12v vs 24v Need electrical geniuses...

[Acesneights1]

OK, This is a CUCV question but over at Steel Soldiers they'll run you out on a rail when you consider modifying the factory system. My CUCV (1986 Chevy k30 6.2dsl) has two 12v alts wired in series . The second one is isolated to provide 24v. The starter in the truck is 24v but the rest of the truck is 12v. The 24v is knocked down to 12v via a big resistor on the firewall. Here's my issue. The turck has vbelts and they suck. I recently acquired a serp belt setup for a 6.2 but it uses only one alt. I wish to keep the 24v start so converting to 12v is not an option. Trust me, in cold weather the 24v is a godsend. Now I considered just using a single HD 24v alt in place of a 12v with the serp but after thinking about why GM used two 12v in series in the first place I came up with the fact that the rest of the truck being 12v a 24v alt probably couldn't work because the ign circut only provides 12v to excite the charging circut ?/ Am I correct in that ? So if so a single 24v alt won't work cause I cannot provide 24v from the ign circut to excite it.. Any ideas ? I probably could fab a mount for a second alt with the serp belt but I would think that will leave me zero room for future a/c.

 

[83GMCK2500]

I cannot answer the electrical question directly, but what is the serp setup off of? Is it possible that a dual alt package was available on whatever it came off of? In that case all you might need to do is track down another bracket.

 

[Acesneights1]

early 90's 6.2

 

[Franko914]

Can you take pics?

You cannot knock 24v down to 12v with just a resistor, big or @#$%^&* big... it doesn't work that way.

Pic of alternators "wired in series," pics of batteries/connections to alternators, etc. I can try and dig up some schematics but those pictures can tell a story on their own.

 

[Acesneights1]

Actually that is exactly how the M1008 works. A huge resistor on the firewall drops the rest of the truck to 12vs. To me it would have been easier to just use a series parallel like the Old Macks did but the Military designed so that these trucks could be used to jumpstart everything elese and also for NATO compatiblity on the radios accesories etc. IIRC the radio plugs in the truck are 24v but I am not sure. Everything else is 12v. Most guys just chuck the second alt and take the resistor out and put a 12v starter in but lemme tellya It was 15f tonight and the old CUCV cranked over like a SOB .

 

[Acesneights1]

Here are a few. It's dark and cold out right now but you can see the batts are hooked in series then go to a big resistor on the firewall. The starter is 24v so it has it's own feed from the batts.The pass side alt is the isolated one. If you read the output terminal on the drivers side alt it will read 12. If you read the output terminal of the pass side alt it will read 24v.