# Question on converting amp / volts to watts

Discussion in 'Electronic Repair' started by Hoopster, Sep 22, 2005.

1. ### HoopsterGuest

Hello,

I just purchased a product and the motor has 4 different speeds. The
box says 0.7 amps / 120 volts.

I'm assuming that you just multiply the amps x volts to get the watts
which would be 84 watts. Is that correct? If it's correct is that the
max on the highest setting? Meaning if you put it on the slowest
setting would it be under 84 watts?

Sorry for the newbie / dumb type questions, but I know nothing about
this stuff.

Thanks in advance for any help.

Hoops

2. ### Ken WeitzelGuest

Hi...

You're promoted from newbie to... to... to whatever comes next

Ken

3. ### Eric VeyGuest

And if you want to have some real fun, get a clamp-on multimeter (these
things don't cost as much as they used to). Then get a cheap 6' lamp
extension cord and carefully split the wire for about a foot, taking
care to keep both wires insulated. Plug your device in to the extension
cord, clamp over the hot and you can see exactly how much current the
motor is using at each speed.

It's a gas.

4. ### Mike BergerGuest

Nominally, yes, you multiply amps x volts to get watts. But it's
not completely accurate due to "power factor". But lets not
complicate things.

The figure on the box normally reflects the highest amount of
current it should draw under normal operation. Depending on the
device and how it's controlled, a lower speed doesn't necessarily
mean lower current.

5. ### James SweetGuest

Power factor can be pretty significant, the amperage draw of an inductive
load can easily be double what the actual power draw is.

6. ### AsimovGuest

"James Sweet" bravely wrote to "All" (23 Sep 05 03:18:53)
--- on the heady topic of "Re: Question on converting amp / volts to watts"

JS> From: "James Sweet" <>
JS> Xref: core-easynews sci.electronics.repair:342872

JS> Power factor can be pretty significant, the amperage draw of an
JS> inductive load can easily be double what the actual power draw is.

An ac motor, at the moment it starts, typically draws about 3 times
its rated current.

A*s*i*m*o*v

.... The current limits placed are based on resistance