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24 volt cranking system on military Chevy diesel t

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jdemaris

04-26-2005 20:23:53

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I'm looking at a couple of military vehicles - a Chevy K3500 with 6.2 diesel and a Chevy K5 Blazer with 6.2 diesel. Does anyone know the general theory of operation of the electrical system in these things - i.e. how the h*ll does it work?
They both are set up the same - 24 volt starter motor, dual 12 volt batteries, dual and separate 12 volt alternators, and the the rest of the electrial system - I think - is 12 volt. I don't see a series-parallel switch, but maybe it's hidden. Most of the wires are covered with plastic harness covers, so it's kind of hard to tell just by a quick look.

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Rimshot

04-27-2005 19:48:13

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Re: 24 volt cranking system on military Chevy dies in reply to jdemaris, 04-26-2005 20:23:53

As a government agency we were able to get a 1987 1 ton 4X4 6.2 with less than 45,000 miles. It cost us a dollar. Ended up spending $4500 on it in about 3 years!!! Nothing but a money pit!!

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Vapet

04-27-2005 15:50:37

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Re: 24 volt cranking system on military Chevy dies in reply to jdemaris, 04-26-2005 20:23:53

As someone stated below each battery has its own alt. Number one battery is the front one don"t remember which alt. is #1 but you could figure that out. Been working on these for several years at voctech school. We got a service manual from National Guard. Biggest trouble has been glow plug circuit. This maybe due to many drivers who don"t understand the system. If you have a specfic question I"ll try to help you.

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jdemaris

04-27-2005 19:49:40

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Re: 24 volt cranking system on military Chevy dies in reply to Vapet, 04-27-2005 15:50:37

I'd just trying to figure how these military versions are different from civilian. I may be buying a few low-mile trucks mainly for parts - especially the engines - and I've been wondering how much stuff has to be swapped when the military compents are put in civilian trucks.
As far as glow-plugs - the non-military had their problems too until the Delcos were no longer used. AC Delco has been making some genuine crap the past few years. Beru is making some of the best glow-plugs in the world. Funny thing is now, go buy yourself a Delco glow-plug for a GM diesel - and guess what's in the box? It's a Beru, repackaged.

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Vapet

04-28-2005 08:55:48

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Re: 24 volt cranking system on military Chevy dies in reply to jdemaris, 04-27-2005 19:49:40

Just off the top of my head, change the glow plugs to 6v. Don"t think I"ve checked voltage to injector pump solenoid. And of course the other electrical compoents. The glow plug problems we have had are with the control module which is under dash next to brake release. Sometimes only bad conections other times fried. Did install civilian control on one truck did ok.

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Mike M

04-27-2005 08:24:31

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Re: 24 volt cranking system on military Chevy dies in reply to jdemaris, 04-26-2005 20:23:53

From my experiences with the 6.2 I had I could never understand why the military would want them ? Except maybe the NAVY to use for anchors.

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jdemaris

04-27-2005 08:45:51

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Re: 24 volt cranking system on military Chevy dies in reply to Mike M, 04-27-2005 08:24:31

I can't say the same; I love them. I've been using them since G.M. gave up on their absolutely awful converted Oldsmobile gas-to-diesel 350, and hired Detroit Diesel to design the new 6.2 (and later 6.5). Not very powerful but very reliable. My 6.2 Suburban is just getting ready to turn 500,000 miles and the engine has never been apart - except for routine injector changes, waterpumps, etc. I can't say the same, however, for the rest of the truck though. 6.5s were just as reliable until they tried to meet new emission standards and went to microprocessor control injection. Then later, of course, GM gave up and went to the Japanese Isuzu Duramax. I've got six vehicles with 6.2s, never had a major problem with any of them, and not one has under 200,000 miles. I've also got a Ford IH powered 6.9 truck - best starting diesel I ever owned, but a real fuel hog compared to the 6.2s. F250 Ext. cab, 4WD, 8600 GVRW, 3.55 gears and C-6 auto - gets 11-13 MPG always - empty or loaded and just about any speed. Not too bad when pulling a trailer or camper, but it bugs me when it gets the same running empty. I've got a Chevy 6.2 3/4 ton 4WD - but lighter duty - that will get 21 MPG empty with a wind at my back.

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Bob

04-26-2005 22:07:59

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Re: 24 volt cranking system on military Chevy dies in reply to jdemaris, 04-26-2005 20:23:53

Starting:

Link

Charging:

http://www.tpub.com/content/trucks1.25ton/TM-9-2320-289-20/css/TM-9-2320-289-20_862.htm

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jdemaris

04-27-2005 05:34:09

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Re: 24 volt cranking system on military Chevy dies in reply to Bob, 04-26-2005 22:07:59

Thanks for the URLs. I tried reading the diagrams but kind of ran out of patience. I have to try again later - I downloaded them all. They are chasis wiring diagrams, not electrical schematics - so there are no component values given, and the wires are hard to trace. I see there are some components labeled "diode" and "supressor" and "relay", but their actual function still eludes me.

