Batteries in series and parallel

[soundguy]

Hi all,
I have 2 accessory batteries and a starting battery. The starting battery is going to remain for starting only.

I have a trolling motor on the bow, and a 12/24V dc receptacle. That receptacle has 4 leads from the 2 accy. batteries connected to it. Selecting 2 forks gives 12V and the other 2 gives 24V. The trolling motor is 24V.

My Question(s):
Can I safely parallel the 2 batteries thus having equal drain when all of the other accessories are connected and still have the 24V trolling motor operate?

Is this bad for the batteries?

Is this bad for the charger? (dual pro)

If paralleling is ok, can I use one bank of the charger to charge both paralleled batteries and use the other bank for the starting battery?

Thanks,
Caine

 

[Silvertip]

Re: Batteries in series and parallel

Absolutely not! But I say that with reservation since you have not provided enough detail. 1) Is there a 12/24 selector switch on the receptacle panel? 2) How many wires are there in the cable to the trolling motor (should be either two or three). Two 12V batteries in parallel provide 12V. Two 12V batteries in series provide 24V so you cannot have a series and parallel connection at the same time or you will have sparks. You can however, pull 12V from one of the batteries if you wish. But you cannot use 24V AND provide 12V from BOTH batteries at the same time. Whatever 12V accessories you want to operate will not significantly affect the drain on the batteries. As for the charger, it more than likely has isolated outputs for the two banks (I assume its a two bank) so it doesn't care if one battery requires more charge than the other. It's made as though its two separate chargers. The start battery rarely needs the high charge rate of an onboard charger so I would let the engine charging system take care of that. If you insist on providing another charging source, consider a Shumacher battery "maintainer". They completed potted so are water proof, have a float feature and can be mounted right at the start battery. They provide a 1.5A max output but that will rarely be needed. Its the float or trickle feature that keeps the battery up to snuff.

 

[soundguy]

Re: Batteries in series and parallel

Thanks for the reply, Silvertip
To clarify..
1- There are 4 wires going to this receptacle:

Select 2 blades and you get 12V, select the other 2 and you get 24V. So, the receptacle jumps for 24V.
Of coarse, there are 4 wires going to the receptacle. 2 per battery.

2- there are 2 wires going from the plug to the foot control. I'm pretty sure there are 2 wires from the foot control to the trolling motor. It is 24V though.

So even though the receptacle is doing the jumping and the batteries do not need to be in series for the trolling motor to see 24V it does not look like I can not parallel the batteries. Right?

This is what I want to do:

Remember, the receptacle gives the 24V, not wiring the batteries in series. (if that matters)

So, no parallel?
The only reason I want to do this is currently, all of my accessories are on one battery. That causes one to drain faster. If they were in parallel, they would both drain equally.

 

[Reel Poor]

Re: Batteries in series and parallel

There is NO way to get 24 volts from batteries wired like in your diagram. The only thing other thing besides 12 volts will be sparks.

 

[Silvertip]

Re: Batteries in series and parallel

Here is a typical 24V wiring scheme. Notice the POS and NEG connections between batteries. Wire the batteries in parallel at the batteries and then try and make a series connection at the connector. You have a very large short circuit.

Here is the only way you can power 12V accessories from a 24V system. As was mentioned, you cannot wire two batteries in a series and parallel configuration at the same time. The receptacle is just that -- it a way to connect and disconnect power. It has no magical ability to distinguish between 24 and 12 volt systems.

 

[Silvertip]

Re: Batteries in series and parallel

One of two things is wrong. If your boat is wired the way your diagram shows, the motor will not see 24V and the wiring is wrong. If the motor does see 24V, your diagram is wrong. But since you said you did get 24V at two terminals and 12V at the other two, proves your diagram is wrong. Compare it carefully with the one below. Note the green wire.

 

[soundguy]

Re: Batteries in series and parallel

Thanks for the info.
Currently the batteries are not in parallel. The outlet (as pictured above) automatically wires the batteries in series using the 4 cables.
This is how it is wired now:

I just wanted to parallel the batteries so the accessories would pull from both batteries.

Looks like I can't do it though.
Thanks for the help..
Caine

 

[Reel Poor]

Re: Batteries in series and parallel

Does you trolling motor have a 12/24 volt switch built into it?

Your diagram in the above pic is still not providing 24 volts to the trolling motor, it's only two 12 volt ckts. The only way to get 24 volts there is via a switch in you trolling motor. There is no such receptical as you are describing that "automatically" converts/connects wiring to provide 24 volts.

 

[soundguy]

Re: Batteries in series and parallel

Does you trolling motor have a 12/24 volt switch built into it?

There is no such receptical as you are describing that "automatically" converts/connects wiring to provide 24 volts.

The trolling motor is 24V and has continuously variable power.

Please go to this page:
http://www.marinco.com/scpt/ProdPage.php?loadItem=2018BR_Marinco Shore Power

and then scroll down to the "Related Links" and read the "Trolling Motor Plug Instructions"

That is the receptacle I have.
Caine

 

[Silvertip]

Re: Batteries in series and parallel

That receptacle is nothing special. It merely moves the green wire I showed in my last diagram above from the batteries to the receptacle. Read the last sentence of the second paragraph in the link you posted and your question will be answered for you AGAIN! It specifically says you must not have jumpers between the batteries. You cannot connect the batteries in series and parallel at the same time as you show in your first diagram (or in any other form for that matter). You will burn up the wiring and possibly burn down your boat. This is exactly why I asked if you had a 12/24 switch. Leave the wiring as it is -- it's doing no harm. Or else run the accessories off the start battery and let the engine take care of keeping that battery topped off.

 

[ManOfwar690]

Re: Batteries in series and parallel

um ya the first diagram he gave you is correct.. do not do what u have presantly or you will burn. also a cpu is recomended for what u are proposing computerised charging unit as to keep the bateries from over chargin eather of the threei would do the first diagram that he gave u and then run a green and black wire to your bow for your trolling mtr . unless you like towboat

 

[Silvertip]

Re: Batteries in series and parallel

ManofWar -- Who is "you" and who is "he" you refer to. If you mean the first diagram posted in this thread is correct -- I assure you it is not!

 

[eatropefish]

Re: Batteries in series and parallel

Silvertip: I've been looking at onboard battery chargers and wasn't sure of the operation--until now. Your diagram answered my question about how to charge two batteries wired in series. I tire of dragging my trolling motor batteries in and out after every trip. You are truely a wealth of information and I appreciate your sound advice.

 

[Silvertip]

Re: Batteries in series and parallel

Glad I could help and thanks for letting us know we were able to answer a question. Everyone here tries hard to provide advice but we rarely hear back from folks indicating if the advice was helpful. Charging two 12V batteries connected in series to provide 24V requires a two-bank charger with isolated outputs. The charger is simply two totally independent battery chargers in a single housing. One set of outputs connects to each of the two batteries. If the outputs are isolated from each other in the charger, the charger doesn't care about the series connection. It's only a problem if the charger grounds are common with each other.

 

[eatropefish]

Re: Batteries in series and parallel

I get it -- Thanks in large part to your diagram.