24v trolling motor sanity check

[VonTrollicus]

Fixing up our new old boat (1996 sea nymph SC 175) and replacing the trolling motor and all wiring issues.

Current setup is (3) 12v batteries - starting + (2) new deep cycles all hooked up to an on board charger.

The deep cycle batteries have their positive terminals hooked up to a blue sea 4 position switch 9001E https://www.amazon.com/dp/B000K2MCR2/ref=cm_sw_r_cp_api_i_4ZAoFb672DDY4 and the negative terminals to a common bus.

Basic 24v wiring for the batteries in series would have me connect the positive from battery A to negative from battery B:
https://www.minnkotamotors.com/sites/minnkotamotors_site/files/wiring-batteries-in-series.pdf

It seems to me this would cause a loop in the system if using the 1+2 option so I'm wondering if there's any way to make use of the switch capability or if I need to swap it for a 3 way switch and if utilizing a common negative bus will cause any issues also.

Maybe just over thibking but don't want to get ahead of myself and have to rewire or replace a bunch of fuses / hurt any devices.

Thanks!

 

[gm280]

I think the typical 1, 2 or "both" switch isn't the best option for your setup. Since you are wiring two 12 volt batteries in series to get the voltage you need for your trolling motor, the "both" position isn't going to work for your situation. I would get a separate charger for the 24 volt setup and leave it out of the 1, 2 and "both" setup.

I am sure there are circuits available to cover your setup, but I don't know of any off the top of my head. You certainly don't want to short out any battery and cause a fire. So unless you can separate the 24 volt series setup, to be able to charge the three batteries, I would leave the 24 volt trolling motor batteries out of the switching setup.

In your situation, you can't use the three battery grounds all tied together and merely switch the position sides to charge the batteries. And that is because the series setup would short out one of the batteries coupling the grounds together. JMHO

 

[Faztbullet]

You don't need a selector switch on trolling batterys.Is you charger a dual bank?

 

[VonTrollicus]

Collected my thoughts a bit better, here is what I was thinking (if possible - looking for any input here please)

Solid lines are the independent 12v and 24v systems
Dotted lines would tie them together in the switch and avoid having all 3 grounds tied together.

I haven't put meter leads on to test.

Alternatively (and easier) I'd leave wiring as is and then just swap out the 4 pos switch with a simple on off and have the deep cycles connected as 24v and then just tap off one deep cycle for all 12v items minus starting.

 

[VonTrollicus]

You don't need a selector switch on trolling batterys.Is you charger a dual bank?

I realize I really worded the initial question poorly. I'm not so much interested in charging, but being able to run a 24v system for the trolling motor in conjunction with a 12v system that can switch between batteries to even the load (IE, today i use battery 1 and next trip I'll use battery 2 so they have more even use long term)

Edit - for more clarity, I'm using the 3 bank NOCO on board charger (https://no.co/gen3) and if I understand correctly, it can be hooked up to the batteries even if used as 24v in series as long as each battery is hooked up to a dedicated bank and the internal circuitry will adjust accordingly.

 

[gm280]

Let me see if I have this correct. You have two batteries setup to be a 24 volt trolling motor supply. And you also want to use either one via a switch to power 12 volt issues. If that is correct, then it is doable with the proper setup. And that is because such a switch (and I have the exact same switch) groups all the negative battery terminals together. I see instant fire as well. And that is because the negative terminal of the second series battery would be tied together to the positive terminal of the first battery which also has it's negative terminal tied with the second battery. And that is called a SHORT!!!! The instant you connect all the negative terminals together, you created a huge short!

 

[VonTrollicus]

Let me see if I have this correct. You have two batteries setup to be a 24 volt trolling motor supply.

Yes

And you also want to use either one via a switch to power 12 volt issues. If that is correct, then it is doable with the proper setup.

Not specifically, for the shorting reasons you mentioned. Looking to see if tying in the third battery would allow me to grab 12V from the one of the 24v trolling batteries OR 12V from the starting battery.

And that is because such a switch (and I have the exact same switch) groups all the negative battery terminals together. I see instant fire as well. And that is because the negative terminal of the second series battery would be tied together to the positive terminal of the first battery which also has it's negative terminal tied with the second battery. And that is called a SHORT!!!! The instant you connect all the negative terminals together, you created a huge short!

Yes! trying to avoid shorting the battery. However, not certain if the third battery will prevent the possibility of a short in normal operation.

 

[gm280]

Okay I drew up a little pictorial to hopefully show you how you can use a DPDT (Double Pole, Double Throw) switch to use either the 12 volt battery or ONE of the trolling motor series batteries. If you are wanting to select either one of the 24 volt serried trolling motor batteries, then you will need a very high current 3P3T (Three Pole, Three Throw) switch. Otherwise you WILL short out a battery and I know you don't want to do that... The key is to break one circuit and isolate it, then connect up the other circuit so no two batteries are together via a positive and negative terminals possible shorted together.

 

[VonTrollicus]

Okay I drew up a little pictorial to hopefully show you how you can use a DPDT (Double Pole, Double Throw) switch to use either the 12 volt battery or ONE of the trolling motor series batteries. If you are wanting to select either one of the 24 volt serried trolling motor batteries, then you will need a very high current 3P3T (Three Pole, Three Throw) switch. Otherwise you WILL short out a battery and I know you don't want to do that... The key is to break one circuit and isolate it, then connect up the other circuit so no two batteries are together via a positive and negative terminals possible shorted together.

Perfect, thank you!