Goodman Furnace works Intermittently Generator Power

Bebop

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

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.

pecmsg

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

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

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

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

@mattmia2
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.

Jamie Hall

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.

Bebop

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.

HomerJSmith

THD (Total Harmonic Distortion) is the specification in choosing a generator. Many generators have THD at or above 12%. THD is the distortion of the sine wave. Electronics, especially, those circuit that use the sine wave for timing are problematic. The power company's THD is less than 2.5%. If your generator company doesn't advertise their THD, it is probably high.

There are meters that can measure THD, but they are a bit pricey.

In my Munchkin training, we were told about a boiler that had your problem when running on a generator. Somehow, as I remember, the thermostat created a part of the problem. The solution was a line conditioner.

My stand alone portable generator advertised a THD of less than 5%.

Derheatmeister

Put a UPS between the Gen and the equipment.

hot_rod

Doesn't the RPM change also change the voltage on basic generator? My older welder generator seems to vary a lot depending on load.
That seems to effect microprocessors on heating equipment also.

Where's Moe, he does a lot of generator installation. He would know.

ChrisJ

hot_rod said:

Doesn't the RPM change also change the voltage on basic generator? My older welder generator seems to vary a lot depending on load. That seems to effect microprocessors on heating equipment also. Where's Moe, he does a lot of generator installation. He would know.

It changes the voltage some what but the regulator should keep that in check. It'll effect the frequency more than anything.  I don't see it effecting the wave produced at all.

I've never personally seen a conventional alternator produce anything but a very decent sine wave.  I suppose just because I've never seen it doesn't mean it's impossible but it does mean I don't believe it right now.


I'm using a very cheap brushless alternator and it powers everything in my house including an ECM blower just fine.  Voltage stability isn't perfect but it's by far good enough.  I think 115v near full load and hot vs 125-127v unloaded per side.

People seem to just repeat what they've heard or seen others say but usually do not understand why.  Just like all of those who parrot the only brand to own is Onan.  Cheap inverters maybe, but cheap conventional alternator produce a square wave?  I doubt it.  Doesn't even seem possible honestly.

Jamie Hall

I'd agree with @ChrisJ here. The bigger and better alternator designs are, I'll grant, noisier and perhaps not as efficient. But -- they produce pretty decent power (at least my two do -- an older 16 KW Craftsman (rebranded Generac) and a not quite so elderly 16 KW Northstar). If the governors are working properly, even the frequency stability is very good (well -- not good enough to run a synchronous clock or hi-fi turntable, but less than 1 hz droop no load to full load). The voltage is, or should be, almost constant -- again, perhaps a couple of volts droop. Most of the voltage droop people see is in the connecting cable to the transfer switch, which is often undersized.

The modern compact inverter generators are, granted, quieter and more fuel efficient -- but you get what you pay for. Check the total harmonic distortion spec. if you want to run any electronics with them.

Derheatmeister

Bad Sine wave on offgrid systems is very common..A customer had a Kohler gen in Camp Hale CO...
A APC UPS came to the rescure and keap the Viessmann WB2A running for 15 years without having to change the LGM 29 (CPU).
BTW Viessmann will not warranty any Gen Voltage supplied Systems for this very reason !

ChrisJ

@Jamie Hallany decent turntable from the late 70s should be quartz controlled.

Jamie Hall

ChrisJ said:

@Jamie Hallany decent turntable from the late 70s should be quartz controlled.

Late 70s... well, my B&O is that recent, The Empire, ESL, and Bogen/Lenco ones aren't (but the Bogen/Lenco doesn't count -- it's variable speed, 15 to about 85. I use it for old 78s (which are more or less 78s...)).

ChrisJ

Jamie Hall said:

@Jamie Hallany decent turntable from the late 70s should be quartz controlled.

Late 70s... well, my B&O is that recent, The Empire, ESL, and Bogen/Lenco ones aren't (but the Bogen/Lenco doesn't count -- it's variable speed, 15 to about 85. I use it for old 78s (which are more or less 78s...)).

Empire 698?

That's early 70s no?

My technics SL1800 mk2 was.

Jamie Hall

Yes. 698. It's a lovely turntable. I got it around 1972, I think. It's running a B&O SP12B cartridge (unobtanium -- when the stylus wears out I'm not sure what's next). Belts, oddly enough, are still easily available. Synchronous motor. The ESL is earlier -- but not running at the moment, since I can't find the mounts for the motor (which are completely shot).