M1083 alternator/charge controller voltage issues

[Grimbo]

When the engine is running I’m seeing 32v on the 24v post and 14.2v on the 12v on the relay panel, the 14.2v appears good, but the 32v is high.
I took a pic of the readings on the regulator and alternator when running, excuse the wobbly text.
basically 24.2v on the left post of regulator, 32v on the right hand post.
if I switch the driving light circuit off, the voltage will dropto 28.2v which appears correct. Any ideas on what to check, I don’t want to replace the pricey regulator if it is something else. Thanks

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[GeneralDisorder]

What year is this truck? Does it have the LBCD or the PPD?

 

[Grimbo]

It has the PPD, but it was cooked so I joined the wires. 12-12 and 24-24.
the truck is 1996

 

[chucky]

It has the PPD, but it was cooked so I joined the wires. 12-12 and 24-24.
the truck is 1996

Were both lights blinking green on the altenator ?

 

[GeneralDisorder]

Well I would be cleaning all your connections and ground points. I'm not sure on the A0 trucks what the AC terminal on the VR is connected to - that terminal is an output from the VR and in the later trucks it goes to the LBCD and is the load sense used by the LBCD to disconnect the batteries.

But long story short the AC terminal is a frequency based output or a PWM (haven't scoped it personally) signal being generated by the VR and taking DC voltage readings there is meaningless.

The fact that you have 32v on the E terminal means the VR knows what the system voltage is and should be regulating the alternator's stator winding to keep it down at 28v. That suggests the VR is potentially bad. But I have also seen a bad ground at the LBCD (which you don't have so......) cause intermittent high voltage - it will pull the VR output high through a mechanism that I still do not understand and which the engineer at Niehoff I spoke with was also unable to explain......

Clean every connection (especially grounds) that you can get to. Make SURE that the VR's E terminal stud is seeing the same voltage you are reading with your meter. I've seen poor connections where the wire/terminal reads higher than the stud it's connected to due to corrosion. I would also pull the AC terminal wire off the VR just for good measure since that's not going to affect the voltage output.

 

[GeneralDisorder]

Were both lights blinking green on the altenator ?

It looks like he has the older VR without the lamps.

 

[chucky]

It looks like he has the older VR without the lamps.

Oh i didnt know they ever came without that alt from stew/stev in the 90s learn something new every day !

 

[Grimbo]

My regulator does not have the lights unfortunately

 

[Ronmar]

As General alluded to, the rear regulator terminal on that alt/reg is a sensor output. On the A0 trucks this wire simply goes to the STE connector under drivers dash. On this reg it is probably labeled F-. The field winding has battery voltage connected to one end(28V output terminal) and the regulator pulses the other end of the field winding to ground to build/control the field current and it controls the field in this manner to regulate the 28V output(Like most every other auto alternator on the planet). The F- terminal samples right where the regulator connects to/grounds the field winding. That info can be used to determine alternator load using the Standardized Test Equipment kit that nobody has

In this case I will tell you to disconnect that rear terminal as the truck doesn’t use it anyway. But if the wire attched to the terminal has developed a short to ground somewhere along the way to the cab connector, it could be pulling field current besides what the regulator is trying to pull, and causing the alternator to make extra voltage unregulated.

The 14V is pulled out of the middle of the stator/output windings via SCRs(switchable diode switches) and it is controlled like a switching power supply. The fact that it is correct tells me the regulator is at least doing that part right.

it is also possible that there is an internal short in the regulator pulling field current un commanded, or even a short in the field winding inside the alternator chassis.

If removing the wire on the rear regulator/F- terminal does not restore normal output. With the truck shutdown, unplug the regulator and restart the truck. You wont be making any 14v(will see battery 12v on that output terminal) but you should also not see anything on the 28V beyond battery voltage. If you do, you probably have a short to ground in the field winding inside the alternator chassis. If there is no increased alternator output then the issue probably lies in the regulator…

 

[Grimbo]

thanks a ton Ronmar, that’s a lot of good info that can cave my head in. Will dive into this in the next few days. I will let you guys know what I find and I do appreciate the feedback.

 

[Suprman]

Rotate your batteries one spot each the front two could be bad.

 

[Ronmar]

Better still, charge them get them load tested and only re-install the best two

 

[Grimbo]

Thanks Gents, I had charged them, but will seperate, charge and load test then re arrange. The help is appreciated.

 

[Grimbo]

Ok Gents, I am seeing some light thanks to you. I did the tests on the alternator, with the VR unplugged we lost charge V on 12 and 24.
with It plugged back in, charge was 14.2 and 28.4. As soon as the service drive(lights) were turned on, the 28.4 went up to 31.2, and this would change with hi/lowbeam.
last ditch as you suggested and disconnected the batteries, 12v bank both tested at good at over 1000a/h, but low and behold the 24v batteries failed miserably giving 100a/h and 400a/h each. I have the really bad bat on charge overnight but have little hope for it. It has distorted. The batteries are marked April 2017. I will replace with 4D gels. I have some concerns that a voltage issue cooked those 24v batteries, but will measure everything tomorrow when batts are hooked up. Thanks for the help.

 

[Ronmar]

Thats kind of surprising, it is usually the 12v batts that are toast as the A0 has a 12v vampire and because of the lighting loads, the 12v side has trouble fully recharging with the undersized alternator.

4 wet cell 6T batts is way too much for the 100A dual volt alt. Anything AGM even more so... It is basically two 50A alternators trying to feed 240AH at 12&24 respectively. If discharged those batts are looking for 60A from the alt(25% of AH capacity in amps) All by themselves, so instant long term alternator overload Just from the batteries, not even starting to count the truck loads on top of that(lighting is 22-26A).

you have two that could feed 1000A, install one of those in an inner/closest to frame, 12-24v location and the other one in an outer/furthest from frame ground-12 position and wire them in. A pair of 6T wet cell batts at 120AH are still a little large when you include truck loads, but are a much friendlier match for that horrendously expensive alternator. they are also plenty of energy for the truck…

If these are hawker AGMs, then even a pair of those is too much for the alt. AGMs are looking for 45% of the AH rating during charge, so a pair of AGMs is nearly as much load as 4 wet cells. The alt and battery combination on the LMTV is one of the largest engineering mistakes I have ever come across. Sadly they occasionally happen in the land of milspec… as an example my 2000 Tacoma has a group 24 battery with about 70AH capacity. That batt is looking for about 18A out of the alt to charge. It has about 15A of truck load when everything is turned on. It has an 80A alternator, so less than 50% load worst case. Most autos are setup this way. They got it way wrong with the LMTV. They added the LBCD to disconnect the batts to save the alt on the A1, and finally fielded the 260A alt on the A1R, but because they introduced the AGM batts about that time it was an absolute necessity anyway.

If you are getting new batts, a pair of group 31s is an excellent match for the alt. A pair of these is also what Cat specced for the power equipment that uses these engines, so it is plenty of power to start and operate the truck. Your alt and your wallet will thank you.

I run a pair of 31s in mine...

 

[Grimbo]

Got the batterys switched out etc, a;; good on that front. Started motor, 14.2v on 12v terminal, 36v+ on 24v, I shut it down real fast with no apparent damage.
Would this alternator bolt onto the 3116?
C.E. Niehoff & Co Generator 76761-N1603-2 28 VDC 450 Amp Voltage Regulator N3211

 

[Ronmar]

Well if you disconnected the wire from the rear reg terminal and that didnt fix the overvolt, and your alt isnt making any voltage with the regulator disconnected completely, you probably only need a regulator...

There is a troubleshooting tree in the neihoff manual that will help you confirm this.