the corner posts place without tools.  To cover a solar panel I flex the Lexan up till it pops under the center cap.  Removal is just as easy.  This makes it quick and easy to clean a panel.  As previously tested, there is no loss of charge current due to the transparency of the Lexan.  The Lexan covered solar panels operate at the same temperature as if they were fully exposed.   TOP

There were many times during my 2020 modifications when I needed extra power at the slip so I added a large portable solar panel resting against the side of the cockpit.  Later I discovered that the panel received full illumination for at least the first 4 hours of the day and is better protected from the wind by standing against the companionway.  This reflects the experience of living on board.  Once I started work I moved the panel to the side of the cockpit for 2 more hours of light, albeit decreasing output. 

TEMPORARY RIGID SOLAR PANEL (Panache version 5, 2020)
(This panel along with the 2 on the hatch were regulated with a Renogy MPPT controller)
The Renogy "experiment" did not go well.

- The back of this panel is protected with 1/4" plywood coated with Sikkens Cetol.  While the wind never knocked it over, it is now secured with a line (not shown) tied through the plywood when it stands against the companionway.  Fortunately it can just fit inside the starboard locker (Tech Tip B19) between the drop boards and the fenders (31.5x13)".
- The panel is wired in parallel to the two panels on the sliding hatch using a third input cable, all connected at Bkr 12.  The combined flow of electrons continue their merry ole journey to the battery ready for the next demand of juice. 

NOTE - While moored in my slip I quickly came to the realization that several small panels located in different places and/or pointed in different directions stand a better chance of charging at full capacity than a single large panel.  This has to do with a shadow spending less time blocking a small panel.  For this reason I replaced the two rigid panels on the sliding hatch with two 35W shade tolerant flexible panels.  If extra power is required I may install an articulating panel on the pushpit.   TOP


FLEXIBLE SOLAR PANELS (Panache version 6, 2021) - The dimensions of the gritty none-slip area on the sliding hatch is (31 x 25)" which is perfect to install a couple of (15x24)" flexible panels.  So during the winter of 2021 the 2 thin film rigid solar panels on the sliding hatch were replaced with 2 Go Power Flex-35 monocrystalline flexible panels.  The two 35W panels cover ~90% of the hatch and are equipped with bypass diodes to maximize efficiency.  It was too difficult to make the panels removable so instead I fashioned a 1/8" thick plywood panel to cover the panels for stepping the mast or working in that area.  Covering the panels is the simpler solution.  It's cheap insurance and I hate when things get thumped for a minor foot slip. 

The solar panel wires were run under the hatch for weather protection and cosmetics.  A terminal strip is installed on the underside of the hatch to connect the panels in parallel or to install blocking diodes, should they prove necessary.  While I experimented at home to determine that diodes are not required, reality onboard may be different.  Go figure!

The first job was to remove the old hardware that supported the rigid solar panels for ~20 years and restore the hatch.  Clark never intended hardware to be installed on the cored sliding hatch so to protect the wood core I glued the feet with Sikaflex.  Its amazing how well the Sikaflex held but the chisel and hammer won in the end.  Some acetone and a tiny wire brush on my Dremel Tool removed the stubborn stuff deep from in the non-skid.  A drill bit removed the Sikaflex inside the screw holes.  Next, the screw holes were filled and sealed with G/Flex epoxy.  Painting the hatch was the last step to protect the epoxy and restore the water tightness.  Time to let it cure.

(Two Go Power Flex-35 solar panels regulated by a Genasun GV-10-Pb-12V MPPT charge controller).

- I decided to position the flexible panels with the cables at the forward end of the hatch where they can go through the top with an easy, low strain, curve.  I can't emphasize how important that will be over the years with exposure to the sun.  Orienting the solar panels cables as such keeps the cockpit end of the hatch clear where I "tend" to lean against it with the heel of the boat.  It is a comfortable place to stand with a nice motion in big waves. 
- The panels are fastened to the top of the SJ23 hatch with screws through the SS corner grommets.  I drilled two additional holes through the long sides of the panel to prevent them from fluttering in a side breeze.  Fluttering is a great way to age a panel quickly!  The 1/2" thick hatch has a balsa core so the screw mounting and cable entry holes were sealed with G/Flex epoxy.  The holes were drilled oversize, filled with epoxy, the hardened epoxy was drilled out to pass the cables, then sealed with Sikaflex.  I have experienced no leaks.  See Tech Tip G08 for the technique. 

Fig 1 - Sizing up the hatch for two new flexible solar panels.  They are a perfect fit!

Fig 2 - The previous rigid solar panel mounting hardware was removed and the hatch restored by filling the screw holes with epoxy.  The new flexible panel mounting and the cable entry holes were also sealed with epoxy to protect the balsa core.  Afterwards the surface was painted with 3 coats of acrylic.

The two cable entry holes shown in Fig 2 were drilled at a shallow 150 using a Pocket Hole Drill Guide clamped to position and support the bit.  Both holes were lined with epoxy to protect the balsa core and to restore the strength.  The non-skid on the hatch was painted white to protect the epoxy and to match the colour of the solar panels.  The underside of the hatch was also painted white to brighten the cabin and make it easier to clean.  With cables in place (Fig 4) the holes were sealed with silicon sealant and capped with a custom fabricated UHMW clam shell for support and protection.

A final dry fit on Panache confirmed that the cable bundle and terminal strip can just slide freely over the sill through the full sliding distance of the hatch.  Better to be safe than sorry.  The gap between the bottom of the hatch and the top of the sill is 3/4" if you install a 1/8" thick UHMW glider under the hatch rails.  See Tech Tip B04

Fig 3 - A dry fit of the #10 wires with a natural curve through the entry holes. 

Fig 4 - The custom UHMW cap over the cables form the top half of the entry hole and help to guide and seal the cables.  The #10 cable was formed to this curve to eliminate long term strain.  The orange tagged cable is the positive one.

