Thread: Current, wattage, HP and 3 Ph motors

Originally Posted by ncarcher

i think t4me put it best. I could not find the sq. Root symbol (still can't)

thankyou!

Hi Simon,

On that CCT it appears to show a lubrication pump? If it's any good that's a handy little bonus.

Regards
Ray

Originally Posted by RayG

Hi Simon,

On that CCT it appears to show a lubrication pump? If it's any good that's a handy little bonus.

Regards
Ray

Hi Ray,

yes I have kept all that, including the motor that raises and lowers the treadmill.

The pump is driven by a small 110V induction motor so I have kept the pump and the transformer that drives it. Was thinking of using the pump to set up a one shot lubrication system and have it plumbed to both the lathe and mill. Just open the valve and run the pump for a few seconds..... something like that anyway.

The actual pump is interesting, it's contained in a small plastic case and contains an arm with two rollers that rotates on a shaft. Inside is a flexible tube that the lubricant flows through and as the rollers move around, it squeezes the tube and forces the lubricant through. Very simple design.

Cheers,

Simon

In the service manual linked, page 50 has the parts list. The first item is Drive Motor 2HP, so I suspect that the unit is actually 2HP rather than 3HP.

Rather a mute point anyway. Electric motors will draw as much current as they need to to handle an imposed load. The power rating is a measure of how much power can be drawn without overheating the motor. Slow the motor, and you slow the fan and reduce cooling flow and hence lower the power rating of the motor unless you have auxiliary cooling fans etc.

Originally Posted by malb

In the service manual linked, page 50 has the parts list. The first item is Drive Motor 2HP, so I suspect that the unit is actually 2HP rather than 3HP.

Rather a mute point anyway. Electric motors will draw as much current as they need to to handle an imposed load. The power rating is a measure of how much power can be drawn without overheating the motor. Slow the motor, and you slow the fan and reduce cooling flow and hence lower the power rating of the motor unless you have auxiliary cooling fans etc.

Perhaps the motor is rated to 3 HP but the control board, due to maximum speed restriction of the treadmill will only allow a max. of 2 HP?

So, my mill has come standard with a 2 HP motor. Are you suggesting that I can replace that with a 1 HP, 2 HP or 3 HP variable speed motor and it won't make any difference?

Also, I assume if you slow the motor and slow the cooling fan, then you reduce the power going into it anyway. Isn't that the point?

Simon

Originally Posted by malb

Electric motors will draw as much current as they need to to handle an imposed load.

That assumes that the motor is capable of handling the imposed load.

no Simon
if you have a load that requires 3hp you must have a motor that can handle that load...A 1 or 2 hp wont do
putting a 3hp motor on a 1hp load will work...its just inefficient and higher upfront cost...but if you get the motor for zilch then its just inefficient

and your treadmill motor is specifically manufactured for frequency driving(refer motor ID plate) ..most standard motors are not designed for frequency driving much above 60HZ..they work above this but are not manufactured for it

A 400hz VSD/VFD could theoreticaly drive a standard 1440rpm motor to 12000rpm ....(this is synchronous speed)...but the motor would be destroyed if one tried
motors for high frequency input are purpose built.

How many wires go into the motor, does it have any brushes?. Nearly all treadmill motors I've seen are variable speed 2Hp DC controlled by PWM speed controllers.

Hi guys,

Originally Posted by Graziano

How many wires go into the motor

According to the wiring diagram 5 wires. Ground, two for a thrm cut out and three labled phase 1, phase 2 and phase 3. The motor has PH. 3 on the label.

Eskimo, I nearly got to see what a 3hp motor looked like at 12000rpm. The manual for my VSDs says the factory setting is 50Hz, it wasnt. Luckily the ramp was set at around 25 seconds.

Stuart

Originally Posted by Stustoys

Hi guys,

According to the wiring diagram 5 wires. Ground, two for a thrm cut out and three labled phase 1, phase 2 and phase 3. The motor has PH. 3 on the label.

Eskimo, I nearly got to see what a 3hp motor looked like at 12000rpm. The manual for my VSDs says the factory setting is 50Hz, it wasnt. Luckily the ramp was set at around 25 seconds.

Stuart

Ahhh RTFM! I'm gonna plead "Lack of caffeine"

Originally Posted by Stustoys

Hi guys,

Eskimo, I nearly got to see what a 3hp motor looked like at 12000rpm. The manual for my VSDs says the factory setting is 50Hz, it wasnt. Luckily the ramp was set at around 25 seconds.

Stuart

Hi Stuart,

What would have happened if you let it go? Can a VSD drive a motor to such hi RPM'S? If so, would it just be a matter of the bearings failing after they reach their limits?


Also, Malb's point has me thinking. When you vary the speed of a 3 ph induction motor via a VSD or VFD, are you actually varying the HP output of the motor as well?

Will a 2 HP motor produce and draw the same current at 500 RPM as it would when it's dialled up to run at 1000 RPM? Is it putting out 2 HP and both speeds?

Now throw in Vectoring, which I assume contains a feedback circuit to ensure the motor speed remains constant regardless of the load which it is under. Does this then change things or does a 2 HP motor always draw 1500 Watts (during running, not start up) regardless of its speed?

I hope I have worded the question properly....

Cheers,

Simon

Hi simonl,
The pump you describe is a peristaltic pump, Wikepedia have a good description.
tinkera

Originally Posted by tinkera

Hi simonl,
The pump you describe is a peristaltic pump, Wikepedia have a good description.
tinkera

Hi Tinkera,

You are correct, in fact the picture looks almost identical to the one I have. Glad my more than woeful description at least made some sense! Thanks for the info.

Just in case anyone else is interested here is the link to the Wiki article.
http://upload.wikimedia.org/wikipedi..._pump_head.jpg

What makes this pump perfect for lubrication is firstly it's relatively low output as about what you would need for a lubrication system. Secondly, being a positive displacement pump, you can have the coolant lower than the pump and still not have to worry about priming the pump if air bubbles get into the system since positive displacement pumps will pump gas as well as air. Unlike centrifugal pumps that will only pump fluids.

Cheers,

Simon

Cheers,

Simon

Originally Posted by eskimo

That assumes that the motor is capable of handling the imposed load.

Actually it doesn't make that assumption at all. It's a simple fact that if the motor cannot handle the imposed load, it either trips it's own protection, a fuse or breaker in the supply network, or destroys itself.

The point I was making is that the manufacturers power rating is an indication of the amount of heat that the motor can disipate without damage, not the hard limited input power consumption.

Originally Posted by malb

Actually it doesn't make that assumption at all. It's a simple fact that if the motor cannot handle the imposed load, it either trips it's own protection, a fuse or breaker in the supply network, or destroys itself.

The point I was making is that the manufacturers power rating is an indication of the amount of heat that the motor can disipate without damage, not the hard limited input power consumption.

Hmmm... you are assuming the stall current will destroy the motor... What about stepper motors, brushless DC, shaded pole motors etc etc...

The manufacturers power rating is a function of many factors, how the motor is wound, number of turns per lap, wire gauge used, number of poles, how efficiently the magnetic flux is transferred to the rotor and so on... You can't expect to get 10 hp out of a 3 hp motor just by loading it... As you increase the load beyond the torque that the motor is capable of, the motor slows down and the hp ( the work done the motor) decreases linearly with rpm.

hp= torque*rpm / 5252

Lower rpm = lower hp

Regards
Ray