M1083 alternator/charge controller voltage issues

Grimbo

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Lenoir, north carolina
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

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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.
 
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Ronmar

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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

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Lenoir, north carolina
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.
 

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