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Discussion Starter · #1 ·
My 2.5 ton Trane central a/c starts up fine when powered by my 9200/7500 gas powered generator. Strangely, the generator doesn't change in the slightest when the a/c compressor kicks on. No surge, no bog, no nothing. Even stranger, the Trane a/c doesn't run at full speed. The 20 inch exhaust fan outside spins noticeably slower. So, there's very little volume of air being pushed out of the vents. It's somewhat cool, but not as cold as it should be. I thought that if the generator survived the a/c kicking on, without the generator's breaker tripping, I'd be home free. Not so, apparently. What am I missing here?
Thanks,
Polesaw
 

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Have you checked the voltage at the condenser when it is running?
Is this a newer style A/C unit with electronic multistage or variable speed capability? If so, what are the model numbers for the condenser and the blower units?
That particular Firman has a THD at full load of 11%-14% and could be causing an issue.
 

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Just for comparison, a Honda Eu7000 inverter easily runs a Dual Compressor Variable Speed Trane heatpump. The 1st stage is a 18,000 BTU compressor which runs (depending on how thermostat time and RH settings are set) up to 60 minutes at low speed. Then 1st stage compressor shuts off and 2nd stage, a 32,000 BTU compressor starts. The Eu7000 has no trouble at any point and has power to spare at the 3 ton 2nd stage level.
 

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Discussion Starter · #6 ·
Thanks for the comparison information, Pipe. Confirms that my Firman's 9,400 surge watts and 7500 rated watts "should" run a Trane 2.5 ton a/c. Alas, it only kinda sorta runs it.
 

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Some reports from Eu7000 users report total harmonic distortion of 4%. For reference, the grid power in New York is commonly rated at 6%. GenKnot already posted the Firman numbers. I would not run any non-DC appliance with that generator.
 

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The only thing not suggested yet, and it may not matter, but the Firman uses a frame bonded neutral. You did not mention if that was disconnected for use with the house service. I assume it was not. If you are using a basic inlet connection box and interlock or a non neutral switching transfer switch, then when on the Generator you have two paths for neutral current to take. The normal neutral but also the ground which is not supposed to have any current on it. There should only be one place where Neutral ties to ground and that is in the house main service panel.
My setup here is an unbonded Westinghouse 9500DF <23% THD through a 50 amp inlet box and a Reliance Controls transfer switch. I have a 3 ton Coleman (YORK) two stage AC fitted with a soft start kit. It is not a variable speed inverter type though. My 9500 running watts (7500W de rated for fuel and altitude) powers everything thing connected via the transfer swtich without issue. This includes the AC, Refrigerator, computers, QLED flat screen, microwave, smart home devices, LED light bulbs, smart dimmers (@ 60Hz or below), cable modem and wireless access points. I do have UPS on things I don't want dropping out and I have a whole house surge suppressor in the main panel, a surge supressor installed across the inlet box at the transfer switch, and another one installed at the HVAC air handler in the attic. Everything is working off the dirty power 9500DF and others report their dirty power gensets are working for them too. Try ruling out the bonded neutral either by disconnecting it at the generator or by using a neutral switching transfer switch. Tip: You can make up a bonding plug (a plug with ground and neutral shorted together) for your Firman to use when it is not neutral bonded by virtue of being connected to the house.
 

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Have you checked the voltage at the condenser when it is running?
Is this a newer style A/C unit with electronic multistage or variable speed capability? If so, what are the model numbers for the condenser and the blower units?
That particular Firman has a THD at full load of 11%-14% and could be causing an issue.
That THD is probably a conservative estimate. The THD for the Firman H07552 is around 25%. That's a awful lot and I think you're correct that it's likely what's causing some of the wonky behavior.
 

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That THD is probably a conservative estimate. The THD for the Firman H07552 is around 25%. That's a awful lot and I think you're correct that it's likely what's causing some of the wonky behavior.
Yeah, the THD might be higher than specified on the Firman website. I did see your waveforms for the Firman P03602 here: (1) Generator Oscilloscope Waveform Measurements | Page 5 | Power Equipment Forum

I put my Champion waveforms here: (1) Generator Oscilloscope Waveform Measurements | Page 11 | Power Equipment Forum

And my new WEN waveforms (which are better than grid power) here: (1) Generator Oscilloscope Waveform Measurements | Page 12 | Power Equipment Forum
 

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Yeah, the THD might be higher than specified on the Firman website. I did see your waveforms for the Firman P03602 here: (1) Generator Oscilloscope Waveform Measurements | Page 5 | Power Equipment Forum

I put my Champion waveforms here: (1) Generator Oscilloscope Waveform Measurements | Page 11 | Power Equipment Forum

And my new WEN waveforms (which are better than grid power) here: (1) Generator Oscilloscope Waveform Measurements | Page 12 | Power Equipment Forum
Yeah man, the waveform on my Firman was something to behold. I knew it wasn't going to be pretty before I scoped it, but I was surprised it looked as noisy as it did. I'm glad I never really used it for much before I got my inverters. I can still use the Firman, but it will be for the electric percolator and the hot plate. I had thought the HO series from Firman was a bit cleaner, but only an inverter is going to give a really clean signal. A non-inverter generator will still have a significant amount of THD compared to wall power or an inverter.
 

