Using two batteries in parallel

[DiscoDavis]

All,

As part of a new project, picked up a vehicle that was originally equipped in a time before a bunch of fancy dual battery technologies were available. 2x yellow tops now wired up in parallel with one manual disconnect switch to separate the starter bat from aux. Winch is wired to the aux, starter bat is left alone. When vehicle is parked, I was told to manually separate the batteries so they do not discharge eachother (way more of an issue when I had one heck of a crapola starter battery, an old diehard platinum).

>Starter, alt, wired to MAIN POS
>MAIN POS wired to AUX POS
>winch wired to AUX POS
>both NEG grounded together on T case
>Mystery black wire (4 ga or 2 ga) wired to AUX NEG, can't find where it goes to ( I think this is winch ground?)

In the last week I have had to either jump my starter bat or get a jump more times than I ever have... hence picked up a matching 34/78 yellow top to avoid the serious discharging.

I'm going to try and wire up one of those manual isolator keys to be easily accessible, but would it be good to include one of those solenoids the dual battery systems use? Would you have to wire up from the solenoid to ignition signal? Would like to keep it simple.

Lastly, a major concern is both theft and the winch being live while parked. I heard horror stories from Oz where anyone with the right controller could mess with a winch, potentially catastrophically. :Wow1:

I respooled the hecka long winch cable so I know at least the old yellow top was in good shape, and the other is now brand new. Any forseen problems running the same models wired up together all the time?

thanks.

 

[dwh]

What he said.

http://forum.expeditionportal.com/t...ke-a-cheap-isolated-dual-battery-setup-for-50

 

[Factoid]

For your set up and intent (shut off winch power and isolate batteries from each other), a DPST (dual pole, single throw) battery cutoff switch is the ticket. Insert one set of poles between the winch battery and ground (mystery black wire). This shuts off the winch. Insert the second set of poles between the two battery negative terminals. This isolates the batteries from each other. Now you have one switch that accomplishes your stated objective. Here's an example of a DPST battery cutoff switch for about $50, but you can find all sorts including ones with removable handles, locking features, and remote control.

http://www.partdeal.com/cole-hersee...map=77185194&gclid=COvr59rAnNICFQEdaQodi1MGpA

 

[mpinco]

I would add a Bluesea ACR between the starter and 2nd battery. I run a ACR in the engine compartment of my LR4 and a e-Series switch on the trailer to switch between two batteries on the trailer.

 

[DiscoDavis]

Guys,

Thanks for the suggestions. And yes, I have read that 50 dollar battery thread over and over again the last few years.

Solenoid is on order, I picked up enough cables and terminals to at least keep the batteries isolated when parked, and mostly isolated for charging purposes.

You'll see a build thread soon

 

[DiscoDavis]

For your set up and intent (shut off winch power and isolate batteries from each other), a DPST (dual pole, single throw) battery cutoff switch is the ticket. Insert one set of poles between the winch battery and ground (mystery black wire). This shuts off the winch. Insert the second set of poles between the two battery negative terminals. This isolates the batteries from each other. Now you have one switch that accomplishes your stated objective. Here's an example of a DPST battery cutoff switch for about $50, but you can find all sorts including ones with removable handles, locking features, and remote control.

http://www.partdeal.com/cole-hersee...map=77185194&gclid=COvr59rAnNICFQEdaQodi1MGpA

I have something like this, but one of the old school keys that rotates and pops out to take with you... Lucky boy Sheepdog's 90 actually came over from France with one installed.

 

[LR Max]

I ran two optimas in parallel for 10 years. A Yellow top and a Red Top. No problems, no solenoids, cut offs, etc. Just two batteries connected via a #2 gauge wire. The yellow top was brand new, while the red top was 2nd hand. No problems.

After 10 years, the yellow top died, then the red top died the following year. Replaced with a DEKA. I'm converted. One battery now is all I need. I've winched many times with the engine off, no issues with the battery being dead. Also used it many times to drive the starter motor to move the vehicle. One battery, easy and simple.

I put those little post-to-wingnut thingies on my battery, so I could easily install/remove items onto the battery. One such item was the winch. I leave the winch physically disconnected from the battery. Considering...AT MOST, you'd use a winch one trip per month, it was fine. Kept it disconnected. I've gotten into the habit of doing a check before going out, and afterwards. This is when I'd connect/disconnect the winch. Works fine. If I'm out wheeling and get stuck, and need to winch, no extra hassle to pop the hood and connect the winch.

So my 2 cents from experience, go simple. Seems to be fine. Save your $$ and get one of those little portable jump packs. Those are THE SHIZZLE and far more useful than a 2nd battery under the hood. Also nice to carry in the DD for daily use if needed.

 

[rruff]

So my 2 cents from experience, go simple.

