LMTV Conversion to 12V

[WLFFJoshua]

Please forgive me if this thread exists somewhere else and I've missed it. We just acquired a 1078 LMTV (A0 i think) and I'm attempting to find a replacement for the Niehoff alternators that seem to be such trouble for folks. My idea is that I can acquire a Delco or some other good quality brush-less unit, adapt the bracket or replace it, and then have all the 12V power I need. 24V power could be supplied by a step-up converter since (please correct me) there doesn't seem to be much constant 24V draw on anything, just ECUs, a few solenoids and maybe one or two other switches and lights. Less than 20 amps 24v by my estimation. So if i can power these items and charge the batteries I should be ok. And there are DC-DC step-ups that will easily supply 30 amps in a watertight configuration.

I'm hoping that this method will let me hook up the 12v alternator output to the existing 12v wiring (plus converter) and then the 24v output from the converter to the existing 24v wiring with no real indepth conversion process. The goal is to have easily maintainable alternator (no Niehoff) and larger 12v capacity since most aftermarket accessories are 12v.

I could use some feedback on the pitfalls of this plan, or any firsthand knowledge of such things. Or else point me to the thread they already talked about this on. Thanks for your help.

 

[Berend]

Use an 24v alternator and than make 12v with an inverter for the lights. That is done before .


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[Keith Knight]

pretty sure the starter is 24 volt.

 

[Berend]

Not pretty sure 100% sure


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[fuzzytoaster]

The Starter is 24v. The start relay solenoid on the frame near the power steering fluid is 12v but the rest is 24v.

Source: pulled one this morning.


As for turning the truck completely 12v the alternator would need to be replaced, starter replaced, some relays, exterior lights replaced, and go through the wiring from the battery box up through to the PDP since there's dedicated 12v & 24v but that's getting into preference on how you want to do it.

 

[WLFFJoshua]

The 24v only set up may be an OK route. I was looking for about 120 amps of 12v current though, and I wasn't sure of getting a step-down converter that could handle that. Likewise, I don't know how a 24v 100 amp alternator (like a Delco 33SI) would provide 12v 120amp through a converter. So I figured put the big 12v alternator on that would handle the largest load, and convert to the 24v load that's smaller. But if someone else has already done it (the 24v w/ converter to 12v route), then there's obviously a solution in that direction. I'll take a look at how it might work for me.

And that's right about the starter being 24v, but I didn't count that since the starter never really loads the alternator. Didn't know about the starter relay (thanks much). I do think the exterior lights are already all 12v on the FMTVs. Another reason I was trying to keep the added lights and so forth 12v was uniformity with other commercial truck lighting.

Also, I was trying to keep all the relays switches and so forth as stock since all the trouble-shooting is based on the stock configuration, so the whole dual voltage thing stays intact without fooling around in the electricals too much. Definitely not wanting to cook anything.

 

[snowtrac nome]

i guess when my nehoff alternator dies i will look for an alternative, right now it seems to be pretty robust i jump start equipment and run winches off of mine with no problems. i think converting is going to cause more problems. plus you would give up the advantage of a 24 v starter for teh cold

 

[coachgeo]

Transmission is 24v (or at least parts of it are) and very picky. IMHO that alone is a can of worms you do not want to go down. IMHO keep it OEM or upgrade with OEM like.. or go full 24v.

Consider adding a second 12v alternator and battery. Set it up dedicated to its own 12v circuit to run the 12v stuff you want to add that are of the high load nature that you want to install..

 

[Ronmar]

CTIS is also 24v... A 100A alt @24v will meet 100A @ 12v thru a converter no problem. Watts are watts regardless of the source. 100A @12v = 1200W. 1200W@24V is only 50A...

why you need so much 12v capacity? The total lighting load is about 25A and that is the lions share of it, so you would have 75A left over with the common Busman 100A converter... the good thing about this is it is relatively easy to do, only really 1 wire to remove(12v line from alt). You can also add other 24-12 converters if you have something specific to power beyond the 75A you have available...

