Current, wattage, HP and 3 Ph motors

[simonl]

Hello all,

I have a 3 phase variable speed (frequency) motor that I have waiting for a project. Question is, to work out the wattage of the motor is it the same as for a single phase electric motor as in Volts x Amps = Watts, then divide by 746 for horsepower?

The spec plate says it draws 6 amps, so does that mean about 1400 watts and just shy of 2 HP?

Cheers,

Simon

[.RC.]

6 amps per phase?

[simonl]

6 amps per phase?

Dunno. It was off a treadmill which had a standard 10 amp plug so I can't see it being anymore than 10 amps total either way. Probably less.

Simon

[Ueee]

Hi,
Your voltage should be 440 so 6 amp would be 2640w.......
Ewan

[Ueee]

But after your last reply thats more than 10 amp.....

[simonl]

Hi,
Your voltage should be 440 so 6 amp would be 2640w.......
Ewan

No, it's 240 V 3 Ph.

Cheers,

Simon

[NCArcher]

What else does the spec plate say? Treadmill motors are often non standard with a special VSD to control them. My treadmill motor is 2HP but it is 240V DC I think.

Edit: too slow

[simonl]

The only reason the motor is 3 Ph is because they use a dedicated VFD to vary the speed of the treadmill. Some treadmills use a DC motor and vary the duty cycle by PWM but this one uses a 240 V 3 Ph motor and a VFD.

Cheers,

Simon

[NCArcher]

I make it 3HP.
E x I x root3 x power factor

[RayG]

Dunno. It was off a treadmill which had a standard 10 amp plug so I can't see it being anymore than 10 amps total either way. Probably less.

Simon

Are you sure it's a three phase induction motor, it's not brushless DC by any chance?

I can't see a treadmill having a 415 V 3 phase induction motor, but who knows?

There should be a name plate, if not some other identification.

Regards
Ray

PS... Seems like there were 3 or 4 posts while I was typing, 240 x 6 x 1.732 x 0.85 = 2.2 kw 3 hp it is..

[Ueee]

I would say your 2hp would be right then.
Never thought of treadmill motors as good speed controlled motors. Oh dear something else to look out for. Mind you, DC would be great with PWM (now you speakin my language) and feed back as you can still get close to full power at low revs.
Ewan

[Tools4Me]

Hello all,

I have a 3 phase variable speed (frequency) motor that I have waiting for a project. Question is, to work out the wattage of the motor is it the same as for a single phase electric motor as in Volts x Amps = Watts, then divide by 746 for horsepower?

The spec plate says it draws 6 amps, so does that mean about 1400 watts and just shy of 2 HP?

Cheers,

Simon

Simon, what you need is this formula: P(W) = √3 × PF × I(A)× V(V)

Your fully loaded 6A motor will have a power factor of about 0.8PF on our 415V 3 phase mains. √3 is about 1.73 or thereabouts.

So that's about 3,400W or 4.6Hp in the old money.

[jack620]

Something's not right here. 3400W is a HUGE amount of power for a treadmill. In any case, you wouldn't be able to plug it into a 10A GPO if it drew 3400W.

I also tend to think it might be a brushless DC motor.

[Ueee]

Something's not right here. 3400W is a HUGE amount of power for a treadmill. In any case, you wouldn't be able to plug it into a 10A GPO if it drew 3400W.

Tools4me assumed like i did, that is 415v, but its only 240, so if you pop that into the calculations you get 1992w, but i'm not sure if the PF would be the same.

Hmmm i think the only sure thing is that you have a motor.

You don't have one of those power meters that you plug in do you? you could plug it into one and run it on full to see what the draw is.

Ewan

[Ueee]

Simon, what you need is this formula: P(W) = √3 × PF × I(A)× V(V)

Your fully loaded 6A motor will have a power factor of about 0.8PF on our 415V 3 phase mains. √3 is about 1.73 or thereabouts.

So that's about 3,400W or 4.6Hp in the old money.

Tools4me,
Am i right in thinking that to work out any 3 phase wattage you use the square root of the no of phases? So it a motor is running on, oh god brain failure, delta? only, you would use the square root of 2 (i think i'm right in thinking that a motor in delta only uses 2 phases, star is 1 and star/delta is all three)? I know plenty about DC and single phase, but three phase is, well, 3 times as complicated.

Ewan