Couple decades ago on my ghetto system I bought 3 $30 Walmart starter batteries and wired them in parallel. Used them for starting and deep cycling continuously for a couple years before they'd die and I'd spend $90 again. Not ideal, but it worked well enough.

Now I'm wondering about the opposite approach to simplicity. If a trio of 100ah 12v deep cycle AGM batteries would have any problem starting my truck? Based on this spec sheet, I don't think so. http://files.upgi.com:8086/UPGFileService.svc/GetSpecSheet/45978

Each one will supply 275A @11.1v for 5 minutes. Shorter durations are not listed. But 825A should be plenty.

 

[rruff]

So my 2 cents from experience, go simple.

Couple decades ago on my ghetto system I bought 3 $30 Walmart starter batteries and wired them in parallel. Used them for starting and deep cycling continuously for a couple years before they'd die and I'd spend $90 again. Not ideal, but it worked well enough.

Now I'm wondering about the opposite approach to simplicity. If a trio of 100ah 12v deep cycle AGM batteries would have any problem starting my truck? Based on this spec sheet, I don't think so. http://files.upgi.com:8086/UPGFileService.svc/GetSpecSheet/45978

Each one will supply 275A @11.1v for 5 minutes. Shorter durations are not listed. But 825A should be plenty.

EDIT: Guess I answered my own question. This from Trojan:
"Can I use my deep-cycle battery as a starting battery?
deep-cycle batteries can be used for engine starting but starting batteries should not be used for deep-cycle applications. A deep-cycle battery may have less cranking amps per pound than a starting battery, but in most cases a deep-cycle battery is still more than adequate for the purpose of starting an engine."

I get that some people feel more secure having the starter and DC batteries isolated in case the DCs get drained too far to start the vehicle. But assuming that you pay some attention to your batteries state of charge, is there any reason not to have all DC? I'm aware that you need a big cable to the engine starter.

 

[LR Max]

"Can I use my deep-cycle battery as a starting battery?"

Yes. Used my yellow top many years like that. No problems.

 

[LandCruiserPhil]

After being a dual battery guy for a ton a years I have now run my duals in parallel permanently wired together and carry a jump box. I see this to be the best set up going forward with current technology. Your batteries are treated better when it comes to discharge and charging, you double your available AH, and have a jump box for back up if ever needed. In the past running separated duals I would work one battery hard and be close to 50% discharged. Discharging one battery 50% and the other at 95% and starting the charging is much are and shortens the life verses running a parallel set up where both batteries are discharged 25%. Less to go wrong and all around a better performing system running dual batteries in parallel.

 

[rruff]

Your batteries are treated better when it comes to discharge and charging, you double your available AH, and have a jump box for back up if ever needed.

My thinking too. A dedicated starting battery is a waste of weight and space.

It's highly unlikely you'd ever need that jump box. DC batteries should not be drained below ~50% on a regular basis, and if you are out in the boonies you will surely be paying attention to them.

 

[DaveInDenver]

My thinking too. A dedicated starting battery is a waste of weight and space.

This is true, normal starting duty isn't very tough on batteries and it's mostly wasted weight and capacity. I've scratched my chin on how to better optimize my layout. Dual PC1400, which means I don't really have that much house battery (65 A-hr) but too much starting.

I will caveat to say that I use my starter to get me moving sometimes when I stall on the trail and in that scenario I do want substantial starting capability. I'm moving the whole truck, usually uphill, in gear. Of course it's going to be in low range so there's mechanical advantage. But this is somewhat similar to a dead engine winch pull, it's all energy dumped from the starting battery until the engine catches and the alternator comes online. It's also something you'd only ever see in a stick shift truck.

So I'm not ready to completely give up the 900 CCA and 130 reserve minutes. A PC1400 would be able to drive me (or winch) with a dead engine for a few minutes if I had to. Perhaps to move a dead truck to a better place for recovery. So having just enough battery to start the engine may not be the most ideal place to cut excess.

 

[rruff]

So I'm not ready to completely give up the 900 CCA and 130 reserve minutes.

The DC battery will actually give you more though. A 100ah DC will typically have 240 reserve minutes. 480 if you are using a pair and ditch your starting battery. I think you are much more likely to kill your starting battery doing that, as you will tend to drain it down too far.

 

[LandCruiserPhil]

My thinking too. A dedicated starting battery is a waste of weight and space.

It's highly unlikely you'd ever need that jump box. DC batteries should not be drained below ~50% on a regular basis, and if you are out in the boonies you will surely be paying attention to them.

I agree 100% and if you are only draining your batteries 20-25% on a regular basis they will have much longer life, says my battery coach.
For me I frequently travel to remote areas solo and the Jump box is my AAA for off road.