What's 24v and what's 12v

[acesneights1]

OK. I read the ENTIRE faqs, and other than a vague reference in the Wiki, I still am not sure. I have what i believe to be an M1008. I was told that ONLY the starter is 24v and that the glows, lights, ESO are all 12v. But the Wiki said the blackouts and glows were 24v ???
Can we clairy what exactly is 24v on the m1008

 

[ralbelt]

From what I have read only the starter is 24v

 

[Westech]

Well for the most part.. the black out light are 24V also if you want to get all tech about it. lol

 

[acesneights1]

That's what I'm trying to figure out.

 

[mangus580]

Well for the most part.. the black out light are 24V also if you want to get all tech about it. lol

Actually no, they are 12v.

The only thing that is 24v is the starter, glow plugs and charging system.

 

[acesneights1]

I was told the Humvees have 24v glows and the M1008 has 12v ?
I guess I'm wondering around my CUCV tomorrow with a VM.

 

[mangus580]

The physical glow plugs themselves are indeed 12v, but the 'system' is 24v.

 

[acesneights1]

the controller ? Is 12v going to the glows or are they 12v glows being hit with 24v ? I have a set of ac delco 60gs from one of my 6.5s . I was going to use them in this truck. Also one of the mechanics at the fleet maint where the truck came from "thinks" someone may have put a 12v starter in a 24v truck. How can I tell if I have a 24v starter? Anything to distinguish it from a 12v ?

 

[mangus580]

The voltage that actually goes to the glow plugs, is variable. The voltage is dropped down by the resistors. I would NOT suggest using the 60g's in it. They will not last as well as the wellman 070.

As to the starter, unless someone hacked your wiring, it should be 24v still.

 

[Csm Davis]

the starter is straight 24v the generator gage is 24v the glowplugs are 12v running off 24v with a drop down from the big resistors on the fire wall the alternators are 12v with a funky ground set up so they can be run into the same wiring for 24v most radio setups are 24v also, almost everything on the trucks is 12v

 

[Wile E. Coyote]

There was a mid-life mod done on some CUCVs which bypassed (and sometimes removed) the glowbar resistor mounted to the firewall and wired the feed circuit to the glow-plug relay to the front battery (12V side) instead. Apparently it was done to aid slave-starting it in a dead-battery condition. I've seen some trucks with the mod done and many without it.

24V is only used for the starter and for the radio bus. There's a 24V fuse at the bottom of the fuse block (10A if memory serves) which goes to the 24V voltmeter. Starter solenoid is also 24V but I *think* the starter motor itself is the same as that used on the 12V ones. Civvy trucks have the 12V solenoid and use two batteries wired up in parallel rather than series.

Charging system...think of it as one alternator charging each battery. The front battery (nearest the rad) is the 12V battery which runs all the same stuff you'd expect to see on the civvy K5 Blazer. Back battery is the hi-side, and its Positive terminal goes straight to the 24V distribution block. Again, all that does is feed the glow plug circuit glowbar resistor...the starter...the voltmeter...and the radio bus behind the passenger's seat and nothing else.

 

[M725]

the starter is straight 24v the generator gage is 24v the glowplugs are 12v running off 24v with a drop down from the big resistors on the fire wall the alternators are 12v with a funky ground set up so they can be run into the same wiring for 24v most radio setups are 24v also, almost everything on the trucks is 12v

Resistors on the fire wall 99% of the time go bad. I lost count on how many trucks I seen them by passed with a wire off the battery close to the front.

 

[acesneights1]

where can you get one if it goes ? Sounds like a good thing to have a spare of.

 

[charlietango]

mine is bypassed. no problems with it

my auto-glow relay has also been changed to a manual switch. both are continuous problems with those trucks and lots of times just bypassed to make them "simpler" K.I.S.S

 

[ida34]

Resistors on the fire wall 99% of the time go bad. I lost count on how many trucks I seen them by passed with a wire off the battery close to the front.

I have not seen a resistor go bad yet. I have seen people remove them thinking they fried the glow plugs. This is because the resister must see a set current draw to drop the voltage. When one plug fails the current draw drops and the voltage rises. If is like a snowball effect as they extra voltage will cause the next plug to fail and so on. The more plugs that fail the more voltage is supplies to the remainder of the plugs. If it is not diagnosed quickly it will take out all the plugs and a lot of people think this is because the resister failed. Some people also think the resistor failed because when they check the voltage on both sides they find 24 volt on both sides. If they would wait and check the voltage when the glow plugs are cycling they would find the proper 12 volt output if all the plugs were functional. Not trying to negate what you are saying but I have seen a lot of misdiagnosis in regard to bad resistors.

 

[acesneights1]

well, Some idiots put 24v glows in my CUCV. No wonder it was hard starting. FWIW I checked my glows with a voltmeter and had around 12v. The worst part is they went through the trouble to make little adapters to make the 24v's work with the round terminals.

 

[solarmon]

dem 12 volt pugs do NOT like 24 volts

I just finished putting 8 new glow plugs in my 1008.. Seems one of the big resistors between the 24 volt source on the passenger firewall and the glow plug relay on the drivers side went out, the voltage shot up, and the glow plugs all fried, and, to ad insult to injury, the high current draw also heated up the relay and toasted the primary coil.

I put in a Borg Warner S (or was that M?) 55 relay, and REMOVED the resistors the wires from the 24 volt connector . I then connected the wire from top (hot) side of the glow new plug relay to the 12 volt connector on the firewall right next to it. I actually used the one that originally went TO the resitsors, as it has a fusible link in it.

Now I'm positive I will always have 12 volts to the glow plugs, with NO danger of a voltage surge from a bad resistor ever again. Just can't understand WHY the army just HAD to go through all that voltage-reducing BS instead of just using the easily available 12 volts. . . (.oops.I forgot. .the right way, the wrong way, and the Army way)

Must have done something right, as it starts like a mad dog now.

Now, I guess I'll proceed with mounting my new 9.00x16 STA Superlug tires.

 

[solarmon]

I have not seen a resistor go bad yet. I have seen people remove them thinking they fried the glow plugs. This is because the resister must see a set current draw to drop the voltage. When one plug fails the current draw drops and the voltage rises. If is like a snowball effect as they extra voltage will cause the next plug to fail and so on. The more plugs that fail the more voltage is supplies to the remainder of the plugs. If it is not diagnosed quickly it will take out all the plugs and a lot of people think this is because the resister failed. Some people also think the resistor failed because when they check the voltage on both sides they find 24 volt on both sides. If they would wait and check the voltage when the glow plugs are cycling they would find the proper 12 volt output if all the plugs were functional. Not trying to negate what you are saying but I have seen a lot of misdiagnosis in regard to bad resistors.

In my case, the resistor WAS actualy shorted. ..but then, I think there was some rodent activity in there (old Army radio repairman (31E20) here. .actually sorta know what I'm doing)