24 Volt systems

[Beanerboy]

Ok guys, working on M1009 for the company. I know the charging system on these are a bit different from the M1008. Does one generator charge the 12 volt system and the other charge the 24 volt side? I put brand new batteries on the vehicle and it ran fine for a bit but now it is over charging one battery. It boiled out the distilled water fill caps. Are both generators supposed to charge at 12 volts?

 

[NDT]

Both alts put out 12 volts, one charges one battery and the other charges the other. Regulator in the alternator is shot, easy fix.

 

[Beanerboy]

Ok guys, working on M1009 for the company. I know the charging system on these are a bit different from the M1008. Does one generator charge the 12 volt system and the other charge the 24 volt side? I put brand new batteries on the vehicle and it ran fine for a bit but now it is over charging one battery. It boiled out the distilled water fill caps. Are both generators supposed to charge at 12 volts?

Thank you!!

 

[Recovry4x4]

Oh, BTW, M1009 and M1008 share the same charging system. It's the ambulances and a few shelter carriers that have the 200A system.

 

[Beanerboy]

Both alts put out 12 volts, one charges one battery and the other charges the other. Regulator in the alternator is shot, easy fix.

Alright NDT, I showed my boss's and they said one does charge at 12 and the other at 24. I haven't read in the TM any where at says that. now i have tested them with the truck running and I do get one at 14 and the other at 27-28.

Oh, BTW, M1009 and M1008 share the same charging system. It's the ambulances and a few shelter carriers that have the 200A system.

Yes, I have noticed that but a few wiring things are different. These trucks were saved from the junk yard. They had “mechanics” work on them in White Sands New Mexico the had them dropped off to us here in Fort Irwin, Ca. We have been trouble shooting, repairing, part swapping just to make them run from point A to point B with nowhere in between.

 

[NDT]

Alright NDT, I showed my boss's and they said one does charge at 12 and the other at 24. I haven't read in the TM any where at says that. now i have tested them with the truck running and I do get one at 14 and the other at 27-28.

Yes, I have noticed that but a few wiring things are different. These trucks were saved from the junk yard. They had “mechanics” work on them in White Sands New Mexico the had them dropped off to us here in Fort Irwin, Ca. We have been trouble shooting, repairing, part swapping just to make them run from point A to point B with nowhere in between.

Well there’s your problem, one alternator is putting out 27-28, no wonder your battery is boiling.

 

[Keith_J]

Passenger alt charges the rear battery. Driver alt charges front. Measure at the batteries, not frame ground. The back battery negative is the same as the front battery positive.

The passenger alternator needs an isolated negative, this is connected to the positive terminal on the front battery through a fusible link. The 12 volt output of the passenger alternator is connected to the positive terminal on the back battery, again through a fusible link.

This is how 24 volts is managed with only 12 volt batteries and alternators. On original CUCVs, both alternators are the same. The driver's side alternator negative is connected to the engine ground.

 

[Beanerboy]

Passenger alt charges the rear battery. Driver alt charges front. Measure at the batteries, not frame ground. The back battery negative is the same as the front battery positive.

The passenger alternator needs an isolated negative, this is connected to the positive terminal on the front battery through a fusible link. The 12 volt output of the passenger alternator is connected to the positive terminal on the back battery, again through a fusible link.

This is how 24 volts is managed with only 12 volt batteries and alternators. On original CUCVs, both alternators are the same. The driver's side alternator negative is connected to the engine ground.

Thank you for that. I removed the genes from that blazer and one CUCV. Took all four to Autozone to verify functionality. Turns out the 2 off the blazer were bad and one on the CUC was bad. The main thing is that we purchased one from a local auto part store. One was purchased from a one vender. The other two were on the trucks when we got them. The two we purchased were two of the three that are bad.

 

[NDT]

Ok one thing you need to be aware of, one alternator has to have an isolated negative , it’s a special unit not available at Auto Zone. You can convert a standard one over, but it’s easier to just fix your bad alternator with a new regulator, which is the same.

 

[Beanerboy]

Ok one thing you need to be aware of, KeithJ said the alternators are “the same”, well no they are not, one has an isolated negative , it’s a special unit not available at Auto Zone. You can convert a standard one over, but it’s easier to just fix your bad alternator with a new regulator, which is the same.

Thanks for that info. Our boss just took 5 to a alternator rebuild place. Now we have 3 more to add to that. The guy there said that the ones we took are the originals off the trucks.

 

[Keith_J]

Ok one thing you need to be aware of, KeithJ said the alternators are “the same”, well no they are not, one has an isolated negative , it’s a special unit not available at Auto Zone. You can convert a standard one over, but it’s easier to just fix your bad alternator with a new regulator, which is the same.

I said the original alternators are the same. Same GM part number, same national stock number.

 

[NDT]

I said the original alternators are the same. Same GM part number, same national stock number.

OK Sorry Keith I forgot about that and you are quite correct. I edited my post. Apologies.

 

[Tow4]

Just make sure whoever tests the original alternators puts the tester ground lead on the negative ground post, not the case. Otherwise the alternator will not work.

 

[Keith_J]

OK Sorry Keith I forgot about that and you are quite correct. I edited my post. Apologies.

Thanks, synthesis of multiple posts can be an issue, I just want this relic to be informative, if not recursive.