Alternator 12 and 24 volt

[Keith Knight]

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?

 

[Ronmar]

the only one I can think of like that was a custom rig called the dual alt, but like the other dual alt configs proposed to replace our dual volt alternators, it suffered from the same series wired independently regulated alternator issues(impossible to maintain balance). Not sure how they even performed the shaft coupling, but they had issues with them and no support from the creator… It also wound up being pretty long if I recall, so if you wanted a second alt for some reason, I am not sure if you could fit two inline in the space we have… they would have to be smaller alts I think…

 

[Skyhawk13205]

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.

 

[Keith Knight]

Well 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.

 

[GeneralDisorder]

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.

 

[MatthewWBailey]

What about a PTO driven 260 or 570 under the bed?

 

[Ronmar]

Well 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.

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

 

[coachgeo]

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

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.

I wanna do two alts but for different reason (one dedicated to house/aux. batts. ) still brainstorming on how to do it. Also want two cause I got two for a screaming deal lol

 

[MatthewWBailey]

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

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.

 

[GeneralDisorder]

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.

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.

I know the CAT ECM for example will happily run 12v or 24v - at 24v it only draws about 1.1 amp with the engine running. I've ran a 3126b with my bench/bypass harness and my bench power supply. It is setup for 24v already in our trucks - that's just an example.

The only piece I'm not sure about is the WABCO ABS unit - IIRC it gets fed 12v (don't quote me) - but it's also inexpensive for a DC-DC converter especially if it's just a few amps for one or two devices.

The biggest issue is going to be running things we, as civilian owners, wish to add. Lots of "accesories" still want 12v. Though more and more are 12/24 now I have noticed. My Haloview camera system is 12/24 and lots of other stuff I have bought in the last few years is similar.

The Neihoff stuff is pretty dang good though IMO. Once you get past the 100A stuff at least. I have yet to encounter a 260A or it's regulator that was actually "dead" - even the core units that were "bad" - it's always some physical damage or stripped threads. Without fail every one I have dealt with works fine when you give it the environment it wants, good connections, and good batteries. And the price..... well all I can say is that you have to shop around, do your homework, and do a lot of digging with NSN's and part numbers, and so forth. Deals can be found. You just have to want it and do the legwork for it.

 

[Ronmar]

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…

 

[Suprman]

The lmtv first gen tcm is max type its 24v

 

[Ronmar]

The lmtv first gen tcm is max type its 24v

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 me

On the A0 they sent both 12v battery and 24v ign to the transmissions via the VIM(why doesn’t make a lot of sense to me) so it requires a few small changes to go straight 24v to the trans, mainly swapping out the two 12v relays in the vim with 24v relays. The TCU uses battery power to feed to the relays it applies voltage to for control.

 

[Suprman]

There are two style wtec2 tcms. Physically they appear the same. One is basic and its 12v only and limited to 5 forward gears. The max tcm, which the lmtv uses, is 12-24 and can do 7 forward gears.

 

[MatthewWBailey]

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…

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.

 

[coachgeo]

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.

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.

 

[Ronmar]

If you had a 12v alternator with an isolated ground(ground as a second output, not attached to its chassis), you could put it in series with a normally chassis grounded alternator, just like you can wire two 12v batteries, or 2 solar panels in series +to-. The batteries would be connected - on the first batt to chassis, +12v to - on the second(12-24v) battery giving you 12 and 24v outputs referenced to ground. If you connect the normally grounded chassis alt to ground and 12v on the first battery, and the isolated ground alt to the 12 and 24v battery + terminal connections, the two alts would regulate as normal to their individual regulator settings. If these set voltages were ~the same, they would/should charge a balanced set of series batteries to ~equal voltages… yes it should work…

 

[Aviator4x4]

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?

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.

 

[Ronmar]

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.

Thats the best way IMO, run a common straight 24v alt and use a converter from your 24v battery to feed the 12v loads.