Voltage Regulator Dead?

[Tanabi]

Hey guys;

So I have a 1989 M998 HMMWV with the 200 Amp dual-voltage alternator/generator and the HMMWV airconditioning kit installed from Midwest Military Equipment. My 12 volt output is wired to the "center" post of the batteries, and the AC unit takes its 12 volt source off the alternator's 12 volt post. (or I guess, 14 volt technically )

The alternator is "new" (a refurb unit I got about 2 years ago), and I've had the AC kit installed for a few months with no issues. A couple days ago, I was driving home and I noticed the truck was running off battery (needle in the yellow). It was doing this weird super misty rain that was soaking everything, so I figured a short maybe? It was way too dark and wet to go diagnosing that night, so I parked it.

I went to the TM and started down the troubleshooting procedures. Belts seem good. Connection from alternator to battries tested okay. I started up the truck, and the volt needle went up to the 'Generate' line, hung there for about a second, then dropped to batteries. With the engine running, I confirmed no amps were coming out of the alternator (both outputs). The TM didn't specify how to do this, so I used my multi-meter, amps setting, and went from the output post to the ground to read the amps -- I got flat 0 out of the 12 volt, and I got like, a fractional amp out of the main 24 volt post. I shut it down, took all the connectors off the alternator, I cleaned everything up, I went around and tried to ID any shorts (didn't see any likely suspects). Started the engine up, same problem.

Now my batteries aren't strong enough to start the engine anymore -- I could barely get it started this last time (it's cold out and it took about 3 cranks to get it to go) so I need to go get them recharged. I'm suspect that the voltage regulator is dead, but I can't do the last test (unplug the regulator and jumper 'A' to ground and see if current is produced) until I get my batteries re-charged. I'm about to drop them off at Autozone to get that done, but I was wondering what you guys thought? Short, regulator dead, both?

If the regulator is dead, is that something that is fixable or do I have to get another one? The TM says get another one, but I'm tempted to take a crack at opening it up and seeing what I can do with it.

 

[papakb]

It sounds like the regulator has gone south on you.

To measure current output you do not go between the output post and ground. That's how you measure voltage. To properly measure current you need to disconnect the cable from the output terminal and put your current meter in series between the terminal and the lead. Either that or use a clamp on amp meter rated to measure DC around the cable. Be aware that not all clamp on meters will read DC current. The majority of them used by electricians are AC only.

 

[mechanicjim]

https://www.ceniehoff.com/Documents/Ctrl_Hyperlink/TG0017B_uid882013200562.pdf

thats the troubleshooting guide for the 200 amp

https://www.ceniehoff.com/Documents/Ctrl_Hyperlink/TG0019A_uid12172009217332.pdf

that's the guide for the 210 amp

For the AC unit(air conditioner) when possible I would move its power source back to the batteries the 14v stud on these regulators was only meant to carry 50 amps and if your AC unit pulls too much it can over heat the regulator butter to have battereies provide the power and the ALT play catchup.

follow the troubleshooting guides they will rule out the Alternator and vehicle side.( check that IGN is getting power with key on/ engine run)
Ignore the dash gauge for voltage they tend to mis read, instead use a multi meter to check the voltage ( don't use the AMPs setting on the MultiMeter). And use a clamp on ammeter if you want to see how much Amperage there is.
For fun put your multi-meter to continuity and put the red lead into the Amp port( if it buzzed the fuse is still there if no buzz you got no fuse / amp part of meter wont work.)

 

[Mogman]

The above troubleshooting guide is very good, forget trying to get any current measurements, voltage is all you need, basically if you see battery voltage at the output terminal and at the exciter terminal and the voltage running is not around 28V it is probably an alternator/regulator issue.
Do charge the batteries before trying to troubleshoot, no need in having more than 1 issue at a time.
I purchased a 200A alt/regulator that failed testing, a seasoned HMMWV guy told me he had never seen a bad alternator, so I replaced the regulator and at least as far as my situation goes he was right.

 

[Milcommoguy]

Best way to burn out your AMP range shunt or fuse internal to meter. Might want to check, CAMO

 

[Tanabi]

So, this is a weird one on me. Turns out the problem was the batteries. Bear in mind, the batteries were (apparently) fine -- I tested voltage on them yesterday, and I was able to start the truck up normally once, and then a very cold 3 or 4 crank start a second time, so they had charge. But when I brought them into Autozone, they said they wouldn't recharge. They were just in my 3 year waranty, so a free pair of batteries later and I've got a running truck again. Seems to be okay now.

I will take the advice to move the AC unit to the batteries to heart, though, and I'll see about routing the power there instead. But I think (hopefully) I dodged an expensive bullet this time

 

[Mogman]

Absolutely move all acc. loads to the batteries, I also would while running at med idle test the battery voltage with the AC on and off, make sure the alternator is balancing the load (same voltage on both batteries) or you could kill another set of batteries.

