Running Heil N9mp100 furnace on generator

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Old 12-31-11, 08:06 AM
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Running Heil N9mp100 furnace on generator

I did not find this mentioned. I have recently purchased a portable generator (Generac GP7500e) for emergency home back up power. This is fed into the main home load center via a back feed breaker and interlock kit. One of the two main reasons I did this was to provide water (well pump) and heat in the event of an outage during the cold season. I would not be running this all at once, so if well pump is needed all other loads will be shed. However, I am not sure if my gas furnace will operate on the "dirty" power of the generator. I have not had a chance to do a test run yet. Does anyone have any input on this model furnace for voltage tolerance ? From what I read some have 0% others have up to 5% voltage tolerance. I cannot find the specs for my board, just the part number.

Thanks.
 
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Old 12-31-11, 11:23 AM
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the main thing is to ensure your generator and common wire are properly grounded. Most furnaces MUST see voltage between hot and common and hot and Ground. If the furnace is variable speed then you will need to hold a tight tolerance with the power.
 
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Old 12-31-11, 01:45 PM
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Thanks for the info. I will have to check the book to verify if it's variable speed or not. Also the gen is tied into my home load center, so it's ground and neutral are done at the same point in the panel with the house wiring. Is that sufficient for this? My furnace is also hard wired in, they did not do the plug into receptacle type installation. It is on a 15amp breaker shared with the gas hot water heater in the panel. Then gen backfeeds a 30 amp double pole breaker on the panel with an interlock kit so I don't feed the grid.
 
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Old 01-01-12, 09:09 AM
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it should work, but you are in uncharted territories as the furnace was not designed to be run with a Generator. I have seen a lot of control boards fail because of attempted use with a generator. And then I have also seen a lot work.
 
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Old 01-01-12, 09:37 AM
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What limitations does your generator manufacturer suggest on the kinds of equipment it should be used to power?

Most furnaces these days have a low voltage circuit that operates a circuit board containing electronics and integrated circuits I would expect want to see good quality sine wave voltage, which you probably aren't going to get from a home generator.
 
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Old 01-01-12, 11:49 AM
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This is really annoying. I am not liking these new digital furnaces so much ....

There are no limitations as far as this mentioned in the manual. However I did find on their website when asked that this unit has a THD of 28%....OUCH. I have no idea if it will work. The best / worst case would be to run it and have have it fault. Worst,, well I loose the board. I guess I will wait for warmer weather.

Heil Main Control Circuit Board 1172550 [1172550] - $166.00 :

That is the board (new part number replacing what I have for part number)
 

Last edited by hvactechfw; 01-01-12 at 01:03 PM.
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Old 01-01-12, 07:46 PM
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A good option might be to put the generator's power through a higher capacity ups. (1000 watt rated would be needed for a furnace, maybe more)

*The power going to the furnace, that is - not the entire house.

UPSs convert incoming ac to dc, then back to either AC. (dc is used to charge battery)
 
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Old 01-01-12, 08:01 PM
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Actually, you probably on need fifty watts or less of "good" power to operate the transformer and low voltage circuit board.

I suppose electrical code people would object to special wiring for that, though.



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Old 01-01-12, 08:06 PM
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Hmmm.

It occurs to me that the power for the circuit board is usually 24 VAC, but most of the sensitive electronics and integrated circuits are going to operate on DC.

That implies that many circuit boards probably have a bridge rectifier to convert the 24 VAC to a quality DC power supply. That would probably clean up fairly dirty AC power input to the circuit board, I would suppose.
 
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Old 01-02-12, 08:45 AM
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Sorry for the link post above that was edited. That was in error.
Thanks for the suggestions. The wife is not allowing me to do a test run for now because it is winter and she does not want my to potentially fry our circuit board. I can order one, but I don't want to do that if I don't need it, and we don't want to be without heat for any length of time due to a trial run.

I have read about people using a UPS. I was not sure how I would put that in line with the furnace only for the generator power side. This furnace is wired into a shut off switch, not plugged into a normal outlet.

**From what I read I would need a double conversion UPS. If I try one that is rated to run the whole furnace that would include the blower motor, induction motor and board etc it seems to be cost prohibitive. Did I read the previous post meaning a smaller UPS to put inline between the power source and just the circuit board as it is the only sensitive item needing the help? If so I can see that being very possible with a simple wiring change. Or am I missing something ?

