Mep 803a dropping loads

[jmenende]

Something that should be stressed about exercising the switches on these generators, especially for those who are inexperienced: BE SURE TO DO IT WITH THE GENERATOR OFF, not running.

And with care. These switches have a plastic shaft that yoy can easily shear off if they are stuck.

 

[Farmitall]

This is true for S8 the Voltage/Phase reconnection switch.

S6 the AM/VM switch can be changed while the set is running though.

Yes, I agree, but one cannot go wrong by exercising any switch while cleaning with the set off.

I emphasize this more so for the benefit of those who might not be knowledgeable of the S8 switch. No harm done by adopting a blanket procedure for all switches with the set not running.

 

[peapvp]

We found out over the last 8 years that this erroneous tripping increases with Humidity and Temperature which points to the fault indicator and a breakdown of the conformal coating of the PCB inside the fault indicator

 

[peapvp]

This would be in addition to the other possible causes

 

[Light in the Dark]

What did you find?

 

[jmenende]

What did you find?

Gonna load bank her today. Could not go to the shop in the last couple of days.

 

[jmenende]

Gonna load bank her today. Could not go to the shop in the last couple of days.

OK, after loadbanking her for a while, she would not trip easily. I could take her to 16kw and after a few mins she would drop the load but no overload light would come on. So its probably a bad fault panel. Im gonna leave it as is since it does it job of dropping the load just not turning on the light.

 

[peapvp]

OK, after loadbanking her for a while, she would not trip easily. I could take her to 16kw and after a few mins she would drop the load but no overload light would come on. So its probably a bad fault panel. Im gonna leave it as is since it does it job of dropping the load just not turning on the light.

Would this be correct then to say that the frequent intermittent dropping / e-stop of genset was caused by dirty switches and the faulty fault indicator panel did not turn on the over current indicator light?

 

[jmenende]

Would this be correct then to say that the frequent intermittent dropping / e-stop of genset was caused by dirty switches and the faulty fault indicator panel did not turn on the over current indicator light?

Yes, no parts were replaced. Contact cleaner and the excersizing of the switches did the trick.

 

[peapvp]

Yes, no parts were replaced. Contact cleaner and the excersizing of the switches did the trick.

Thanks jmenende, we usually recommend replacing the Switches and the fault indicator panel (or having it repaired) since the switches basically have reached the end of their live.

 

[zarathustra]

What can happen with the am/vm switch is that it can develop a slightly charred set of contacts internally, yet still make a connection. That slight char creates a tiny resistance. Current across that tiny resistance creates a voltage. That voltage plus the normal voltage generated by the current sensor is enough to tell the generator it is in overload and drop the load as one is increasing the load.
I fought that problem for some time.... 16 amps was the most I could get before a load drop. I found it when i measured the voltage across two terminals on the am/vm switch that were supposed to be connected together and got voltage across what should have been a dead short.
Replaced the switch and it works fine.

I never would have thought that the am/vm switch would cause a faux overload, but it makes sense if a high-resistance contact on the switch adds voltage to the overload sensing circuits. Overload circuit is just doing what it should.

If exercising the switch "cures" the problem, rest assured that it will be back.

Note that Steel Soldiers member "kloppk " pointed me in the right direction with a good block diagram of the am/vm switch.