mep831 inverter

[royerator]

Have been spending a lot of my time trying to get this Thing so it can produce power. Finally, it is starting to look it may be reliable, however, I noticed that the two bolts I used to secure the inverter to the box is sparking between the bolt heads and box; I used extra long bolts with a oversized nut as a spacer and in this tiny bit of clearance (between bolt head and box frame) there is sparking going on. Does anyone know if this inverter is supposed to be isolated? I'm confused because it seems like it is pressed up against the medal tab with the two bolts holes so it should already be grounded... I only read 10v between inverter and box when this sparking is happening. is my inverter toast? even if it is it seems to work except for the sparking.

 

[kloppk]

I just check my two 831's and the inverter housing is bonded to the generator skid & frame.
It wouldn't make sense for the inverter housing to float since this could create a shock hazard to anyone servicing the set.

Current should not be flowing between the gensets frame and the inverter housing.

Is the sparking occurring only with a load on the set or even without a load?
Only with the contactor closed or all the time?
Do you have the ground bar installed?

My guess based on your description is... I suspect there is a short inside of the inverter to the inverters case. This would cause current to flow thru bolt to the genset frame, thru the ground bar, to L0 and back to the inverter.
My next hunch is an issue with the PMA windings and wiring and one of them may be shorted to ground.

If it were me, with the set shutdown I'd..
- Disconnect all loads from the set
- Disconnect the battery
- Remove the ground bar
- With a meter verify there are no shorts to ground from at the L0, L1 & L2 output lugs
- With a meter verify there are no shorts to ground from at the L0, L1 & L2 at the inverters output terminals
- Disconnect P15 & P16 from the inverter
- With a meter verify there are no shorts to ground at each of the pins in P15 & P16

 

[royerator]

Thanks for your reply kloppk,


Good advice. I couldn't find any grounds, but I did realize that the back 6 bolts were missing...also the side tab I was talking about somehow does not make a ground to the chassis. Once I put a ground from the chassis to the case of the inverter...all **** broke loose (speed hunting and voltage going wild). When I isolated the inverter, I got 75 vollts AC. I know this may make me a reckless person...but I'm seriously considering red tagging it out as do not run because of major inverter malfunction; however, I can keep it around for myself if the local power plant boiler malfunctions.

Anyway, I don't know if anyone else with inverter shorts can be helped by my post...but I had exactly the same symptoms as the original thread (noticed the shorting after a rain). For anyone else, I would say my side tab was not grounding the case and I had no bolts in the back to provide the ground...however, to check an intermittant ground aggravated my moisture, maybe providing a good ground with alligator clips or other conductor may check how well the inverter is grounded...I would think if you get bad results with a proper ground, you may have 2 problems; inverter short and bad inverter ground.