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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

12 and 24 volts

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OJ
Master Marine Consultant

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USA
4382 Posts

Initially Posted - 08/06/2013 : 12:14:08

So if I wired my (2) 12 volt batteries in a series to send 24 volts to a trolling motor, could I still send just 12 volts to the rest of the boat?

1989 C25 TR/WK, #5822
1973 McVay Minuet 19
1975 Jester 12
1981 C25 SR/SK, #2428
1981 C22 SR/SK,
Tanzer 16
Sunfish

"There is nothing, absolutely nothing half so much worth doing as simply messing about in boats." Kenneth Grahame

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 08/06/2013 : 13:27:44

Not without some method of stepping down the voltage with something like [url="http://www.amazon.com/Volt-Converter-Transformer-Aircraft-Airplanes/dp/B009TA9AS0"]this[/url].

There's nowhere on the system to pull 12 volts from because you've effectively just made a single 24 volt battery. Electrically there's no longer any distinction between the two 12 volt batteries, they just happen to be contained in two separate (but electrically connected) containers making the single 24 volt battery.

If you decide to go the stepdown route, make sure you size the transformer for your load. The one I listed above is only rated for 60 watts, but there are much larger one$ available.

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britinusa
Web Editor

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5404 Posts

Response Posted - 08/06/2013 : 13:44:22

If you connected just one of the batteries to the boat, that would be 12v.

But you cannot connect both batteries in Series and parrallel at the same time.... Boooom!

Paul

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OJ
Master Marine Consultant

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4382 Posts

Response Posted - 08/06/2013 : 14:27:26

Ah, this must explain why the previous owner installed a battery case for a 3rd battery.

So, what about charging the two main batteries (tied together) with a solar charger???

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britinusa
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Response Posted - 08/06/2013 : 15:53:54

<blockquote id="quote">quote:<hr height="1" noshade id="quote">But you cannot connect both batteries in Series and parrallel at the same time.... Boooom!
<hr height="1" noshade id="quote"></blockquote id="quote">

I guess you could charge them with a 24v solar panel!

With any number of similar voltage batteries connected in series, you can connect to the + & - on any single battery and get that battery's voltage.

If you wanted to be clever, you could have a couple of switches with lockouts to switch between series and parallel, then you could switch to 24v for trolling and 12v for othertimes.

But then I have to ask.... a trolling motor on a 25' sailboat? Couldn't you just setup a 12v fan in the cockpit and point it in the right direction

Paul

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OJ
Master Marine Consultant

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Response Posted - 08/06/2013 : 17:58:43

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by britinusa
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">But you cannot connect both batteries in Series and parrallel at the same time.... Boooom!
<hr height="1" noshade id="quote"></blockquote id="quote">
But then I have to ask.... a trolling motor on a 25' sailboat? Couldn't you just setup a 12v fan in the cockpit and point it in the right direction

Paul
<hr height="1" noshade id="quote"></blockquote id="quote">
We've had some unfortunate luck with the Yamaha 9.9 4-stroke lately. Last fall mud wasps built a nest between the timing belt and cam pulley resulting in the timing belt jumping one tooth and bending the valves. A dock neighbor convinced us his mechanic could walk on water so we had him rebuild the top end (new valves, magna-flux and shave the head, seat the new valves, etc) for $840.00. Started the motor this spring and it sounds like a sewing machine - valves clicking. We dropped the motor off yesterday and have no idea when we'll see it again. So we are hooking up a 24v trolling motor just to get us from the dock to the wind and back. It will also be nice to have a fallback propulsion unit. . . at least that is the thinking.

Edited by - OJ on 08/06/2013 18:00:07

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