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Old 11-07-2022, 04:31 PM
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I have a Coleman 120 volt 2200 watt single phase generator that I used to power the house with 120 power when we lose line power for years without a problem including the furnace. Last winter I had to put a new mother board in the furnace and now it will not run when using the generator. I have a three prong 120 volt plug going to the generator connected to q 220 volt plug with the hots jumpered and the ground to ground so I can back feed from the garage to both 120 volt circuits. I brought out the Hobart gas drive welder and back fed 220 to the house and the furnace runs fine. The outlet shows 120 volts with the polarity being correct when using the 120 volt generator. The only thing that I can find odd is when testing the 120 volt generator is it gives 120 volts from the hot to the neutral but nothing to the ground. Any ideas why the furnace won't run with the 120 volt generator and runs fine with the 220 volt generator.
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Old 11-07-2022, 05:30 PM
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The smaller generator is probably not producing clean sine wave power.
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Old 11-07-2022, 05:32 PM
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Have you checked voltage coming out of the two legs? If the gen isn't running fast enough it won't generate a high enough voltage which may be causing your issue.
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Old 11-07-2022, 05:35 PM
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Quote:
Originally Posted by mccutter View Post
Have you checked voltage coming out of the two legs? If the gen isn't running fast enough it won't generate a high enough voltage which may be causing your issue.
The 120 generator reads 140 volts with nothing running but nothing to ground
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Old 11-07-2022, 07:31 PM
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Quote:
Originally Posted by Samcord View Post
The smaller generator is probably not producing clean sine wave power.
This would be my bet.
digr, is this an inverter type generator that runs as fast as needed? If so... it's a square wave and not true sine.

Electronics often rely on a clipper type of voltage supply that snips off a piece of the sine wave with the right voltage range in it. A square wave goes from 0 to 120 instantly, there is no ramping up from zero.
So the furnace sees no power.
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Old 11-07-2022, 07:39 PM
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The generator is probably 20+ years old Is it possible that the generator shows no power to ground that the furnace senses that? All the furnace does is click like its trying to start
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Old 11-07-2022, 08:09 PM
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how about I go into the generator and run a jumper from neutral to ground? When the power goes out I shut off the main beaker in the panel and the 220 volt water pump and back feed from the garage, I am just being lazy not wanting to drag out the welder for a short outage.
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Last edited by digr; 11-07-2022 at 08:20 PM.
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Old 11-07-2022, 09:09 PM
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Quote:
Originally Posted by digr View Post
I have a three prong 120 volt plug going to the generator connected to q 220 volt plug with the hots jumpered and the ground to ground so I can back feed from the garage to both 120 volt circuits.

I dont quite understand this. In a normal 240v circuit, the two hots will have 240v between them, and 120v between the hot and neutral/ground. But the two hots are not the same phase (180 degrees apart). So if i understand what you did with the plug, you would still only get 120v output, because the two hots are "jumpered" meaning the same 120v used for both hots, you won't get 220v result from that. Not an electrician, so could be way off base. And if it was working before, I don't understand that.
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Old 11-07-2022, 09:25 PM
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Quote:
Originally Posted by unfinished View Post
I dont quite understand this. In a normal 240v circuit, the two hots will have 240v between them, and 120v between the hot and neutral/ground. But the two hots are not the same phase (180 degrees apart). So if i understand what you did with the plug, you would still only get 120v output, because the two hots are "jumpered" meaning the same 120v used for both hots, you won't get 220v result from that. Not an electrician, so could be way off base. And if it was working before, I don't understand that.
The reason for jumping the hots on the 220 plug is to back feed both sides of the main beaker box supping the entire house with 120, all 220 circuit are turned off, it worked before until I installed a new mother board in the furnace
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Old 11-07-2022, 10:50 PM
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The new board does not like the old generator. I have heard this from more than a few people.

Let me see if I understand correctly about the 220 volt welding machine generator. When you connect this you are running it into a 220 volt breaker to supply 220 to the house. you have the ground and neutral connected in the buss bars in the box. Like normal power from the power company. and the furnace works. correct?

In your info from the 120 volt generator you have no 120 from hot to ground but you do from hot to neutral. And furnace does not work.

The only difference I see here is the neutral and ground are not tied together when the furnace does not work.

Based on what you have provided and what I have read similar to the link below. If it were mine I would tie the ground and neutral together like you are talking about and let the heat run. However I would not want to spend your money to find out my theory if I were to be wrong.

Somewhere in what I read it has something to do with the flame proving sensor.

I found the info in the link below.

https://diy.stackexchange.com/questi...-a-portable-ge



Scott
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