How many watts does a 2hp electric motor draw.

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bjdw, Sep 15, 1:35am
on start up.Thanks.

johnf_456, Sep 15, 1:46am
There is a lot of variable, you need to be more specific.

bjdw, Sep 15, 1:49am
Chinese air compressor with a 2hp electric motor.

I have to go back to work now.

weasle, Sep 15, 2:29am
about 1500 watts

saxman99, Sep 15, 2:48am
I think it'll be more like 2500W for a second or two then settle to about 1500.

twaymouth, Sep 15, 2:56am
electric induction motors can draw up to about 7x their rated running current on start-up, particularly if they are under load. Under the worst possible conditions this motor could draw up to 45A for a few seconds however it will usually be much less that this, about 10 - 15A

doug207, Sep 15, 5:17am
How so!

2ho = 1.49kw/1490W

johnf_456, Sep 15, 5:19am
It's not as simple as that, as seen above

doug207, Sep 15, 5:40am
Watts are not drawn, amps are.

One would expect said motor to have the spec on it.

Current draw will also vary with heat and load.

lugee, Sep 15, 5:45am
Yes, but thats 1.49kW in OUTPUT kinetic energy, not input electromagnetic energy. Since electric motors aren't 100% efficient, its significantly more than that on the input side.

taipan4, Sep 15, 6:21am
watts are a product of amps X volts X power factor(0.8 to 0.9)

taipan4, Sep 15, 6:23am
X power factor usually around0.8 & around .8 for efficiency

noodle34, Sep 15, 6:45am
Everyone is over complicating it. There is 746 watts in one horsepower

bjdw, Sep 15, 6:51am
I've had a pretty good look at the motor and can't find any specs on it (I wish it was that easy).

The purpose of the question was to figure out what size generator would be needed to run an air compressor with a 2hp motor.

Thanks

morrisman1, Sep 15, 7:00am
the original poster said on startup. It will draw lots then will settle down to approximately 25% more than their rated output. The amount of spike will depend on things like intertia, speed of spin up, load on motor etc. Best way is to measure it if you want a definite answer. Im guessing you are working out how big you need a generator to be!

noodle34, Sep 15, 7:00am
Heat will change current draw bugger all in this situation. The motor is rated at 2hp this is its maxamum work output. Justy take a simple formula 1 HP =746 watts so 2 HP = 1492 watts so a 2kva generator would cut the mustard but 2.5 or 3 kva probably better.

Dont over complicate things this is as straight forward as 1 mile = 1.59kms

NZTools, Sep 15, 7:01am
It works out a whole lot more efficiant to have a petrol powered compressor. I cant be arsed working it out exactly, but you will probably need AT LEAST a 5 kva generator (more if it's a cheap over rated chinese genny) to get it started.

kwaka5, Sep 15, 7:03am
just remember you'll need around 5 times full load current for starts. You may or may not get away with less but you'll stress the motor as it starts on some load every time

bjdw, Sep 15, 7:03am
It's sounding like it the generator with the 2000W continuos and 2500W surge wouldn't be anywhere near big enough which means it will probably end up cheaper to buy a petrol powered compressor.

But if the price difference isn't much you can have a compressor AND a generator.

But having only one machine means less things to breakdown.

NZTools, Sep 15, 7:05am
You need to base your calculations on how much current the motor draws on startup. A 2 kva generator would trip out or stall as soon as the compressor turned on.

noodle34, Sep 15, 7:06am
Remember a compressor has a unloader valve so the compressor is not loaded up when it starts

kwaka5, Sep 15, 7:07am
still draws around 5-7 times full load current on startup. You'll just stall out the gen set if it's too small. On much bigger motors connected to gen sets, if you cock up the starting you'll just break the crank.

bjdw, Sep 15, 7:09am
Not maximum out put, MINIMUM output otherwise it's misrepresentation and breaching the fair trading act and yadda yadda yadda

noodle34, Sep 15, 7:13am
Any motor draws 5-7 times full load on start up but 1500 watts * 7 = around 10kva that is not nessacary it is only instantanious load and as long as the gene has the right curve circuit breaker on it it should not trip.
Take a 2400 watt 9 inch grinder running off a standard household 3 pin plug draws 70 amps on start up but yet we run it off a 20 amp breaker

kwaka5, Sep 15, 7:16am
Full load current will be around 11.8 amps. Startup will be around 70 amps.