MEP-003a - Temporary Voltage Fluctuation

[DieselAddict]

I've searched through the forum here and I've not been able to find this problem discussed yet.

On my MEP-003a I started it a couple of days ago to load test it. Everything started and ran fine except for the voltage. The voltage fluctuated above the setpoint. It didn't just bounce around but it changed in a shift. It would be fine at 240v then it would jump up to about 255v. After a short time (seconds) it would drop back to 240v. If I rotated the voltage knob the voltage followed the knobs movement but it continued to shift back and forth.

After it runs for a few minutes the fluctuations stop and the voltage is rock solid. After the voltage was steady I connected it to the house and loaded it up with the water heater, dryer, and heatpump on the house and the voltage stayed rock solid (80% or so load). I could adjust the voltage smoothly with the voltage adjustment knob. I verified the voltage was steady with a Fluke VM.

Today I opened up the control panel and all the wires are good and solid. Nothing looks burned or overheated on the VR board. Everything is very clean. When I started the generator after the inspection it had the same issue. The voltage bounces back and forth for a couple of minutes then steadies out. Today I didn't touch the voltage knob and when the fluctuations stopped the voltage was back perfectly to its setpoint of 240v.

This fluctuation didn't happen when the generator was last run around the first of November. I run it once every 4-6 weeks and load it up. I've been wanting to see how it starts and runs in the cooler weather. Both days when I've run it and noticed the fluctuations the temps has been in the 40s. The last time it was run in November the temp was in the 70s.

Tomorrow I'm going to take the voltmeter and check the output of the VR board. I've looked through the schematics and it appears that the exciter output is terminals 17 and 14 on the VR board and I should see a steady output around 3v DC. Can someone confirm that I'm correct there?

Has anyone else seen that problem?

Any thoughts or insights would be appreciated.

 

[R Racing]

just for grins and giggles did you try turning vr12 and vr15. had 1 with a bad spot that drove me nuts !!!

 

[DieselAddict]

Man. I knew I was leaving something out. I did give the MT pots on the board a turn in each direction then returned them to their original position.

 

[dangier]

If you haven't done so already, I would go over all the screw connections in the control panel to make sure they are getting good connection. Including the vr board. Resolved some of my phantom issues. Also check the all ground connections.
David

 

[jamawieb]

By chance are you using a volt meter to check the voltage or going by the gauge alone? I've had gauges that would do the same thing, only after using a volt meter is where I found the problem.

 

[DieselAddict]

I did use a VM to check the voltage. It was following the gauge.

 

[Isaac-1]

I had one that did somewhat the reverse of this, was stable for a while, then once warmed up voltage would be unstable, I ended up the AVR board with one of Jim's retrofit drop in replacement boards. Eventually I may get around to troubleshooting the components.

 

[CDR]

Mine does the same thing but only by +-3 volts

 

[jamawieb]

More than likely its going to be some component on the VR board. There is a capacitor or something that is starting to go bad. I would suggest Isaac-1 idea of getting Jim's updated board. It's a small investment but at least you wouldn't have to worry about the VR board anymore and if you could fix your current board, you would have a back-up

 

[R Racing]

True story. Had a VR board issue. Bought 1 of Jims boards. I was planning on changing it out. Fired up the generator and it works perfectly. So Jims board scared it to work cause it has worked since lol

 

[DieselAddict]

A bit of an update. I've not been able to get out and test it over the last few days. I just ran it with the VM attached to the output of the VR board and I did see a little fluctuation that was tracked by the voltage gauge on the panel. The fluctuations were small and in less then a minute it had settled down to a nice steady output. I was getting ~240v on the gauge while the VR output was 2.045vdc.

The temperature today is a good bit warmer than when the voltage was fluctuating plus the sun was shining on the side of the generator where the VR board is. It felt comfortably warm to the touch. So not a good test for the unstable condition but it does reinforce that the problem is likely temperature dependent.

During this run I tested the range of the VR adjustment knob and watched the meter follow the knob position smoothly. Across the range of the VR control the DC voltage on the VR output board rose and fell between about 1.85v and 2.12v.

I'll post more info as I collect it.

If this does turn out to be something that requires a VR board replacement I'll for sure get the updated one from Jim. I don't know Jim but from looking at his location we are practically neighbors.

 

[mrheiser]

My mep-803a voltage tends to fluctuate, around 5+/- volts depending on load. Anyone know what part I should be looking at replacing? Thanks, Matt

 

[Guyfang]

Chris,

Sounds like the VR board. We often saw this problem, but ignored it, as for the most part, it did not impact our loads. And it was short lived. It seems like it was always cool to cold, and then settled down when the set was warm. In the norm, we always hit a new site, emplaced our sets, then started them, before going on to something else. By the time the sets had warmed up, we came back by with cables to hook up, so we simply never noticed the problem.

Only later, when we received some new equipment, did we notice the problem, and then only because we were on our missile site testing the new equipment. Mostly, resoldering all the solder points fixed this problem. Later, we received "new" VR cards, (had almost the same part number, but a -3 or -4 behind it. Cant remember it fully, it's been too long. I do remember that our TROSCOM LAR, (Logistic Asstence Rep.), simply told us to "live with it".

 

[flydude92]

It sounds like you have a component that is sensitive to temperature. As the temperature warms up the component begins working properly.
I used to get these when repairing TV's a long long time ago.
I used to take a can of compressed air (for cleaning computer keyboards for example), turn it upside down and spray each component separately to cool it.
In your case when you hit the one that is the problem I believe will start to act up. Replace that component.

Brian

 

[Guyfang]

That's thinking outside the envelope. I like that!

 

[Triple Jim]

I don't know Jim but from looking at his location we are practically neighbors.

I didn't realize how close we are, Chris. I have a friend who lives on the Eno river near Hillsboro, and I occasionally ride a motorcycle down the country roads to visit him. If you ever need any help and the weather is nice, let me know. I could bring a spare regulator so you could swap them and see if that's the trouble, for example.

 

[DieselAddict]

Thanks Jim, I'll keep you posted. Currently I'm on a project in Portland Or so our distance is a lot more than it would normally be.