- Two hole power lugs in Fig 5 are used on the terminal strip for a connection that doesn't loosen, ensuring a zero Ohm connection.  The vacant terminals are to configure the panels for 2 Schottky diodes, should they become necessary. 
- This is also where the 28" loop of flexible wires connect to the boat wiring harness on the starboard bulkhead.  The wire loop is covered in a nylon sheath to organize the conductors as a unit.  I also replaced the previous smaller boat wiring harness with larger gauge (#10) wire to minimize loss, routing it further away from the VHF radio.

Fig 5 - The cable harness is secured in place and sealed at the entry holes.  The flexible cable to the boat harness was secured by a cable clamp next to the terminal strip.  The cable bundle and terminal strip just cleared over the sill. 

Fig 6 - Since the solar panels are not removable thin plywood will protect them when I work on the mast.  This is a prototype to test feasibility.

- On a sunny February day I stood the Flex-35 solar panels on my South facing deck and connected them to the AGM battery via a Morningstar SunSaver MPPT charge controller.  The sun was about 200 above the horizon with thin clouds scooting by.  The panels charged the battery at 1-2A during overcast and slightly over 3A during the brief exposure of full sun.  Pretty good considering the low angle of the sun.  The current dropped off to 1A during the overcast.  Despite this, the battery reached absorption mode after 2 hours on the first day and reached maintenance mode after 2 hours on the second day.  These solar panels do not require full sun.  Their sunlight "acceptance angle" is quite wide and can generate power even on a cloudy day.  The performance improvement going from 5W to 70W is impressive. 

Fig 7 - Top view of solar panels installed on Panache.  Click here for a different view.  I also painted the rails white. 


Fig 8 - Flex cable "compressed" with hatch closed.


Fig 9 - Flex cable extended with hatch open.  In either case the flex cable is out of the way.  Its now soft with the sheath covering the wires.



HINT - To test the operation of each solar panel, darken one panel with a towel and view the charge current and voltage of the exposed panel on the solar meter.  Then cover the other panel and repeat the measurement.  Since these Go Power Flex-35 panels are equipped with bypass diodes, pulling the towel back slowly reveals the operation of each segment of the panel.

PARTS - Go Power Flex-35 monocrystalline panel, Schottky diodes,

"This installation demanded perfection since the skipper has been known to steer Panache by the edge of the sliding hatch.  Therefore, the panels were centered on the hatch, parallel with the center line of the boat.  This is a tad difficult since the shape of the none-skid on the sliding hatch is a trapezoid.  This work was painstakingly slow; laying out hardware, measuring, determining pros & cons, contemplating (tick, tick), reaching a final design, measure again, prep, paint, work a bit, epoxy, wait, scrape a bit, paint, repeat, etc.  Actually it was a perfect "time consuming" project for the first COVID19 winter."   TOP

(Regulating power is about protecting the battery and appliances)

LINEAR REGULATOR (~1980s onward) - A regulator must be used to prevent over charging a battery, especially a flooded battery where the electrolyte can be gassed off.  Up till the 1990s the only choice was a linear regulator.  The silicon blocking diodes D1 & D2 (both diagrams) were required to prevent discharging the battery at night or to steer the charging current to the battery.  Today the one way path for charge current is accomplished within the electronics of a solar charge controller.

Panache originally had a shunt regulator and I seriously considered a series regulator, thinking it to be superior.  I soon learned the difference is negligible.  This argument can probably be won by the same person who can argue politics over religion!  There are three problems with a linear regulator; it is barely functional with the shade & weather variables on a moving boat, it applies very little voltage to the battery when the light is weak and the external 1N4007 silicon blocking diodes drop the voltage to the battery too much.  So I abandoned my shunt regulator in favour of a MorningStar SunGuard SG-4 PWM charge controller.

A solar "charge controller" is the marketing term used today for what was initially called a "smart" regulator.  The electronics is significantly improved over the original linear regulators to maintain some charge current during the low light of dusk, dawn or shadow.  Some charge controllers have a low voltage disconnect (LVD) feature to cut off the load when the battery voltage is critically low, protecting the battery from permanent discharge damage.  Given equal operating environments, a charge controller easily out performs a linear regulator. 

SOLAR PANELS WIRED IN PARALLEL WITH BLOCKING DIODE - The rigging on a sailboat has a habit of blocking sunlight to a solar panel as the boat heels one way and then another.  The hull also turns relative to the sun, thereby casting a moving shadow over the panels.  For these reasons I installed a solar panel on either side of Panache's sliding hatch, so at least one panel is illuminated.  They are wired in parallel for maximum charge to the battery and limit Voc to the controller. 
NOTE - One panel produced less power than the other which revealed a silicon blocking diode I forgot to remove from the external wiring harness.  Removing it increased the panel output .6V, resulting in a slightly more charge.  The battery voltage increased from 13.1V to 13.9V as the panels produced equal power.

  1. Panel with Blocking Diode - If your panels are equipped with an internal blocking diode (after ~1990s) then you can connect them in parallel sending the combined output to the charge controller input.  All the power will go to the battery.  DO NOT exceed the input power rating of a PWM controller.  It is OK to exceed the input power of an MPPT controller provided you don't exceed Voc.  This was Panache's configuration with the two rigid panels on the sliding hatch. 

    (How to Test a Solar Panel for an Internal Blocking Diode - Other than reading the panel documentation or physically seeing the diode, you can use a variable DC power supply e/w current limiting to test your solar panel for the presence of an internal diode.  Darken the panel so the output voltage is 0V as measured with a voltmeter.  Then connect the power supply to the solar panel wires, (+ to + and - to -) with current limiting set to ~100 MA.  Slowly turn up the power supply voltage to 15V while monitoring the current.  If no current flows (only uamps = no current) a diode is present.  If current flows, the panel needs an external Schottky diode wired in series to block current from the other panel.  Never having seen this current I think it would be in the low milliamp range.

  2. Panel Without Blocking Diode - If your old (~before 1990s) panels are NOT equipped with an internal blocking diode then you must add an external Schottky diode in series with each to prevent the shaded panel (lower output voltage) from absorbing the power from the illuminated panel (higher output voltage).  Wire the combined outputs to the charge controller input as shown at right.  All the power will go to the battery.
    - Select a
    Schottky diode that can handle about 50% more current than the panel can generate.  It must also have a peak inverse voltage (PIV) of >30V.  Its best to mount it on a terminal strip where it can also radiate heat.  Hanging a diode "mid-air" on a wire is just asking for trouble.

