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Thinking out side the box, does any know of a 12 or 24 volt alternator with a shaft on both ends that we could couple the other 12 or 24 volt alternator to in line to help save space?
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The problem is you don't have a 12v side and a 24v side, you have 12v out of the middle of 24… in this case it is a basic arithmetic problemWell that idea sucks!
I don’t understand the balancing part. My simple thinking is just 12 volt to the 12 volt side and 24 volt to the 24 volt side.
there has been some hmmm on this one. Not enough belt wrap on either alt. and the material it is made of.... is potential vibration crack are things that have been brought up.There is a guy on Facebook page that built 2 alt brackets with a 24v and a 12v. I think the issue again is balancing the loads.View attachment 921560
Why even have it? In 2024 I'm trying to Figure out what's the point of a dual voltage alt? Aside from surplus, which is also a mute point bc these neihoffs run better at the single voltage.The problem is you don't have a 12v side and a 24v side, you have 12v out of the middle of 24… in this case it is a basic arithmetic problem
Voltage on batteries in series is additive. IE 13.65 + 13.65 = 27.3. 27.3V coincidentally is the standard 24v regulator voltage setting and 13.65V per battery is a good low-mid range charge voltage(wont cook off so much electrolyte being applied long term like over the road trucks run).
the standard 12V automotive regulator setting is 14.5V. This is designed to help maintain a good state of charge with typical short duration automotive use, but it is a little high for long term charging…
The dumb regulators know only one thing, make regulated voltage. So if you apply 14.5v to the 12v battery in a series string with the first alternator, the 24v alt still only knows to make ITS rated voltage of 27.3, and it only applies enough voltage to make up the difference between the 14.5 and the its 27.3. This leaves the 12-24v series battery being starved with only 12.8V which is below the minimum accepted float voltage of 13.1…
this can be done, but it requires a custom regulator on the 12v alt set to 1/2 of the 24v alts output like 13.65 to go with a 27.3v alt. This is what the dual volts we have now do, switching/regulating the 12v output to 1/2 of the 24v Nominal regulated output. I could probably trick a 24v alt with remote sense into delivering double the 12v output with a couple of diodes, but something has to be done to make this work/balance the voltage seen by each battery.
Isnt math fun![]()
There isn't much point. You could (I think, in theory.....) re-wire the truck to run 100% 24v since all the lighting that was 12v to "take advantage of commercially available parts" has now been replaced with 10-30v LED's that could care less. And the existing wiring is oversized for 24v being designed for 12v current..... moot point with the LED's drawing a fraction of what the incandescent lighting drew...... The FMTV, HMMWV, and the CUCV are the only military vehicles that I'm aware of that even have 12v systems. Everything else is strictly 24v..... MRAP's that are loosely based on the FMTV may also but I've never wrenched on those.Why even have it? In 2024 I'm trying to Figure out what's the point of a dual voltage alt? Aside from surplus, which is also a mute point bc these neihoffs run better at the single voltage.
From what I have seen from Allison, they made that change somewhere in 95. the fact the A0 has no 12v switched ignition power pretty much confirms what you are saying, that none of the LMTVs are 12v only. Based on the year I was thinking it was possible, but the 24v only ignition aspect just dawned on meThe lmtv first gen tcm is max type its 24v
That's why I left a 3rd battery in there just as a 12v reserve, connected to the victron 12v output. At worst, it's a spare trolling motor battery for bass fishing, fully charged.There is no point really. I think ~95 the Allison went from 12v only to to 12 or 24v input, As mentioned new LED lighting doesn't really care. 24v only gauges are a little less available, but they are out there. Even our own gauges on the A0 are bastards, 24v gauges with 12v lighting… With the availability of 24-12 converters, you can make a 12v bus anywhere you need or want one quite easilly. And in a pinch, you can still draw 12 out of the series 24 battery bank to get you home if a power converter fails…
for future clarity.... so each alternator's ground went directly to battery it charged. The grounds between 12v battery's were connected as well. All stayed balanced and happy.It can be done, but requires consideration of the balancing - the CUCV did this correctly in the 80's. You use two 12v isolated ground alternators - one for each battery. The CUCV's Delco 12si isolated ground 100A alternators were paired either with a pair of 6T's or a pair of group 31's. This was a decade before the FMTV, worked and balanced perfectly, and was twice as powerful (200A total) with half the batteries as the FMTV.
1. Your LMTV build is very inspiring. I have exhaustively stalked all your pictures on steel soldiers and as soon as I saw your truck on youtube pop up, subscribed and watched.Thinking out side the box, does any know of a 12 or 24 volt alternator with a shaft on both ends that we could couple the other 12 or 24 volt alternator to in line to help save space?
Thats the best way IMO, run a common straight 24v alt and use a converter from your 24v battery to feed the 12v loads.1. Your LMTV build is very inspiring. I have exhaustively stalked all your pictures on steel soldiers and as soon as I saw your truck on youtube pop up, subscribed and watched.
2. Why not run a 24v 28SI alternator to the battery box, then run a 24v->12v converter/balancer to supply the 12v to the cab ? I am super hoping that @Xengineguy guy designs a 28SI 24v alternator mount for the trucks next. The quality and design of ecohubs and his door internals components is excellent.
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