Generator Capacity/Math Question

in-too-deep · Jan 31, 2012

Need to run an air compressor with a generator. Tag on
comp. motor says 16 amps at 115 volts. Amps multiplied by
volts equals watts correct? 16 x 115 = 1840 watts. A 2500
watt continuous generator will power it sufficiently correct?
Thank you folks.

John730D · Jan 31, 2012

Your starting load is going to be around 2800 watts. If your generator has a surge higher than that, it should work.

in-too-deep · Jan 31, 2012

I didn't think about the starting draw. Thanks John.

buickanddeere · Jan 31, 2012

Does the compressor unload while starting?

When purchasing a generator for this application. Find one that with a switch from combined 120/240V to all 120 operation on a 30amp twist-loc plug for use on a motor home.
5500W would be a minimum all on 120V. A 5500W genset with just 120/240V will have difficulty or won't start the load.
What brand and model are you thinking? Motor starting loads on a reciprocating compressor among the most difficult to start.

Aaron Ford · Jan 31, 2012

I have a 3500 watt (5K surge) generator and a 33 gallon craftsman compressor. The generator will not start the compressor. It tries to. It wants to. I almost starts it, but alas, no start. The generator runs fine and runs my home in power outages. I can run the hot water heater, fridge, lights, etc. But not that danged compressor.

Aaron

RodinNS · Jan 31, 2012

The run amperage is not your main concern. The start amperage is... I suspect it will draw more like 20-25 amp to get rolling... so you need a generator that will put that out. Probably going to be into more like 7000 watt before you get that.
If you really want to be sure you can get a current clamp and hook it over the hot leg going to the motor... or find that leg in the breaker panel and watch the draw on the clamp when the motor starts. A cold start would be particularly telling...
Many motors also have the starting draw stated on their info tag but that would only be a guideline.

Rod

JMOR · Jan 31, 2012

(quoted from post at 20:44:11 01/31/12) The run amperage is not your main concern. The start amperage is... I suspect it will draw more like 20-25 amp to get rolling... so you need a generator that will put that out. Probably going to be into more like 7000 watt before you get that.
If you really want to be sure you can get a current clamp and hook it over the hot leg going to the motor... or find that leg in the breaker panel and watch the draw on the clamp when the motor starts. A cold start would be particularly telling...
Many motors also have the starting draw stated on their info tag but that would only be a guideline.

Rod

ne more type experience: Gen will start 2hp compressor (has pressure sw activated unloader) , but when pressure coming down from full tank & pressure sw re-starts, NOW same gen will NOT re-start, because before it can get up to speed, the unloading is kicked out & it is trying to start against 90 PSI. Had to insert a small tank (about 1 quart) between compressor & check valve to give time for motor to reach speed before seeing 90PSI tank pressure. Yes, 'ruggin', but alternative was larger generator or else always start from empty tank.

in-too-deep · Jan 31, 2012

Thank you for the replies. Thinking we'll buy a "compresserator" all in one unit instead.

buickanddeere · Feb 1, 2012

Amps X volts = watts only with DC or AC loads such as electric heaters and incandescent lamps which operate at unity power factor . 16amp running will be a peak of 160amp for the first cycle then drop to 50-60 amp until the motor reaches 1700+ rpm. Anybody ever notice how much an air compressor dims the lights when plugged into the electric utility that has
Millions of HP spinning the generators? Think of how hard your little Briggs or Honda portable gen set will have to work?

Generator Capacity/Math Question

in-too-deep

Well-known Member

John730D

Well-known Member

in-too-deep

Well-known Member

buickanddeere

Well-known Member

Aaron Ford

Well-known Member

RodinNS

Well-known Member

JMOR

Well-known Member

in-too-deep

Well-known Member

buickanddeere

Well-known Member

Similar threads