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Solar panel on 2 batteries vs one panel for each battery

 
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Spiralinguist



Joined: 12 Aug 2021
Posts: 9

State or Province: NY
C-Dory Year: 1992
C-Dory Model: 22 Cruiser
Vessel Name: Thug Tug
Photos: Thug Tug
PostPosted: Sat Sep 04, 2021 1:50 am    Post subject: Solar panel on 2 batteries vs one panel for each battery Reply with quote

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.
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ssobol



Joined: 27 Oct 2012
Posts: 3362
City/Region: SW Michigan
State or Province: MI
C-Dory Year: 2008
C-Dory Model: 22 Cruiser
Vessel Name: SoBELLE
Photos: SoBelle
PostPosted: Sat Sep 04, 2021 11:38 am    Post subject: Re: Solar panel on 2 batteries vs one panel for each battery Reply with quote

Spiralinguist wrote:
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.


You could also get a mooring cover so the boat doesn't accumulate water from the rain.
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thataway



Joined: 02 Nov 2003
Posts: 20779
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
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PostPosted: Sat Sep 04, 2021 1:27 pm    Post subject: Reply with quote

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.

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Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
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Spiralinguist



Joined: 12 Aug 2021
Posts: 9

State or Province: NY
C-Dory Year: 1992
C-Dory Model: 22 Cruiser
Vessel Name: Thug Tug
Photos: Thug Tug
PostPosted: Sat Sep 04, 2021 3:54 pm    Post subject: Voltage sensitive relay Reply with quote

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.
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thataway



Joined: 02 Nov 2003
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City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Sat Sep 04, 2021 4:06 pm    Post subject: Reply with quote

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.
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localboy



Joined: 30 Sep 2006
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City/Region: Lake Stevens via Honolulu
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PostPosted: Sat Sep 04, 2021 6:48 pm    Post subject: Reply with quote

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.

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Wife to her husband pointing @ us...from the bow of their 50-footer; Prideaux Haven 2013
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