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Author Topic:   Charging Three Batteries In Separated 12 and 24-volt Systems
rayjs1963 posted 02-18-2010 12:23 AM ET (US)   Profile for rayjs1963   Send Email to rayjs1963  
Hello everyone. New guy here. This site seems to have a lot of really good info and a whole lot of boating subjects, but I do have a question. I have a 1998 Sundown jet boat with a 175-HP Mercury sportjet in it. At the stern there is one battery to start the main motor. In the bow I have two deep-cycle batteries hooked together for my 24-volt electric motor. Is it possible to use the main motor to charge all three batteries at the same time? The main is a 12-volt system and the electric [trolling motor] is 24-volt. I'm not too sure if this can be done, and, if so, if it can be done easily or not. I would just be nice to have the main motor also charging the electric motor batteries while I'm running up and down the river to different spots.

Thanks and I'll be looking forward to any replies and suggestions. Maybe it's not worth the hassle.--Ray

jimh posted 02-18-2010 09:40 AM ET (US)     Profile for jimh  Send Email to jimh     
It is possible to charge three 12-volt batteries in a mixed 12 and 24-volt system from a single charging source that supplies 12-volts, however, it is not straightforward or simple. There are two approaches:

--construct an elaborate switching system to temporarily connect all the batteries in parallel for charging. This would temporarily make the 24-volt system a 12-volt system. All batteries would be charged in parallel. This is not a good solution for two reasons. The switching would be complex. Charging batteries in parallel is not the best approach. There are some devices that try to do this automatically, charging one battery at a time.

--find a specialized charger unit which is a DC to DC convertor that converts a 12-volt input to a 24-volt output. The engine charges the main battery. The main battery and engine charging current power the DC to DC convertor. The DC to DC convertor output charges the 24-volt system. This is the best approach. You do not need to modify the boat wiring very much at all.

Here is one product:

There are several other similar products which are marketed especially for bass boaters. This search will point you to some other options: trolling+motor+from+outboard&ie=UTF-8&oe=UTF-8

jimh posted 02-28-2010 08:18 PM ET (US)     Profile for jimh  Send Email to jimh     
[Several suggestions of devices to satisfy this charging situation were offered, but none of the suggested devices actually met the requirements. These comments have been deleted--jimh]

Here is another product that meets the criteria required by the initial inquiry, that is, it charges a 24-volt series connection of two batteries from the charging current supplied to a third 12-volt battery by the boat engine charging system:

rayjs1963 posted 03-02-2010 01:29 AM ET (US)     Profile for rayjs1963  Send Email to rayjs1963     
[Thanks] for the replies, links and info. I will be looking into all of this just as soon as I can get the time and energy to do it. I weld for a living, and well have two jobs and kinda get tired in the evenings and have a hard time motivating myself to do some things. but I will be looking into this. I appreciate it and will be talking to you all soon.--Ray

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