How do I charge a battery for my dinghy while crusing

[AZ-Oldguy]

I have a group 27 battery to run a trolling motor on my dinghy. I can charge it easily enough when at the dock, but when underway or when cruising, how can I best charge it, either off the boats alternators or off the house Bank? What size wire do I need? Do I need a diode or Choke or some other equipment to protect either the wire or the batteries?

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[hugosalt]

I use a gp 27 battery for my dinghy trolling motor when I cruise.
I when need to charge I connect to house bank which is connected to solar panel.
Also when not using the dinghy gives me extra amp hrs on house bank.
Keep in mind ...
Have a small deep cycle battery, think 35 amps (wheelchair)
for short runs and back up.
My power needs are not great.
Cruising is usually not more than 2 weeks at a time.
Dont use dinghy every day and not for long when used.
Usually motoring in/out harbors enough to help charging.
Have a small solar panel for dinghy battery that I have not set up yet.

Not ideal if long term cruising but fits my need so far.

[hugosalt]

Solar panel has controller.
Wires to trolling battery very heavy duty, dont remember gauge.

[Tayana42]

For a number if years we cruised locally with a trolling motor on our dinghy. In order to have adequate power for a confident week of use we upgraded to two golf cart batteries in the dinghy. That gave us plenty of range but was a lot of weight to move from the boat to the dinghy or to drag up the beach. We recharged the batteries with a Honda 2000i generator.


S/V B'Shert

[Sardean]

I use the normal charger plugged into my inverter, only on sunny days or if motoring. Yes there are minor losses for the engineering minds but they are negligable. And yes there are other ways but this is simple. Also my house batteries are lead acid and the ones I charge are gel so using the charger makes sure they charge correctly.

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[tkeithlu]

I'm guessing that you are charging the house bank off an alternator on your engine. As long as you don't overload that alternator, you can simply include the dinghy battery in the house bank. I did burn up a few alternators before I learned that a 60 amp alternator cannot be expected to put out 60 amps continuously, but with a much better alternator charging system (Balmar alternator and fancy voltage regulator) I was able to add a satellite battery to the house bank. In my case it fuels the electronics if the house batteries go underwater, but the principle is the same. The wire size is dictated by the distance to your charging source (or the house batteries) and the amps you want to put in. It helps if the batteries are of the same sort - all deep cycle flooded in my case. If your source is a genset, the same principles apply.

[AZ-Oldguy]

Tkeithlu, what size wire, I would only be 4 feet from the house batteries. The house has 2 gp31 agms, the dinghy battery is a gp 27 flooded. Thanks everybody who has replied.

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[AZ-Oldguy]

I would like to charge up all 3 with the "house" alternator, and I am hoping in the near future, to start installing a couple of solar panels, at which time I might give the dinghy its own panel.

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[StuM]

Originally Posted by tkeithlu

I'm guessing that you are charging the house bank off an alternator on your engine. As long as you don't overload that alternator, you can simply include the dinghy battery in the house bank..

The OP said he is using AGM house and the trolling battery is FLA.

Not good to mix different types of batteries into one bank when charging.

[RaymondR]

Originally Posted by StuM

The OP said he is using AGM house and the trolling battery is FLA.

Not good to mix different types of batteries into one bank when charging.

If the AGM house battery charge controller is set for 13.8V it would not overcharge the FLA which usually has 14.4V maximum. The problem will be eventual sulphation of the FLA from not being fully charged. He could parallel with the house batteries to bulk charge the FLA trolling battery then top it up with a charger from an inverter. Alternatively a separate MPP regulator from the panel busbars would probably do the job.

[Moontide]

As a practical matter you can just run some wires from any 12 source (battery terminals or even a cigarette lighter plug) to the dinghy battery. Will basically be "stealing" juice from the other batteries. Would be best when charging the house batterties to get the voltage up for a full charge, but will still put amps into the dinghy battery without a charger. Don't really need to be giant wires since the battery will not be taking that much amperage.

Doesn't meet all the technical aspects, but works.

[ingrid75]

It's really quite simple: 1. Give the trolling motor to someone who fishes in a pond. (That's what it was designed for) and 2. Buy a small gasoline powered outboard motor for your dingy. 'Cause that's what they were designed for.

[knockabout]

don't electric outboards charge the battery if left down when towed

[peter57]

Originally Posted by ingrid75

It's really quite simple: 1. Give the trolling motor to someone who fishes in a pond. (That's what it was designed for) and 2. Buy a small gasoline powered outboard motor for your dingy. 'Cause that's what they were designed for.

Hi Ingrid,

I have a Torqeedo electric battery powered, equivalent to 3hp,it is the best small dinghy motor I have ever owned and have been using them since the mid 1960's. No petrol on the boat anymore, no mixing if two stroke, Goes every time by pushing a button, breaks down into three easily handled pieces, can lay it any way up or down any side and can stow it anywhere down below without stench. In saying this it is quirky thing at first and a few things I don't like about it, but have grown to love it.

Cheers,
Peter.

[Dave22q]

I don't like charging a mixed battery bank. All the experts say do not do it. An inefficient but effective way to avoid this is run a small inverter off your A/C to power an charger connecting to your dinghy battery. Wastes amps but the equipment costs less than replacing batteries.