Multiple Batteries

So this forum seems to be the most knowledgable...
hey im trying to run another battery for all my electronics, ie winches lights etc...
do you guys know whether to put the two batteries into a series, or into a parallel lineup...
series i would get more amps and volts would stay the same, but parallel it would get more volts and amps would stay the same....
so which one do i do....
thanks in advance

You could connect two 6 volt batteries in series or two 12 volt batteries in parallel.

I'm not sure I have ever heard of two 6 volt batteries in series in a Jeep application. The main advantage of using two 12 volt batteries connected in parallel is backup. If one battery goes down, you will have the other battery to keep your system running. With two 6 volts, if one goes down then your entire 12 volt system is down.

Your engine wants cold cranking amps and your accessories want deep cycle amps.

If you plan on running two 12 volt batteries in parallel you will want to buy two identical batteries at the same time and connect them with an isolator.

http://www.hellroaring.com/battery1.php

Since most of the stuff on your vehicle is 12 votls, you need to keep the voltage there.
You have the series / parallel backwards. In series the voltage doubles, and in parallel the current doubles

ah ha...thanks for the help guys

How much stuff do you have to run?

You can run quite a bit of stuff on one good battery, including the winch. The lights should be running off the alternator. If you go out by yourself and want the back up of another battery, then you'll need to keep the batteries seperated so if you loose one you still have the other.

muddymopar said:

series i would get more amps and volts would stay the same, but parallel it would get more volts and amps would stay the same....
so which one do i do....
thanks in advance

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Reversed. Connecting batteries in series adds voltage, but not current. Connecting batteries in parallel means same voltage, but adds up the current.

If you connect two 12VDC batteries at 200Ah in series, you get 24VDC at 200Ah.

Connect the same two batteries (12VDC @ 200Ah) in parallel, and you get 12VDC @ 400Ah.

Identical batteries are especially important when connecting batteries in series - as you end up with batteries draining each other below a certain threshhold (and you effectively draw batteries x lowest current rating before it gets hairy.) It's a bit less important in parallel - but banks of batteries should still be the same ratings, and the same age (if you have a pair of batteries that work together, get them both at the same time and use them at about the same rate.) If you isolate one battery from the other, but they're still connected in parallel (like with deep cycles on isolators,) you can get some room with age and ratings - but you still want to keep things fairly close. Banks on either side of an isolator should still be identical (two batteries on each side of an isolator should be two sets of twins.)

The main reason to run a secondary battery would be one of the following:

1) You have a massive high-draw accessory that sees at least occasional use. Like a winch (drawing anywhere between 200 and 450A - given vehicle weight and added goodies and much and such - especially if you're dealing with mudding...

2) You have electrical accessories that you want to use with the engine not running - like radios, refreshment gear (blender, fridge, ...) or inverters and power tools.

3) You have lighting you want to use with the vehicle off - work lights or something like that.

Note the largest factor tho - stuff you want to use, powered electrically, with the engine off. Or, you use an electrical winch a lot.

Im putting in 2 batteries in my rig, I run a decent sized inverter, have a portable mig welder that requires2 batts and will be adding a winch one day. Im running them parallel with a isolator and thinking I might put a switch on them to run together or seperately.
Jeremy

in2fords said:

Im putting in 2 batteries in my rig, I run a decent sized inverter, have a portable mig welder that requires2 batts and will be adding a winch one day. Im running them parallel with a isolator and thinking I might put a switch on them to run together or seperately.
Jeremy

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Use a constant-duty solenoid. You can usually get them with higher current ratings for less $$$, and you can wire them (easily!) to override in either direction you want. Wiring diagrams for doing so are on my site, under "Instructions."

(Haven't I mentioned this elsewhere recently?)

Does your portable MIG rig want two batteries to get to 24VDC, or just to supply ample current? It does make some difference...

5-90 said:

Use a constant-duty solenoid. You can usually get them with higher current ratings for less $$$, and you can wire them (easily!) to override in either direction you want. Wiring diagrams for doing so are on my site, under "Instructions."

Click to expand...

