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Old 02-26-2014, 01:13 PM   #1
City: San Mateo, Ca
Country: USA
Vessel Name: Hercules
Vessel Model: R21 RANGER TUG
Join Date: Feb 2014
Posts: 1
Solar battery charger

Am installing a 5watt solar charger on my R21 Ranger Tug. I have 2batteries wired in parallel. The negative posts are tied together. The positive posts are not tied together but have numerous leads running from them to a Perko switch in the pilot house. I'm assuming that I should connect the negative charger wire to the negative post of either battery (since they are tied to each other) but am unsure of how to wire the positive charger lead to the batteries. I'm planning to have the Perko switch in the "off" position and to splice a leg onto the positive charger wire so that it terminates on both positive battery posts which ties them together while charging. Am I on the right track? Thanks.


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Old 02-26-2014, 01:34 PM   #2
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City: Essex, Ct
Country: USA
Vessel Name: Bella
Vessel Model: Mainship Pilot 34
Join Date: Aug 2012
Posts: 2,000
Well, let's back up a minute and talk about your DC wiring system. On a simple boat straight from the factory, what you often have are two batteries. Both negatives are tied together and from there go to the main DC panel and the starter ground lug. One battery's positive is connected to the #1 position on the Perko switch and the other positive is connected to the #2 postion. You probably also have critical systems like bilge pumps directly wired to one of the batteries with a fuse near the battery. The common side of the Perko switch goes to the house panel and to the engine starter.

So, does this describe your system accurately?

If so then the Perko switch is used to isolate one of the batteries so that you can use it on the hook to power the house loads and then even if that battery is run down, you can switch to the other battery and start the engine.

If you wire anything such as a solar panel directly to both battery positives, you defeat the purpose of the Perko switch and both batteries can run down simultaneously while on the hook, leaving you with no battery starting capability.

So, assuming that both batteries are the same size and type, then designate one as house and the other as the starting battery. It would even be good to put a label on the Perko switch to that effect. Then wire the solar panel to the common terminal of the Perko switch. Or even better still wire it to the output side of your DC panel breaker like the one that feeds the cigarette lighter output. The solar panel will back feed to the battery through that breaker. That way you can use that breaker to protect the wire to the solar panel. You just have to use a wire size that matches the breaker rating- 14 gauge or 15 amps and 12 gauge for 20 amps.

Then leave your Perko switch on all so it keeps both batteries charged. Then when you get to an anchorage switch it to the house bank to protect the starting battery.

Sorry for the long winded explanation. The bottom line is wire the solar output to the common terminal of the Perko switch and keep it set to all to charge both batteries while not in use.


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Old 02-26-2014, 04:20 PM   #3
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City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 8,455
5 Watts at 12V is less than 1/2 amp. You'd be lucky to recharge a flashlight with that. I'd recommend you get the 12V Bible for Boats and study it closely. Then ditch the 5W panel and get something sufficient for your battery bank size.

Also look into combiners or automatic charge relays (ACRs) and solar controllers.

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Old 02-27-2014, 05:13 AM   #4
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Join Date: Oct 2007
Posts: 14,908
A batt that is brand new may loose 1/2% of its charge per day , an old batt that is near replacement 3% per day.

Size your charging system to hold old batts , and perhaps run the bilge pump for an hour a day.

A charge controller will be required to keep from overcharging.

Solar is a good investment as it is a great way to get the batt set to 100% full , a requirement for long service life.

85W panel, 12A Trace , worth the effort and expense.
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