Solar panel on 2 batteries vs one panel for each battery

Spiralinguist

I have a 22’ c Dory with 2 batteries. One starts and is charged by the engine and the other is wired to one 100w solar panel via a controller. I would like to link the 2 batteries in parallel when not in use so the solar panel charges both the batteries. Is this wise or possible? I would like to add more panels but space up top is limited. I could also wire the engine battery to a second, separate controller and solar panel. (More expensive) How do I know if the controller can handle a second or even third 100w solar panel? The controller is a Wanderer Li 30A PWM Charge Controller. I was thinking of linking the 2 batteries via a auto jumper cable when not in use and then just unclipping a red/positive clamp when using the boat. It’s kept in the water so that’s why I want the battery(s) to be continually charged since the bilge works when it rains. I appreciate any experience and advice.

ssobol

thataway · Posted: Sat Sep 04, 2021 1:27 pm Post subject:

You want a "combiner"--also called a Voltage Sensitive Relay. When the charging voltage is over 13.7 (+/-) it combines the starting and house battery. This works from the engine alternator, shore power charger or solar panels.

Using a battery jump cable is not desirable for multiple reasons; including potential for not removing, possible incorrect hook up or failure to connect, and danger of un covered clamps shorting the battery.

Your solar charger although not the most desirable should work fine up to3 100 watt panels. (30 amps at 12 volts = 360 watts). Maximum Power Point Tracking (MPPT) and Pulse Width Modulation (PWM) are different, and the MPPT is best for multiple panels or where one panel may be shaded or where the batteries or panels are a slight mismatch.

Generally 200 watt panels at 12 volts will maintain the batteries enough to sustain the use of one of the chest type freezers by Norcold, ARB, Engle, Dometic or one of the 12 got refrigerators which the C Dory comes with.

If you can mount the panel so it tracks the sun--or at least is at right angles to the sun's beams most of the day you will have higher output.

Spiralinguist · Posted: Sat Sep 04, 2021 3:54 pm Post subject: Voltage sensitive relay

I have never heard of a voltage sensitive relay. That sounds like the answer so that the solar panels will charge one or both batteries and the alternator can likewise charge one or both. I think I can fit two panels if hi change the orientation. The one is now installed lengthwise on the center of the roof if I install two they can be mounted so the longer part of the panel runs port to starboard.

thataway · Posted: Sat Sep 04, 2021 4:06 pm Post subject:

Ideally you would want to build an articulating mount, so you can better track the sun, than the panel lying flat. Since you ar in NY, the Sun will always be South of your location.

localboy · Posted: Sat Sep 04, 2021 6:48 pm Post subject:

Dr Bob is correct as usual.

I installed a mini Add-A-Battery in our 2006 and removed the original battery switch. A couple of years ago, I added a simple solar system; 110 watt semi flex panel with 30 amp PWM controller. Controller is attached to the house battery but once it tops out, the panel will charge the start battery. Keeps up with the refer draw in the summer months, in full sun. Happy with the results for minimal cost.