MEP-803a batteries not charging

[Wdgellatly]

I purchased a mep-803a that had never been used, literally bought and placed on the shelf. 2.8 hours. I installed New batteries, new diesel, fluids checked, runs like a brand new one should (I have it powering my barn with 3 phase power for old woodworking machinery). Currently have about 40 hours on it.

The ammeter has always sat at zero, but I assumed everything was working. However, the batteries are not charging, so I had to pull them, take them to the house and charge them. I’ve read through older posts, checked the alternator (good), checked the FU1 fuse (good), and verified power downstream of the fuse (good).

now here’s where I’m lost. I lose the wiring in the wiring harness, and see an item called the Battery Charging Ammmeter shunt (MT4) on the schematic, but I can’t find it on the generator. This may or may not be my issue, but I’m just trying to walk through the schematic. The ammeter shows to be powered from this shunt, then flows to the solenoid, to the batteries.

i appreciate any insight and/or recommendations, Thanks in advance!

Respectfully,

Bill

 

[nextalcupfan]

MEP-803a panel lights flickering

I appreciate the coaching, you guys are great! CR1 looks okay visually, I tugged on it some with no change in behavior. This is an intermittent issue though, took me half an hour to catch the clip above, so that complicates the verification process. I have a 24V test lamp with alligator clips...

www.steelsoldiers.com

Top right, to the right of the relays.

 

[Guyfang]

I purchased a mep-803a that had never been used, literally bought and placed on the shelf. 2.8 hours. I installed New batteries, new diesel, fluids checked, runs like a brand new one should (I have it powering my barn with 3 phase power for old woodworking machinery). Currently have about 40 hours on it.

The ammeter has always sat at zero, but I assumed everything was working. However, the batteries are not charging, so I had to pull them, take them to the house and charge them. I’ve read through older posts, checked the alternator (good), checked the FU1 fuse (good), and verified power downstream of the fuse (good).

now here’s where I’m lost. I lose the wiring in the wiring harness, and see an item called the Battery Charging Ammmeter shunt (MT4) on the schematic, but I can’t find it on the generator. (Its in the control panel. Can not be your problem. It works, or it dont. If it dont work, you would have NO DC power anyplace in the control cube. Look like this)

With batteries topped off, measure voltage at the Slave Recpt. What you got?

Start the set. Measure at the Slave Recpt. Before and during start. What you got?


This may or may not be my issue, but I’m just trying to walk through the schematic. The ammeter shows to be powered from this shunt, then flows to the solenoid, to the batteries.

i appreciate any insight and/or recommendations, Thanks in advance!

Respectfully,

Bill

Open to read comments.

 

[Ray70]

I would not be surprised at all if your alternator ( more likely the regulator mounted on the back of the alternator ) is dead.
If the fuse is good and everything is hooked up correctly, my next step would be to test the alternator, then once that is verified, then proceed to the ammeter, if the alternator doesn't fix the issue
If you take a volt meter and check your 24V with the machine off, you will likely find about 25 VDC. assuming batteries are charged.
Now check the TM or wiring schematics again ( I know you already started to review them ) But here is a quick description as I recall it:
You should have 24V going into the alternator / regulator on the Exc. terminal of regulator. If that proves good, continue on. If not you probably have an issue upstream of the alternator.
Now start the machine and check it again at the Pos. post on the back side bottom of the alternator.
If voltage is not in the 28 or higher range, I would suspect a bad alternator. ( or regulator mounted on alternator )

 

[Wdgellatly]

Open to read comments.

