MEP-802a Low Alternator Voltage Output

[ethernaut85]

Hello Everyone

I recently picked up a 802a that does not charge. I have checked output at the alternator by placing a multimeter across the positive and negative leads as described by the TM. I am getting around 24 volts +/- 0.5v. According to the manual, it says that the alternator needs replaced if the multimeter reads less than 27v or so. Does anyone have any suggestions on anywhere else to look to make sure that its not the alternator but something else? I used my multimeter on the diagnostics port on the front while the genset was running and all the readings were in the 22v range except (d) which is the battery charging circuit which was ~24v.

In addition, I've read about the remote fuel drain fitting leaking which my generator does. How can this be rectified? We started taking off panels to get the fuel tank out but 50 bolts later we are still shy of removing the tank.

Thanks in advance for the help!

 

[DieselAddict]

I had a 802 that didn't charge and the root cause was failed diodes in the alternator. Worth a shot to see if that's the problem.

 

[ethernaut85]

I had a 802 that didn't charge and the root cause was failed diodes in the alternator. Worth a shot to see if that's the problem.

Are the diodes shown in the exploded diagram of the alternator in the TM?

Did you end up replacing the diodes?

 

[DieselAddict]

Yep. I replaced the diodes and all was good.

This is the alternator I had on my unit - http://www.prestolite.com/pgs_produ...il_id=19373&item=8MR3005CA&product=ALTERNATOR

The Prestolite part numbers for the rectifiers are:

0180000G98S $13.76 (includes diode trio)

0180000F83S $5.83


Here are a couple of photos to see what was wrong with mine. It had been rebuilt when the generator was rebuilt but one of the rectifiers were assembled incorrectly from the factory.

 

[ethernaut85]

Yep. I replaced the diodes and all was good.

This is the alternator I had on my unit - http://www.prestolite.com/pgs_produ...il_id=19373&item=8MR3005CA&product=ALTERNATOR

The Prestolite part numbers for the rectifiers are:

0180000G98S $13.76 (includes diode trio)

0180000F83S $5.83


Here are a couple of photos to see what was wrong with mine. It had been rebuilt when the generator was rebuilt but one of the rectifiers were assembled incorrectly from the factory.

Great, thanks for the info. We will take a look at it. A new alternator is an expensive option. We will keep the thread updated.

 

[mlaxton]

Great, thanks for the info. We will take a look at it. A new alternator is an expensive option. We will keep the thread updated.

Yep. I replaced the diodes and all was good.

This is the alternator I had on my unit - http://www.prestolite.com/pgs_produ...il_id=19373&item=8MR3005CA&product=ALTERNATOR

The Prestolite part numbers for the rectifiers are:

0180000G98S $13.76 (includes diode trio)

0180000F83S $5.83


Here are a couple of photos to see what was wrong with mine. It had been rebuilt when the generator was rebuilt but one of the rectifiers were assembled incorrectly from the factory.

I have ordered both rectifiers for back up, whether is a regulator that can fail as well correct? Do you know where to source that?

 

[Zed254]

Fuel drain leak is covered by Daybreak in his parts list: https://www.steelsoldiers.com/threads/the-infamous-well-nut-info.154411/#post-1875261
A lot of guys prefer the bulk head fitting replacement: https://www.steelsoldiers.com/threads/ultimate-well-nut-repair.171091/

 

[Guyfang]

Do keep in mind, that there are two different alternators, and you have to compare the part number on the alternator to the part number in the TM. In all probability, its the new alternator. BUT there are still a few old one out there.

 

[mlaxton]

Do keep in mind, that there are two different alternators, and you have to compare the part number on the alternator to the part number in the TM. In all probability, its the new alternator. BUT there are still a few old one out there.

Are you referring to the rectifiers?

 

[Guyfang]

No, the battery charging alternators. Two different kinds were used on all TQG's. take a gander at the -24P TM. As they do not look alike, its easy to see what is what. The regulator pictured above is for the new alternator.

 

[Zed254]

My notes on alternators for the MEP-802A and MEP-803A generators:
Alternator: PRESTOLITE LEECE NEVILLE 8MR3005C CAR 8RG3063 GENERATOR ALTERNATOR TRUCK 24V , NSN 6115-01-368-2911. Actual part number is 8MR3005CA, NSN 6115-01-459-1661. The 8MR3005C will need the head rotated per Green Mountain.

 

[Light in the Dark]

Here is whats in an 803 thats headed out Saturday, almost all are the 8MR3005C by my memory.

 

[SCg Steve]

Trying to breath life into an old thread, but does someone have a photo of the wired up alternator on an MEP803A? I’m trying to verify if mine is wored correctly as it is not charging the batteries , with a new alternator.

 

[Light in the Dark]

Have you checked the fuse behind the gauge panel to see (1) that its present, and (1) that its in working order? How is yours wired up now, can you share a photo?

 

[SCg Steve]

Have you checked the fuse behind the gauge panel to see (1) that its present, and (1) that its in working order? How is yours wired up now, can you share a photo?

I wired it up identicle to how the other was when i replaced it.

 

[SCg Steve]

I wired it up identicle to how the other was when i replaced it.
View attachment 872370

I’ll check the fuse in the AM and report back. Thank You.

 

[Guyfang]

This help?

 

[SCg Steve]

I’ll check the fuse in the AM and report back. Thank You.

This help?

Thank You so much! Verified that the alternator is indeed wired correctly, and found that it was the fuse as Light in the Dark suggested. The fuse holder wasn't in all the way and that was the issue. Thank You guys so much for your help!

 

[SCg Steve]

Have you checked the fuse behind the gauge panel to see (1) that its present, and (1) that its in working order? How is yours wired up now, can you share a photo?

Thank You so much! Verified the wiring of the alternator, and as you suggested, the fuse holder wasn't seated completely and that was the issue! Thanks so much!

 

[Light in the Dark]

I love cheap fixes