Furnace running on generator

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Old 11-05-12, 05:49 AM
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Furnace running on generator

Last week during Sandy's blackout my buddy call me to check out his furnace, he said it was working 5 minutes on generator then stop. I found Nordyne furnace correctly connected to 6000W generator working together with refrigerator. I easy found burnt control board in furnace. Next day I went to supply for new control board and gentlemen behind the desk tells me this day he sell all 15 boards he had on shelf and is waiting for delivery. I just wondering if someone have an experience with board #903106. Same Control board is installed in Nordyne, Miller, Gibson furnace. What can cause damage to this board? i suspect floating ground from generator.
 
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Old 11-05-12, 06:11 AM
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I would say most likely he has a modified wave generator.
This type of generator is able to run some electronics but possibly not the furnace control board.

A true sine wave generator may be in his future.
 
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Old 11-05-12, 06:59 AM
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Most generator don't put out "Dirty" power, so that will ruine any electronic stuff that is plugged into it.

An Inverter
generator puts out cleaner power.
 
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Old 11-05-12, 09:54 AM
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I have seen that problem with inverters which convert DC battery power into AC. Inexpensive units use a modified form that makes block like steps as the current alternates. This is OK for simple devices like a incandescent light bulb but many electronics can not handle it and require a sine wave like is supplied by the power company. The gotcha is that I have never seen a modified wave coming from a generator. All the inverter generators I have seen produce a nice, clean sine wave and most generators of this type are 3'000 watts or smaller.

I assume your friend's 6kw generator is a traditional style where the voltage and frequency are controlled by the motor's rpm. I would first check that the generator is producing the correct voltage and frequency and watch is as you add & removes loads. It's possible that the governor is not working properly and the current it's producing gets wacky with the additional load of the fridge. The voltage & frequency could drop with the load of the fridge running and then when the fridge turns off the volatage & frequency could spike.
 
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Old 11-05-12, 10:15 AM
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Most furnace ignitions controls have their own power supply.

They take 120VAC and use a transformer to convert that to 24 VAC, then a full wave rectification circuit to convert that to 24 VDC with a smooth voltage using an inductor and capacitors to make a good DC power supply.

Of course, the circuit board in question may not have those features, or there could be some other defect in the circuit board or power supply.
 
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Old 11-05-12, 10:40 AM
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Originally Posted by SeattlePioneer
They take 120VAC and use a transformer to convert that to 24 VAC, then a full wave rectification circuit to convert that to 24 VDC with a smooth voltage using an inductor and capacitors to make a good DC power supply.
Shhh...Generator companies...more precisely their marketers...are busy upselling people on inverter generators by scaring them into believing their "old" generator will destroy "sensitive electronics". Never mind the fact that most these "sensitive" devices have nice internal regulated DC supplies Facts sometimes can interfere with profits, you know.
 
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Old 11-05-12, 11:39 AM
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Replay

He used 6kkW Power Stroke generator, I watched it for while and I do not believe there was any voltage droop. What about grounding. If furnace is disconnected from sub panel and generator is on wheels all system is really not bounded to ground (earth). In this case even static discharge can destroy control board?
 
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Old 11-05-12, 01:11 PM
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Guy, depending on the quality of the DC power supply in any particular piece of equipment it is entirely possible for the transients and electrical noise from an inexpensive generator to pass right through the DC power supply or to actually destroy the DC power supply.

A person DOES need to know that high quality inverter generators are not cheap. If you see an "inverter" generator selling for less than a grand it is probably a cheaply built Chinese copycat with an inferior inverter. These inferior inverters are more likely to damage sensitive electronics than a higher quality non-inverter generator.
 
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Old 11-05-12, 07:02 PM
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A person DOES need to know that high quality inverter generators are not cheap.
Precisely. I got suspicious of the inverter-genny hype when I saw ones flooding the market that cost LESS than "pure sine" DC inverters. Was this "Buy an inverter, get a 4-stroke engine free!"? Doubt it. Even the cheapest standard generator doesn't create transients on the AC waveform like a cheap inverter does. Even at full rated load the waveform is "lumpy" but there are no odd-order harmonics or spikes...nothing that could bypass the capacitors in a DC power supply of a TV, furnace, computer, etc.
http://bellsouthpwp.net/j/o/johngd/f..._generator.pdf
 
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