traverse517

I have a Generac portable generator, 15kW, model 004582, purchased in 2003. The generator has always been able to power two Carrier furnaces and most electrical appliance in the house with the exception of the microwave ovens. The light comes on and the display works but the magnetron doesn’t seem to energize in both ovens. Even though the ovens are different brands and different sizes, they never worked while on generator power.

Recently the blower motor on one of the furnaces seized up and subsequently took out the control board.  Carrier service replaced the motor and control board and everything worked normal. 

About a week ago we lost power and had to run the house on the generator.  The furnace with the replacement motor and control board would not run on the generator. The blower motor would not come up to speed.

I had the generator checked by a Generac authorized service and they said everything was ok.

Voltage: 240 AC

Frequency: 59 - 60 Hz

THD%: 4.6 - 6.0%

I am at a loss to figure out why the furnace that has the replacement parts won’t work with the generator. I have seen where some people say it’s because there is a floating neutral on the generator, the neutral is not bonded to ground like with utility power. Others claim the control board is super sensitive to frequency of the incoming power.

I am wondering if anyone else has had a similar experience or suggestion on how to trouble shoot this problem.

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78buckshot
It is very likely that the new version control board is more sensitive to the unsteady frequency. Is the furnace blower a variable speed?
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traverse517
Yes it has multiple speeds
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78buckshot
I repaired a furnace 2 days ago with the newest circuit board, furnace did not like the new one, three boards later we found a "new old stock" board that responds correctly, and all this on utility power. I assume you mean variable speed, those motors are three phase with a module mounted on the end that converts single phase to three phase and then dc controlled. The board and motor do not like dirty power.
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traverse517
I am no expert but i know it becomes dc at some point. Replacement parts: 
437D61B3-67F1-4F13-B22F-A509961AA864.jpeg  615497C7-D863-49E2-81D6-168AA285B081.jpeg 
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traverse517
traverse517 wrote:
I am no expert but i know it becomes dc at some point. Replacement parts: 
437D61B3-67F1-4F13-B22F-A509961AA864.jpeg  615497C7-D863-49E2-81D6-168AA285B081.jpeg 

old parts:
D6FAA138-D573-4273-876E-64806292BBD4.jpeg  B0A33C0B-C95A-431E-AC0C-773D93EFF7BC.jpeg 
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78buckshot
OK, so you do not have a variable speed blower but the board is the brother of the one I had issues with. The motor itself would run fine on generator power but the new replacement board is too sensitive to dirty power. If it is a big problem for you I would call your HVAC guy and ask him if he could locate a "new old stock" HK42FZ010 board.
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traverse517
Thanks for your help! I will give it a try to find some NOS control boards
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Thesandman
78buckshot wrote:
OK, so you do not have a variable speed blower but the board is the brother of the one I had issues with. The motor itself would run fine on generator power but the new replacement board is too sensitive to dirty power. If it is a big problem for you I would call your HVAC guy and ask him if he could locate a "new old stock" HK42FZ010 board.


Would a 2018/2019 model also potentially have this issue or are they much "cleaner"?
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78buckshot
Are you asking about a new generator being "cleaner" or asking about a new furnace and how would it respond?
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Thesandman
I'm curious if a 2018 generac would have the same issue with sensitive electronics.  My understanding is that the evolution controller makes for a much cleaner power output- at-least as good if not better than power off the utility grid.
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murphy
There is no way that a 4 pole alternator is cleaner than a utility alternator which has something like 36 poles and a monster flywheel to stabilize frequency.
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Cobranut
murphy wrote:
There is no way that a 4 pole alternator is cleaner than a utility alternator which has something like 36 poles and a monster flywheel to stabilize frequency.


A 36 pole alternator would only spin 200rpm at 60hz.
Actually, most steam turbine driven utility alternators are 2 pole, and run at 3,600 rpm.  The 12 to 15 foot diameter turbine blade tips run at well over Mach 1 at sea level.  The only thing that keeps them subsonic in operation is the high static pressure, which greatly increases the speed of sound.  If you ever lost that static pressure in operation, the turbine would explode due to the shock waves from the supersonic blades.
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78buckshot
sandman, an inverter generator will have pretty clean output but you would need to have a bunch of them to equal the current output of your 15kw. So the answer is you won't get as good of frequency control from an air cooled generator, either permanent or portable.
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Thesandman
Thanks for the responses.  I just assumed that the THD of the grid was 5% as that seems to be the bar portable generators are trying to reach  
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Cobranut
Thesandman wrote:
Thanks for the responses.  I just assumed that the THD of the grid was 5% as that seems to be the bar portable generators are trying to reach  


I'd expect grid poert to be far below 5% THD.  Probably more along the lines of 0.5% or so.
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