Marine electronics 12v/24v questions: Off-topic discussion forum: Grassroots Motorsports Magazine

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Nov. 3, 2010 4:33 p.m. curtis73 HalfDork

I have a 19' I/O that I occasionally use for fishing, so I bought one of those outdrive-mounted electric motors. Its 24v (which I'll really need for a 2600-lb boat).

Is my only option to have 3 batteries? Two in series for the elec motor and one separate for the rest? I was looking at some on-board chargers that do up to 5 batteries, but they are all 12v. Then I was looking at our car pusher here at the shop (24v) and it uses an onboard MinnKota 12v, 2-bank charger.

I guess I need some electrical knowledge. I'm pretty good, but not that good. How does the 12v charger on the pusher charge batteries that are wired in series for 24v? On my boat I'd love to just use 2 batteries and step down to 12v for the starter, lighting, and other accessories. Any way to do that?

I want a setup that is plug and play, meaning having two or three batteries, access to 24v and 12v, be able to charge all batteries from the alternator or a separate on-board 120v charger box. Possible? Or am I just nuts?
Nov. 4, 2010 5:45 a.m. foxtrapper SuperDork

You use two batteries. Run them in parallel for recharging and for normal use.

When you need the 24 volts you throw the switch (which will be big) and change the configuration of the batteries to series, and remove one from the boat circuit. You can rig it to either remove both batteries, or just one.
Nov. 4, 2010 6:55 a.m. FlightService Reader

foxtrapper is right.

++1 for you and a smiley face!
Nov. 4, 2010 3:40 p.m. curtis73 HalfDork

what if I wanted to go with three batteries for more "simplicity" (not having to throw a switch)

How can I get the alternator to charge all three?
Nov. 5, 2010 7:54 p.m. turbo2256 New Reader

curtis73 wrote:

what if I wanted to go with three batteries for more "simplicity" (not having to throw a switch)

How can I get the alternator to charge all three?

There are "smart " marine battery chargers that would do the job.
Nov. 6, 2010 9:54 a.m. Tommy Suddard SonDork

I'd suggest three batteries.

Usually you want deep cycle batteries for the trolling motor, and a starting battery for the engine, no? Also, this keeps the trolling motor from draining your starting battery and leaving you stranded.

Also, the trolling batteries usually aren't charged by the engine. Buy a little onboard battery charger and hook it up to both the trolling batteries and the starting battery.