I was planning on using a Marine dual Batt switch, you know the big red knobs with option for either or both. Besides being a manual operation is there any drawbacks vs using solenoids?

5-90 said:

Does your portable MIG rig want two batteries to get to 24VDC, or just to supply ample current? It does make some difference...

Click to expand...

Yeah, they need to be in series and the way for me to control "heat" is by using different lenghts of cables. Its a real simple unit that uses a drill for line speed. No cool onboard stuff like the premier welders but it will get the job done in a pinch.
Thanks, Jeremy

Gah. Having to run them as 24VDC but charge them as 12VDC may make things difficult - I don't know an easy way to do it with OTS equipment offhand. An isolator won't do it, and you'll have to be able to run both batteries "at the same time, for the same duration" to keep them "paired" and not have them drain each other (makes things more difficult.) Check to be sure - since most automotive welders seem to be able to run on 12VDC.

It would actually be easiest to set it up as a secondary electrical system - using a 24V alternator (heavy Diesel or Military trucks run 24VDC, Light Truck Diesels run 12VDC,) a bank of batteries, and just using the common chassis ground (the secondary circuit will still be isolated from the primary circuit.)

Failing that, you'll need a very large DPDT switch (rated for a couple of hundred amperes,) which will allow you to reverse the connections on the second battery by flipping the switch. No, I've no idea where you'd find a switch that big, offhand, without getting an open "knife" style switch...

OTS = Off-the-Shelf
DPDT = Double Pole, Double Throw.

OH, I see what your saying now. Yeah, when I go to use the welder I disco from truck and rewire them manualy. Im hopeing that I rarely have to use it anyway. I am going to use that switch incab and and prolly only when using the inverter. since I have no heater/A/C box under the dash I have plenty of room to run the inverter, wiring and airbox(hope the sound doesnt drive me nuts).
Jeremy

One thing to be careful of.
I set up a dual battery system using a 200 amp continuous duty solenoid set up with a 3 pos switch.
-Normal position was connected only when ignition on for charging.
-Pos 2 was disconnected all time.
-Pos 3 was connected all time (for jump starting)

I was using an Optima Red Top for standard and a Yellow Top for aux (winch, lights, compressor, inverter, etc)
After early replacement of the Red Top I found out that Optima (and everyone else, it turns out) strongly recommends NOT using two different types of batteries in a parallel system unless an isolator or "smart solenoid" system is used.
Apparently if there is any difference in the two batteries, charging them together is a problem.

thanks for the help guys

Just for everyone knows a semi runs 3-4 batterys in parallel without an isolator.

Here's a great link about this subject.

BillaVista's Dual Battery setup

TNT said:

Just for everyone knows a semi runs 3-4 batterys in parallel without an isolator.

Here's a great link about this subject.

BillaVista's Dual Battery setup

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Yah - it's usually a bank of two large batteries (BCI group 27 or larger,) or a pair of banks in series/parallel - since heavy Diesels run on 24VDC, vice 12.

Even so, the batteries are usually replaced in banks, rather than singly.

5-90 said:

Yah - it's usually a bank of two large batteries (BCI group 27 or larger,) or a pair of banks in series/parallel - since heavy Diesels run on 24VDC, vice 12.

Even so, the batteries are usually replaced in banks, rather than singly.

Click to expand...

Most of the semis are 12 volt. 24 volt is used mainly on heavy equipment.

Semis run 3 or 4 925CCA group 31 batterys in parallel.

TNT said:

Most of the semis are 12 volt. 24 volt is used mainly on heavy equipment.

Semis run 3 or 4 925CCA group 31 batterys in parallel.

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Meh - that's my confusion. Worked on too much off-highway equipment...

TNT said:

Most of the semis are 12 volt. 24 volt is used mainly on heavy equipment.

Semis run 3 or 4 925CCA group 31 batterys in parallel.

Click to expand...

my diesel ram runs 2 batteries in parallel with no isolater as well
even with that, when both grid heaters run in the winter, the headlights dim, wipers and windows slow down etc. etc.
when going to a multi-battery system without an isolator, be sure to get two of the same exact batteries, with as close a manufacture date that you can, both brand new.