  3. A Charge Controller for each Panel - The best system performance (most expensive but with redundancy) is a separate charge controller for each panel with the outputs connected in parallel.  No blocking diodes are required as the controllers perform that function.  The combined power will go to the battery.

  4. Solar Panel(s) with Outboard Generator - A slight variation on this configuration is an outboard motor generator connected in parallel to a single or dual solar panels.  The generator consists of a magnet in the flywheel spinning by a stationery pickup coil.  The coil has a diode in series with it to produce positive pulses (a half wave rectifier) of power, generating ~(5-6)A current.  Connecting the generator in parallel to the solar panel(s) is not a problem since the generator diode also blocks current generated by the solar panels.  The solar controller is the blocking diode for the solar panel.  No external diodes are required and the combined power will go to the battery.   TOP


SOLAR CHARGE CONTROLLER (PWM or MPPT) - Very much superior to a linear regulator are two types of solar charge controllers; one type uses Pulse Width Modulation (PWM) and the other uses Maximum Power Point Tracking (MPPT). 

PWM - During bulk charging a PWM charge controller applies all the solar panel voltage directly to the battery.  In absorption and maintenance modes a PWM charge controller is essentially a DC to DC converter that charges a large capacitor which is then discharged into the battery in pulses.  This is the mode when a PWM controller has gain.  It is about 50% more efficient than a linear regulator. 
MPPT - An MPPT charge controller is about 15-20% more efficient than a PWM controller, achieving this by continually measuring (tracking) the maximum power point (E & I) of the solar panel to be applied to the battery.  This is a clever technique to transfer the most power, during all 3 charge modes listed below.  Get to know them intimately. 
With either of the controllers, the output is adjusted automatically in proportion to the solar panel illumination (shade, angle & temperature),
the temperature of the controller & battery, the battery voltage and finally the wiring. 


(good technology for sunny weather)
(performs better than PWM, even in cloudy weather)
This mode charges the battery to ~(80-90)%.
The output power of the controller is constant, passing whatever power the panel produces.  This is the mode in which PWM gains nothing. 
- During low morning and evening light it continues to charge extending the charge time, albeit slower.
This mode charges the battery to ~(80-90)%.
The controller continually measures (tracking) the maximum power point of the solar panel to create a current gain, charging the battery to the limiting voltage of the controller (set by the type of battery).  This is the mode in which MPPT gains over PWM.
This mode charges the battery to ~(90-98)%.
As the battery voltage rises to the controller limiting voltage, the output changes to DC pulses.  If the charge controller is installed next to the battery the internal temperature compensation can reduce the output to protect the battery.
This mode charges battery to ~(90-98)%.
As the battery voltage rises to the limiting voltage of the
controller, the output is proportionally reduced.  The output is also limited by the temperature of the controller and battery.  There is little current gain in this mode.
When the battery is at full charge ~(98-100)%, the controller output is further reduced to a trickle by reducing the pulse width to maintain battery charge. 
When the battery is at full charge ~(98-100)%, the controller output is further reduced to a trickle to maintain battery charge.
The PWM pulsing action during the absorption and maintenance modes applied to a flooded battery minimize plate sulphation and prevent the electrolyte from gassing off.  This leads to long battery life and health. 
If an MPPT charge controller is configured to charge a liquid filled battery most can automatically perform a monthly equalize charge across all cells.  Other battery types are also charged for long life and health.

Beyond this, the description of solar panels and charge controllers gets very technical and is beyond the scope of this Tech Tip.  It helps if you understand Ohm's Law, I=E/R.  For a more detailed description of pulse width or power point track charging, go the Morningstar web site.  Learning is a daily exercise that tickles the brain!


PWM SOLAR CHARGE CONTROLLER (2004) - The SunGuard SG-4 PWM charge controller manufactured by Morningstar has an electrical efficiency ~50% greater than a linear regulator.  That's like adding a second solar panel and it costs about $30 Can, (2004).  Good bye linear regulator.  The output is pre-set to 14.1 VDC which is optimized for a flooded, gel or sealed/AGM battery.  It is internally temperature compensated to adjust the output voltage which is OK if it is installed next to the battery.  These features make the SG-4 ideal for a pocket cruiser like a SJ23.  Given the electrical performance, waterproof packaging and reasonable cost I installed an SG-4 controller in 2005 and have had zero issues with it. 
PS: I was considering upgrading to the SunSaver MPPT controller until
I removed the external blocking diodes shown in the diagrams above.  Turns out they were redundant since my rigid solar panels were equipped with an internal blocking diode.  The battery voltage increased .6V which made me a happy camper.  The SG-4 is equipped with an internal Mosfet that is far more efficient and doesn't reduce the charging voltage to the battery.

  • SIZE - About the size of a 2" cube.

  • TEMPERATURE COMPENSATION - Internal.  For optimal charging locate the controller adjacent to the battery to "measure" battery temperature.  Operating range -40C to 60C.

  • CHARGE RATING - 4.5A input from a 12V solar array.  It can handle 64W total array output to charge a 12V battery. 
    DO NOT exceed the input rating of 30 Voc.

  • EQUALIZE CHARGE - Cannot equalize charge a battery.

  • BATTERY SELECTION - The output voltage charge curve is a compromise setting for most battery types.

  • EFFICIENCY - About 75-80%.

  • CONNECTION - The controller has 4 wires; 2 for solar array input, 2 for battery output.  Ground connection is negative battery.

  • INVERTER - Connect an AC inverter input directly to the battery.  The surge current during start up is too high for a charge controller.

  • Also check out the section on Electrical "Noise" reduction.

PRIMARY BUSS BARS - When I acquired an AGM battery I thought it high time to clean up the hickety potch wiring to the battery under the settee.  This is when I fabricated the primary buss bars for Panache.  Its quite an improvement and a bit of overkill for such a small boat but the electricity doesn't know that!  You can read more about this in Tech Tip E02.


