MEP804a Under Voltage Shut Off?

[natethefkngreat]

I've been experiencing issues with my 804a gen set. It has 805 hours on it. Ran good for 3+ years on an intermittent bases powering 3phase equipment. It starts as normal and runs but it sounds like it's not idling/running right, like slightly under powered. I'm very good at tone/pitch when it comes to equipment. I close the AC CIRCUIT INTERRUPTER and it puts out normal power. It'll run for 10-15 minutes then shut itself down with a fault light under voltage. The voltage on the front panel will show the Hertz start to bounce around then it shuts down.

I did do the TM 2.54 Over/Under Voltage Relay testing. It did not shut down or have a OverVoltage fault light wire 137A. It did have a UnderVoltage fault light with wire 141A disconnected. The VR Fuse shows continuity.

I have checked the fuel to make sure I didn't have water in it. My friend who helped me diagnose it thinks the VR is bad. I don't think it is because the fuze isn't blown. But it didn't pass the OverVoltage fault light test.

What next steps would you advise me to do?

 

[natethefkngreat]

@Guyfang @155mm

Does it sound like my VR is bad?

 

[natethefkngreat]

I have double checked the MPU to make sure no shavings we’re stuck on it. Got it to 2.98VDC. It was having trouble starting.

It currently starts and runs but will shut off after a minute with load on it UnderVoltage fault light.

 

[87cr250r]

Is it shutting off and then faulting under voltage or faulting under voltage and then shutting off? It seems like under voltage shouldn't cause a shutoff trip.

 

[natethefkngreat]

Is it shutting off and then faulting under voltage or faulting under voltage and then shutting off? It seems like under voltage shouldn't cause a shutoff trip.

It’s UnderVoltage then shutting off.. It has like a sputtering like effect as it shuts off.
It also has that slightly lower than normal running range. Doesn’t sound like it’s with enough RPM..

 

[Evvy Fesler]

Do you have any pictures? Please take a set of them all around and also the panel before and after the fault. Sometime members see things that you may not be seeing.

 

[Guyfang]

Do you have a DMM, Multimeter that reads hertz? If so, plug it in the 120 volt outlet. Turn it on to read hertz. Start the set. Set the hertz to 60 hertz. Watch the DMM. Is the DMM reading gone, RIGHT now or does it go down slow? Then the under volt light comes on?

 

[87cr250r]

Many voltage regulators derate as RPM drops. The lower voltage decreases the power output and helps the engine recover speed after a large load change.

If the engine is sputtering and not maintaining speed the loss of voltage is likely just a symptom of an engine side problem.

 

[Guyfang]

That's why Evvy's suggestion of a film is good stuff. The under volt light is probably a sign that the Engine RMP has fallen past the lower RPM threshold, and the gen set kicks out the K1. Then the K5 relay kicks in to turn on the Fault light.

 

[natethefkngreat]

 

[natethefkngreat]

It runs ok until about the 1:33 minute mark when I have someone put load on the genset. I had a video of 4:00 minutes prior to this.

 

[Guyfang]

That could be a fuel supply problem.

Have you changed fuel filter and maybe looked at the tank since you got this set?

 

[natethefkngreat]

That could be a fuel supply problem.

Have you changed fuel filter and maybe looked at the tank since you got this set?

It has been some time that I have replaced the fuel filter. I will do that then report back.

The VR still shows that’s it’s good, would that be a correct assumption?

 

[Evvy Fesler]

Mine made noise like that, too. I had a broken up diode ring, but that’s not your problem. I confused what I was hearing and the lack of power as being the VR. Actually, I had two problems. A broken main generator (that’s where the diode ring is) and a faulty fuel system. The fuel system was the cause of that noise that I heard in your video.

Be careful… there’s an old saying. When all you have is a hammer everything starts to look like a nail.

In other words, my problem probably isn’t your problem. Still, check the engine and fuel systems. Send pictures all around; especially on the fuel injection pump side.

 

[natethefkngreat]

Mine made noise like that, too. I had a broken up diode ring, but that’s not your problem. I confused what I was hearing and the lack of power as being the VR. Actually, I had two problems. A broken main generator (that’s where the diode ring is) and a faulty fuel system. The fuel system was the cause of that noise that I heard in your video.

Be careful… there’s an old saying. When all you have is a hammer everything starts to look like a nail.

In other words, my problem probably isn’t your problem. Still, check the engine and fuel systems. Send pictures all around; especially on the fuel injection pump side.

@Guyfang had helped me trouble shoot my alternator not charging a few years ago.. I couldn’t figure out the problem and I’d charge the batteries manually.. Then my friend helped me trace and multimeter the issue.. A diode was blown, and the wire had a break in it.. I have 2 other 804 gensets.. 1 is a A and 1 is a B that I rod knocked.. I took the diode from the blown one and ran a new wire to the alternator.. It fixed my charging problem.. Been about 3 weeks since I fixed that..

Now I got this issue.. My other 804a has a TRC VR in it, while the genset I’m running doesn’t have the same.. The blown 804b has the TRC VR as well.. I haven’t made time to get the spare 804a up and running, it has 4 hours on it..

 

[87cr250r]

In my commercial generator experience (excluding Cat C9 powered sets), the voltage regulator is the most common part to fail, second to the injection pump. The voltage regulator is easy, they either work or they don't. You can tell it's the VR because a properly functioning generator head will produce voltage from residual magnetism when it has no load. The voltage will be low and drop immediately to zero once a load is applied. They don't do anything else.

 

[natethefkngreat]

Alright men, I changed my fuel filter and the generator has been running for a good hour now.. I loaded it down and it seems to be back to normal!

I appreciate all of the help, insight and brain storming you guys have provided!

 

[Evvy Fesler]

Alright men, I changed my fuel filter and the generator has been running for a good hour now.. I loaded it down and it seems to be back to normal!

I appreciate all of the help, insight and brain storming you guys have provided!

Men? Guys?

 

[natethefkngreat]

Men? Guys?

I have always stuck my foot in my mouth! My apologies, Comrades?!?

Thanks Ladies and Gentlemen! And any other pronouns out there too.. I’ve never been politically correct..

 

[Evvy Fesler]

I have always stuck my foot in my mouth! My apologies, Comrades?!?

Thanks Ladies and Gentlemen! And any other pronouns out there too.. I’ve never been politically correct..

LOL, someone has to keep y'all on the straight and narrow!