MEP-804B Overvoltage Shutdown

Arty

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Hi. First off I want to say that this site is amazing and I found a wealth of information on here so thank you everyone for that.

I have a MEP-804B built in 2010. Upon start it gives over voltage error and shuts down. With the A1 completely disconnected it runs fine with the under voltage light illuminated. Once the A1 is installed I get overvoltage and the unit shuts down. I have the MWO and installed a new KTK-3 equivalent fuse yesterday. Fuse does not blow. I've tried starting it and kept it running for under a minute or so with S1 in the start position and the voltage seems to move fine based on where i set the voltage knob to. The frequency registers right at 60 hz as thats where i have it set with the internal 50/60 toggle switch. I guess my question is , where do I start?
 
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kloppk

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Does the set have the correct T1, R16 & Voltage adjust potentiometer to work with the TRC VR you put in?
A set with a Libby VR uses different T1, R16 & Voltage adjust potentiometer.
 

Arty

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Does the set have the correct T1, R16 & Voltage adjust potentiometer to work with the TRC VR you put in?
A set with a Libby VR uses different T1, R16 & Voltage adjust potentiometer.
Yes i verified with a chart i found online. 20k ohms potentiometer, TRC transformer, i guess i havent verified the R16 resistor. Am next to it now, how would i tell?
 

Arty

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Yes i verified with a chart i found online. 20k ohms potentiometer, TRC transformer, i guess i havent verified the R16 resistor. Am next to it now, how would i tell?
Side note, the transformer was preinstalled, so thats what i used to verify that its a trc vs the libby.
 

kloppk

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Was the TRC VR you put in a known good one?

Have you performed the tests in the -24 TM for the VR and the voltage adjust pot?
 

kloppk

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Was the TRC VR you put in a known good one?

Have you performed the tests in the -24 TM for the VR and the voltage adjust pot?
 

Arty

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Was the TRC VR you put in a known good one?

Have you performed the tests in the -24 TM for the VR and the voltage adjust pot?
I have the TM just not sure what the -24 is. I plan to do the voltage regulator tests today. I will report the results.
 

Arty

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I have the TM just not sure what the -24 is. I plan to do the voltage regulator tests today. I will report the results.
Just realized didnt answer the first part, it is not "known" to be good. It may very well be the culprit. Thanks for all your help. I will report results of the test later on today.
 

kloppk

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TM 9-6115-643-24 is the Support & Maintenance TM. It has troubleshooting procedures for most aspects of the genset.

It's available for downloading in the "TM" section of this forum.
 

kloppk

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I produce a replacement A1 VR for the 804B. Should after your testing and troubleshooting determine the VR you bought is NG I have them available for shipment.
 

Guyfang

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Hi. First off I want to say that this site is amazing and I found a wealth of information on here so thank you everyone for that.

I have a MEP-804B built in 2010. Upon start it gives over voltage error and shuts down. With the A1 completely disconnected it runs fine with the under voltage light illuminated. Once the A1 is installed I get overvoltage and the unit shuts down. I have the MWO and installed a new KTK-3 equivalent fuse yesterday. Fuse does not blow. I've tried starting it and kept it running for under a minute or so with S1 in the start position and the voltage seems to move fine based on where i set the voltage knob to. The frequency registers right at 60 hz as thats where i have it set with the internal 50/60 toggle switch. I guess my question is , where do I start?

Kurt, Arty,

The reason I jumped in here is the red statements. The gen set shuts down for over voltage. The Quad fuse doesn't blow, when you hold S1 in the Start position and, you can adjust the AC Voltage. If the A1 is bad, and trys to over volt the set, why is the quad fuse not blown? You did reset the fault on the fault indicator?
Open to read comments.
 

kloppk

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As I recall the exciter winding draws 1 amp or less from no load to full load. If the VR is putting out say 2 amps of current into the exciter I could see it overvolting and not blowing the 3 amp fuse.
 

Arty

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TM 9-6115-643-24 is the Support & Maintenance TM. It has troubleshooting procedures for most aspects of the genset.

It's available for downloading in the "TM" section of this forum.
Here are the results of the A1 and pot tests...

h. range is 4 to 12 vdc, I'm getting 11.2 volts
j. range is 110 to 160 VAC, I'm getting 158 VAC
I. it says I should get no more than 2 ohms at full CCW position however mine goes no lower than 4 to 5 ohms. Ohms increases rather smoothly however caps out at 15330 ohms and never get to maximum of 20k ohms.

I also did the separate pot test. results are as follows.
- Outer terminals do not produce the indicated 20k ohms, instead they read 15330 ohms. Center and one outer terminal read from 15330 down to as low as 11 ohms or vice versa but never to 0 ohms as indicated in the -24 manual.

By reading all other posts I know you guys are very seasoned in this but I wanted to confirm one thing with you guys. It seems the manual points to these steps for under voltage and no current situations. Is this also the proper troubleshooting steps for over voltage situations as well?
 
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