Help choosing a small 3 phase motor 1

[PaulJohnson]

Hello Again !
I need to purchase a motor for a machine I'm building about 750w 1400rpm and I'm not sure whether to go for a single phase 240v or 3 phase. I don't have 3 phase supply so if i went that route then I'd be getting into a controller which I may need anyway for speed control.I'll be adding pulleys to slow the driven shaft to 500rpm.I will probably need the ability to switch direction of rotation so don't want to get the wrong motor that can't easily be switched.Not sure about the start capacitor and run capacitor options pro's and con's. Under £100 seems to be the going rate for this size
Any help appreciated
Thanks

 

[SceneryDriver]

These guys should be able to help:

http://www.orientalmotor.com/products/ac-motors/ac-induction-motors.html

I'd recommend a 3ph motor over a 1ph motor. You won't get good speed control from a 1ph motor. A VFD of the size necessary to run your motor can be powered from a single phase source, even a wall outlet.

Gearing/belting down the motor to get close to your necessary output speed is a good idea. You get more speed range, and you increase your available torque as well. I usually shoot for my output speed to be approximately 80% of motor base speed. That way, I have some headroom if I need to increase speed later, without exceeding the motor base speed.


SceneryDriver

 

[PaulJohnson]

I was told a 3 phase would be better, how about the forward/reverse issue ? is it possible to do this via the VFD or is it more complicated like swapping wires over ?
Thanks

 

[btrueblood]

Some VFD's can allow reversal of the motor, but swapping any two leads of a 3ph motor will also reverse its rotation direction.

 

[jraef]

All VFDs can reverse a 3phase motor. The VFD output is all done with bit twiddling anyway, so if you want it to reverse, you twiddle the bits that make the output go the other way. It is MUCH simpler than doing it electro-mechanically.

For you, you will have a contact closure input on the VFD that tells it to Run in Fwd, then another one you set up to tell it to Run in Rev and if they are both Low, it stops. Or you can have one that tells it to just Run and Stop, then another one that when you command it, tells it Fwd or Rev based on it being High or Low (On or Off). Your choice.

If variable speed is of value to you, I would not consider doing this any other way.

"Will work for (the memory of) salami"

 

[PaulJohnson]

Thanks for the info and based on that I'm going to get a 3 phase motor and one of those £85 VFD's off ebay apparently they can switch direction and have facility for remote speed control.I also believe that the VFD can increase the speed of a motor beyond it's normal rating up to 3500 rpm ?

 

[squeeky]

Another advantage of a VSD is that you can run at any speed from 0 to 200 % and have different speeds and ramp times for each direction, i.e., lift slowly and tip. Then fast down to the start point reduce the cycle time. There is a de-rating factor if you run slowly for any duration. ROT is 35 Hz on a 50 Hz machine.

 

[ScottyUK]

There are a lot of caveats on running above base speed which squeeky should really list... but it is possible in certain circumstances.

 

[squeeky]

Thanks. Going too fast may cause cooling problems as the fan become inefficient and up to rated frequency the torque would be constant and the power would alter to load. After rated frequency the torque drops off because of the voltage frequency ratio. After rated speed there is no more voltage and as the frequency rises heritage cannot increased above nominal.

If you buy single phase VSD to run your motor, you need to connect the motor up in the delta connection.

I have a very nice spread sheet where you put your values and it produces a graph of the results and red
Lines danger operating areas. If you want this you will need to tell me how to get it to you.

Above 100 Hz you may need to look at your bearings as well as forced cooling.

 

[jraef]

Word of warning, if the cheap VFD you are looking at has no brand name in the ad, and/or you can read the name Huanyang on it anywhere, that is the cheapest piece of junk on the market. They are flooding Fleabay with those things at hard to believe cheap prices, but the vendors often fold up and disappear before the drives fail. Internally, the construction is so sloppy and slipshod that they HAVE to know they will fail in short order. But the origin is China, so you have no recourse against the mfr., in fact you cannot even contact them. They sell everything by proxy through these fly-by-night front companies.

"Will work for (the memory of) salami"

 

[PaulJohnson]

Yes the one for £85 is Huanyang
Can you suggest a decent one as prices vary a lot how about this one
Link
£160 "Engineers mate" they sell motors too
Thanks