MEP803a Battery Charging Issue

If the alternator is not putting out the right voltage, then the rubbing the post is not really going to tell you anything. Thats what I was trying to write. Its not a matter of you having a parasitic "load", or draw, on the batteries, and its draining them. Thats not your problem. The alternator will not properly charge them. Different matter.

I am having the same problem with my generator and thank you all for the help everyone is providing.
I do have a simple related question,
Are they batteries just for starting or do they need to stay charged for operation of the generator

Per the -10 TM...

"Two batteries are required, one on each side of the generator set. The batteries are electrolyte serviceable, lead acid, 12 volt type, connected in series. After starting, the generator set is capable of operating with batteries removed. A diode and a fuse, located behind the control panel assembly, protect the generator set if the batteries are incorrectly connected."

So you can jump start it and run the set without any batteries installed.
Just be sure the unconnected battery cables can't come in contact with anything.

Is the alternator working properly on this machine? You still need 24V after starting to run the fuel pump, fuel solenoid etc.
So it will only work if the charging system is working and just the batteries are no good or removed.

So it can run with charged batteries and a bad alternator (for a while) or no batteries and a good alternator?

That is correct.

Thank you for the help. I know it's all in the TM but a last minute request for a big generator left me with no time to do my homework.
Thanks again to everyone that shares their knowledge

If you have good batteries but a bad alternator, run it with chargers on the batteries to get yourself a little more run time.... or just fix the alternator!

nextalcupfan said:

To me that sounds like the diodes are fused in the alternator, meaning a bad regulator.
Can you take the alternator somewhere to be tested?

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Thanks for the reply. I just got the alternator back and as many suspected, the diodes and rectifier needed to be replaced. I just got the repaired alternator installed and now the ammeter never goes positive after the start. Just after the start it's maxed out on the negative side of the gauge and over the course of 10 seconds it slowly worked its way up to -2A. I let the generator run for around 5 minutes and the needle never moved above -2A. I checked the voltage across the posts on the alternator and it read 28.6V, much better than before. I checked the wiring on the alternator and it was all correct. I have seen some other threads discussing troubleshooting the battery charging system and I had gone through those checks but I'll start going through them with the new alternator installed to see if any new clues come up. If anyone has any thoughts based on the new behavior of the system I'd be happy to hear them.

Thank you,
Adam

Could you have the wires to the ammeter gauge connected backwards? Even with fully charged batteries the gauge should normally read high amp draw after first starting the gen and gradually head back to zero or near zero. That is exactly what your ammeter is doing, except it is starting in the wrong direction. Reversed wires would exhibit exactly what you are seeing.

The fuse good in the control cabinet?

Check the meter first. Easy, and the wire numbers are on the wire and the wire schematics are on the door. THEN look at the alternator.

This might help

I've had more than 1 over the years with the wires reversed on the meter! Definitely sounds like you found one as well.

zarathustra said:

Could you have the wires to the ammeter gauge connected backwards? Even with fully charged batteries the gauge should normally read high amp draw after first starting the gen and gradually head back to zero or near zero. That is exactly what your ammeter is doing, except it is starting in the wrong direction. Reversed wires would exhibit exactly what you are seeing.

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Thanks for the suggestion, that's exactly what it was. Whoever worked on the set before me labeled the wires with a + and - correctly but then installed them backwards on the gauge. I ran it for a half hour, drawing as much power as my house could ask for, and it all seemed to work fine and the batteries charged. This community is great, thanks to everyone for all the help!

Well gentlemen I've read all the threads, I think, but I just put new batteries, new battery charge alternator on my 803, checked the wiring on the ammeter, checked fuse and the unit run great and puts out plenty of power to the house...issue is my ammeter will not go to the positive side. it's staying around -2ish. What am I missing? Could the ammeter be bad? How do you adjust the ammeter. It has an adjustment screw on the front.

Check to see if the wires are reversed on the meter.
When you first start it up does the gage go to the right or left.
If it goes to the left your wires are reversed.

All wires trace correctly.

Guess next step is to leave it alone for 3 or 4 days and see if there’s any power loss in the battery closest to the charge alternator.

Just FYI, it's not possible to discharge only one battery because they are wired in series. A parasitic drain will draw from both batteries.

If one battery is discharging, but not the other, it's due to self-discharge of that battery, meaning the battery is bad, not the alternator.