Undervoltage fault during exercise cycle

u28514 · Sat Feb 09, 2019 9:14 am

2009 Generac 20KW
Serial #-0006100924
MDN #-2627779642
Description-20KW GT999 Guard+
200 SE
Fuel-LP
Unit maintained on a regular schedule

Undervoltage fault has occurred 5 times since the unit was installed. Only occurs when temperatures are approximately 15° F or below. Has occurred only during the exercise mode. Unit operates as expected during loss of power or when temperatures are above 15°/20°F in exercise mode. The fault engages shut down mode, which is cleared by turning unit to manual mode, and then to history, and the fault clears after returning to manual mode. Any clues?

Sat Feb 09, 2019 10:41 am

There are 2 possible explanations, 1 is easy to fix, the other not so much...

1 is that the unit is running rough during its low speed test and stalling. This is easy to change and I'd recommend it anyways... In the 'Edit' menu, find 'Exercise Time' and set the Quiet Test feature to Off. This will make the unit run at normal speed during its exercise.

If that does not correct the issue, it could be caused by slip ring frost. There's really only 2 options here. A new controller kit with updated hold off times for the field boost excitation, or some type of inner cabinet heat to keep the frost issues down.

Birken Vogt · Sat Feb 09, 2019 11:34 am

2009 would have had the beloved pre-Nexus controller would it not? No facility for slip ring frost control?

Sat Feb 09, 2019 5:32 pm

Birken Vogt wrote: ↑
Sat Feb 09, 2019 11:34 am
2009 would have had the beloved pre-Nexus controller would it not? No facility for slip ring frost control?

They have come out with new 'firmware' (built into the Nexus panel) but it addressed this problem. There is an entire replacement kit available which comes with a relay powered from E1 that will add field boost until the E1 comes alive and opens the relay. Based on his serial number and the actual 'undervoltage' code I'm guessing this is Nexus without actually looking it up.

nrp3 · Sat Feb 09, 2019 6:59 pm

Wasn't the early A board nexus prone to random undervoltage? Especially 20kw it seems.

Sat Feb 09, 2019 7:14 pm

nrp3 wrote: ↑
Sat Feb 09, 2019 6:59 pm
Wasn't the early A board nexus prone to random undervoltage? Especially 20kw it seems.

They did have some issues, I only suggested the frost issues since he mentioned the cold temps.

Either way, the new PCB is going to be pricey, but would probably solve the problem if it's not related to the stalling during exercise I mentioned earlier. You would be able to tell by the alarm log vs run log times. I can price it out for you if you'd like. Just shoot me a PM.

nrp3 · Sun Feb 10, 2019 7:19 am

I've had a few 20kw with the random undervoltage with the A board and solved it by using the nexus with adapter harness. I do some checking naturally before I just replace it though, looking at when the faults occur during the year to rule out the frost thing, check the brush resistance, etc.

Is that kit you mentioned different than the field boost kit with the resistor and the diode? How many have you used on the Nexus units. Have a 14kw with B board that does the undervoltage thing at random times during the year. Been through all the usual tests and good readings to find nothing and not be able to get it to fail while there. Wondering if that board sometimes just doesn't produce enough or any field boost. I put a conversion board in there to test for awhile to see whether it was the board.

Sun Feb 10, 2019 1:50 pm

The kit is a 2 fold kinda deal. The new 0H6680D board (also comes with the 0SRV conversion kit) will have a new firmware in it that has the same hold off time the Evo boards do to allow a 'warm up' before throwing an Undervoltage code. This allows the relay & field boost kit to get the rotor going before the time runs out. It is a relay that gets its coil power from E1 (generator power winding) and when the coil energizes, it drops the field boost kit off the 4 wire. I personally haven't installed any due to the very high cost of the kit, I just know that it's available.

nrp3 · Sun Feb 10, 2019 5:37 pm

Do you have a part number for that kit? I'd like to check it out. The operation makes sense. This has the newest board and the conversion harness in it and we'll have to see whether it needs that next step.

Sun Feb 10, 2019 8:44 pm

nrp3 wrote: ↑
Sun Feb 10, 2019 5:37 pm
Do you have a part number for that kit? I'd like to check it out. The operation makes sense. This has the newest board and the conversion harness in it and we'll have to see whether it needs that next step.

Check the GenService docs section for 0K1401 Instruction Sheet. There are 2 kits, 1 for current D boards without the conversion kit, and 1 with the conversion kit. the firmware to look for is ver. 1.45 or higher on the D controller if it's already installed. List on the kit is $987