Which battery isolator type to use with M939A0 A1 trucks.

[goldneagle]

I want to install a separate battery bank for the 18,000 lb winch i am adding to my M923. I looked up the Installation instructions on one brand of battery isolators. There are 2 different types of the isolators. 1 has 3 large terminals only. The other also has an exciter terminal on it. Which type isolator should i use with the standard alternator that is on the M939 truck? Also what amp rated isolator do you recommend?

 

[Suprman]

Are you trying to run 12 volt off your 24 volt system or a separate 24 volt battery bank? I don't believe the stock alternator can provide enough current to charge 2 banks of batteries. If you want to run 12v you can get a power converter.

 

[goldneagle]

Are you trying to run 12 volt off your 24 volt system or a separate 24 volt battery bank? I don't believe the stock alternator can provide enough current to charge 2 banks of batteries. If you want to run 12v you can get a power converter.

I am adding a 24 volt battery bank. No 12 volt taken off this bank. I just need to know if I need the isolator with the exciter terminal or one without to go with the existing alternator.

 

[Suprman]

I would get a basic isolator good for 24 volts at 100 amps or so. I would leave the regulator lead on the main bank like it is. I am pretty sure the stock alt won't be happy it takes a good amount of power to charge 2 banks.

 

[74M35A2]

My opinionated answer to your question would be to use the standard 3 post style, that one should not have any additional exciter wires. 100A should suffice as a guess without knowing more details such as intended batteries you will use, duration of time winch is run, etc....

More batteries is more weight your winch will be pulling, and more claim of space. Why not just run it from the batteries you already have? The engine will likely already be running anyway (not sure how you intend to use the winch, but I think we are yet waiting for a successful electric winch self recovery story in the 5 ton category). Stock alternator is marginal at best, but upgrades are available, including from me. You could also just add a second 24V 70A Delco clone for $100 and run that to your additional battery bank, then link the 2 banks with a marine disconnect if either alternator craps out.

 

[ke5eua]

Golden, you can ditch the isolator and use a 200 amp solenoid instead.

Just have the solenoid activate when the truck is on and have it tie the two bank together.

All an isolator does is keep the secondary bank from drawing on the primary bank by using either high amp diodes or solenoids.

 

[goldneagle]

My opinionated answer to your question would be to use the standard 3 post style, that one should not have any additional exciter wires. 100A should suffice as a guess without knowing more details such as intended batteries you will use, duration of time winch is run, etc....

More batteries is more weight your winch will be pulling, and more claim of space. Why not just run it from the batteries you already have? The engine will likely already be running anyway (not sure how you intend to use the winch, but I think we are yet waiting for a successful electric winch self recovery story in the 5 ton category). Stock alternator is marginal at best, but upgrades are available, including from me. You could also just add a second 24V 70A Delco clone for $100 and run that to your additional battery bank, then link the 2 banks with a marine disconnect if either alternator craps out.

I have an update to the setup we were originally discussing. My friend Allen came across (2) 100AMP 28 Volt Leece-Neville alternators at $60 each. Could not resist getting one at that price! We had them both tested at an alternator shop. Both tested good. My friend Allen installed one on his M923 and it worked fine. He used 3 of the original wires for the connection. Ground, Positive and IGN.

Yesterday we installed the 2nd one on my M923. The only difference was that I had the 3 bolt Cole Hershey Isolator on my system. We connected the Ground and IGN wires to the new alternator and spliced the positive wire and extended it to the Battery 1 terminal on the isolator. We also ran another wire from the Alternator terminal on the isolator to the Positive terminal on the alternator. We ran a wire from the Front set of batteries to the Battery 2 terminal on the isolator.

When we started the truck the alternator did not produce any voltage. So I had Allen jump the Alternator Terminal to the Battery 1 terminal on the isolator. The alternator started to produce the proper voltage! This was a momentary jump between terminals not continuous.

I am assuming the alternator is not being excited with the current wiring setup. The alternator looks the same as the one I have seen on HEMTT trucks.

Can someone help figure out what is done wrong and some solutions.... I am including pictures of the install.

 

[TCD]

Never mind my error as I have a 923-A2...

(I had previously asked what it took to install the alternator.)

;-(

Tom

 

[74M35A2]

You may not have the isolator wired in correctly, the isolator may not be working correctly, or your $60 purchase could be a bum deal. Start by wiring the alternator up same as your buddy's truck, get the isolator out of the equation. See if it works. If so, then it is the isolator or the way you are wiring it. I think one of the PCB solenoids also connects the alternator to the battery bank? In stock form? I have not studied it in detail, sorry. As a cheat, clamp a jumper cable from the alternator B+ to the starter solenoid terminal B+ or directly to your second battery in series B+. Also check for +28v on the excite signal to the alternator. Basically, check to see if the alternator works correctly hooked up as intended, and go from there.