Current, wattage, HP and 3 Ph motors

[RayG]

Hi Ewan,

Well, power is ALWAYS volts times amps, the complication is that , first the current lags the voltage, and that phase shift is represented by the power factor, if it was a purely resistive load the current and voltage would be in phase, second the voltage applied to the coils is the voltage between the phases, so for 415 3 phase, the voltage between any phase (and neutral) is 240V... confused yet.. 240 times 1.732 = 415

Regards
Ray

[Ueee]

Hi Ewan,

Well, power is ALWAYS volts times amps, the complication is that , first the current lags the voltage, and that phase shift is represented by the power factor, if it was a purely resistive load the current and voltage would be in phase, second the voltage applied to the coils is the voltage between the phases, so for 415 3 phase, the voltage between any two phases is 240V... confused yet.. 240 times 1.732 = 415

Regards
Ray

Hence the 415v! (a genuine light bulb moment that one...) I know you can take any one of the phases and get 240 single phase, and understand that a motors load is not like a single resistive coil, but still don't get how a motor can run on 2 phases only.....

I worked for an Electrician when i was 15 or so, but we mostly did remote solar installs, nothing big, so i didn't know 3 phase existed till i moved to the city and got my apprenticeship at 16.

Ewan

[simonl]

Hello all,

Keep coming with the replies. I learning lots, mainly learning just how little I know!

The motor is definately a 240V 3 phase induction motor. It's from a Lifefitness 9000 treadmill. They use a dedicated motor and controller made my Emerson. I will take a photo of the motor tomorrow when I get home from work. For anyone interested, here is a link to the service manual of the treadmill, it contains an electrical shematic on page 55. http://www.sportsmith.net/images/pro...c%20Manual.pdf

It is important to note that the treadmill does not actually exist anymore, only the motor and the control board. So it's not working (it was working before I took it apart!) as I need to add an imput signal into the control board. Well, at least that's my theory!

Cheers,

Simon

[eskimo]

Well, power is ALWAYS volts times amps, the complication is that , first the current lags the voltage, and that phase shift is represented by the power factor, if it was a purely resistive load the current and voltage would be in phase, second the voltage applied to the coils is the voltage between the phases, so for 415 3 phase, the voltage between any phase (and neutral) is 240V... confused yet.. 240 times 1.732 = 415

thats why I take my motors to the rewind shop if they dont work....bloody too complicated for me...I must have been asleep when they tried to teach me that stuff at tradeschool

[eskimo]

. So it's not working (it was working before I took it apart!) as I need to add an imput signal into the control board. Well, at least that's my theory!

Cheers,

Simon

looking at the wiring diag you may well be right

cant fathom why they have two feeds coming from the trany but?...why not just take the 240v straight to the VSD/VFD?...all the trany does is reduce the voltage to 120 for the main control board

[Ueee]

looking at the wiring diag you may well be right

cant fathom why they have two feeds coming from the trany but?...why not just take the 240v straight to the VSD/VFD?...all the trany does is reduce the voltage to 120 for the main control board

Its an American product so the systems are designed to run on 120v, hence the tranny.
The controller probably uses a PIC or ATMEGA so it and the display will run on 5v dc (via switchmode driver on the controller board)

You will need all the bits to make the motor work probably, the VFD will be made specially for the treadmill.

Ewan

[morrisman]

HI

I did basic electronics course years ago ..forgotten most of it

I remember RMS values though. RMS = root mean square . e.g., the 240 v single phase actually has a peak of around 340V . THE 240 V is the RMS value , it's not an average value , but it's the value that equates to a DC circuit . RMS means we can use OHMS law to work out amps , power etc etc.

Power factor relates to the reactive component of the load , either inductive or capacity . Big factories used to have big caps on their system to nullify the inductive loads of motors etc. lower PF is the goal .

Can somebody explain how 3 phase is available from 2 wires ? The normal power grid ( like is used here ) has 2 wires ..how do they get 3 phases from 2 wires ?

MIKE

[eskimo]

Its an American product so the systems are designed to run on 120v, hence the tranny.
The controller probably uses a PIC or ATMEGA so it and the display will run on 5v dc (via switchmode driver on the controller board)

You will need all the bits to make the motor work probably, the VFD will be made specially for the treadmill.

Ewan

yeah I know it was designed to run on 120v and the trany is there for that...but why two (2) x 220v feeds to the VSD?...they both come from the 220V secondary of the tranny...maybe the VSD wants 220...but if so why is it so critical...why cant it run on 240?

[Stustoys]

cant fathom why they have two feeds coming from the trany but?

I wonder if its just to keep the current down?

why not just take the 240v straight to the VSD/VFD?

My first thought was isolation, but autotransformers dont do that.

all the trany does is reduce the voltage to 120 for the main control board

And 221V for the motor.

Stuart

Thanks for the edit Ray, I'd been scratching my head half the night over that one lol

[eskimo]

and the motor is 240v...so Simon says

I wouldnt have thought that the VSD was demanding it required 220v...normally they are very tolerant of a wide voltage range

[simonl]

Hi all,

Thanks for the input so far. Here is a pic of the motor as promised. Have a look and tell me how many horses are inside it!

Also, what does SFA stand for. I know SFA about it and I'm sure it doesn't mean that! Assume it's to do with power factor, it's not that important to me but since I've got the brains trust looking at it I may as well ask as many questions as I can!

Cheers,

Simon

[NCArcher]

SFA is an American thing. It stands for Service Factor Amps. You'll note that there is a SF rating of 1. on the line above.
It is part of the US electrical code and has to do with the thermal protection applied and the expected life of the motor.
Oh and it's 3 HP

As for the two 221V supplies to the VSD, I think you'll find that is a standard loom configuration so that they can manufacture one loom and apply it to many different models. Other models may have multiple VSDs or some other component connected to that same plug.
The VSD will probably work on a wide range of voltages but the control board needs 120V.
And Morrisman, the VSD takes a single phase supply and reproduces it twice offsetting the wave form by 120° each time to give you 3 phases. A bit simplistic but basically what happens

[Stustoys]

I wouldnt have thought that the VSD was demanding it required 220v...normally they are very tolerant of a wide voltage range

Good point. But the controller on the 240V wiring diagram is labeled 120V. So maybe they use the same VSD and 220V was as high as they could take it without changing components?

*edit* but that would mean it was way over built for 120V??? Who knows what they were thinking lol

Stuart

[Ueee]

SFA is an American thing. It stands for Service Factor Amps. You'll note that there is a SF rating of 1. on the line above.
It is part of the US electrical code and has to do with the thermal protection applied and the expected life of the motor.
Oh and it's 3 HP

Hi,
Can you give us the formula you used to get to 3 hp?
Ewan

[NCArcher]

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

...

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..

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

I think T4Me put it best. I could not find the sq. root symbol (still can't)