Portable generator causing central AC compressor to run strange

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Old 04-17-20, 09:00 AM
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Portable generator causing central AC compressor to run strange

I bought a Duromax xp12000eh portable generator (Rated Gas-9500w/Surge Gas-12000w, Rated Propane-9025w/Surge Propane-11400w) in hopes of running my entire house if needed. 50amp inlet box was installed and wired to the main panel with a 50amp breaker. Not using a transfer switch. Several weeks ago my son and I went through the house and each breaker with a clamp meter to measure amps. After yesterdays test run with the generator and testing numerous appliances at the same time, I am happy with the generator to power my home.

Now comes the central AC. It is a 5 ton Amana ASX16 single speed scroll compressor that was installed June 2018 with a Goodman air handler. Clamp meter read 49amps on start during my testing with a LRA rating of 135. I installed a 5-2-1 kit which brought the startup down to roughly 34amps.

I tested the AC by itself under generator power using propane with every other breaker off. The generator stumbled slightly once but recovered rather quickly. I noticed the AC compressor sounded different at startup and the fan had roughly a 2 second delay to start VS starting almost instantly while running off normal power. Also, while running on generator power, it appears the fan was not running at fun speed and there was a vibration coming from the unit that would cause the grate to make a noise. You can hear all this in the videos.

I read another post about testing the frequency but unfortunately that was after the fact :gah: ....and if that's where I need to start I will have to hook the generator back up.

Generator Start
https://youtu.be/kexY6G2NEls

Normal Start
https://youtu.be/vnGifVpeYrg
 
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Old 04-17-20, 10:56 AM
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Generator:
Peak amps @ 240V - 50
Running amps @ 240V - 39.58

A hard start kit helps but the starting load is still challenging that generator. I haven't seen many portable generators run a large A/C system. Don't forget you have the air handler blower running too.
 
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Old 04-17-20, 08:27 PM
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Air handler measured 6amps at startup and 3.5amps running. Combined with the compressor starting its still under what this generator should be able to handle. Im just not sure where to start looking to diagnose the problem. I don't want to keep forcing the AC to start while using the generator to diagnose the problem if I am putting unnecessary stress/wear on the compressor and/or fan motor
 
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Old 04-17-20, 09:32 PM
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The problem..... in my opinion it's the generator.
Measured starting load and actual starting loads aren't always the same.
34A for starting that condenser is optimistic.

You can see by the way the condenser fan is delayed in starting that there is a momentary shortage of power. It may have something to do with the length of the wiring between the generator and the panel and the panel to the condenser.

You could try the generator right at the condenser.
 
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Old 04-17-20, 09:58 PM
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I was thinking about pulling the wire from the AC breaker box at the unit and wiring directly into a plug for the generator to see what happens. The distance from my inlet box/main panel to the actual AC is about 80 feet.

I suppose now is the time to invest in a quailty meter since I have read countless posts about cheap meters not giving a true reading especailly when it comes to in rush amps.

Is a Fluke 325 overkill or exactly what I need because it will also read frequency compared to thier lower end models that will not.
 
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Old 04-20-20, 08:58 AM
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I've got a similar gas generator, but it's a Generac from HD. Same watts. I can run the whole house on mine, less the AC. I did try the AC once alone and it wouldn't do it. I never measured the draw on the AC, just tried it. I decided it just wasn't worth trying to run the AC with the gen. I notice too some things just don't work with that manufactured AC from the generators, it's not a sine wave, more like a square wave from what I've heard, but I've never put the scope on it. I know my Dishwasher won't work with it and the microwave runs at about half power. Actually running the whole house is a bit of a misnomer, I keep things to a minimum when using the gen. I've got 2 refrigs and a freezer, plus the submersible pump, the oil burner doesn't take much but I notice when we still had incandescent lights, it wouldn't handle much of them. And the LED lights act funny with my old X10 type dimmers on them. Back after Sandy we were without power for a week and it got pretty hot in the house, we moved downstairs.

I used to turn off all the breakers and turn them on one at a time with the gen, but I finally gave that up, I just turn off the main breaker and let it go and use the on/off switch on the gen, and be careful what's plugged in, no space heaters, electric oven, dryer, etc. You can live without those things for a while. Also no electric hot water heater here. I've got about a 25' cord from the gen to a 30A 240 outlet I back feed into the panel with a double plug cord. I know it's not right, but it works and didn't cost me $1000 or more for an electrician and switched sub panel. But I wouldn't let just anyone use it.
 
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Old 04-20-20, 01:01 PM
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Hi, just curious, no transfer switch? how are you connecting to your panel?
Geo
 
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Old 04-20-20, 03:20 PM
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Last 3 sentences explain it.
 
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Old 04-28-20, 10:39 AM
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Interlock kit on the panel. Inlet box wired to a 50amp breaker that back feeds the main panel.
 
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