Trolling Motor Battery Charge - SailNet Community
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post #1 of 6 Old 08-14-2018 Thread Starter
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Trolling Motor Battery Charge

I use a trolling motor for my dinghy. On extended cruises I have to change out the battery with my starter battery and start the motor with the house battery to recharge it. What I think would work is attaching a pigtail with a twist-lock connection to the house battery (without removing). So all I have to do is pull out the pigtail, add it's mate to the dinghy battery and connect them. Now, start the engine and let the charging begin! So . . . stupid idea or what. Be gentle.
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post #2 of 6 Old 08-14-2018
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Re: Trolling Motor Battery Charge

What size trolling motor? How much dinghy cruising are you doing that you are running down a battery so bad you need to switch it out? I assume a standard group 24/27 AGM for the trolling motor? So 105AH or so, so roughly a half hour full throttle to 50% on a 55lb thrust motor, or about an easy 1.5 mile range round trip. I suppose you are doing multiple trips a day?

The basic idea as you have said it is fine, I just dislike pulling the starter battery, seems to defeat the purpose.

Oh I think I see. You are saying your only way to charge it is to swap it out, than absolutely just add a pigtail and connect it to the house batteries to charge it (provided 12v bank of course). There are more complicated solutions (isolators, charge balancers, etc.) that might/would charge a bit faster, but that is totally workable.
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post #3 of 6 Old 08-15-2018
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Re: Trolling Motor Battery Charge

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Originally Posted by DonScribner View Post
I use a trolling motor for my dinghy. On extended cruises I have to change out the battery with my starter battery and start the motor with the house battery to recharge it. What I think would work is attaching a pigtail with a twist-lock connection to the house battery (without removing). So all I have to do is pull out the pigtail, add it's mate to the dinghy battery and connect them. Now, start the engine and let the charging begin! So . . . stupid idea or what. Be gentle.
If it's a true starter battery, it's the WRONG battery to run your trolling motor, and you'll likely ruin it. This is especially true if your trolling motor is running it down so far that you can't start the motor with it afterwards. Any discharge beyond 50% will drastically reduce its lifetime.

I can't suggest anything except more batteries. When I used a trolling motor I bought a 12350 AGM battery which has much less capacity, but was much easier to transport. If you buy two you can swap them out easily as needed and recharge on the boat. Rather than buy a second battery I decided to buy a 2.5 HP Suzuki, which weighed less than the batteries and has much longer range.

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post #4 of 6 Old 09-06-2018 Thread Starter
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Re: Trolling Motor Battery Charge

All my batteries are "deep cycle". But if you listen to MS, who's a marine electrician, they are not actually deep cycle. We took a two week cruise and swapping out the batteries worked fine. We never had a problem but I was just wondering if there's an easier way.
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Re: Trolling Motor Battery Charge

I used to add a group 24 battery to my house bank same way you are considering. Adding amps to house bank and then
using for trolling motor when needed. Never a problem as we motored often enough and is supplemented by solar.
Now group 24 battery has been replaced with 2 smaller AGM's. ...and still works out well.
My dinghy use is on the light side, heavy use probably would not work out as well.
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post #6 of 6 Old 09-08-2018
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Re: Trolling Motor Battery Charge

You might consider putting an AB switch on the house battery and connecting it to a charging outlet in the cockpit so you can plug a charging cable to that and charge the trolling motor battery on deck or without removing it from the dingy. Then you won't be needing to lug that trolling motor battery around so much.

Personally I find the 31 lb Honda BF2.3 I use less of a bother than lugging heavy batteries around and dealing with range anxiety. Lets face it your likely burning more fuel charging the trolling motor battery by running your main engine when you didn't really need to than if you just ran a gasoline powered outboard plus it only takes a few moments to recharge the gas powered outboard using a 8/10 lb 1 gallon gas can.

A spare trolling motor battery charged via solar would take fossil fuel out of the equation if you have space to set that all up but then you will have two heavy and expensive batteries to deal with along with the high cost of setting up the solar.

Indeed do what fits best for you however despite driving a full plug in electric car I am not 100% sold on using trolling motors as primary propulsion on a dinghy.
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