SIMPLE dual battery set-up

[woytovich]

Can I hook up 2 batteries without any switch/solenoid/isolator? Positive to positive would yield 12v right? I know I loose the security etc etc of the switch/solenoid/isolator solutions (and I'm going to install the isolator I have at some point) but I'd like to get the 2nd battery in the truck and off the shop shelf sooner rather than later... Are there any real problems with this approach? Am I being penny-wise and pound-foolish with my install time and effort?
Thanks,
mark

[Pighead]

No problem. That's what I been running for years.

[hoser]

Ideally, the batteries would be identical.

[sandcruiser]

positive to positive and negative to ground would keep it 12v

but if the batteries are different brands/models and/or different ages then you are likely to kill the newer battery from overcharging. That is to say that the older battery will require more juice to charge it than the newer battery. That extra juice will keep the alternator's voltage regulator pumping out the volts, which will boil off the electrolyte from the already-full newer battery, thus damaging it.

For a weekend, it would probably be just fine. But longer term is probably a bad idea.

[woytovich]

Being a belt and suspenders kinda guy I had planned to do an isolator AND a solenoid dual battery set-up: isolator to keep the charging organized and a solenoid to allow me to join the batteries for winching or to deal with a dead starting battery. I bought the solenoid and isolator from WranglerNW a couple of years ago and am now thinking about installing it... I can't find my paperwork/wiring plan...

Can I do this? Is this (see pic) how the above SHOULD be wired (I left off the ignition wire to the isolator and the switch wiring for the solenoid)

Is there more info out there from some "official" source that I have not been able to find via Google?

TIA

[shinny]

"but if the batteries are different brands/models and/or different ages then you are likely to kill the newer battery from overcharging. That is to say that the older battery will require more juice to charge it than the newer battery. That extra juice will keep the alternator's voltage regulator pumping out the volts, which will boil off the electrolyte from the already-full newer battery, thus damaging it."

This doesn't make sense with my, perhaps simplistic, view of how a charging system functions. Doesn't the voltage regulator prevent this? It should be trying to provide the same charging voltage independent of what's hooked up to it. Any 12V shouldn't be damaged by a properly functioning alternator/regulator. The only issue I can think of right now is if you had a poor battery, could it partially drain the good one?

[woytovich]

If the ONE voltage regulator on the ONE alternator thinks that one of the 2 batteries needs a charge it'll provide amps to do that to BOTH batteries: the one needing the charge and the one not needing the charge. Potentially "overcharging" the one that didn't need a charge. Is that right?

[woytovich]

I have a question:
Given 2 identical batteries and given that one gets mostly drained during a winching episode (batteries NOT joined). In the NEXT winching episode if I were to choose to join the 2 batteries with the solenoid will the good battery want to power the winch AND try to charge the mostly dead battery at the same time? Would this result in a HUGE drain on the good battery (moreso than just the winching would demand)?

If this is so would it be true that any time one battery has less of a charge than the other and you join them via the solenoid that the "good" battery will use part of it's output to charge the "bad" battery effectively reducing the power available for the intended use?

And if this is the case then one would want to always keep both batteries equally charged at all times and always drain them at the same rate? This would seem to make the case for going with the "simple" solution of just wiring the 2 batteries together without a solenoid or isolator...

I'm going to ask this of WranglerNW as well...

mark

[sandcruiser]

my understanding of the situation is this:
In order to charge a battery, the alternator produces a "high" voltage of up to around 15v for a discharged battery. To float it along and run your car's electrical system, the alternator produces around 14 volts (14.2? 13.8? something like that) I could be confused, it might only be 13.4v. But regardless, your alternator doesn't put out "12" volts unless the battery is depleted far enough or the load is high enough that it can't produce the higher voltage.

I found the following table at The 12volt Side of Life (Part 1)


So if you have two batteries in your rig, and one is older and charges more slowly/incompletely due to have sulfation or cracks or low electrolyte, (etc etc), then the alternator is going to try to get the lower battery up to 12.9v. But it will be charging both batteries. So when the fresher battery is fully charged, it is going to continue to receive higher voltage than it needs, thus boiling off electrolyte and generally overcharging the battery.

I'm not an expert, I'm just regurgitating what I've read on the subject.

I have run two batteries as described- no isolator, just the two batteries. Battery life in that setup wasn't good.

My favorite way to run dual batteries is still the following:
Leave your entire stock system alone, minus the stereo, disconnect that completely from the stock system.

Add a second alternator. Add a second battery and connect the positive to the alternator, the negative to ground. Put all of your aux. loads on the 2nd battery/alt (also add the stereo to the 2nd battery/alt).

It is a hassle to add the 2nd alternator, but other than that, the system is really painless and does a great job of addressing the issues for which most people want a 2nd battery. It should also make your winching/offroad lights/fridge work better as you've got more available amps coming off of the 2nd alternator because it doesn't have to run the engine, fan, headlights, etc.

One thing: you've got to be very careful with wiring stuff so that you don't ever cross the positive wires, or you'll end up with the situation that I had: two alts charging two batts and killing them off quickly :(

If you want to get fancy (I wouldn't) you could add in a marine switch such that would allow you to connect the two batteries for very heavy loads like winching, or for starting the truck if the stock battery goes dead.

But part of the beauty of having the batteries completely isolated is that you can't flatten your starting battery by winching off of it.

Side note: you can get an inexpensive alternator for about the same amount of money you would spend on an isolator/switch/wiring/lights/etc system. So the bracketry is about the only obstacle to doing the dual alts

Shoot, I don't even need dual batteries and I'm getting excited about doing a dual alt/batt system

[alia176]

lol, you went from a "simple" design to a typical dual batt setup (Wrangler, Painless, others)...!!!

[woytovich]

Originally Posted by alia176

lol, you went from a "simple" design to a typical dual batt setup (Wrangler, Painless, others)...!!!

Why do less when you can do MORE!

Actually the initial question was meant to ask if I could (should?) get this connected (and the second battery off the shelf) and operational while I worked out the wiring of the "real" system... now I'm ready to go with the "real" one I guess....

[Boston Mangler]

Doesnt get easier and more bombproof then this:

80 Series Dual Bat System