Batteries not charging - Suggestions?

[Stein]

Sorry about the long post but I believe when asking a question it's best to give as much information as possible to make the job for the person answering the question as easy as possible. Here's the background and where I am today.

86 CUCV, was 24V. Found out resistor pack for glow plugs was bad and 24V was going to glow plugs which fried them.

Replaced all eight fried glow plugs and did 12V swap to allow me to eliminate the bad resistor pack.

Batteries won't charge. I suspect they weren't charging before the 24V swap. It was warm out a few months ago and I was able to start it a couple dozen times until the battery reserve was getting low so I put the charger on the batteries.

Now it's colder and I can only get a couple of starts out of it.

Recently had the 4 year old Interstate 950CCA batteries load tested as the Insterstate store. The guys said they both tested at 1200CCA.

Anyway, I went back, reinstalled the batteries and swapped the alternator with the other that I removed from the driver's side. Still not charging.

Last night I went back through the Roscommon directions step by step to make sure everything was done exactly by the book. It was.

Earlier this week I had the trickle charger on for a day. Had 13.1 V in the batteries right after I took the charger off. Left them a day and it settled back to 13.01 after they stabilized. So far so good.

Started it last night and it fired right up. I don't know how to specifically check an alternator for output. So all I did was put the meter on the hot terminal and ground the other. It was showing 12.28V which was also the battery voltage after I shut it off.

Now I'm suspecting the batteries again. As I said, they showed 13.01 V before turning the key. The truck was in the shop so it was warm. One cycle of the glow plugs and 2-3 seconds of cranking was all it took to start. I have a hard time believing that battery voltage could be as low as 12.28 after one easy start.

So, if you read all of that,

1) Shouldn't I see a 13.5-14V reading on the alternator hot wire when running?

2) Will it not show the charging voltage if a battery or the batteries are bad?

3) Do you agree that at a minimum I should have the batteries load tested again somewhere else and they are probably toast?

4) Is there a voltage regulator somewhere that could be bad and not let the alternator charge the batteries? This is my first diesel/GM in 20 years.

 

[80' 427]

1) Shouldn't I see a 13.5-14V reading on the alternator hot wire when running?
Yes

2) Will it not show the charging voltage if a battery or the batteries are bad?
No it will still show 13.5 to 14 when it is charging. Maybe more if the batteries are shot.

3) Do you agree that at a minimum I should have the batteries load tested again somewhere else and they are probably toast?
You can but I still don't think that is the problem.
4) Is there a voltage regulator somewhere that could be bad and not let the alternator charge the batteries? This is my first diesel/GM in 20 years.
voltage regulators are internal to the alternators. Take both the alternators to the parts store and have them tested. I suspect they are weak or bad.

FYI why didn't you just call me.
__________________

 

[Stein]

I was going to at least take in the one that was off the truck but I'll pull the other tonight and take both alternators in tomorrow.

Don't you think that it's still weird that the batteries only show 12.28V after one start on a full trickle charge?

 

[80' 427]

The glow plugs pull a lot of power and so does the starter. I guess I am not sure because most times I never check the after start power with out a charging system.

 

[chicken joe]

I was going to at least take in the one that was off the truck but I'll pull the other tonight and take both alternators in tomorrow.

Don't you think that it's still weird that the batteries only show 12.28V after one start on a full trickle charge?

if its cold out im surprised its not lower. i think your alternator is shot. when its running and everything is working correctly you should have the same voltage at every point +- a little for resistance. but like you say when its running it should be 13-14. i think your getting the battery reading on the back of the alternator, cus its not charging.

hope that makes sense and helps. good luck
mike

 

[Massboy]

Did you rev the motor up at all after starting. I remember my m1009 wouldn't charge at all until I revved it up to energize them to start charging. I would always have at least one red warning light on until I did that. Maybe that is your problem.

 

[Stein]

Hmmm...possible. I didn't that time.

That said I have been driving it and it still doesn't charge. During deer season I put at least 200 miles on it one week.

Alternator off and I'm taking both in for testing tomorrow.

 

[Massboy]

If you've been driving it then it's revved high enough and should be charging. Most likely the alternators.

 

[diesel4me]

I have not had much experience with the military setups with dual altenators,I think one is isolated from ground and is specially built?..

If they are like the typical 10SI ones on a gasser,with the two prong plug on the,both of the wires should have voltage with it running,,and only one with the engine off ,but the key on...that one energizes the field coils ,if it doesn't get juice it wont put a charge out..(some vehicles will self-energize after you rev it up to 2000 rpm or so ,even if this wire is "dead")...

It could be both are working but have one or two out of the three diodes are blown,and let the batteries discharge when sitting,and that limits the output also..not sure if your typical parts store can test the one with isolated ground or have one on the shelf, I doubt they will..