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MEP-831a Unbalanced inverters? 240 split mode, Leg 1 and Leg 2 have 20v of difference.

Chadodesu

Hacker / Modder
3
1
3
Location
Manitoba, Canada
Hello folks,

First time post here, partially because the recourses are so great, I never have to post a question.

Issue:

In 240/120 Split mode, Leg 1 and Leg 2 are unacceptably out of balance.
Leg 1: 105v, Leg 2: 124v

Background:
  • 2007 GovPlanet MEP-831a with .8 hours on it.
  • Had to harvest AUX pump to replace main pump to get going.
  • Installed missing fuel separator and bulb assembly.
  • Injector pump was seized and needed to be repaired. (purchased new one to have on hand as backup in case walls are scored)
  • Speed control needed to be re-calibrated as per the TM, got everything running at the perfect 3600 RPM, etc.
  • Speed controller has flakey pots and will need to be replaced. (pushing in on gain pot makes unit unstable)
  • Low Pressure switch dead, replaced with guage to confirm pressure. Cranks at and runs cold at 125 PSI, runs warm at about 80 PSI. (replace LOPS)

Tests:

In 120 mode the generator creates perfect 120v / 60-61 hz on the legs as it should.
Load tests 3KW no problem, RPM's ramp, minimal black smoke during ramp.
Loaded with 1500 watts on each leg.

In 120/240 split mode:

When first starting, after switching 120/240 mode, speed controller needed to be adjusted to match perfect RPM's and maintain stability.
I noticed my LED work light flickering on the convenience receptacle. ( I assumed low hz but, but could have been the voltage)
I measured Leg 1 (common with the receptacle) and it was outputting 105v
I measured Leg 2 and it was putting out 124v

The front mounted voltage adjust pot (working) was adjusted, and the gauge displaying a perfect 240v
I forgot to measure hz of each leg. :rolleyes:
Both legs would load up on a 120v 1500w heater.

It did not enjoy a 240v 4000 watt heater. (understandable but I want to know my equipment limits even if it means breaking it)
Black smoke, Boost control could not save the RPM's from dropping.

Does this bias voltage mean that there is an issue with one of the inverters inside the frequency converter?
I took my voltage readings directly from the top of the A8 under the red plastic insulator.

I did my best to search before posting, if it has been resolved elsewhere, then please point me in the right direction.

Thanks everyone! 🤜
 

Scoobyshep

Well-known member
1,137
1,511
113
Location
Florida
Not sure on the inverter sets, but traditionally an unbalanced voltage is a neutral bond issue (neutral tied to ground) or lack thereof.
 

kloppk

Well-known member
Steel Soldiers Supporter
2,145
3,526
113
Location
Pepperell, Massachusetts
In 120/240 mode is the voltage discrepancy the same regardless of load?

3,600 RPM is a bit high. At no load the RPM should be 3,050 and at full load the RPM should be 3,450.
 
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