Guyfang,

A picture is worth a thousand words! Thank you so much! I Found it, right in front of my nose; that, and the huge markings of “MT4”. I’ve got 25.3 at the shunt and the ammeter. I believe Ray 70 is right, alternator probably isn’t working. Standby…

 

[Wdgellatly]

I would not be surprised at all if your alternator ( more likely the regulator mounted on the back of the alternator ) is dead.
If the fuse is good and everything is hooked up correctly, my next step would be to test the alternator, then once that is verified, then proceed to the ammeter, if the alternator doesn't fix the issue
If you take a volt meter and check your 24V with the machine off, you will likely find about 25 VDC. assuming batteries are charged.
Now check the TM or wiring schematics again ( I know you already started to review them ) But here is a quick description as I recall it:
You should have 24V going into the alternator / regulator on the Exc. terminal of regulator. If that proves good, continue on. If not you probably have an issue upstream of the alternator.
Now start the machine and check it again at the Pos. post on the back side bottom of the alternator.
If voltage is not in the 28 or higher range, I would suspect a bad alternator. ( or regulator mounted on alternator )

Ray70,

Thank you for your time and expertise! I believe you are dead on here. Prior to start, batteries are providing 25.4. After starting, the the power out of the alternator shows 23.9, so it appears the alternator isn’t working. Would you agree?

 

[Guyfang]

FIRST, Check your wires. Everything hooked up right? Then say it a bad alternator. Assume nothing, test, test and test. Then you KNOW.

 

[Wdgellatly]

FIRST, Check your wires. Everything hooked up right? Then say it a bad alternator. Assume nothing, test, test and test. Then you KNOW.

Guyfang,

I believe the wiring is correct (me trying to decipher the TM). The positive output shows 23.9. It hasn’t been ran since 2012 during its final test… Here are some pics

 

[nextalcupfan]

If I'm reading the schematic correctly.
Negative: Wire 100AE
Positive: Wires 180C & 180D
Exciter: Wire 137T

Negative is going to Starter ground
Positive wires goto P6-27(180C) & #28(180D) > J6-27(180A) & #28(180B) > FU1-2 > FUSE > FU1-1(112B) > MT4-1 > CR1(112A) (I could keep going but I would be here all night)

I've heard about issues with CR1 being undersized and failing causing no charge condition.
CR1 is at the left on the main board with all the other resistors.


Exciter Wires goto 137T > P6-34 > J6-34(#137S) > TB5-12 > R15-1(#137E) & S14-7(#137K) & K12-7(#137C) -(Jumper to TB5-11)- TB6-4(#137A) & P4-15(#137B) & K19-A(137D) & P4-14(137M) (Again I could be here all night....)

Personally I would unhook the Positive wires and Exciter wires off the alternator and start checking where I lose power.
My initial guess would be either CR1 or your Exciter isn't getting power.

If that didn't pan out I would find the charging system troubleshooting procedure in the TM and follow it to the letter.

 

[Wdgellatly]

If I'm reading the schematic correctly.
Negative: Wire 100AE
Positive: Wires 180C & 180D
Exciter: Wire 137T

Negative is going to Starter ground
Positive wires goto P6-27(180C) & #28(180D) > J6-27(180A) & #28(180B) > FU1-2 > FUSE > FU1-1(112B) > MT4-1 > CR1(112A) (I could keep going but I would be here all night)

I've heard about issues with CR1 being undersized and failing causing no charge condition.
CR1 is at the left on the main board with all the other resistors.
View attachment 861696

Exciter Wires goto 137T > P6-34 > J6-34(#137S) > TB5-12 > R15-1(#137E) & S14-7(#137K) & K12-7(#137C) -(Jumper to TB5-11)- TB6-4(#137A) & P4-15(#137B) & K19-A(137D) & P4-14(137M) (Again I could be here all night....)

Personally I would unhook the Positive wires and Exciter wires off the alternator and start checking where I lose power.
My initial guess would be either CR1 or your Exciter isn't getting power.

If that didn't pan out I would find the charging system troubleshooting procedure in the TM and follow it to the letter.

Nextalcupfan,

Thank you for your P.H.D. Level examination of the TM; I’m struggling going through trying to locate and follow the reference numbers. I do have 25.4v at the Excitor, and I have followed the troubleshooting guide, and found 23.9 output from the alternator ( and it should be 27.5-29.5). The procedure says the alternator is defective, and to replace. I’m hoping to diagnose a bit more to see if it’s something I can repair…

I really appreciate your help with this!

