Solar Question for charging boat batteries

TigerhornTigerhorn Registered Users Posts: 1
I have a boat I keep in my dock at our lake house about 3 hours away on a lift (manual lift- no dock power). I want to rig up a solar system to keep the boat batteries charged. I am not sure of the brand or amp hours on the batteries but lets assume 100. I will find out more on my next trip out to the lake in a couple of weeks. The boat has 3 12v batteries (2 wired in series for 24v trolling motor and 1 solo 12v for engine cranking). I have a covered dock but a good southern exposure and could mount panels on the dock poles that hold up the roof and have them face south. During my research I would like to use a waterproof Anderson connector from the panel to the charge controller with the charge controller mounted in the boat and panel on the dock so I can disconnect when using boat and reconnect when in dock. My rookie questions for you all are two fold.

1. Having the 2 battery "banks" - 1 24v (2 batteries in series) and 1 12v solo - what kind of charge controller should I get? How should I wire the batteries from the charge controller? I would prefer to use just one panel and charge controller if possible even if more costly. Is it possible to use one panel and charge controller as I would like to keep the panel profile small as possible. 

2. There is a battery trickle charger for AC mounted in the boat and connected to all three batteries for those times when I have the boat out of the water and can plug in to 120v outlet...should I disconnect this or will it be fine being connected even though no AC present? If it helps this charger is a marine 15 amp 5-5-5 triple bank charger. Bass Pro XPS IT - made by ProMariner

Thanks for your help!!


  • EstragonEstragon Registered Users Posts: 3,127 ✭✭✭✭✭
    edited April 2018 #2
    There are a few ways to do this.

    1. If having AC power at the dock would be useful (for lighting or to plug in a radio, for example), you could add a small inverter and battery to provide AC power to the existing AC trickle charger. A controller with a load control function could be used to charge only during daytime.

    2. If not, the best solution is separate panels and controllers for each bank voltage IMHO.

    3. Less ideally, but may work for trickle charging, you could maybe use a single 60 or 72 cell panel and two pwm charge controllers (one for each voltage). Multiple controllers on a single panel or string is normally not a good idea, but 2 pwm types might work in this application.

    4. You could probably even get away with trickle charging all three batteries at 12v in parallel from a single charge controller. The AC trickle charger will be doing something along these lines, but may be able to limit voltage on each output. The risk is that the parallel connection only shows the controller the average state of charge for the three batteries, as if they were a single battery. As they're actually separate batteries, they may have distinct states of charge and charging/floating needs.

    I'm not aware of any controllers capable of charging three banks independently, but they may exist. There are some readily available for charging two banks independently which you could use to charge the 12v battery on one output, and charge the individual 12v batteries in the 24v bank in parallel with the other output. The wiring would be similar to the 5/5/5 AC charger, except the two positives and two negatives from the 24v bank would go to a common 12v output. The two output controllers likely wouldn't handle two different voltages, so you would not want to wire the single 24v + and - wires to the second output. Multi-voltage controllers likely exist, but I suspect they'd get pricey for this application.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Solar Expert Posts: 2,501 ✭✭✭✭✭
    An inexpensive PWM charge controller with a 12V nominal  20W panel for the 12V battery ,  the same but 2 × 20W panels in series for the 24V would do the lob, I use this on my escavator which may sit for months without use. Because your situation needs to disconnect a DC circuit breaker to turn off before disconnect would be advisable, as well as different, polarized configuration connectors to prevent mistakes. Using a single controller is not the best solution nor a single panel because dual voltage, these controllers can be had for <$10 and work well in a trickle charge application. The AC trickle charger could remain connected, as with the controllers, these PWM controllers do consume a very small amount of energy without PV input, so they either need to be disconnected if left for extended periods of time without PV and remember ALWAYS  power up the controller with the battery first to establish nominal voltage reference.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
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