I have read so much about generators over the last couple of evenings.

1850sq ft house, wanting a backup genny for the whole thing.

3-ton single stage A/C unit... 83.9 LRA --> 18.5kW to start.

I have read articles about voltage drop (i.e. the compressor might pull 83.9 amps but it will do so with a 30% voltage drop.

I have read articles about soft starts and how you can reduce starting amps (LRA) by 70-75%.

Basically I need to know how many watts to allocate in a generator estimate to my A/C.

With a soft-start I'm looking at 230V * 83.9A * 0.3 = 5.8kW to start

RLA = 15.4A so approx 3.5kW to run in max conditions

https://texags.com/forums/34/topics/3184462/0#discussion
Do you need dual fuel or just gas?
I just bought a champion 8750 inverter but i haven't even put oil or gas on it yet, based on your calcs it seems like it should do the trick. You could even go a little smaller and get a pair of 4ks and a parallel kit if you had a need/ desire for a camping generator.
Don't forget to interlock your panel

In reply to Charismatic Megafauna Thanks, I looked through that thread but didn't see what I was looking for. Will look again.

I figure a 10k is more than enough. Probably will go gas and or propane and eventually pipe it to ng

Your numbers look pretty good to me. I have a similar size house with a 4 ton unit. Before I installed a soft start I measured the starting amps which turned out to be in the 70 amp range which was much lower than the LRA. After installation startup was around 26 amps. Running amps are in the 13 amp range. I have a 9500W generator that runs it with no problem.

Is a soft start something you can install yourself?

Yes, it's pretty straight forward. You have to make 4 connections. The instructions are pretty generic so it requires a little bit of thinking. I put mine in an enclosure for more protection and had to add add some length to the wires to make it reach the AC.

In reply to YZ250 What was your listed LRA vs the actual? Maybe I just buy a fancy amp-draw multimeter to read it.

I just installed a microair soft start and took my starting amps from 125 down to 30. Impressive little box for sure. I have a Champion 7500 watt dual fuel generator I never even unboxed, but recently bought a 13k Duromax since it was on sale. I did a lot of the same calculations as you and your math is fine. A 10k generator is more than enough.

In reply to TXAG 05

TXAG 05 said:

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Is a soft start something you can install yourself?

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If you have ever wired up anything in a house before yes

Bringing this back to life because I'm trying to determine the appropriate soft start for this unit.


91 LRA with a 2 stage compressor.

https://www.microair.net/products/easystart-364-3-ton-single-phase-soft-starter-for-air-conditioners

Click on the which model do I need

I did something similar on my house a few years back. Was able to get the LRA from 60 to 23A and run my AC, several freezers and a few other essentials on a 7kW Honda.
I have tested it out numerous times without issue if you don't count my mother-in-law deciding to do laundry and use the microwave at the same time. My set up runs about 3500-4500W under typical load including AC.

Your AC would probably pull too much for that but as others have suggested something in the 10-12kW range would probably work well.

In reply to '03ag Nm

In reply to Tx-Ag2010 Hm. Not great news. My generator is 5500 watts continuous on natural gas. I could do better no gasoline but I have a natural gas line in the backyard it runs on. It's been great when needed but I've never used it in the summer with AC.

Don't really want to buy a bigger generator but it may come to that.