 

[pclausen]

I got the exact same readings on a 802 I was working on last week when probing the plus and minus terminals on the alternator. Ammeter showed it not charging while running, but did move slightly into the discharge section with the fuel pump running.

Swapped in a spare alternator and I started getting the correct readings and the ammeter also showed I was charging the batteries with the set running.

I don’t know if the voltage regulator is serviceable on the alternator, but hopefully so.

 

[Light in the Dark]

There are parts available for these alternators. I had to send (3) out a month or two ago to be rebuilt... cost me like $125/ea to have them redone properly. The biggest challenges was parts availability from Prestolite (go figure!). All three had cooked negative diodes, and one needed a new regulator as well.

 

[pclausen]

That's good to know. Looks like new ones are available for about the same amount:

Prestolite 8MR3301G 24v 40amp Alternator John Deere Dozer Tractor Generator for sale online | eBay

Find many great new & used options and get the best deals for Prestolite 8MR3301G 24v 40amp Alternator John Deere Dozer Tractor Generator at the best online prices at eBay! Free shipping for many products!

www.ebay.com

When I get a chance, I might tinker with the one I have that doesn't put out voltage.

 

[DieselAddict]

Here is what I found when I took one apart. Two of the diodes had been installed in the incorrect orientation on the rectifier. The alternator was a fresh rebuild. The part was defective from the factory. After replacing the rectifier its still making power today, 7 years later.

If you can get parts they are pretty simple to work on. Just need a decent soldering iron.

 

[Ray70]

The VR is easily replaced, If you can find one available, but its not serviceable in itself.
Sometimes if you search around you can find reasonably priced new ones, but search by the Prestolite PN's not MEP-80X alternator.
Also try Prestolite 24V alternator and Leece Neville 24V alternator.
If you don't find anything, go for a rebuild!

 

[Guyfang]

See this tag? It tells me someone worked on the alternator. Huh. That never happened in the Army. Alternator bad?
1. Remove bad alternator.
2. Install Brand new alternator.
3. Turn in to Tech Supply bad alternator.
Bad alternator went to DRMO, Electrical Scrap Bin.

In al the time I worked on Generator sets, I never saw a tag like this. So maybe you should take it off and take it apart. Its broke, You can not make it more broke. If you can not spot something have a pro do it, or buy a new one. I think at the end of the day, you will find buying is not only faster, but maybe cheaper in the long run.

 

[Guyfang]

That's good to know. Looks like new ones are available for about the same amount:

Prestolite 8MR3301G 24v 40amp Alternator John Deere Dozer Tractor Generator for sale online | eBay

Find many great new & used options and get the best deals for Prestolite 8MR3301G 24v 40amp Alternator John Deere Dozer Tractor Generator at the best online prices at eBay! Free shipping for many products!

www.ebay.com

When I get a chance, I might tinker with the one I have that doesn't put out voltage.

• Do not post links that are known to "go dead" after a short period of time. Posting links to Ebay fit into this category. Second warning.

 

[Light in the Dark]

View attachment 861744
See this tag? It tells me someone worked on the alternator. Huh. That never happened in the Army. Alternator bad?
1. Remove bad alternator.
2. Install Brand new alternator.
3. Turn in to Tech Supply bad alternator.
Bad alternator went to DRMO, Electrical Scrap Bin.

In al the time I worked on Generator sets, I never saw a tag like this. So maybe you should take it off and take it apart. Its broke, You can not make it more broke. If you can not spot something have a pro do it, or buy a new one. I think at the end of the day, you will find buying is not only faster, but maybe cheaper in the long run.

I've seen that tag a LOT in the last 3-4 years on RESET machines.

 

[Guyfang]

Then I stand corrected. I only worked on them here in Germany. And stopped in 2010. I still would take it apart. you cant make it more broke.

 

[Wdgellatly]

Then I stand corrected. I only worked on them here in Germany. And stopped in 2010. I still would take it apart. you cant make it more broke.

Gentlemen,

I’m back at work out of town for the next week; I hope to diagnose further once I’m back home. Thank you all for your direction and expertise!

Respectfully,
Bill