Use 3 of 4 existing batteries for a Trolling motor?

[Aquanut2]

Wondering if anyone has tried using three of the four batteries wired in series before? Aside from the risk of drawing them down in theory this should work. I have 4 batteries on my Marlin there is a left and a right bank with a selector on each side for 1, 2 or Both. Looks like the house is also wired on the starboard bank so my thinking is I could use the two on Port bank with the second batt on the Starbord side in series to get 36v. 12v should still flow as designed and the existing 4 bank charger will charge when on shore power.
Thoughts? A lot cheaper and lighter than buying 3 more w another charger.
Thanks

 

[wspitler]

I don’t think that will be simple. Be real careful. Taking a parallel bank and turning it into a series bank will require additional switching as well taking a parallel battery out of a parallel bank and adding it to your other two series. Lots of opportunity to fry things. Remember to get a series circuit you must connect a negative terminal to a positive terminal on a different battery to give 24V then the negative terminal to the positive terminal on your third battery to get 36V. Your current set up has a common ground to all batteries and only the positive terminals are switched. On my scout I use one of my two starting batteries in series with a completely separate battery to provide 24 V. Be very careful and draw out a circuit diagram before you begin. I would not attempt it, too much trouble!

 

[SkunkBoat]

What he said......

 

[seasick]

Kaboom!
Your current batteries share a common ground. That is used for connected 12v loads and charging. Connecting as you suggest may cause a dead short or possible the application of 24v to 12v loads.

 

[Aquanut2]

Yikes th

Kaboom!
Your current batteries share a common ground. That is used for connected 12v loads and charging. Connecting as you suggest may cause a dead short or possible the application of 24v to 12v loads.

Yikes thanks for that tip this 04 boat already has enough elec gremlins in it I've been chasing. Rethinking a Lithium 36v solution that's lighter and takes up less space albeit 3x's the $$

 

[seasick]

Separate battery pack/bank with separate charger is probably the best approach. I don't know how your boat sits right now but give some thought about weight of battery pack and location in the hull.
Let us know how things turn out.