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Discussion Starter · #1 ·
I am buying a standby generator.
How big a generator do I need to run a 2.5ton Trane XL140?
I would be willing to shut everything off but the A/C for a few hours to cool the house off and then turn the A/C off.
I can live without A/C for a couple days so I doubt I will go for that, but would like to know my options.
 

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fla. full load amps off the model sticker x 240 volts = wattage, also you need power to your furnace or air handler unless it is a package unit. generators are good for lights and power saws but the uneven Hz/frequency of the power from 58-62 cycles/Hz is BAD for any circuit board and can fry them unless you get a very large and expensive power conditioner. not real good for the AC either. rough guess of 40 amps x 240 volts = 10,000 watt genny plus the furnace load.
 

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I am buying a standby generator.
How big a generator do I need to run a 2.5ton Trane XL140?
I would be willing to shut everything off but the A/C for a few hours to cool the house off and then turn the A/C off.
I can live without A/C for a couple days so I doubt I will go for that, but would like to know my options.
Take the running load amps or RLA (FLA maybe) off the outside unit dataplate and then double it.
Example;

RLA = 30A x 2 = 60.

60 x 240 = 14400watts. Get a 15kW minimum for this unit rated 30A.

This is a ROUGH rule of thumb and other things may contribute. I only say minimum as a starting point. Keep in mind the starting current can be 5-7 times the running current.
 

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lra, locked rotor is 3 x rla but I tend to use fla instead. locker rotor is when the compressor is seized and the maximum current is drawn and that is what they rate the points in the contactor for. nonetheless 3x the maximum running amps for a hot day should be enough to rate a generator for in case the AC stops/starts quickly and the freon pressures have not had enough time to equalize. my AC is buried in the snowbank so I cannot get the #s off it.

he has a trane furnace with an expensive circuit board and definetly the generator will damage that.
 

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he has a trane furnace with an expensive circuit board and definetly the generator will damage that.

I have a Goodman 93% furnace that probably has an expensive circuit board in also. I ran it on my generator for a week back in 2006 when we had 2' of snow on Oct. 13 and we lost a lot of trees that took out the power lines all over our area. I probably risked damaging the furnace? Any thing to do to prevent it? (other than to not run it and freeze.)
 

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I bought an expensive power conditioner from an electronics shop and it filters out any power issues and maintains a proper frequency. costs close to $200. then if necessary I unplug my furnace and plug it into the conditioner and then run a #12 gauge extension cord out to the garage and generator keeping it under 35 feet to prevent voltage drop. a power conditioner is NOT a surge protector device but an actual filter. got mine thru active electronics in winnipeg.
 

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Discussion Starter · #12 ·
he has a trane furnace with an expensive circuit board and definetly the generator will damage that.
The generator claims to have less than 5% harmonic distortion, less than 1% voltage fluctuation and "constant 60hz."
Assuming it actually does that, its not much different than utility power.

Trane tells me to check with either my Trane dealer or the generator installer.
My Trane dealer doesn't know.
The generator installer "thinks" it ought to be okay.
 

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of course the generator co. is going to claim their product is perfect, I also have some real estate to sell you. Unless they put a power conditioner with it then the frequency can vary with the speed of the generator or it would have to be electronically governed rather than mechanically. I would not trust them. The high end Lennox SLP furnace board has a self check for frequency and will lockout if it varies from 60 so it is rather important. we do get a lot of damaged boards in the summer from utility problems/surges/brownouts but why take the chance and create your own problem. to each his own.
 

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the governor is a speed control to maintain a constant speed/frequency irregardless of the changes in load. if it is a HIGH quality generator vs your basic Honda/Coleman 5000 watt utility generator then you may be OK. with the advances in cheaper/mass produced electronics it may be now feasible for them.
 

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he is a country guy right? I like Dwight Yoakam and some country acts but not his.

You were in business, " like the cheques in the mail". people don't lie do they?:no::laughing::yes:
 

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Discussion Starter · #18 ·
A company selling the generator in question says the 8kw will run a 3ton A/C. I asked them where they got that information. They said it was supplied by Generac. They told me to look at the LRA on the plate; if it is under 50, the 8kw will start it.

Mine says 104! Presumably that means I need a 20kw generator to run it. That ain't happening.

So, is my LRA extremely high for a 2.5 ton A/C, or is Generac lying through their teeth when they say the 8kw will start a 3 ton A/C? Or is the company just confused?
 

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Every piece of equipment is different. They can't really use a blanket statement like that. This is EXACTLY why my first reply was that it's not running the AC, it is starting it that is the problem. Your Compressor will NOT pull 104 amps EVERY time that it starts. You can add a hard start kit to the unit (if it does not have one from the factory) to help lower the starting amps.
 

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Every piece of equipment is different. They can't really use a blanket statement like that. This is EXACTLY why my first reply was that it's not running the AC, it is starting it that is the problem. Your Compressor will NOT pull 104 amps EVERY time that it starts. You can add a hard start kit to the unit (if it does not have one from the factory) to help lower the starting amps.
Actually it will pull LRA everytime it starts. Might only be for 1/100 of a second, or it could be for 3 seconds. usually a good hard start kit can keep it to less then 1/10 of a second.


LRA is the draw it will have to get the rotor moving from its stopped position.


Most digital amp meters aren't fast enough to show the true amp draw of a motor starting. An analog meter will though.
 
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