AviationBanter - View Single Post - Air Compressor Horsepower/Wattage/Amperage

**Ron Rosenfeld** · June 27th 07, 02:56 AM posted to rec.aviation.homebuilt,rec.aviation.owning

On Tue, 26 Jun 2007 09:51:18 -0700, wrote:

On Jun 24, 5:20 am, Ron Rosenfeld wrote:
...
Ron, what peak starting current should I expect on a single-phase,
240V, 3/4h.p., running current=7.8A motor used to lift my hangar door?
I want to rig up a genny to lift the door during a power failure. The
gear train on the door is rigged so that all of the cables are slack
(i.e. only motor inertial) when the motor starts.

mgm17160, I really don't know. I'd be surprised if it were as much as
double the running amps, but there's no good way of telling without
measuring.

With no measurement, I would size the generator to be able to handle a
surge equal to the Locked Rotor Amps as calculated by the nameplate code
rating on the motor. Or just try a genny that can handle a surge of
15A/240V.

A problem with small, inexpensive, gasoline fueled generators is that,
unless you are religious about exercising them, they usually won't start
when you need them. And, unless you have a mission-critical situation,
it's overkill to put in something that you can set and forget.

I, too, have a door that is not amenable to any kind of mechanical backup.
I happen to have an extra 120V inverter I could hook up -- but the cost of
batteries and a step-up transformer to set up the system is excessive,
especially given that I've only been stymied by a power outage at the
hangar once or twice in the past seven years.

--ron