Single phase or 3-phase motor for blower

[nbog]

I am considering buying a small regenerative blower (1 HP)
and default option is 1-phase motor. I want to control the speed using variable frequency controller.
Is there any advantage of getting 3-phase motor here?

Thanks,
Nick

 

[zdas04]

People use 3-phase motors to reduce the current flow in any given wire. With a 1-hp (say 110V) motor you are looking at something less than 8A. Going to 220V 3-phase changes that to about 1A per conductor. There is nothing wrong with an 8A load and you don't gain anything worth gaining to drop it to 1A.

David

 

[MikeHalloran]

One time I bought a 1 HP 'high pressure blower' for a show display. I specified a single phase motor, mostly out of familiarity.

When we took the display to an actual show, the blower kept popping breakers. You pay big bucks for a 15A circuit at a show, and much bigger bucks for bigger circuits.

I got a scopemeter and a current sensor and measured what was going on. The starting current peaked around 48A, and stayed above 30A for quite a while as the blower got up to speed.

Luckily, it was a dual- voltage motor, so I was able to kluge up a timer and a relay to start the motor with reduced current in one leg. After 6s or so, it was rotating feebly, but fast enough to limit the peak current to ~39A, which the show breakers tolerated.

If I had it to do over again, and had the spending priority that an upcoming show allows, I'd order a 3 phase motor (same price) and a smart drive (now under $200, but then nearly $1000) that could accept 115V/1/60 in and produce 230/3/variable out, and ramp the motor start so the supply wouldn't see much of a transient above the steady state 7A or so.



Mike Halloran
Pembroke Pines, FL, USA

 

[nbog]

Thanks for the tips.
Nick

 

[zdas04]

Mike,
I can't believe I disregarded start-up surge (that is typically 6-10 times steady-state current). The VSD add-a-phase technology has indeed made small hp 3-phase motors reasonable.

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[ScottyUK]

Variable speed drives almost all produce a three phase output, thus requiring a three phase motor. There are a few single phase VSD's, but they are obscure exotica and will only work correctly with certain designs of single phase motor. The three phase motor is an inherently better design of machine than a single phase motor: smaller, lighter, more robust, better torque/speed characteristics, etc. If you have the option, as you appear to have, then use the three phase mtor every time.

Mike,

Not sure how you get 230/3/variable from a 115/1/60 input unless you have a transformer in there. More common is (say) 230/1/50 in, 230/3/variable out.

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I don't suffer from insanity. I enjoy it...

 

[swn1]

3-phase motors have simpler magnetic design and are more efficient. Single-phase motors rely on frequency-dependent components to make them turn, whereas the magnetic field in a three-phase motor rotates naturally. VFD apps should be 3-phase if possible. The drive can take 1-phase input for small loads.

Using a drive would allow you to "soft start" the motor. Another possibility would be to close a damper on the input side of the blower (or cover it with cardboard etc) while starting. That won't reduce the magnitude of the inrush and starting current but it will substantially reduce its duration.