Dual Battery Setup Help

ntsqd

Heretic Car Camper
The whole point of the ACR is to isolate the second battery when the alternator is not charging and the primary battery is not charged. Forcing the ACR to stay closed during cranking means that any starting current supplied by the aux battery will be routed through the ACR. This most definitely is NOT a good idea as these solenoids are not rated to handle starting current.

If you do not want to allow the ACR to be automatic then you're better off not getting one. Use a Cole-Hersee continuous duty solenoid instead. Wire it to activate with a manual switch or only when the ignition is on or however you wish to. Choose the solenoid with care. Some have a fairly high current capacity, others have a very low current capacity.

The bus bar is used on boats because they do not have a common ground. Can use it on a land vehicle, but excepting some particular circumstances it would be extra cost for not much gain.

Perhaps you'd get better advice if we knew all of your goals & uses for the system?
 

TwoTrack

Buy Once, Cry Once
I just want a dual battery system that I can turn on/off. I use this truck as my DD as well and don't want the system running constantly. I want to power my offroad driving lights, camper lights, other small misc electronics (laptop charger/phone) and eventually a fridge. I would like to place the battery behind the driver seat in the extended cab as well as the on/off switch. All the while keeping the total cost, including battery to around $400 max.

**also a small air compressor

What kind of current capacity do you think I need to look for?
 
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wrcsixeight

Adventurer
The Cell phone charger might consume 0.4 amps. Mine draws 0.3 amps when charging and playing music through it's own speakers.

My Laptop can consume almost 8.0 amps if watching a DVD and charging the battery at the same time. Fully charged battery and typing this, about 3.4 amps.

My 3 year old fridge now draws about 2.4 amps when the compressor is running, and it runs less than 33% of the time, so it uses about 1 a/h per hour.

Having a dual battery system you can turn off can be as easy as adding a toggle switch onto the wire which activates the dumb solenoid. You can do it for under 400$ easy. The biggest $$ item will be the AGM battery for behind the seat. Get one with at least 68 amp hours.
 

TwoTrack

Buy Once, Cry Once
Okay, after a little more research I think I may understand these a little bit better so I'm going to try again...

If I take a continuous duty solenoid and attach the two batteries positive terminals to the two large posts on the solenoid. Then wire both battery negatives to one another. Then I still have two small posts left on the solenoid. One is the ground. The other I can wire to a on/off switch.

Does this sound better? I will draw up a diagram tonight once I get home to make it easier to understand. But it makes sense to me, at least right now it does.:confused:

Thanks everyone for you input and help so far.
 

dwh

Tail-End Charlie
I use this truck as my DD as well and don't want the system running constantly.

You're probably better off with it on all the time. Batteries have a self-discharge rate; they drain just from sitting. Letting a battery sit at less than full charge for any length of time - even a few days - will cause sulfation. Over time, as the sulfation builds up, the total capacity of the battery goes down.

If it's a daily driver, then it's a good idea to let the system keep that aux battery topped up, since keeping a battery fully charged is the best way to extend its life.
 

wrcsixeight

Adventurer
You got it. That is the simplest way to do it.

Use a lighted toggle switch. You can power this lighted toggle switch from a wire which is only hot when the engine is running/ or ignition on, or you can power it directly from the battery.

Here's a diagram I quickly drew up for someone else.
DumbSolenoidwiring.jpg
 

dwh

Tail-End Charlie
If I take a continuous duty solenoid and attach the two batteries positive terminals to the two large posts on the solenoid. Then wire both battery negatives to one another. Then I still have two small posts left on the solenoid. One is the ground. The other I can wire to a on/off switch.

Yup, it's a standard dual battery charging and isolation lash-up known as a "split-charge relay":

http://www.powerstream.com/battery-isolator.htm

(your wiring diagram is at the bottom of that page)

Fancy ones from National Luna, SmartGauge, Powerstream, Sterling Power and others have computers to switch the solenoid on/off.

