what amp draw will I likely see?

Posted by RB on August 30, 2005, 12:23 pm

Need a ballpark figure for the likely amp draw I'll see on a 4 ton
residential air con and air handler unit for 1800 sq ft house. I don't know
if air handler runs on 220v or not. I know the air conditioner unit does run
on 220v.
I've got a 30 amp portable genset (that's 30 amps at 220v), and I just want
to be sure it'll run my a/c and air handler units.

Posted by gfretwell on August 30, 2005, 1:33 pm

wrote:
show/hide quoted text
It would probably run it just fine, the trick is starting it.

Posted by Mark on August 31, 2005, 10:04 am

On Tue, 30 Aug 2005 13:33:10 -0400, gfretwell@aol.com wrote:
show/hide quoted text
Oh yea.
A 30A gen is probably around 5500W ? So, that should have about an 8KW
surge on it. You just might start it with absolutely no other load on the
generator. The problem is, you can't then power up other stuff in the
house because the A/C will cycle on and off and then you'll overload the
generator.

Posted by davefr on August 30, 2005, 4:22 pm

Look at the nameplate on the condensor unit. (I'm guessing it's about
10-15 amps). Now look at the nameplate on the air handler. (I'd guess
it's about 1-2 amps).
Now when both induction motors start up they'll want gobs more current.
(probably about 3X).
That means your generator will need to supply a surge current that
could range between 35-50 amps. I think that'll end up being outside
the motor starting envelope of your genset.
To be 100% sure, try contacting the A/C unit's manufacturer and get the
motor starting code. Now do the same for the generator.

Posted by RB on August 30, 2005, 10:31 pm

Thanks for all the responses. I think a hard start gizmo is what I was
being told about, but it somehow came out in my head as a "soft start" unit.
Our house is 1800sq ft, and very thermally "lossy" (built in '65) . Doesn't
have storm windows, or even thermopane glass. All I know is the 4 ton unit
runs a lot keeping the house at 76 degrees.
The thing about using a couple of high efficiency window units is probably
my best bet, short of going to a big, pad mounted genset. And, really, they
would do us fine for keeping comfortable at night during extended power
outages (the last one was 3 weeks during hurricane Ivan).

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