Bouncing Kilowatt meter (percent power) MEP-004A

[1800 Diesel]

Ok this one has become another mystery that I could sure use some help with. I'm working on two of these sets & both had the same problem--the percent power meter was bouncing whenever the sets were running. Both would read as loads were added but you had to just average the needle movement to get an approximate percentage. On one set I simply replaced the meter & the problem was solved. On the 2nd set a meter swap did not correct the problem. I changed out the TWC with a known good one and the needle still bounces even after installing a 3rd meter. Of interest is that when I was removing the wiring from the original TWC, I noticed one of the jumpers was installed on the incorrect terminals. When I connected the replacement TWC I followed the wiring diagram from the TM. Has anyone everr heard of field or depot personnel straying from the wiring diagram in the TM? This adds to the uncertainty when trying to troubleshoot & repair.

The only other possibility (from an earlier Sewerzuk-Leedawg discussion) is that one of the CTs is bad but I have no idea which one of the three affects the percent power meter.

BTW, both of these sets have had the single phase conversion completed & both have been load-tested.

Thanks


Edit update:

Have eliminated the TWC & near certain the current transformers are good, though at least one of the connections on one of the CTs had a slightly lower resistance when compared to a properly working unit. None of the CT resistance values showed "zero". Has anyone ever changed out the 4 CT assemblies. I haven't traced all the wiring but it looks to be a nightmare to change these out. Hopefully I'm mistaken.

I also installed another TWC & tested voltages at all 14 terminals with the unit running but no load. All terminal values were near equal (comparing each TWC) but for both TWCs, the - & + terminal values are both erratic and not a constant or near constant voltage as found on the correctly-operating unit. Doesn't this indicate that something is feeding the TWC & causing a problem on the - & + output to the KW meter?

I also removed & tested the tactical relay assembly. The 3 resistors tested correctly at near 8 ohms (though the TM info incorrectly states that when testing across terminals 4, 3 2 & 1, the values should all be 7 1/2 ohms. As wired, the resistors seem to be tied together so a value of ~15 ohms is found when testing at least 2 of the connections. I also found a near-tight but not fully tight ground connection inside the box & tightened this connection...could not start unit up last night but will start today for more testing.

Today I'll do some testing on the the load measuring unit but after that I'll be at a dead-end.

If any of you sparky types can help I would appreciate any wisdom.

Thanks

Edit with voltage readings at TWC - & + terminal & at KW meter terminals. (All no load with main contactor open)

These readings from terminal to frame ground:

- terminal on TWC: 50-200 VDC (erratic) (working unit 42 VDC & stable for both terminals)
+ terminal on TWC: same as above

- to + terminal on TWC: 2-6 VDC (also erratic)

These readings taken on KW meter terminals:

- post to ground starts at ~38 volts and then drops down to ~9 VDC (working unit 42.5 VDC & stable)
+ post to ground starts at ~38 volts & then drops down to ~7 VDC (working unit 42.5 VDC & stable)

KW meter post-to-post 0.5 VDC (working unit 0.1-0.2 VDC)

 

[1800 Diesel]

Doing a "self-reply" as I added an update to original post & didn't know if the thread gets bumped to the top or not.

Thanks