Dual voltage or 28 volt alternator?

[Kevin Means]

Our M1083 has an OEM dual voltage 100 amp alternator, which seems to work fine. However, when we bought the truck, we also bought a new C.E. Niehoff 260 amp alternator, because our plan is to install a 12 or 24 volt roof AC unit on the cab, and I think the factory 100 amp alternator wouldn't be up to the task, or at best, would be running on the ragged edge. I finally got around to un-boxing the new alternator today and noticed that it's a 28 volt (only) alternator - no 12 volt output. So now I'm trying to decide how to proceed. Should I swap the new 28 volt alternator for a dual voltage 260 amp alternator, or just stick with the 28 volt alternator and make some work-arounds?

Our rig has the WTEC II transmission controller, and I think it needs 12 volts - not 28. Could I simply install a Victron 24 to 12 volt 100 amp DC to DC converter and run the 12 volt stuff in the cab off that? If I stick with the 28 volt (only) alternator, are there landmines in the path that I'm not seeing? Thanks

Kevin

 

[Ronmar]

What year is your trans controller? After ~94 the controller can run EITHER 12 or 24. That is also the voltage output to the VIM relays controlled by the TCU, so those relays(neutral start) would have to be swapped.

From the 3060 Troubleshooting manual:
NOTE: Model Year ’94 and earlier (92-94)WT Series Electronic Controls operate on 12VDC. Vehicles with a 24VDC
system require a voltage equalizer or converter to supply 12V to the electronic control system. Model
Year ’95 and later transmissions operating on 24VDC require a 24V VIM and a 24V wiring harness
which includes shielding for the turbine and output speed sensors.

I converted mine to straight 24 on the 100A dual volt with a converter for the lights. my trans was post 95 so i shifted it to 24v batt and 24v ign vis the 12v batt and 24v ign it was originally wired with. I also moved the needed VIM relays(neutral, reverse and center difflock req) up into the main panel like the later A0 and A1 trucks to also delete the VIM.

At any rate, a 24-12 converter could meet all your 12V needs, including the transmission if you have a pre 95 controller.

The dual volts lose a lot of output capacity when the 12v is fully loaded. with a full 60A 12v load, the 100A unit only puts out ~1930 Watts, or 2/3's of the 2800W of a fully loaded straight 28V@100A alt... Any heavy electric loads I would definitely make 24V for this reason. The line losses and cable requirements are also a lot more favorable...

 

[GeneralDisorder]

That 260A single voltage unit - will it fit the 100A mounting? I've never run across that unit. Looks like a HMMWV style alternator. Maybe for the Ambo...... Those are drivers side mount so they mount "weird" on an FMTV.

The 260A and 300A dual voltage units designed for the FMTV platform require different mounting than the 100A and neither will clear the shock mount without modifications.

 

[Third From Texas]

Yeah, you're going to have to fab up a mount no matter what unless you drop back down to the 100a 24/12 alt.

So have at it. I'd use the 24v 260a with a converter and a custom mount.

 

[Kevin Means]

Yeah, I was wondering about the fit. Our shop can fab brackets as needed, so think I'll stick with the 28 volt, 260 amp unit as RFT recommended. Ronmar... our M1083 is a '98, so if I understand your post correctly (I can be a bit slow) I'm now assuming that everything will work on 24 volts - right? Can't tell you how much I appreciate the knowledge base and willingness to help.

Kevin

 

[GeneralDisorder]

The one concern I have is the availability of that unit. Admittedly I run a rare, expensive unit myself but I have a brand new spare and the 300 uses the same fitment as the relatively common 260A dual volt so I can swap to one of those with zero changes to fitment.

 

[GeneralDisorder]

Yeah, I was wondering about the fit. Our shop can fab brackets as needed, so think I'll stick with the 28 volt, 260 amp unit as RFT recommended. Ronmar... our M1083 is a '98, so if I understand your post correctly (I can be a bit slow) I'm now assuming that everything will work on 24 volts - right? Can't tell you how much I appreciate the knowledge base and willingness to help.

Kevin

The lighting system is still 12v. Ronmar knows the changes needed to accommodate the VIM and TCM.

 

[Ronmar]

yep, you will still need the 12V for all the lighting, but that is a simple converter like a Victron Orion 70A model.

Is this truck a WTEC 2 or 3 transmission controller(they started phasing in the 3's in 98 )...

 

[Kevin Means]

Ronmar, I'm pretty sure it's a WTEC 2 controller, because it has the two displays vs. the single display. (Let me know if I got that backward)
General, I agree. Carrying a spare is definitely something I want to do. I found some identical 260 amp alternators online (new), so I know they're available if Plan A doesn't work.

Plan A is.... After I do the swap to the new alternator, I'm going to see if I feel like it would be practical to swap back to the stock 100 amp alternator in a pinch. Of course that means I'd also have to carry the original bracketry with me, but that shouldn't be a problem. If I decide that that's not going to work (perhaps because of electrical issues) I'll pick up another 260 amp unit. The truck only has 1700 miles on it, and the stock alternator works and looks like new. Be a shame to spend another $2500 + if the stock alternator would get us by.

Kevin

 

[Ronmar]

Ok, well a wtec3 would have been easy as they are already all 24v. On the side of the TCU in the drivers dash there should be a date sticker just to confirm you have a 95 or newer TCU. Then it is simply a matter of shifting the battery input to the TCU in the power panel from CB35(12v) to CB43 and replacing the 12v neutral start relay in the VIM with a 24v relay…

you can also leave it all as is and feed the 12v buss with a converter. The potential issue here though, and it is also an issue with the A0 ignition circuit, is that during a cold start, if the 24v browns out low enough it can cause the 24-12 converter to drop offline, which will interrupt the start. On the A0 they control the 24v ignition(control panel relay K2) using 12v thru the ignition switch. How bad this is depends on the low voltage cutoff point of the 24-12 converter.

they of course did away with this “feature“ on the A1 trucks and use 24v to control the ignition relays

I converted ignition control over to 24v and put a 24v relay in the K2 position. But another way would be to simply add a 12v line from battery power thru a switch to feed and backup the 12v bus as a cold start assist…

the simplest way is a 24v trans and ignition control, then the 24-12 converter is only feeding the lights and it doesn’t really matter if that drops out during a cold crank/start…