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Back in the 1980s, I aquired a UPS for my Apple IIe PC. The device used a square wave inverter with a couple of 12 VDC lead acid gell cells. Made a hum sound when it ran. Guess what? The old Apple and it's CRT monitor ran fine off off it. Even tech from 40 years ago was able to deal with, lets say, less than near perfect sine wave power. As I mentioned before, everything I have wanted to power off a rotating generator has run without issue. I would rule out other potential issues before I splurged on a solution costing 2 to 4 times more for half the capacity. If one spent the same money on a conventional generator as a pare of inverters, the wave form would be just as good with twice the output.
 

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The only thing not suggested yet, and it may not matter, but the Firman uses a frame bonded neutral. You did not mention if that was disconnected for use with the house service. I assume it was not. If you are using a basic inlet connection box and interlock or a non neutral switching transfer switch, then when on the Generator you have two paths for neutral current to take. The normal neutral but also the ground which is not supposed to have any current on it. There should only be one place where Neutral ties to ground and that is in the house main service panel.
My setup here is an unbonded Westinghouse 9500DF <23% THD through a 50 amp inlet box and a Reliance Controls transfer switch. I have a 3 ton Coleman (YORK) two stage AC fitted with a soft start kit. It is not a variable speed inverter type though. My 9500 running watts (7500W de rated for fuel and altitude) powers everything thing connected via the transfer swtich without issue. This includes the AC, Refrigerator, computers, QLED flat screen, microwave, smart home devices, LED light bulbs, smart dimmers (@ 60Hz or below), cable modem and wireless access points. I do have UPS on things I don't want dropping out and I have a whole house surge suppressor in the main panel, a surge supressor installed across the inlet box at the transfer switch, and another one installed at the HVAC air handler in the attic. Everything is working off the dirty power 9500DF and others report their dirty power gensets are working for them too. Try ruling out the bonded neutral either by disconnecting it at the generator or by using a neutral switching transfer switch. Tip: You can make up a bonding plug (a plug with ground and neutral shorted together) for your Firman to use when it is not neutral bonded by virtue of being connected to the house.
I have the same Westinghouse 9500DF powering a 4Ton AC, lights, 2 fridges, tv, etc…and it works great. Have a Hard Start Kit. Only thing I do not have is the surge protectors yiu mention and would love some Information on what you bought? Also, what soft starter did you use?
To the original poster it seems you must have an issue with voltage ?
 

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I have the same Westinghouse 9500DF powering a 4Ton AC, lights, 2 fridges, tv, etc…and it works great. Have a Hard Start Kit. Only thing I do not have is the surge protectors yiu mention and would love some Information on what you bought? Also, what soft starter did you use?
To the original poster it seems you must have an issue with voltage ?
The whole house surge suppressors are the panel specific type which occupie 4 unused breaker positions with pig tail wires to the neutral/ground bus bar. Each unit can shunt 65K Amps and needs two breaker spots. Two of them can shunt 130K Amps. They shunt at 150 Volts. For the Reliant Transfer Switch I choose a square D 80K amp which I picked up at Home Depot. That one is a universal design which I installed through a knock out on the transfer switch sub panel box and wired to the inlet box plug. It only sees the power coming through the inlet box which in my case is the generator. But some day may be a battery bank powered inverter. For the type two in the attic I used a Leviton surge which replaced a typical electrical box 15 Amp receptacle. It is another layer protecting the air handler (fan and controller including smart thermostat) Because the transfer switch has meters built in one for each side, I can see how the generator power balances and how much power is used. In my tests, with the AC running at stage 2 and everything on in the house, I observe about 4KW balanced within about 300 Watts. The 3 Ton AC was installed about two years ago. I called the company who installed it and holds a maintenance contract with me to install a soft start. They mentioned they do a lot of them mostly for the solar battery inverter backup customers but a few generators as well. Their man was out and put it in and tested it in about 45 min. I think it is an Emerson unit. But then the 9500 was starting it before. I was worried about abusing the compressor motor though. It did dramatically reduce the lights dimming on compressor start. As a side note, I when through the whole house and replaced every outlet, gfi outlet, and switch with commercial grade devices using the screw terminals instead of the the consumer grade stab downs the builder used. The outlets are much tighter and the switches quiter. Eliminated the issue where one smart device was spontaneous rebooting which called my attention to the issue.
 

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Okay, thanks for the info. I have a Interlock Switch or plate so the 50 amp breaker powers the entire panel when the Main of OFF.
I just turn on the breakers I need to run EITHER the Up or Down AC as I have never tried to run both (3 & 4 Ton). Now, possibly using 2 Easy Starts (Soft Starters) would allow me to run both AC's but not really necessary. That would put me at a run rate of 7500 watts which would make the generator run though gas and oil like crazy

So, I assume I would need a whole panel surge protector not just one for a Transfer Switch? I appreciate your message
 
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