PANACHE CHARGE WIRING with PWM CONTROLLER (2016) - In the diagram below (top view) the DC pulses originating from the SG-4 controller are fed directly to the battery via short, low impedance wires.  This is the desired wiring configuration for a single battery.  The ferrite beads completely attenuate the DC pulses sent to the power panel wires, ensuring clean DC power for VHF and AM/FM radios. 

  • The A PWM charge controller must be connected directly to the battery and physically close to it so the impedance of the output wires does not attenuate the high frequency charge pulses (PWM).  It should also be installed physically close to the battery so it senses the same temperature as the battery.  Both of these ensure the highest possible charge efficiency while protecting the battery. 
    NOTE - So DO NOT connect the SG-4 controller at the power distribution panel.  Doing so will apply the DC pulses to the boat's wiring harness and the "noise" will be heard on the VHF, AM/FM radio, or other sound system, making them almost unusable due to electrical noise.  The "PWM noise" sounds similar to ignition noise from an outboard engine operating at a constant RPM.  So, assuming your engine didn't radiate ignition "noise" before you installed the controller, a constant pulse rate after the installation is the telltale sign the interfering signal is coming from the controller via the wiring. 
    The solution is to install a ferrite RF noise suppressor bead over each wire that feeds power into the boat's electrical system as shown above.  Most ferrite beads do an excellent job of attenuating PWM & RF interference signals on a wire.  It is usually best to install a ferrite bead close to the
    signal source; battery or battery buss bar.  In an extreme case you may have to install several beads is series or wrap the wire several times through the same bead. 

  • You can find an inexpensive source of ferrite beads in the cable bin at your local electronics recycle centre.  That "bump" on the end of a computer power cable is a ferrite bead.  Cut the cable off at either end of the bead and pull the cable out the hole.  Voila a useable ferrite bead. 

  • CONCLUSION - If you consider the variable light conditions on a moving sailboat, a PWM solar charge controller is an efficient device to charge a battery since it can still charge during low light, is dynamically regulated in proportion to sunlight, the electrolyte does not "boil" off and the pulsing output removes any sulphate crystals from the plates of a flooded battery.  For more detail info on pulse charging technology see Tech Tip E04.  


MPPT SOLAR CHARGE CONTROLLER (2020) - When designing the charging system of an SJ23 the charge controller should be considered first since it relates to system sizing and protects the costly battery by charging it correctly.  Problem is, an MPPT charge controller is a pricey component for a small electrical system like on an SJ23.  It's one of the reasons why I stayed with a PWM charge controller for so many years.  Then in 2020 someone offered me a large solar panel that I just couldn't refuse.  Since the input current had the potential to exceed the 4.5A limit of my PWM charge controller it was time for an upgrade.  So which charge controller to select?

(Either of these charge controllers is an excellent choice for an SJ23 as both are fast tracking and neither transmits RFI)

GENASUN GV-10-Pb-12V - This 10A MPPT charge controller does NOT transmit RFI, is extremely fast tracking, has only 0.9MA of self consumption current, and can recover a dead battery.  It was installed on Panache in Spring 2021 and is wired as per diagram below.
Order from GENASUN Canada  10 year warranty.

MORNINGSTAR MPPT SunSaver - This 15A MPPT charge controller does NOT transmit RFI, is fast tracking and has LVD.  The low voltage disconnect is a feature that is just a tad important if you have electric start with a single battery.
Order from an authorized solar supply store.  5 year warranty.

SIZE - (5.5 x 2.5 x 1.2)".

SIZE - (6 x 2.5 x 1)".

RATING - 10A at 34Voc max (140W) input from a solar panel.
(It's OK to oversize the solar array as the extra capacity can maintain the day time charge current during marginal light).

RATING - 15A at 75Voc max (200W) input from a solar panel. 
(It's OK to oversize the solar array as the extra capacity can maintain the day time charge current during marginal light).

EFFICIENCY - 96-98% electrical.  Charge current comes on instantly with sun light.  (Fast MPPT tracking speed at 15 samples/sec while maintaining charge current).  

EFFICIENCY - 94-99% electrical.  Charge current comes on instantly with sun light.  (Fast MPPT tracking speed while maintaining charge current). 

OPERATING RANGE -  -40C to +85C.

OPERATING RANGE -  -40C to +60C.

ELECTRICAL CONNECTION - #10 wire; 2 from solar array, 2 to common negative battery.

ELECTRICAL CONNECTION - #6 wire; 2 from solar array, 2 to common negative battery, 2 to load, 1 for earth ground.

* CONNECTION WARNING * - A solar charge controller must always be connected to battery (load).  Switch the solar input off first to allow you to safely service the system without damaging the controller.  To facilitate this, install a circuit breaker, fuse, or switch between the solar panel and the charge controller input. 

  • INSTALLATION - Connect the output (battery) first, then connect the input (solar panel). 

  • SERVICING - Disconnect the input (solar panel) first, then the output (battery). 

  • Click here if your solar panels are connected in parallel

  • If the solar panels are connected to a terminal strip, it creates a convenient test point to measure and isolate a problem.

  • NOTE - Connect an inductive load (inverter, motor, compressor or generator) directly to the battery posts.  The start up surge current of these devices is too high for a charge controller, even if the controller has terminals to connect a load or is equipped with an LVD feature.

BATTERY SELECTION - A single jumper to select deep cycle battery charge rate for flooded or sealed/AGM.  System charge voltage is fixed at 12V.

BATTERY SELECTION - Dip switches to select battery type for Gel, Flooded, Lithium-Iron Phosphate or Sealed/AGM.  System charge voltage is automatic, 12/24V.

EQUALIZE CHARGE - Auto-equalize 1 per 28 days for a flooded battery.  Disabled for other battery types but check with manufacturer.

EQUALIZE CHARGE - Auto-equalize 1 per 28 days for a flooded battery.  Disabled for other battery types but check with manufacturer.

BATTERY TEMPERATURE - Internal sensor.  For battery protection and optimal charging install the controller close to the battery to reduce the charge current when warm.

BATTERY TEMPERATURE - External sensor.  For battery protection and optimal charging connect the temperature probe to the top of the battery to automatically reduce the charge current when warm.