 

[Milcommoguy]

The last one I saw was potted with a dark black epoxy looking stuff. Take it off and flip it over. Not much of a chance to repair, CAMO

 

[Tanabi]

Absolutely move all acc. loads to the batteries, I also would while running at med idle test the battery voltage with the AC on and off, make sure the alternator is balancing the load (same voltage on both batteries) or you could kill another set of batteries.

Right now, I have my 12 volt alternator post connected to the 'center' of the batteries (the pos. terminal of the rear battery), which is what someone else on the boards posted in some instructions around using the dual voltage alternator. Would you recommend I keep it that way, or should I route the 12 volt post to the location mentioned in the TM -- I don't recall where that is off the top of my head, but it definitely wasn't connected to the battery?

 

[Tanabi]

The last one I saw was potted with a dark black epoxy looking stuff. Take it off and flip it over. Not much of a chance to repair, CAMO

That's a shame. Luckily I (so far) haven't had to do this, but I was afraid it might be a situation where you can't repair it. I guess that makes it water tight, but if it was openable its probably a pretty simple circuit in there.

 

[Retiredwarhorses]

Only a fool or a mechanic would run direct off the 14v tap....not at all what it was designed for.

 

[Mogman]

Right now, I have my 12 volt alternator post connected to the 'center' of the batteries (the pos. terminal of the rear battery), which is what someone else on the boards posted in some instructions around using the dual voltage alternator. Would you recommend I keep it that way, or should I route the 12 volt post to the location mentioned in the TM -- I don't recall where that is off the top of my head, but it definitely wasn't connected to the battery?

Yes that is how it should be connected

 

[Ajax MD]

Yes that is how it should be connected

What is the purpose of this tap? @Retiredwarhorses says it is not to be used for 12v accessories.

 

[Tanabi]

So today I tried to run the truck, and now it does something new, where it will run off the generator for a little bit, then fall off back to the batteries after awhile. I'm back to thinking it's probably the voltage regulator. I'm wondering what I did to kill it (maybe it was running the AC off the 12 volt tap) but I am looking at getting another one now.

 

[Tanabi]

@Mogman @Retiredwarhorses Hey guys ... so my alternator / generator has a Niehoff N3135 on it. I'm not finding any of those available online, but I can find an N3118 which has the same connectors (in a slightly different configuration) and is also dual voltage. Do you know if these are compatible? My searches aren't coming up with anything.

 

[kzeyus]

Trailworthyfab has some 200 amp pull-off regulators

Trail Worthy Fab :: Warning

 

[Coug]

What is the purpose of this tap? @Retiredwarhorses says it is not to be used for 12v accessories.

It's supposed to keep the rearward battery charged up.
I think what Retiredwarhorses meant was it's not to be used to directly power accessories, it needs to be hooked to the battery to act as a buffer for any 12v accessories plugged into it (still limited to less than 50 amps, and still better off using a voltage converter for anything other than minor loads)

 

[Retiredwarhorses]

AM General to this day powers all 12v anything from the rear battery, this includes the TCM.
The 14v tap too the rear battery positive prevents
Imbalance....

 

[Ajax MD]

AM General to this day powers all 12v anything from the rear battery, this includes the TCM.
The 14v tap too the rear battery positive prevents
Imbalance....

I see. I have this style alternator/generator but I don't think the tap is connected. I'll run a wire from the tap to the rear battery.
Currently, we are not running any 12v accessories so we're not harming anything. Normally, I'd never tap an individual battery, I'd use a step-down converter.

Thanks for the info.

 

[Tanabi]

I have my part on order from Trail Worthy Fab and I should have it Tuesday.

In the meantime, i'm experimenting with cracking open the old regulator. So, the old regulator has a smooth resin bottom which is incredibly tough. You can soak it in alchohol and it gets a little softer, but not much ... it was enough that I was able to get my knife in along the edge and pry it up a bit.

Under, there's ... this gritty stuff. It's like some kind of cement made of little round pelets of sand or something. That stuff dissolves in alchohol, but it takes awhile. Drilling some holes in the smooth resin bottom (prepare to lose your drill bit!) then soaking it in alchohol will make it so you can pry that stuff off.

Then, with a combination of alchohol soaks and rounds with a wire brush, I'm almost to the circuit board -- it's pretty deep in there, and I'm not sure what condition it wil be in by the time it is exposed as the removal of this stuff is kind of harsh on the board despite my attempts to be delicate with it.

It looks like the entire interior of this thing is filled with this pellet cement, because the four corners of the circuit board are angled and I can see the cement stuff keeps going and going .... I think they fill these things with whatever the cement stuff is, cram the board in, and then put the smooth resin 'cap' on it.

Unless I figure out a more efficient way to dissolve this stuff, it'll take me weeks to get through the cement. I'm thinking acetone might do more damage, but I don't know what that does to PCB's. I'll have to look that up and see if its worth trying.

If I am able to make a repair procedure for these regulators, I will put it in a new post.