# Sizing generator for home AC



## TX0303 (Mar 9, 2021)

I am looking to purchase a portable emergency generator to power my house and run the AC, per my wife's request. The unit is a 5 ton with a compressor LRA on the sticker of 152.5. I do plan to put a soft start kit on it. I used my amp meter to take some reading on the start up as it stands now, without a kit. My meter only has a Max mode, not inrush. Help me interpret the numbers in to surge watts on a generator. I'll rerun the test after the soft start kit is installed and I can make my generator choice.
The common wire to the compressor pulled max 87.2 amps.
The two feed wires going to the unit pulled 131.9 and 124.6 max amps. Do these numbers need to be averaged since they were 120v readings.
Once running, all wires were pulling between 14 and 15 amps.


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## Browse Deweb (Jan 16, 2021)

TX0303 said:


> I am looking to purchase a portable emergency generator to power my house and run the AC, per my wife's request. The unit is a 5 ton with a compressor LRA on the sticker of 152.5. I do plan to put a soft start kit on it. I used my amp meter to take some reading on the start up as it stands now, without a kit. My meter only has a Max mode, not inrush. Help me interpret the numbers in to surge watts on a generator. I'll rerun the test after the soft start kit is installed and I can make my generator choice.
> The common wire to the compressor pulled max 87.2 amps.
> The two feed wires going to the unit pulled 131.9 and 124.6 amps. Do these numbers need to be averaged since they were 120v readings.
> Once running, all wires were pulling between 14 and 15 amps.


The soft start will reduce inrush, but won't have much of an impact on running amps. I have a 4-ton unit and the running amps for the condenser and the air handler is around 25A @ 240V. My Honda EU7000is puts out about 23A, so that would mean I have nothing left for the rest of the house and I'd be running the generator at or over it's rating, consuming much more fuel and potentially shortening it's life. I decided not to try to run my main AC if we lose power, but we still have a very efficient mini-split AC in the basement that only draws about 1000 watts. We slept in the basement on a pull out couch for those few nights. We still needed to run the pool pump, 2 refrigerators, 2 freezers, oven, microwave, lights and all the other household items. Our last power outage this past summer lasted 3 days and the highest I saw the generator running was at 3500W.

If you can't find a generator that will easily meet your power demands, you could consider buying an efficient mini-split to provide backup air conditioning to a few areas of the home during an outage. I have the Honda because I wanted the best and quietest generator available. Buying a second one and a parallel kit just to run my main AC wouldn't be worth the extra $5k. There are many cheaper and more powerful units, so you should have some options. I don't know if all of them provide parallel capability.


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## ToolLover (Jan 13, 2020)

Geesh! I do not know where you guys are getting those amperage readings.
My 4 ton Scroll unit draws 10.5 amps running.
My air handler draws less than 2 amps.
If the units are 240 VAC, there should be no amperage on the common (ie. Neutral)
If the units are drawing that much amperage running, I suggest you recheck the amperage or have a AC tech check your units.


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## Browse Deweb (Jan 16, 2021)

ToolLover said:


> Geesh! I do not know where you guys are getting those amperage readings.
> My 4 ton Scroll unit draws 10.5 amps running.
> My air handler draws less than 2 amps.
> If the units are 240 VAC, there should be no amperage on the common (ie. Neutral)
> If the units are drawing that much amperage running, I suggest you recheck the amperage or have a AC tech check your units.


Newer more efficient units will draw a lot less current than older technology. My 2006 Lennox 4-ton HS26-048 has a 12.5 SEER, ref page 4 electrical specs:



https://www.lennoxpros.com/docs/Technical/ehb_hs26_0202.pdf



When it comes time to replace it, I'll be looking at a more efficient unit for sure.


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## TX0303 (Mar 9, 2021)

ToolLover said:


> Geesh! I do not know where you guys are getting those amperage readings.
> My 4 ton Scroll unit draws 10.5 amps running.
> My air handler draws less than 2 amps.
> If the units are 240 VAC, there should be no amperage on the common (ie. Neutral)
> If the units are drawing that much amperage running, I suggest you recheck the amperage or have a AC tech check your units.


The unit is only drawing a little over 14 amps when running. The other amp numbers I mentioned are the max reached during startup.
An AC compressor has three wires, Run, Common, and Start. The common wire on the compressor is not the same as a common (neutral). The AC common is one leg of the 240v feed from the contactor switch.


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## iowagold (Jan 22, 2020)

I would look in to replacing the energy hog first...
then see what you really need for a gen set.
look in to an inverter ac unit!!
some of those run on way less power for the same btu of cooling.
shop around for sure!


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## BobS (Aug 26, 2020)

You would need at least a 13+KW rated (not surge) with a 60 amp outlet to start the 5 Ton unit properly. If you undersize the generator, it will stress the compressor (and possibility shorting its life span) by dropping the voltage on startup. If you are able to use a soft start, the startup would be less but it will still require a large amount of power for a portable generator to run. You will be burning a large amount of gasoline (if propane - much more and would need a larger generator) per hour. I would look into a full house standby generator or use portable AC's (one or more) with a much smaller generator. The portable ACs are great if your main unit has a problem. An inverter AC with a high seer will be very expensive. My 23 seer 4 Ton inverter cost 8K.


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