INTERNAL PROTECTION - Over-charging, over-discharging, reverse polarity, over-load, over-temperature and an internal 20A fuse.  No LVD to prevent battery discharge.

INTERNAL PROTECTION - Over-charging, over-discharging, reverse polarity, over-load, over-temperature.  LVD to prevent battery discharge if load connected to LVD terminals.

STATUS LED - Shows charging mode (2 colour LED, very accurate).  Best to post a laminated chart next to the controller to understand the following flash patterns.

 - Battery Charge Status.
 2 sec green flashes = Ready to charge when solar available.
 solid green = absorption or maintenance mode.
 fast short green flashes = charging <3.7A (bulk mode).
 slower, longer green flashes = charging >3.7A (bulk mode).
 long, then short green flashes = charging limit >10.5A (bulk mode).

 - Battery Alarm Status.
 2 red flashes = high temp.
 3 red flashes = current overload.
 4 red flashes = battery V too low.
 5 red flashes = battery V too high.
 6 red flashes = solar panel V too high.
 2 long flashes followed by short flashes = internal error.

STATUS LEDs - Shows charging mode (dual LEDs, very accurate).  Best to post a laminated chart next to the controller to understand the following flash patterns.

 - Charging Status.
 solid green = bulk mode.
 1 sec flash = absorption mode.
 2 sec flash = maintenance mode.
 red - error.

 - Battery Status (SOC)
 Full, Partial, Low. (Lit under matching battery image).

- Temp Sensor = high temp from remote sensor.  

Install the optional external RemoteMeter for precise measurements or use a PC to view 30 days of internal logging. 

Radio Frequency Interference (RFI) - The majority of MPPT charge controllers transmit radio frequency interference (RFI) to some degree due to the internal DC switching.  The sharp power switching generates voltage transients that are radiated as RFI on the boat wiring and through the air, interfering with the boat's VHF or audio equipment.  I've tested the Genasun, SunSaver MPPT and the Victron to know they are amongst the few controllers that don't transmit RFI.  Unfortunately my previous Renogy Rover Elite does, so for this reason it will find another use at home.  More on RFI below.

PANACHE INSTALLATION - The charge controller was installed on the starboard bulkhead with the other electronics as my bench testing has confirmed there is no RFI.  If the status LED shines green the controller is wired correctly.  This Genasun GV-10 is working extremely well on Panache as is the Morningstar SunSaver on my buddy's boat.  Regardless of which charger controller is installed, the flash pattern of the LED shows the range of charge current.  This is operational confirmation at a glance.  For a precise power measurement I read the meter on the power panel.




IMPORTANT for LONG TERM STORAGE - If the battery is left onboard for winter and the solar panels cannot receive sun to maintain the battery charge, then disconnect the charge leads to the battery so the self consumption current of the MPPT charge controller does not discharge the battery.

Oh Oh - One day during my renovation work I used a day's worth of power ahead of a week of cloudy weather.  I was surprised that the 3 rigid solar panels could not charge the battery in this low light.  "Amazing what you discover when you use the boat daily compared to weekend only."  This low charge rate is not viable for daily cruising where the solar array should maintain the battery charge during the day or restore it to full capacity by evening.  It's also bad for the battery to stay discharged.  To determine a suitable charge rate I borrowed a 30W panel for a week and the charge controller restored the Optima AGM battery the first day.  Armed with this knowledge I changed Panache's solar array for 2021.  But this also got my creative juices flowing on a more efficient charge controller. 


NIGHT TIME CHARGE RECOVERY - Most MPPT charge controllers draw power from the battery when the sun doesn't shine.  I was curious to know how long it takes to recover the overnight deficit.  For this test I used a 2A variable power supply to simulate a solar panel with the controller output power charging a 12V sealed AGM battery.  Assuming 6 hours of darkness (no charge) below are my results. 


STARTS CHARGING - ~2V above battery voltage with a smooth rise in charge current that reaches max near instantly. (very fast tracking).
RECOVER NIGHT LOSS - Takes ~2 sec at 10A charge current.


STARTS CHARGING - ~2V above battery voltage with a smooth rise in charge current that reaches max near instantly. (fast tracking).
RECOVER NIGHT LOSS - Takes ~50 sec at 10A charge current.

CONCLUSION - To recover the night time power loss in the morning with either of these controllers takes less time than to drink a cup of coffee which makes either an excellent choice!  You can do the math for lower charge current.  The lower quality charge controller manufacturers don't mention this in their specifications.  Hmmm.

TRACKING SPEED - There are two aspects to this:
  • How quickly can an MPPT controller start charging after the resumption of solar panel output?
    - While tracking speed is seldom an issue for a permanent land based installation, movement and shading are a constant issue on a sail boat.  For this reason you want an MPPT charge controller that can switch the charge power on immediately after the solar panel is illuminated and maintain charge while tracking.
  • How often does the controller sample the incoming power (samples / second) to determine the optimal power transfer?
    - The faster the better and the controller should continue to charge while sampling.  Some don't.

I can't imagine why the fast tracking feature wouldn't be important on every sailboat.  The following are all fast tracking charge controllers suitable for a sailboat; Genasun, MorningStar, Victron, Midnite & Outback.  Outback is designed for a solar array starting at 100W, so too big for an SJ23.  The most inexpensive controllers (not listed here) have slow tracking and should not be considered for the dynamic conditions on a sailboat.

IMPORTANT for LONG TERM STORAGE - If the battery is left onboard for winter and the solar panels cannot receive sun to maintain the battery charge, then disconnect the charge leads to the battery so the self consumption current of the MPPT charge controller does not discharge the battery. 


PANACHE WIRING with MPPT CONTROLLER (2020) - In the diagram below (top view looking into settee) the DC power originating from the MPPT controller is fed directly to the battery via dedicated #10 stranded wires.  This is the desired wiring configuration for a single battery.  While not required with a Genasun or Morningstar MPPT charge controller, I decided to retain the ferrite beads to attenuate any RFI signal sent to the power panel wiring.  If another high load circuit is added to these buss bars, I will slip some ferrite beads over those wires as well.  It is the VHF radio and the media receiver that are affected by RFI on the power wires. 

