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Goodman Furnace works Intermittently Generator Power

Bebop Member Posts: 1
edited March 2021 in THE MAIN WALL
GMH8 Goodman Furnace during recent 4 day power outage.
Ran portable 8000 watt continuous watt troy bilt generator.
Have 8 gauge ground wire from ground lug on generator to house ground rod. Tight.
Generator sits on yard cart with 4 rubber tires (not on ground). Reason extra ground wire.
Ran fine for approx. 10 hours.
Then call for heat and do nothing.
Turn thermostat off and back on after few min. it would start and work several hours.
Then call for heat and do nothing. Off / on it would go.
Change thermostat and repeat working several hours, turn off and it go back working.
Change cord from Gen. to plug direct to furnace. No change.
Generator appear to be Bonded Neutral to my limited knowledge. Continuity from neutral slot receptacle to ground lug / wire. Continuity ground slot receptacle to ground lug / wire.
Work 4 day like that. Back on utility power all is fine.

Any advice appreciated.


  • Ironman
    Ironman Member Posts: 6,876
    Electronics and ECMs don't like square wave power that most portable generators produce. You may need to use an inverter generator which produces clean sine wave power.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • pecmsg
    pecmsg Member Posts: 2,898
    Computers require a Clean Sine Wave. Low end Portable gens Do No have a clean sine wave, most inverter generators do but cost much more!
    EBEBRATT-Ed Member Posts: 12,016
    The generator neutral is supposed to be bonded to the ground if your feeding all loads with extension cords.

    If your feeding a transfer switch or generator interlock into a panel then it should not be bonded
  • mattmia2
    mattmia2 Member Posts: 5,541
    How is a conventional generator going to produce anything but a sine wave? It is a rotating coil in inside another coil, that will naturally be a sine wave. The first thing virtually all electronics do is rectify it and filter it to DC anyhow so unless the filter caps are sized right on the edge of the capacitance needed for the load which is unlikely, even if it were a sawtooth wave from a on/off switched inverter the electronics would still see dc. An on/off inverter can make a lot of harmonics and that noise could interfere with things.

    My mom had a white Rodgers stat from the 80s, the one with the wood/leather contact paper insert that looked like it was from the 70s, that when I was running off of a conventional generator would think it was cooler as soon as the blower motor stopped and immediately call for heat again. The only thing I can think of is the rise in frequency or voltage of the 24vac when the load stopped affected the calibration of the stat. Maybe they were using some trick with frequency.
  • pecmsg
    pecmsg Member Posts: 2,898
    edited February 2021
    From: https://diy.stackexchange.com/questions/138175/does-inverter-generator-mean-it-is-a-pure-sine-wave-generator

    The root problem is that regular gas generators cannot produce a "clean" sine wave because they change speeds slightly during operation. When the speed changes, the wave changes slightly. This isn't a problem for regular electrical devices like incandescent lights, power tools, "basic" refrigerators, etc. They merely need the flow, not so much the sine wave.

    Anything in the "consumer electronics" category, however, is not so lucky. Most of these devices rely on the sine wave for timing, and normal generators won't cut it here. I remember trying to watch TV on a conventional generator after a hurricane a couple of decades ago. The sound was fine, but the tube TV couldn't fill the whole screen. The TV ran fine once power was restored.

    Inverters fix the issue by inverting DC to AC. As the output is consistent, consumer electronics will run relatively well on them. That's the main reason you buy these types of generators. If consumer electronics won't run on them, they're overpriced regular generators.
  • Ironman
    Ironman Member Posts: 6,876
    Every manufacturer of modulating equipment and ECMs that I've dealt with will tell you what I stated above. And I've seen it multiple times in the field when people tried to use non inverter portable generators. ECMs require clean power.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jamie Hall
    Jamie Hall Member Posts: 18,966
    Oddly older slipring excited generators tend to produce a cleaner sine wave than newer ones, but even they are variable. The actual waveform which any of the rotary generators (including the big guys at the utility!) is dependent -- in a complex way -- on the way the field coils and armature coils are wound, and the geometry of the iron in the field and armature. As in so many things, you tend to get -- in a broad range -- what you pay for, as more copper and more iron give better results.

    New inverter generators can also produce something approaching a sine wave -- but again, you tend to get what you pay for. In this case, the necessary electronics to convert what is produced -- which is anything but a sine wave -- to a sine wave.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Bebop
    Bebop Member Posts: 1
    Thanks guys
    I think maybe the slight change in RPM at a few calls for heat may have been the trouble.
    I didn't mention it but during the 4 days and nights it only failed to start approx. 6 times. So 95%+ of the time it ran fine on generator power. But it got got cold while sleeping before \I know it lol.