It's superior to a diode type isolator (like you see in an auto parts store with a big heat sink) and here is why:

http://www.smartgauge.co.uk/diodes.html

Also, there is a common myth about large current surges between the batteries when the solenoid is activated. Here's the math to explain why it's a myth:

http://www.smartgauge.co.uk/nosurge2.html
 
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ntsqd

Heretic Car Camper
With the manual switch comes the question of where to source the power to drive the continuous duty solenoid. If it comes directly from either battery then it will stay on until you remember to turn it off.

If it comes from an ignition source, then it will only be on when the key is in the "run" position.

Forgetfulness is what drove me to buy a ACR. :sombrero:
 

TwoTrack

Buy Once, Cry Once
If it comes from an ignition source, then it will only be on when the key is in the "run" position.

Okay. I think I've got this....but one last question. If I wire it to an ignition source, can I still use a switch.

Would I just put the switch between the solenoid and the ignition source?

Thanks
 

dwh

Tail-End Charlie
Okay. I think I've got this....but one last question. If I wire it to an ignition source, can I still use a switch.

Would I just put the switch between the solenoid and the ignition source?

Thanks

Sure can. That would function only to turn it off by interrupting the power from the ignition switch to the solenoid coil.

If you wanted to also have the capability to jump start from the aux battery, you would need a momentary contact switch, probably best wired to get power from the aux battery (since it would have juice if you'd left your headlights on and killed the engine battery and needed a jump start).

[ame="http://www.amazon.com/gp/product/B001715TYS/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B00004WLKE&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=08VP955XD01ZNY8XVN0V"]Amazon.com: Momentary Button Starter Switch w/Boot: Automotive[/ame]



I have a simple split-charge relay in my truck. I've had the truck almost two years, and can't think of a time that I would have needed to shut it off. But I have needed to jump start it a couple times.

It was on the truck when I got it, and the battery cables were normal battery cables like you can buy at any auto parts store. Those cables were not enough to jump start the truck from the aux battery. I had to bust out my jumper cables, which are custom made out of 2/0 welding cable and are heavy as sin. (Luckily, both batteries are under the hood.)

However after I installed big beefy battery cables, then I could jump start from the aux battery, through the solenoid, without having to use jumper cables.
 

prestidigitizer

New member
Okay. I think I've got this....but one last question. If I wire it to an ignition source, can I still use a switch.

Would I just put the switch between the solenoid and the ignition source?

Thanks

Be sure to keep us posted on your progress! I've got a '09 Ranger I'm looking to do this to, though I haven't picked my battery location yet (not in the cabin though.)
 

alexrex20

Explorer
sorry to bump a thread with my own questions on my own vehicle, but this is something i've always wanted to do. i've done my research and am pretty sure i'm going to use this kit from Painless Wiring, sold through AutoZone. I have credits with autozone from their Rewards Program, so that's a plus.

the Painless setup uses a switched solenoid to allow you run the batteries in 3 configurations:
1. Switch position one isolates the auxiliary battery. No light. (same as OEM as though no auxiliary battery is hooked up)
2. Position two connects the auxiliary battery while the ignition is on. Green light. (both batteries charging)
3. Position three connects the auxiliary battery at all times. Red light. (for jump starting the main battery or max current for high loads like winching)

for a main battery, i will use a Sears DieHard Platinum, the P6 which is recommended for my Pathfinder. i'm not sure what i want to run for the auxiliary battery; maybe an Odyssey or Exide Orbital? i don't want an Optima.

since i'll be running the batteries as a true auxiliary, maybe i'll use the DieHard Platinum as the main, and my current Everlast Gold (Wal-Mart) for the auxiliary. in other setups, they use one battery strictly for charging, and the other battery for everything else. the idea is that there is never any drain on the starting battery, so you will never be left stranded. i think i like the Painless configuration better.

i've thought about isolators, but i think i like the solenoid better. what should i do differently?

i've looked at the Hellroaring and Kodiak setups, and i can't justify the (high) cost, relative to the Painless solenoid setup.
 
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