CONCLUSION - The major advantage of an MPPT charge controller is the power tracking feature that utilizes excess panel voltage to  convert it to useable charge current during bulk chargingBulk charging occurs when the battery terminal voltage has not yet risen to the limiting voltage of the controller.  This is why an MPPT controller is about 15% more efficient than a PWM controller.  With this feature it can typically ram in 35% more power per day resulting in an average 90-95% state of charge compared to 55-60% for a linear regulator.  Just don't expect the charge controller to maintain the battery from moon light, OK!   TOP

RADIO FREQUENCY INTERFERENCE (RFI) - All MPPT charge controllers emit RFI to some degree due to the internal DC switching used to regulate the output.  The majority of RFI is transmitted while the solar charge controller is charging the battery in bulk mode.  Once the controller goes to maintenance mode (battery charged) the RFI is usually much reduced, but still annoying.  RFI on power cable can originate from the alternator, a cooling fan, a DC/DC inverter, certain LEDs, etc.  RFI can radiate through the air or along power cables acting as an "antenna".  You can hear the radiated interference when it breaks the squelch on your VHF radio, intermittent or continuous.  To understand the full scope of the interference listen to a quiet channel on the VHF, other than 16 or 9, with the squelch open.  At times the quality of the NOISE can give you a hint as to the source of the unwanted signal.  Tightening the squelch is NOT a solution as this shortens the receiving range.  My tests show the majority of the signal is radiated from the charge controller input wires and to a lesser degree the output wires.  The RFI is broad spectrum 0-300 mHz, peaking around 150 mHz, as shown on a spectrum analyzer.  We also saw signal spikes that coincide with the switching frequency of the microprocessor in the controller.  These are the noise bursts (squelch breaks) you hear on a VHF radio.

To ISOLATE RFI to a particular device, make use of the power switches:

  1. Confirm that VHF squelch operates correctly and set the volume to a comfortable level.
  2. Confirm if the radio is affected with the NOISE.  It may be intermittent.  Another clue.
  3. If the NOISE is heard, open the squelch.
  4. Remove the antenna connector.  If the NOISE is gone it is being radiated through the air.  If the noise stays on it is radiated on the power cables.  Now you have to chase down the culprit so reconnect the antenna.
  5. Switch off the electrical power to all the devices on the boat, except the VHF.  Shut off the MPPT charge controller by covering the solar panels or open the wiring.  Hopefully the NOISE is gone with one of these actions.
  6. Switch on each electrical circuit, one at a time, to determine which culprit is transmitting the NOISE.
  7. NOISE could come from the alternator, a cooling fan, a DC/DC inverter, a solar charge controller, etc.  Electrical motors in general can be noisy.  But then so can a loose power/ground connection or one with high resistance.
  8. As a temporary solution you may have to operate the VHF with the culprit temporarily switched off.
  9. Follow the steps listed below to reduce or eliminate the RFI.


  1. Twist a pair of power wires around each other, about 8 turns or more per foot, to correct the characteristic impedance to pure resistance. 
  2. Install the power wires away from boat signal wiring.  If the power wires have to cross boat wiring, do so at 900 for the least cross talk.  This is always a good practice. 
  3. Install the VHF co-axial cable away from the power wires.  This is always a good practice. 
  4. The installation of a ferrite bead over each power wire can attenuate the RFI, provided you choose a bead that attenuates in the VHF range.  It is best to slip a bead over each conductor.  The composition of a ferrite bead determines the frequency band it attenuates; 30kHz-100mHz or 100-500mHz are two examples.  I'm not sure what composition determines the impedance of a bead but highest attenuation (dB) is best.  You will have to search through an electronic wholesaler for these.  If one bead isn't effective try installing a second bead adjacent to the first.  Alternatively loop the wire several times through a large diameter bead.  Clamp on beads are easiest to install over existing wires. 
  5. Install clamp on ferrite on the VHF coax cable.
  6. Block RF In & Out - The optimum place to protect a device is to install a ferrite where the power enters the device.  The optimum place to stop the signals from leaving a device (MPPT controller) is to install a ferrite where the power leaves the controller.  In the schematic above, the MPPT controller input and output leads are both protected. 
  7. While bench testing a charge controller I discovered the addition of a power line RFI filter on the input and output leads attenuated the RFI by 30dB.  The interference (RFI) was reduced to only 2 feet as confirmed with a hand held VHF.  Determining this distance is tricky as my body was acting as an antenna.  With my hand close to the radio it broke squelch.  However, these filters typically limit the system current as well so this is a questionable solution. 
  8. Short Out RF - Install a .1 uFd ceramic capacitor across the input and output terminals of the MPPT controller.  The leads must be as short as possible to be effective.  The idea is to short out the RF signal back to its source.  This isn't the best technique but it reduced the signal propagation on Panache from 10M to only 2M distance, resulting in fewer squelch breaks on the VHF.
  9. Short Out RF - Alternatively, install a .1 uFd ceramic capacitor from each wire terminal of the MPPT controller to a thin copper plate installed behind the controller using the MPPT mounting screws.  This shorts out the RF signal to a low impedance ground. 
    To be successful the capacitor leads must be very short, which I couldn't do, so I can't confirm if this technique works.  It might be more effective if the copper plate is connected to earth ground.
  10. So far I tested the Genasun, MorningStar & Victron MPPT charge controllers and confirmed them to be free of RFI.  I'll add others when I can.
  11. IGNITION NOISE - When an outboard engine equipped with an electric starter/generator is operated, the generator and the ignition may create electrical "noise", imposing it on the boat wiring harness.  The noise of either one can make it near impossible to understand speech on the VHF or listen to an AM/FM radio.  The operation of any other sensitive electronics may also be affected. You can eliminate most of this with good electrical connections and ferrites.

Never commit your installation design till all devices work in every mode.  After that it is OK to bundle up the wiring.



