# Question about the actual numbers to look for to run a full home A/C off a portable generator



## texmaster (Mar 6, 2021)

Hi guys,

After that crapstorm blew threw Texas I'm looking at better options for my family than the 2000 watt inverter generator we survived on. Don't want to go the 10-15k route for an automatic whole home generator but I'm getting stuck at how many watts my A/C will actually need at cold start.

Some youtube guys say you take the LRA number, multiply it by 240 and you get your cold start watts you need. Well that hits me up at over 25000 watts but I've seen guys claiming to get their 4 ton working on as little as an 8k max startup with a soft start.

My A/C is only a year old so I dont know if its got the soft start built in or not and if not can I even add without voiding the warranty so any advice would be appreciated.

I'm looking at the 15kV/12kV Champion 100111 Generator with the goal of setting up an outside plug to another panel to run the house.

Here's a shot of my A/C specs.


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## Airstreamer67 (Oct 3, 2020)

The "soft start" goes on the air conditioner, not the generator.

When shopping generator size, remember that the bigger it is, the more gallons it consumes. If you have natural gas, that's usually not a problem. If not, it may be a problem.


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## BobS (Aug 26, 2020)

To get a correct answer you need somebody with a meter with an inrush setting on the AC when starting the compressor (when cold and during a restart). It will record the highest amount of current being used. You would also have to add up the other energy usage that would be on with the AC. You can also check into using a soft start (if your AC can take one - depends on compressor) to help reduce the amount of power needed to start the motor (starting the AC can take up to 300% more power than running it). If you are looking a gasoline generator, realize that it will use approx. 1 gallon of gas per 5KW per hour with propane burning at a much higher rate.


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## Browse Deweb (Jan 16, 2021)

Airstreamer67 said:


> The "soft start" goes on the air conditioner, not the generator.
> 
> When shopping generator size, remember that the bigger it is, the more gallons it consumes. If you have natural gas, that's usually not a problem. If not, it may be a problem.


I have a similar 4-ton Lennox HVAC unit (HS26-048), but it has higher LRA at 129A and running amps (25A) since it is older and less efficient. After speaking with MicroAir about their soft start unit, I decided not to try it with my Honda EU7000IS generator since I don't want to be pushing it consistently near or over maximum load. Running an AC unit this size would use much more fuel and wouldn't leave the rest of the house with any available power. It also wouldn't be good for the longevity of the generator in my estimation. We have a mini-split AC in the basement we can use (which only draws about 1000 watts) if it gets too hot.


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## JohnWhicker (Feb 21, 2021)

My concern with the 15kV/12kV Champion 100111 Generator is not about running the HVAC but rather the sensitivity if the HVAC electronics / controls. Can they handle dirty power? I get mixed messages on this one. My thinking is to have an invertor running all electronics incldjing the HVAC ones and then a normal generator running the big stuff. All that can be wired acordingly in a nice transfer switch / panel. Now the quesion is do the HVAC electronics / control board feeds from the same 40AM double pole HVAC breaker or it got its own breaker?


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## Browse Deweb (Jan 16, 2021)

Good point John. I would think the older HVAC units don't care about dirty power, but any that have circuit boards might be more susceptible. For example, my 4-ton condenser is just a scroll compressor, capacitor, contactor, fan and two limit switches. The air handler unit has a blower motor, evaporator, txv, speed control, 24v transformer and some relays, so not much to go wrong. The mini-split in the basement has digital circuit boards, remote control and other electronics that may be more prone to bad waveforms or frequency changes.


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## BobS (Aug 26, 2020)

I would not be a fan of running any 4 ton non inverter AC unit on a portable (<15KW - not surge) generator. When the compressor starts, it will put a very large demand on the generator which would slow it down until the engine can respond, causing the compressor motor to get a lower Hz and lower voltage while trying to pull more ampere and thereby stressing the compressor armature as the AC starts which can shorten its life. Even with a soft start, there will still be a large amount of power required which will slow the generator down. Before I replaced my ACs with inverters, I would use portable AC's on a portable generators ranging from 5KW to 12.5KW. My 20KW diesel had no issue with a 3 and 4 ton AC. An inverter AC doesn't have the start up power issue of a regular AC. My 6.5KW (Honda gx390 with Mecc Alte generator head) was able to run the 3 and 4 ton inverter AC together until the well pump went on. My Kubota GL11000 (11KW Diesel) AVR does not like inverter ACs (probably feedback issue).


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