MEP-804b no voltage/hz issue

I have two 804b 15k 50/60hz gen set that puts out no voltage or hz. The circuit interrupter does not stay closed and I have a fault light of under voltage. In my experience normally its always the voltage regulator. I have changed that out on both but that did not fix the problem. I checked the resistor on the back of the 50/60hz switch and that reads fine. I did check the voltage on the volt reg coming from the T1 transformer and it was low. I checked the ohms on the T1 and that was low too. The likely hood of the transformer going bad is slim, but I know it does happen. Any suggestions that I might be missing? Maybe a relay or diode.

Just curious but did you ever figure this out? I am having the same issue of no voltage with the under voltage light on with a mep 804a with only 5 hours on it after restoration. Thanks for any info.

Concentrate on getting Excitation. If your S-1 is bad, the exciter will not send voltage to the Main Alternator. Are you guys able to use the schematics? Or, better asked, do you have the schematics? If so, follow the path from the S-1 to the exciter.

I downloaded the TMs this morning and was looking them over. There is a schematic in there, I will have to look it over after work, everything else seems to function on here, just low voltage warning, and when plugging something like a grinder in it only runs at a quarter speed, so I know the light is doing what it's supposed to and inform me that there is low voltage, also the voltage dial does not change the voltage on any setting. I just picked this generator up last week and I'm trying to learn everything about it. thanks for the reply

Grimlock,

There is a color coded schematic in the thread listing, in the TM section, "All the tms you need to work on the MEP-802 and 803". Its larger then the schematic in the original TM, (easier on the eyes) and of course color coded. Much easier to use.

Also, if the Hertz is low, the motor speed of your grinder will be low. That is what really controls speed. Frequency, not voltage. If you are producing enough voltage to run a grinder, even at low speed, it means your excitor is lighting off the Main gen. You need to see what voltage you have at the load terminals, (Not the 110 volt outlet) and more important, what the Frequency, (hertz) you also have. If T-1 one is bad, the meter doesn't work right, but the output will be more or less normal. If your multi-meter doesn't read Hertz, go borrow one that does.

Could you perhaps describe just what the set does, and not does, a tad better? Do you hear the engine speed go up, when you twist the engine speed knob to the right? Does it go down when you turn it to the left? Give us more info,

Weirdest thing just happened. I went to barn to start troubleshooting set and I cranked it up and everything is working as it should. At first the undervoltage light was still on, I pressed the reset/test lights and the undervoltage light went of. This unit was just restored and now only has 6 hours on it, is it possible it needs to be broken in or anything or is there still an issue lurking. Thanks for your time

I just had a thought. If the undervoltage relay tripped, and you did not reset the fault indicator, then its possible the set was still in the fail mode and would not light off the main A.C.

The ground fault circuit interrupter also was not working properly at first, would that also be a symptom of fail mode. Everything seems to be working as it should now. Thanks again

Grimlock,

TEST!!!!!!!!!!!!!! And test again. Seldom will a problem just "go away". Put the set under load. Run it for a few hours. Step the load up, down and up again. Make sure its good to go.

+1 on the test and test concept. I had a MEP831 that ran OK but not great when I got it. I tweaked the speed controller setup and got it dialed in.. I'm thinking GREAT! And it was great for an hour. After an hour or so the speed controller freaked out. Cool it down and it runs perfectly again then BAM, goes crazy. {sigh}

Anyway, test the crap out of that thing.

I plan on testing it but I'm not sure I have anything that will put the set under a load. Can I plug anything 110 up to it? I have a 110 mig welder and air compressor which is about the only thing I have that may put a load on it.

Your mig welder would only put a sporadic load on it.
Got any 110 or 240 volt space heaters available?

now that you say that I do have 2 space heaters I use in my camper, that's a good idea thanks, i'll try that.

You know the real deal Chris. I have had new parts, in the wrapper come to me bad. You just never know. No job left the shop without running at full load for a few hours.

To the OP, where did you find your new voltage regulator? I have 2 of these machines that need them but it seems the 15kw VR kits aren't as easily accessible as the 30 and 60kw machines. Any guidance is greatly appreciated

I have the same problem. Were you ever able to figure the problem out? Engine runs great but low voltage light. On a 1997 mep-804a . Any help is appreciated.

Pope,

Did you work through the troubleshooting diagram? Every problem can have different causes.

Guyfang said:

Pope,

Did you work through the troubleshooting diagram? Every problem can have different causes.

Click to expand...

Have not. I don’t have or know where to get it.

Go to the TM forum here in SS. Look for the TM's for the MEP-804A. Download them. Then we can talk some more.

Roger