I am still just hoping it will work, but the more I read I don't see how the board will so tolerant of these frequency swings.
 

Last edited by madmatt76; 01-02-12 at 09:16 AM.
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Old 01-02-12, 10:58 AM
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Yes, you should find a 120 VAC connections to the low voltage transformer which provides power to the circuit board. Such transformers are commonly rated at 40 volt amps, which means they supply a maximum of forty watts of power, and circuits boards are typically going to use about half that much power.

Post the make and model of the circuit board or ignition control. I'd like to see what you have and see if it seems likely that it would have its own power supply that would provide quality DC power for the rest of the circuit board.
 
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Old 01-02-12, 11:05 AM
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I don't think it has a power supply, but I'm not sure. This is the info I could find on the furnace sticker and the board.

Model:

H9MPD100J14C1

Serial #

A061159763

Date Of Manufacture: 03/2006


Board part number :

HK42FZ0181006

alternate / new part number that replaces above

1172550
 
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Old 01-02-12, 12:13 PM
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There a good enlargement of the new board at:

It obviously uses integrated circuits, which require good quality sine wave voltages probably circa 5-6 volts DC or so. So it's very likely going to have its own power supply built in to provide those voltages --- I can see the parts that likely do that in the upper right portion of the circuit board.

I'd say you'd be pretty safe operating your furnace off the generator power supply.
 

Last edited by hvactechfw; 01-02-12 at 12:31 PM.
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Old 01-02-12, 12:27 PM
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Haha, that's funny, that is the exact same link I provided a few posts back because of that picture. It was edited by a mod I think because I was not allowed to post the link.

Your opinion is giving me hope. I will look better in a little while, but I believe the power supply is mounted right inside the top half of the cabinet right behind the external on / off switch. I think I can hear the slight hum from it when the switch is on and the unit is not running. I didn't even think to look under the access cover. I will post back with a pic.
 
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Old 01-02-12, 12:54 PM
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You are probably talking about the transformer, which would supply 24 VAC to the circuit board.

I would suppose that the circuit board would change that voltage to six volts or whatever is needed, rectify the AC to DC and then smooth out the DC to operate the integrated circuits and other electronics.
 
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Old 01-02-12, 01:14 PM
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[IMG] Uploaded with ImageShack.us[/IMG]

Ok the transformer is all I can find on mine. The black hot lead comes into the transformer from the XFRMR connection point at about the three o clock area you can see on the previously posted full image, and the white comes from the neutrals connections toward the bottom right of the board. The blue and red wires come out of it and plug into the board 24VAC and common. Other than that I see no other power supply. The black and white wires come right from the switch and plug into the neutral section on the board and I think the black one goes into one of the two black relays on the bottom right side.
 
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Old 01-03-12, 02:30 PM
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so this means I don't have a power supply..? Just the transformer.
I know, easiest way to tell is to plug the gen in and try. I however am nervous doing this and damaging the board with it being 8 degrees out right now. I want to get as much input / research done while I wait for warmer weather for the test
 
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Old 01-03-12, 06:20 PM
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judging by the pictures I would say you have a simple furnace. It should run fine on the generator as long as you are properly grounded. I would encourage you to wait for warmer weather for a test run though. Maybe ask about a generator usage on a furnace over in the electrical forum and see what their input is.
 
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Old 01-04-12, 06:02 PM
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Again, thanks for all the input.

I have one last question :

Can anyone provide me with some direction on getting parts for my furnace other than just a contractor ?

Model :

H9MPD100J14C1

I have found things like pressure switch, circuit board induction motors etc. Mine has a cracked transition box assembly. This caused it not to run, or run in spurts with a pressure switch fault. I have one on order through a contractor (still has not arrived) and is "supposed" to be under warranty. Not 100% on that though. I wanted to know the cost of and where to get parts like these if need be in the future. My current unit has been temp fixed with high temp RTV on the crack to keep it running in these cold temps while I wait for the part.

I understand they don't want to supply parts to non contractors but even if I could find the part number to search for. I did not see one on the current transition box when I pulled it out to do the temp repair.
 
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Old 01-04-12, 06:16 PM
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removed link........................................................
 

Last edited by hvactechfw; 01-04-12 at 06:48 PM.
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Old 01-04-12, 06:24 PM
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Thank you VERY much. I actually came across that link, but like an idiot dismissed it thinking it was just for sales of full units.
 
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