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Bob

04-27-2005 07:21:13

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Re: 24 volt cranking system on military Chevy dies in reply to jdemaris, 04-27-2005 05:34:09

Apparently, the 2 12-Volt batteries are connected in series, with a 24-Volt starter.

The batteries are charged by 2 12-Volt alternators with isolated grounds, so the charging voltage of each battery is individually regulated.

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jdemaris

04-27-2005 08:03:15

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Nuclear blast verus electronic controls? in reply to Bob, 04-27-2005 07:21:13

Thanks - it makes sense except it's not exactly a simple system. Sounds like many parts are specific to the military application. I assume since each battery has its own isolated charge system, it makes no difference which battery is tapped into to run 12 volt accessories, e.g. headlights, dashstuff, etc. Very much NOT like the Delco 24 cranking-12neg-12pos system used on the Deere 3020/4020s where a balanced 12 volt load needed to be applied to each battery. As far as what Buick/Deere just mentioned about the avoidance of electronic controls so you could still drive around after a nuclear blast - isn't the field created by such a blast also going to stop the function the diodes and transistors in the alternators, and also the electromagnetic diesel fuel shut-off solenoid? Seems if the military reason was based on that concept, they'd have some sort of mechanical controls for charging and fuel-injection shut-down. I was told - but don't know if it's true - that the mechanical injection was retained on the 6.2 and 6.5 diesels as used in the Humvees due to it's simplicity and overall reliability.

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gspig

04-27-2005 08:17:00

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Re: Nuclear blast verus electronic controls? in reply to jdemaris, 04-27-2005 08:03:15

My understanding of EMP is that it erases magnetic memory. The solid state components are damaged only if the memory causes the short. Therefore, diodes and transistors won't automatically be destroyed, but the memory that runs them may be erased and improper commands could short the components. If there is no computer control, there should be no problem.

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jdemaris

04-27-2005 08:34:12

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Re: Nuclear blast verus electronic controls? in reply to gspig, 04-27-2005 08:17:00

Interesting. Can't say I've ever read up on it. The case of nuclear blast, as displayed in several movies, shows all gasoline vehicles rendered useless - and as explained by an "expert" within the movie, NO electrical systems will work and only diesels will run. In one case, they showed a diesel Suburban that ran but the headlights wouldn't work. I was kind of wondering, within the scope of this fiction, how they got the Surburban started since - going with the script - it would have no starter motor, injection pump solenoid, or glow plugs.

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Bob

04-27-2005 08:51:37

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Re: Nuclear blast verus electronic controls? in reply to jdemaris, 04-27-2005 08:34:12

Essay on EMP... destroys semiconductors due to localized heating...

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caseyc

04-26-2005 20:40:06

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Re: 24 volt cranking system on military Chevy dies in reply to jdemaris, 04-26-2005 20:23:53

my guess would be that the starting is 24v while the rest of the electrical is only 12v. i don't know for sure. i would assume that the 24v starting would be like my 766 tractor for example. it has two 6 volt batt, but it takes 12 volts to start it. the first batt is grounded and the positive runs to the neg of the second batt. the positive of the second batt then goes to the starter. just my guess.

casey in SD

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jdemaris

04-27-2005 05:21:57

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Re: 24 volt cranking system on military Chevy dies in reply to caseyc, 04-26-2005 20:40:06

I've got to look at the web-info the other guy posted. The dual 12 volt alternators kind of threw me off - I'm wondering if somehow they get run in series to create 24 volts, or maybe each alternator charges one battery at 12 volts, or maybe even they are simply in parallel, and extra alternator is "military redundancy." With, at least some of the military stuff I've worked on, the focus is simplicity. I know the miltary special orders these engines, as used in the Humvees, to use the older mechanic fuel injection systems - thus avoiding the trouble-prone electronic systems.

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buickanddeere

04-27-2005 07:43:05

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Re: 24 volt cranking system on military Chevy dies in reply to jdemaris, 04-27-2005 05:21:57

The mechanical control sysstem will still work after the EMP from a nuclear weapon has shorted out solid state electronic componets. The dual alternators will keep a machine running longer should one battery start to fail.

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steveormary

04-27-2005 09:54:05

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Re: 24 volt cranking system on military Chevy dies in reply to buickanddeere, 04-27-2005 07:43:05

Mike M

Ya,the 6.2 might make good anchors. Otherwise just give them the float test.
But what do I know,never run a diesel car or truck.

steveormary

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