2 X 12 volt batteries - don't want a 24v system...

[KenJr]

I recall reading somewhere a while back that it's possible to take 2 x 12v batteries and hook them up in such a way that you get 'double' the life @ 12v.

I don't want to hook them up in such a way that I have a 24v system, I just want to take advantage of an extra battery that I have in my boat and not have to deal with changing the leads if/when the battery is low.

Is this possible to do? I've been googling around and can only find stuff on running 2 12v's in series and thus creating a 24v system.

Thanks!

 

[jtexas]

Re: 2 X 12 volt batteries - don't want a 24v system...

Works great, I run my trolling motor like this. You need two jumper wires, connect 'em positive to positive and negative to negative. Your batteries need to be identical and the same age.

Note that when one batt develops a bad cell, it'll bring down the performance of both, and they'll both need to be replaced at the same time.

 

[KenJr]

Re: 2 X 12 volt batteries - don't want a 24v system...

Cool - I was able to find this.

http://www.vonwentzel.net/Battery/00.Glossary/

I was thinking to myself...I don't want to run them in series...but what about parallel? d

So, one quick question...

What's the best way to charge? I'm reading that you should be able to leave them connected in parallel and they should charge OK. Does it matter where you put the + and - leads from the charger? Should + go on battery 1 and - goes on battery 2 or does it matter?

 

[KenJr]

Re: 2 X 12 volt batteries - don't want a 24v system...

Your batteries need to be identical and the same age.

This isn't what I read. What I'm finding is that the general rule of thumb is that when you run batteries in series you want them to be matched. In Parallel, that's not the case:

http://www.amplepower.com/pwrnews/parallel/

Specifically:

First, a parallel system allows more convenient sizes which yields a greater range of systems. For instance, a 100 Ah battery can be placed in parallel with a 200 Ah unit to obtain a total of 300 Ah. Charging proceeds as expected, with each battery receiving its share of the charge current, and each reaching a full charge at the same time. On discharge, each battery supplies current according to its relative capacity, and both batteries maintain the same percent depth of discharge.

Contrast this with two 6 Volt units. With series connected units, each battery must be of equal capacity. That means that you can only build banks in the capacities that the manufacturers decide to build. Despite close manufacturing tolerances, each supposedly identical battery has different capacity and when the specific gravity is different in each, capacity is further affected. Deep discharges of series cells can cause the weaker cell to be reverse charged. A weak cell in a series string can cause other cells to be overcharged. An open cell in a series string results in a total power loss. For best results, 6 Volt batteries should be periodically charged individually and should definitely be equalized individually with equalizing resistors across each 2 Volt cell. This argument extends to 2 Volt cells when they are packaged individually.

In a series connected bank, an open circuit would mean the total loss of power, but a parallel bank will still function, albeit with less capacity. You'd still have enough power for an emergency call on the radio with a parallel bank. In fact, the failure might be transparent in a poorly instrumented system until a prolonged heavy discharge occurred.

The consequence of a cell short in a parallel bank will be a partial discharge of the remaining batteries in the bank. Even so, a parallel bank with one shorted cell has enough capacity to use the radio, or crank an engine.

 

[vipzach]

Re: 2 X 12 volt batteries - don't want a 24v system...

parallel is what you want. you do not have to have the same size batts for a parallel connection, but it is not a bad idea to have to of the same size and age, because like jtexas said, if one of them develops a bad cell, the other battery will keep trying to equalize the charge and they both will be dead. When you charge them, just hook the +/- to one battery and they both will charge up. Also, depending how close you batts are, I would use a minimum of 8 gauge wire.

 

[GabeNalley]

Re: 2 X 12 volt batteries - don't want a 24v system...

Run them parallel but put a dual battery switch in. This keeps one from discharging the other unless you shut them down and leave the switch on "both". You still hook up the negative the same, but when you run the positives each battery will send a feeder to the switch and then the switch goes to your starter.

Switches are everywhere. Guest switches are the standard. This way you can buy a $20 switch and not another battery at $80.

 

[Silvertip]

Re: 2 X 12 volt batteries - don't want a 24v system...

Don't need to bother with the battery switch. Even with the switch, the minute you select the BOTH position, one bad battery will draw down the other until they are equal and that will happen rather quickly.

 

[GabeNalley]

Re: 2 X 12 volt batteries - don't want a 24v system...

The only good time to switch to both would be when its running, to charge both batts or like you said, it will kill both.

 

[jtexas]

Re: 2 X 12 volt batteries - don't want a 24v system...

we're not talking about a bank that's connected to an outboard charging system are we? If so best check and make sure your alternator can handle it.

On the other hand if you're talking about a 12v bank of deepcycles for trolling motor, bait tanks, or whatever accessories, parallel use will give you more than the combined amp hours since you'll be discharging them more slowly, you'll actually get more power out of them.

Thanks for the info on parallel systems, BTW - that's good to know.

 

[KYHunter2]

Re: 2 X 12 volt batteries - don't want a 24v system...

I have mine connected to make basically a big 12 volt battery. (Parallel)

I bought them both new at the same time. You don't want to use one old one new etc.

I have mine connected to a 2 bank @ 10 amps per bank, guest charger / onboard.



One bank for the two trolling motor batts, the other for my cranking battery. That also runs my bilge ,depth finders, lights, etc.


However you chose to charge them . Do it after each use. Even if they still have alot of charge. They'll last longer .

Never had any trouble , engine keeps starting battery charged just fine.

I've seen people use clips to connect the batts. I use ring terminals . The tighter the connection the better.

I also coat the connections with 3-M liquid tape . It keeps them good and dry , slows or prevents corrosion. And is easy to peel off, if need be.

Also replace the wing nuts with S/S nuts . Easier to get good and tight.

KYhunter

 

[Dunaruna]

Re: 2 X 12 volt batteries - don't want a 24v system...

[colour=blue]Google 'VSR' (voltage sensing relay).

 

[KenJr]

Re: 2 X 12 volt batteries - don't want a 24v system...

we're not talking about a bank that's connected to an outboard charging system are we? If so best check and make sure your alternator can handle it.

No. I have a cranking battery for my 70HP Rude and 2 other batteries for trolling motor, etc...

Based on past experiences and what I've read in the past - is it generally a best practice to keep your trolling motor seperate from everything else?

 

[KYHunter2]

Re: 2 X 12 volt batteries - don't want a 24v system...

Thats what I've allways done. Less chance of interference in your depth finders .

The only thing on my 2 deep cycle interstates , is my trolling motor .

Just hook them in parallel , and go fishing . No need for anything else.

Everything else is on the cranking battery.

KYHunter