  1. STARTER - If your battery voltage is low and you release the starter switch of the outboard, the starter could induce a damaging voltage spike onto the electrical wiring.  Although Panache's has never done this.
  2. INDUCTIVE LOAD - Switching off an electric fan or other inductive load appliance can induce a damaging voltage spike.  The spikes are opposite polarity to the normal power and can therefore damage an LED, VHF radio, Tiller Pilot, or other electronic device that is switched on and not protected from this.  Unfortunately most marine electronics is NOT protected against voltage spikes.

The fix for this problem is to install a Schottky diode across the power leads of the transmitting electrical device.  A Schottky diode can conduct the induced voltage spike quicker than a silicon power diode, resulting in excellent protection.  But if you can't find a Schottky diode then a 1A silicon diode is next best.  Connect the striped end of the diode to motor positive and the other end to motor negative.  Connect it electrically as close as possible to the motor.  Also connect a diode ahead of every LED circuit in the boat.  The normal power flow to or from the motor is not affected.

NOTE - A Schottky diode is a special type of diode with a very low forward-voltage drop and very fast switching speed, (faster than a silicon power diode).  The voltage drop of a Schottky diode is between 0.15-0.45 VDC while the voltage drop of a silicon diode is usually 0.7 VDC.  The lower voltage drop is why it dissipate less power and the faster switching speed is why it can short out the high frequency "noise" spikes.  This translates to better protection and a quieter electrical system.  See Tech Tip E11.  TOP


BATTERY  - The boat battery chemically stores electricity to supply DC power in the absence of sunlight, to discharge high current beyond what a solar panel or alternator can provide, to regulate the system voltage and to absorb electrical noise on the wiring.  To do any of these effectively it's capacity must be capable of supplying power for the designed length of time and the charging system should be sized to power the load and charge the battery as quickly as possible for the next discharge cycle.

  • A battery is an excellent absorber of transient voltages and a major component of an RF ground for the VHF radio. 

  • A battery must be secured in place so it CANNOT be dislodged when the boat lays on her side.

  • For safety reasons a flooded battery must have an absorption blanket under it capable of soaking up the volume of electrolyte. 
    While a blanket is not required for a gel or AGM battery, it wouldn't hurt.

  • A battery should be equipped with a cover or have insulated posts to prevent an accidental short circuit across the terminals.

  • Charge and maintain each battery type correctly as per the manufacturer's recommendations. 

  • As a rule of thumb battery capacity should be double the daily consumption.  A filled or AGM battery should be discharged to only 50%. 


BATTERY AT REST ~12.6 V ~12.6 V ~13.0 V
BULK CHARGE ~14.2V ~14.0 V ~14.2V
ABSORPTION CHARGE ~14.4 V ~14.0 V ~14.4 V
MAINTENANCE CHARGE ~13.7 V ~13.7 V ~13.7 V
EQUALIZE CHARGE ~14.2 V Do NOT equalize 14.5 V.  See battery manual if OK to equalize
BATTERY AT REST ~12.6 V ~12.6 V ~13.0 V

FLOODED BATTERY - While there are many types of batteries, the one most often used on a pocket cruiser is a flooded deep cycle battery.  It can generate sufficient current to crank over an electric start outboard and operate cabin lights plus the "toys" on board while withstanding long term charge/discharge cycles, all without damage.  The fluid level must be maintained up to the split rings in each cell.  Look under the filler cap.  A standard flooded battery is excellent for starting a diesel engine.

GEL BATTERY - A gel battery has the advantage of having vibration resistance & hence extended life.  It is sealed so no spillage but is usually installed right side up for venting and a precaution to leakage.

AGM BATTERY - An Optima Spiral AGM gel battery has the advantage of having superior vibration resistance & hence extended life.  The Absorbed Glass Mat holds the electrolyte like a sponge to eliminate spilling, has 99.99% pure lead plates, and does not require adding water.  It is sealed so no spillage but is usually installed right side up for venting and a precaution to leakage.  This is Panache's current battery and is by far the least expensive battery due to its long life.  It has greatly simplified life on board. 

Has a higher storage rating than a flooded battery.  Is sealed so no gassing or filling cells with water.  Is sensitive to overcharging.  Equalize charging not required.  Voltage holds up better under a heavy load than does a flooded battery.  Has low internal resistance so can be charged/discharged faster than a flooded battery.  The cell structure of an AGM is extremely robust so less likely to collapse under vibration.  The following tips help to prolong the life of your AGM house battery.  Many of them apply to a flooded battery.

  1. An AGM battery is best suited for house use.  A flooded battery is best suited for engine starting.

  2. Charge an AGM to at least 80-85 % state of charge (full capacity) with each charge cycle and get to 100% state of charge as soon as you can thereafter.  While an AGM can be left discharged to 50% for several weeks without damage, it is better to charge to full as quick as possible.  Try not to discharge your AGM battery below 50% state of charge.

  3. Size your most powerful charging source, usually an alternator or AC powered inverter/charger, for a minimum of 20% of bank capacity.  For example, an Odyssey TPPL AGM battery prefers 40% of amp-hour capacity as minimum charge current.

  4. Use temperature compensated charging for all charging sources.  While an AGM battery can take a lot of current from an alternator, the heat created can shorten its life or cause premature failure.  Therefore use a temperature controlled alternator with an external regulator and a battery temperature sensor to regulate the charge current.

  5. Use a smart solar charge controller.  Not all chargers that claim to be smart are in fact smart.  Some solar charge controllers start each day at a new absorption voltage charging cycle.  This is not healthy for an AGM battery that has low self-discharge and minimal parasitic loads when left unattended on-the-hook.  A smarter solar charge controller has a voltage trigger to drop it out of float mode.  If it doesn't drop to the trigger voltage it remains in float mode.

  6. Using the correct float voltage is a critical for an AGM battery.  A charge controller that uses dip switches for programming often lacks the correct charge voltages for both absorption and float settings.

  7. For the best charging performance minimize the voltage drop in the system wiring.  Even a 3% voltage drop at 14.4V means just 13.96V at the battery terminals, thereby under charging the battery.  Incorrect voltage sensing robs you of the fastest charging potential, especially during a short duration, high current charge cycle.

  8. Know your correct state of charge at all times.  This may mean investing in a battery monitoring device to help in overall cycle life.  If you use voltage to determine state of charge be sure to measure it as accurate as possible.

