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Old 04-18-2020, 02:35 PM   #16
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Re: Portable generator causing central AC compressor to run strange


I'm trying to put in perspective the sequence of events that occur from switching on the AC, into the delayed start, then eventually starting. Lets see if this makes sense....

1)Generator is running with no load
2)AC is switched on
3)Generator bogs down/drops RPMs for 1 second and catches itself returning to normal speed
4)At the same time the generator bogs down, the AC compressor/fan turn attempt to turn on
5)Instead of the normal loud click from the compressor while using grid power and instantly turning on, there is 1 click, followed by a second click which then starts to spin the fan

So, is it more likely the generator is under-powered to handle the initial load and when the generator regains its normal operating speed that is the cause of that second click from the AC which then makes it start?

However, if that's the case why wouldn't the fan be operating at full speed?

Just thinking out loud here


Anyway, I tested the frequency with no load directly into the generator 120 outlet and also with a 100ft extension cord (if that matters). The frequency ranged from 62.2 - 62.9. No chance right now to shut off the main house breaker and try the AC at this moment. However, when I get the chance, will a frequency reading taken directly off the 120 generator outlet give me a correct reading when I attempt to start the AC? Or will measuring frequency at the AC itself with a clamp meter be the more accurate way?
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Old 04-19-2020, 12:00 PM   #17
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Re: Portable generator causing central AC compressor to run strange


Frequency is the same no matter where you mesasur e it.

Sixty three Hz in a 60 Hz AC system is not a problem unless there is a clock or timer that needs to be accurate.
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Old 04-19-2020, 12:21 PM   #18
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Re: Portable generator causing central AC compressor to run strange


Based on the video it's having trouble supplying proper power to run it properly, not just a question of starting.

The extra click you described (but i didn't hear in the video) be the sound of the hard start's relay dropping out - only it happens later when on the generator so you notice it.

Normally the hard start's relay drops out a fraction of a second after the contactor engages.
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Old 04-19-2020, 08:43 PM   #19
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Re: Portable generator causing central AC compressor to run strange


Did a little testing today. No load on the generator and all breakers were off besides the AC and air handler.



On Propane
Frequency dropped to 58.5hz on AC startup. 61hz while AC running
28amps on startup measured from one leg before the contactor
Voltage dropped to 180 measured at the contactor when the AC started
Voltage stable at 241 measured at the contactor while AC is running


On Gas
Frequency the same as propane
Startup amps the same
Voltage dropped to 161 measured at the contactor when AC started
Voltage stable at 241 measured at the contactor when AC is running


Normal grid power
NO voltage drop at the contactor
Could not measure frequency



This leads me to believe that the roughly 80 feet from the main panel to the AC is the problem. But I am no expert.


In the mean time, I plan to get a 50 amp plug and wire the AC directly to the generator. If that solves the problem then I don't have many options left. All I can think of is installing a second inlet box right next to the breaker box by the AC itself and backfeed the main panel from the AC line (which I don't want to do). Or, install the inlet box by the AC and physically move the generator if I need to run the AC to cool the house for a while. Thoughts?
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Old 04-19-2020, 08:58 PM   #20
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Re: Portable generator causing central AC compressor to run strange


If the length of the wire from the main panel to the a/c was the issue, the same problem would occur on grid power.

Do make sure the wire going from the generator is the right gauge given the length.

What gauge and length is the wire going from the generator to the main panel?

When voltage drops, starting time is increased causing the generator to be put under starting amps for too long and bog down.

It's possible the generator just can't take the load of a 5 ton a/c starting - you would be better off with an emergency window a/c which than getting a huge 20+kw generator.

There are no guarantees when it comes to being able to start a large motor on a generator.

Just remember that most meters don't respond fast enough to measure true max/min current and voltage.
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Last edited by user_12345a; 04-19-2020 at 09:01 PM.
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Old 04-19-2020, 09:22 PM   #21
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Re: Portable generator causing central AC compressor to run strange


What wire gauge is between the panel and generator?
I’d say your air conditioner is just a bit too much for that generator.
DO NOT keep trying to start it like that. Or you’ll be making another post here for a broken air conditioner.
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Old 04-19-2020, 09:49 PM   #22
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Re: Portable generator causing central AC compressor to run strange


Quote:
Originally Posted by user_12345a View Post
If the length of the wire from the main panel to the a/c was the issue, the same problem would occur on grid power.

