# Generator size for 3.5 ton AC?



## crabjoe (Apr 20, 2020)

With Isaias knocking out power, I now know the Q6500 can't start my AC. My question is, what are the odds of it being able to start it if I add a hard start kit? If no hard start kit, how much wattage might be needed?..... If you can't tell, I'm thinking about getting another inverter generator, probably the Champion on that's rated with a peak of 8750w and running at 7000 watts... If it'll do it, I'll probably pass this B&S to my dad so it won't go to waste.

Anyone have a general idea how much starting wattage is needed per ton of AC? 

BTW, when I got the B&S Q6500, I got it because I needed something quiet with 240v service for my well pump. It runs that just fine... But when I was visiting with a friend's father the other day, he was telling me his 6000 peak watt generator started his 3 ton AC last week when he lost power. That was a huge surprise to me because I wold have thought it would have been tough to start a 2T AC with that. I asked him exactly what model generator it was and dang it.. he couldn't remember, nor could he confirm it was actually a 6000 peak wattage generator. For reason I won't say, I didn't ask to go look or have him look...


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## iowagold (Jan 22, 2020)

do a soft start unit, hard start just will not work as good for generator use.
they use these for the little camper ac units as well as the larger home units.
they slow roll over the compressor for a ramped up current.
a cool bit of kit for sure!
click here for the page with the soft start and more generator connection info


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## dafish (Aug 12, 2020)

So I don't know **** about generators, but I've been down your road a little over my geo furnace. A few things I can share:

You need to ask the A/C mfg, or just look up, what the total FLA of your system is, and your LRA (think starting amps). I would not expect anything portable to start a 3.5T unit that didn't have soft start, for that's got to be something in the area of 90 amps. More that twice your surge.

BTW, if you've a dual capacity compressor you can always unhook the "y" (high capacity call) lead from your thermostat. In general that will reduce compressor RLA by 30%. Personally, my blower motor, while variable, has a "high" setting, and it's not anything like full speed. I doubt I'll ever hit my FLA, and sorta assume I can deduct 30% for the whole things (assuming I unhook "y"). That won't help it start, but IF you can get it started you would have some room to drive other things.

So yea, you want a soft start. Some newer units have them, and I suspect your friends dad has one already in his. Maybe from the factory. 

6KW ran 3 ton? OK, but I that guy should go buy a lotto ticket. My 5 ton is 39amps @ 240V FLA, so 8 amps (at 240v) per ton. 10KW is 41 amps running. A 6KW surge gen is what, something like 20 amps running? Yea, I've got loop motors to run and they didn't but then I don't have an outside condensor unit either, so lets call them close. 24A for a 3 ton. Yea, that's a stretch. If it ran it it was by the skin of it's teeth. Or it was never in high capacity. And as I've said it must have already has soft start in it.

FWIW, therein lies the problem with FLA. A unit in practical use may never hit it. Be a mistake to not consider it though.

I read soft start demand is about 40% of LRA. My LRA is 118A, with soft start it's 41A. 

Here' an example (not for YOUR unit, just a sample) of current demand vs soft start (Intellistart in this case)









So, can 7KWA run a 3.5 ton unit? It's its relatively energy efficient (and you really need to look up your own numbers!!) probably. 

Would I? No.

You've almost nothing left, and the price to move up in power doesn't get pricey yet. If you go 10K you'll be able to support a fridge, a sump pump, even some house lights.


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## drmerdp (Apr 10, 2018)

My EU7000 which is rated for 5500w continuous 7000w intermittently cannot start my old worn out 3.5ton A/C Equipped with a MicroAir soft starter. If I pair it up with my EU2200 It’ll easily and consistently run the AC. With some careful load management fridges, lights and TVs can join the party. But I’m a whole different story.

I personally think an ACCURATELY rated 8kw generator is a bare minimum requirement.


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## iowagold (Jan 22, 2020)

drmerdp said:


> My EU7000 which is rated for 5500w continuous 7000w intermittently cannot start my old worn out 3.5ton A/C Equipped with a MicroAir soft starter. If I pair it up with my EU2200 It’ll easily and consistently run the AC. With some careful load management fridges, lights and TVs can join the party. But I’m a whole different story.
> 
> I personally think an ACCURATELY rated 8kw generator is a bare minimum requirement.


hey dr is the fan on that unit 240 vac? or is it 120 vac?
you might check the caps on the fan... 15 to 20 years is the max life on the caps...
i always say up date the caps on motors and compressors every 15 years.
they just degrade over time.
and that affects the start as well as the run current.


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