  9. Although a flooded battery benefits from monthly equalize charging (higher-than-normal voltage to recover lost storage capacity), it is NOT recommended for an AGM battery.  However, some makers such as Lifeline, state that careful equalization is possible with their batteries.  Equalize charging must be configured correctly (and monitored closely) as the optimal process can vary by battery and situation.  Lifeline can help develop a custom equalization program for your boat batteries.

  10. Avoid installing the battery in an engine room or other hot area of the boat.  Heat shortens battery life.

  11. At the completion of your installation, confirm operation by measuring and recording the voltage at all exposed terminals.  This is extremely important to understand the system, for ongoing maintenance and trouble resolution.

Advantages of AGM Versus Flooded

  • An AGM battery accepts charge more readily than a flooded battery.  A flooded cell convert 15-20% of the electrical charge into heat.  An AGM lose as little as 4% making them prefect for a solar panel.

  • An AGM battery dispenses charge at a higher rate than a flooded battery.  A deep cycle flooded battery cannot deliver more than 25% of its rated capacity in amps without rapidly exhausting its charge.  It is recommended to have a ratio of 4 to 1 between battery bank size and the largest load.  Whereas an AGM is recommended to have a ratio of 3 to 1.  This makes a significant difference when considering engine starting, etc.

  • AGM self discharge is lower than flooded.  A flooded battery can lose up to 1%/day due to self discharge.  An AGM looses 1-3%/month.

  • An AGM battery is not harmed by high current charging (or discharging) provided the charge voltage is correctly regulated, 14.4V max, and the battery temperature is controlled to prevent over warming.  Any higher voltage will kill an AGM battery.

  • An AGM battery operates safely in any orientation.  They are sealed, so can't leak.

Winter Battery Maintenance - Use an AC powered "smart" charger to maintain the battery charge during the winter.  Most of these smart chargers use 3 step bulk/absorption, float to maintain a battery in a healthy stateThe optimal temperature to store the battery is just above freezing, sitting on anything but concrete.  A flooded battery should be charge equalized once a month. 
I charge Panache's AGM battery once a month with a smart charger and use a Honda desulphate charger once a winter to clean the plates. 

DUAL BATTERIES Charged by a SINGLE SOLAR CHARGE CONTROLLER - An AGM battery should be discharged to only 50% of its capacity.  So if you want more capacity you have to add a second battery.  I wired in parallel they can be charged from the same controller.  If wired separately the most efficient way to charge two batteries from a single charge controller is to install a Blue Sea "ADD A BATTERY" switch.  This "A/B" switch is basically a voltage sensitive switch that automates charging of two batteries from a single source without manual switching.  If the ACR senses a charge is present on either battery it will offer the charge to both batteries.  If the battery voltage drops to a preset threshold the ACR will isolate the batteries thereby maintaining the charge in the starting battery.  Switching is achieved with "make before break" logic to maintain battery voltage to the output of the charge controller, thereby preventing controller failure.  Its peace of mind to guarantee all your batteries are charged.  The switch can be manually operated to deal with a power dilemma. 

I finally found the rules programmed into the ACR (Automatic Charge Relay).  Its a very interesting device.

       Battery = 13.6V for 30 seconds or 13.0V for 90 seconds. (Sensed at either the house or start battery).
       Battery = 12.75V for 30 seconds or 12.35V for 10 seconds (Sensed at either the house or start battery).
  3. Engine start isolation feature, momentarily opens the connection between battery banks while the starter motor is engaged.
  4. Over-Voltage Lockout at 16.0V If the sensed voltage at either the house or start battery terminal is 16.0V or higher the ACR will lock out and open itself till the battery voltage drops to the correct value.
  5. Under-Voltage Lockout at 9.5V If the sensed voltage at either the  house or start battery terminal is 9.50V or lower the ACR will lock out and open itself to prevent further discharge.

BATTERY DISCHARGE PROTECTION (LVD) - Many larger sailboats have dual batteries.  One to crank the engine and the other to supply house needs.  I think most SJ23s are equipped with only one battery.  If you want sufficient power to start the outboard, operate the electronics or make that emergency call on the VHF then you must monitor the battery voltage.  Digital VOMs are quite inexpensive these days and I have seen them permanently mounted adjacent to the power distribution panel.  However this demands that you monitor it on a regular basis.  If you can't monitor it and want to preserve the battery charge then you require a charge controller equipped with low voltage disconnect (LVD) or a separate LVD to remove the load automatically.  These devices are equipped with circuitry that monitors the battery voltage to automatically switch off the electrical load at a preset low voltage.  For specific products click on this Google search result   
HINT - Many MPPT charge controllers are equipped with a low voltage disconnect (LVD) feature.

HINT - I go to great lengths to maintain Panache's battery charge by minimizing the load and maximizing the charge capacity.  Most systems are designed with this in mind and many diligent skippers likely do this, thinking it is the optimal procedure.  This practice is OK with a flooded, gell, or AGM or battery when each cell is in excellent condition.  However the problem with this practice is that if a flooded battery is never discharged then with time the weakest cell will have the lowest voltage and the strongest cell will have the highest voltage, the overall battery voltage remaining the same.  Then when the battery power is needed, it can't produce the rated current and voltage for as long as it is rated.  This situation is created by never equalize charging a flooded battery to ensure all cells are charged equally.  If your charging system is not equipped with automatic equalize charging you can achieve a similar effect by cycling the battery occasionally (discharge to 50% then charge it).  The charger senses the low battery voltage and automatically charges it with a voltage higher than float thereby equalizing the cells.  If you discharge by only 20% it should also achieve the desired results.   TOP


2023 Update - After three years of using the GoPower Flex-35 solar panels with the Genasun GV-10-Pb-12V MPPT solar charge controller I have experienced no problems.  The two panels supply all the power I need through sunny or cloudy weather and the charge controller does not generate annoying RFI that prevents using the VHF or AM/FM radios.  It's a working combination that I wouldn't change because I can now operate any device without fear of discharging the battery.

To use the stored electricity on your boat you need to distribute it safely.  So go to Tech Tip E02.  TOP

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