Do make sure the wire going from the generator is the right gauge given the length.

What gauge and length is the wire going from the generator to the main panel?

When voltage drops, starting time is increased causing the generator to be put under starting amps for too long and bog down.

It's possible the generator just can't take the load of a 5 ton a/c starting - you would be better off with an emergency window a/c which than getting a huge 20+kw generator.

There are no guarantees when it comes to being able to start a large motor on a generator.

Just remember that most meters don't respond fast enough to measure true max/min current and voltage.

Quote:
Originally Posted by roughneck View Post
What wire gauge is between the panel and generator?
Id say your air conditioner is just a bit too much for that generator.
DO NOT keep trying to start it like that. Or youll be making another post here for a broken air conditioner.


That bold statement is discouraging but it is what it is. Leads me to believe the generator is too small.



Wire going from generator to inlet box is 6 gauge. Its the conntek 1450ss2 50 amp cord at 15 feet

https://www.amazon.com/dp/B0046C6G7O/


Wire from inlet box to generator breaker is 6 gauge as well


I have a split AC for my finished basement. Central AC is for the rest of the house. I believe the split is 2 or 2.5 ton so if I really needed cool air in the summer, the family and I could be in the basement.



Or, I could invest 300$ in a soft starter and see what happens
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Old 04-19-2020, 10:04 PM   #23
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Re: Portable generator causing central AC compressor to run strange


Your generator is too small and can't do what you want.
You can throw a lot of money into this but get the same result.
It's not a HVAC problem now but if you keep trying to make it work with your undersized generator it will become one.
You can either upsize the generator or buy some portable heaters and air conditioners when the need arises.
Did you check with anyone before you bought the generator?
If you have a 5 ton unit then you most likely have a large house.
You need a 20K unit for the whole house.
And how large is your home?
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Old 04-19-2020, 10:05 PM   #24
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Re: Portable generator causing central AC compressor to run strange


15 feet at 6 gauge, resistance going both ways 0.012, even at 100 amps across that cord -> 1.18 volt drop.

https://www.cirris.com/learning-cent...lculator-table

needless to say i don't think it's the cord.
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Old 04-20-2020, 12:13 PM   #25
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Re: Portable generator causing central AC compressor to run strange


Quote:
Originally Posted by Missouri Bound View Post
Your generator is too small and can't do what you want.
You can throw a lot of money into this but get the same result.
It's not a HVAC problem now but if you keep trying to make it work with your undersized generator it will become one.
You can either upsize the generator or buy some portable heaters and air conditioners when the need arises.
Did you check with anyone before you bought the generator?
If you have a 5 ton unit then you most likely have a large house.
You need a 20K unit for the whole house.
And how large is your home?

This generator powers everything in 3000sqft home without a problem except the AC (well its starts, just struggles). The AC unit is only for cooling. We have oil heat. Stove is gas. Every light in the home is LED. I did quite a bit of testing already using all other appliances (many at the same time, refrigerator, microwave, boiler) and the generator handles the load.



My hope was a 12000watt surge generator could possibly handle the task of starting this AC with all other house breakers OFF with the addition of the 5-2-1 hard start kit.



The AC starts but it is struggling so thats why Im here to find a possible solution instead of buying a larger generator. If the process to buy, try/test and then possibly return a 250lb generator was easy, I would have done that already and tried a larger model. The next model size I would consider would be a 15000watt surge, 12000w running model for almost 1800$. I picked up the current model I have now for 850$ on sale. A 300$ soft start device might be worth a shot when cost is considered. If the soft start doesnt work, I'll look at the 300$ investment for the device as support tool to prolong the life of my AC (maybe, maybe not)


I have lived in this home for almost 2 years and only lost power once for a few hours. Many of my neighbors state that power loss is extremely rare for long periods of time with the exception of a hurricane we experienced in 2012. I truely believe I wont need to use this generator but the idea of having a backup for the whole home makes me sleep better.
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