Dual Battery Isolator Wiring

[kickdeez]

I just put 2 brand new Optima Yellow Top AGM batteries in the burb, along with a brand new 105 amp alternator, and a Cole Hersee 48122 battery isolator for the dual battery setup. The battery isolator looks like this:

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I selected this particular model partially because im a sucker for blue anodized stuff, but mostly because it said that GM vehicles 88 and newer require a battery isolator with an "exciter wire" (the post on the far right of the isolator). FYI: the burb is a 1990. I wired it up as described (not rocket scientology - but I'm also not an electrical guru either), and it wouldn't fire. Starter turns, but fuel pump relay did not click over, interior lights didn't come on, and maybe a couple other things weren't working.

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Troubleshooting approach: Simple switch of the alternator wire over to the Battery 1 post (on the isolator), and everything works again. No harm, no foul. I can drive it as is and everything works. BUT, I know that my auxiliary battery isn't being charged - which defeats the purpose of having this style of battery isolator, so both batteries would charge while running, but if one decided to crap out, it wouldn't drain the other.

So getting to the question(s): Do I really need this model isolator with the "exciter wire" post? I know that the circuit I tapped into has 12 volts when the ignition is in the "on" position. I assume that means when the key is in the "start" position, it has power too. But I am not certain. Can someone confirm if that would generally be true? Cole Hersee also makes the same isolator but without this "exciter wire" post. Should I be using that one instead?

 

[kickdeez]

I am thinking I might have got caught in the squarebody year trap (73-87 + 88-91 suburbans). My gut is telling me that I need the isolator without the exciter wire terminal. But, I will gladly hear any and all opinions/advice/suggestions!

 

[75gmck25]

The year is not the important detail - its whether or not you have a CS130 alternator. Early Squarebody trucks used the 10SI and 12SI alternator, but I don't know when they swtiched to the CS130.

The SI alternators have a Bat terminal screw on the back, and next to it there is a two wire plug like this one https://www.summitracing.com/parts/...ur_al9oOra3NbmnBuRB-vKhOX4yof5mIaArHuEALw_wcB

The CS130 has a four wire plug like this one https://www.summitracing.com/parts/...Y2lOdftrcGqbf-o8PQNsivGht_zBxCf0aArjMEALw_wcB

Bruce

 

[kickdeez]

The year is not the important detail - its whether or not you have a CS130 alternator. Early Squarebody trucks used the 10SI and 12SI alternator, but I don't know when they swtiched to the CS130.

The SI alternators have a Bat terminal screw on the back, and next to it there is a two wire plug like this one https://www.summitracing.com/parts/...ur_al9oOra3NbmnBuRB-vKhOX4yof5mIaArHuEALw_wcB

The CS130 has a four wire plug like this one https://www.summitracing.com/parts/...Y2lOdftrcGqbf-o8PQNsivGht_zBxCf0aArjMEALw_wcB

Bruce

https://www.napaonline.com/en/p/RSE2134521

I am about 90% sure this is the alternator I just put on the truck.

 

[Daveo91Burb]

So my ‘91 burb has a dual batt setup that is factory “style”. I say style because i took all the parts and wiring from my ‘90 burb parts rig and my install may not be perfectly factory.

The wiring on the factory setup is super simple. All it is is a big relay mounted on DS fender well. Relay is triggered with key in on position which then connects positive of aux batt to firewall mounted terminal block. AFAIK, that ties all vehicle systems together EXCEPT starting circuit but including charging system. Without key in on position both batts are fully isolated. Upside: simplicity and factory appearance and in my case, cheap. Downside: aux batt gives no assistance with starting and the factory positive cable on the aux is really small (8 or even 10 ga) so it’s obviously designed to support accessories only. I’ve been thinking about ways to tie them together with the original main battery positive cable to the starter from my parts rig. I think I can do it, just need to find an appropriate relay that can handle that load and is triggered by the purple wire to the starter. I think....

 

[Daveo91Burb]

https://www.gmsquarebody.com/threads/factory-dual-battery-wiring.15855/

 

[Daveo91Burb]

@kickdeez: sorry you probably didn’t get much out of my two posts above - I saw that you already posted on my dual batt thread back in august!

 

[kickdeez]

@Daveo91Burb I did find your info helpful. Unfortunately my setup is a little different (non-factory). I was trying to modify an existing dual battery setup that was installed by the previous owner, but make it work to suit my needs without redoing everything. The “isolator” that the P.O. had installed was really more like a junction block than a true isolator (and I may even be using the wrong term - isolator vs separator). But as I tried to describe in my previous post, my new isolator allows for the alternator to charge both batteries, but if one begins to die, it won’t draw the other battery down. And I think mine works very similar to yours...only the main battery provides power to the vehicle’s electrical system. The auxiliary battery only powers the extra accessories like my winch, air compressor, trailer brake controller, and will power some other accessories that I plan to add in the future.

Anyway, I figured out my problem. I had 2 separate wires coming off the “batt” post on the back of the alternator. One wire originally went to the positive terminal on the main battery, and the other went to a junction block on the firewall (which subsequently connects to the fuel pump relay and other things). So when I took the 1st wire off the positive terminal on the main battery and hooked it up to the designated “alternator” post on the isolator, the junction block on the firewall no longer had power (which meant the fuel pump relay had no power). So, I took the second wire (the one that went to the junction block) off the back of the alternator and ran it to the positive terminal on the main battery, and problem solved. It works like it’s supposed to now.

Thanks for the replies!

 

[shiftpro]

A good isolator will charge the start battery before the second battery. When the start battery is up to snuff only then will the second battery get the charge.

 

[kickdeez]

A good isolator will charge the start battery before the second battery. When the start battery is up to snuff only then will the second battery get the charge.

Send link for a “good isolator”. I’m already disappointed with the charging distribution of this isolator.

 

[shiftpro]

Send link for a “good isolator”. I’m already disappointed with the charging distribution of this isolator.

http://www.fridge-and-solar.net/dual_bat.htm

 

[kickdeez]

http://www.fridge-and-solar.net/dual_bat.htm

I've read through that page a couple times now, and have looked at multiple VSRs for dual battery setups. Can you help me understand where the alternator is supposed to connect? Do you run it to the VSR, the starting battery, the auxiliary battery, or some combination of them?