 

[WLFFJoshua]

CTIS is also 24v... A 100A alt @24v will meet 100A @ 12v thru a converter no problem. Watts are watts regardless of the source. 100A @12v = 1200W. 1200W@24V is only 50A...

why you need so much 12v capacity? The total lighting load is about 25A and that is the lions share of it, so you would have 75A left over with the common Busman 100A converter... the good thing about this is it is relatively easy to do, only really 1 wire to remove(12v line from alt). You can also add other 24-12 converters if you have something specific to power beyond the 75A you have available...

We're building a wildland fire engine and the extra capacity is for lights/sirens, scene lights, 2 uhf radios and/or an ac power inverter (laptop and radio battery charger size) . I may also change out the pneumatic pump for electric (we have a 12v pump on hand I planned to re-use). All the lighting and radios would be the same as our pickups, hence the 12v requirement . Though I can get a 1 wire 24v Delco Remy pretty easily to power things, and I'm sure I can economize on the load.

Say I go the straight 24v route, would the old 12+ from the alternator then just hook to the 12v output on the converter? or do I need to wire the batteries into the setup somehow? I'm pretty handy but I can't say I know much about series-parallel batteries and balancers and so forth. The Bussman converter looks like a safe bet, Daygreen makes a similar product, but it looks more for static installations.

 

[Ronmar]

Say I go the straight 24v route, would the old 12+ from the alternator then just hook to the 12v output on the converter? or do I need to wire the batteries into the setup somehow?

Basically yes. The 12 and 24 lines from the alt already connect to the battery. So you would connect the 24-12 converter to 24 and ground, and connect the 12v converter output to the old alt 12v line and disconnect the 12v line from the battery(Battery is only 24V). Or connect the old/disconnected battery 12v line To the converter and disconnect/remove the old now unused 12v alternator line...

The beauty about doing the 24v bank is you can get better performance out of the existing large DC lines and if you have a 24-12 converter failure, you can still temporarily tap 12v out of the middle of the 24 bank to get back to the barn/complete the mission...

Any inverters used, I would make 24v-120 AC and locate them as close to the battery bank as possible(smaller Shorter cables are better able to deal with Inverter DC surge loads).

 

[WLFFJoshua]

After researching it a little, the 24v alternator +plus converter sounds like the way to go. The Niehoff hinge mount (5 inches wide) will have to be modified or adapted to a J180 hinge (4 inches wide) , but that's the only real modification. I could buy a Caterpillar mount, but that's even more unsecured budget money . Everything else is just finding a place to mount it. I don't think I would even have to move the polarity protection device.

Thanks everyone for the input. If I manage to get this done, where's the best place to write up the process and post for someone else to follow if they want? I'm not much educated on forum posting, but I know most folks hate answering the same questions over and over.

 

[coachgeo]

After researching it a little, the 24v alternator +plus converter sounds like the way to go. The Niehoff hinge mount (5 inches wide) will have to be modified or adapted to a J180 hinge (4 inches wide) , but that's the only real modification. I could buy a Caterpillar mount, but that's even more unsecured budget money . Everything else is just finding a place to mount it. I don't think I would even have to move the polarity protection device.

Thanks everyone for the input. If I manage to get this done, where's the best place to write up the process and post for someone else to follow if they want? I'm not much educated on forum posting, but I know most folks hate answering the same questions over and over.

just start a new thread....

though a link in your opening post in the new thread... that takes a reader to this thread would be a good way to tie together on how/why you came to decision on going with 24v alt. w/ 12v converter.

 

[Ohiobenz]

After researching it a little, the 24v alternator +plus converter sounds like the way to go. The Niehoff hinge mount (5 inches wide) will have to be modified or adapted to a J180 hinge (4 inches wide) , but that's the only real modification. I could buy a Caterpillar mount, but that's even more unsecured budget money . Everything else is just finding a place to mount it. I don't think I would even have to move the polarity protection device.

Thanks everyone for the input. If I manage to get this done, where's the best place to write up the process and post for someone else to follow if they want? I'm not much educated on forum posting, but I know most folks hate answering the same questions over and over.

I've built a complete 24v conversion kit that includes a 200A alternator, all the brackets, bolts, clamps and pieces, other than wires and the Bussman Equalizer. This kit incorporates a serpentine belt conversion and an AC bracket - hard to beat.
PM me if interested.