how to control speed of single phase motor 5

[themroc]

I am chemical engineer and we need to set up an experimental rig in order to meassure pressure drop in gas flows.
For this purpose we use use a 2.2kW single phase air blower with a constant fan speed and gas flow.
We would like to make this gas flow variable, that means change the motor speed continiously.
What kind of electronic device do we need for this.
Is a phase angle regulator the right device.
Can someone give advice on devices and where to by in the UK

 

[itsmoked]

You are very likely S.O.L. on your desire. Single phase motors do not speed control unless they are brush type universal motors and the load is non-varying.

If you want to do this correctly, and effectively, you need to replace the motor with a three phase motor. It should not cost very much as three phase motors are simpler, and smaller, then the single phase motor you will be replacing.

Then pick up a VFD and you can then control the motor accurately, easily, and with only single phase power. You will also automatically have speed and power values available for your activities. VFDs that small are very inexpensive too.(Huge bang for the money!)

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[themroc]

Thanks, what means
what means S.O.L?

Unfortuatelly I do not have the possibility of changing the motor.
How do vakuumcleaner vary their speed, are this 3 phase motors?

 

[MetalworkerMike]

S.O.L means, to paraphrase, 'out of luck'.

Varying the speed of a single phase motor isn't that hard, it's just doing it _accurately_ that is very hard. You can run a single-phase motor of the 'furnace fan' variety through a cheap, household dimmer switch (the kind meant for lighting) and you will be able to vary the speed, but the speed will not be stable - any variance in load will vary the speed of the motor. If that's not a problem then your solution might be simple.
If a consistent speed is important (and for this kind of testing I would presume that it is) then you might be better off with a variable speed gearbox if a three phase motor is not feasible.
A variable speed gearbox will allow you to change the speed of your fan while keeping the set speed of the motor.
A new 3-phase motor and VFD would probably be cheaper than a variable speed gearbox.
Alternatives include a DC motor with a suitable controller, or if you need to do it on the cheap you could make your own 'gearbox' by just swapping chains and sprockets or belts and pulleys between the motor and fan. This assumes that you have access to cheap fabrication. One last alternative would be using the cheap dimmer switch but adding a speed pickup on the motor so that you can keep adjusting it until you get the RPM that you want, assuming that the load is non-varying.

Mike

 

[dipankur]

Why can't they use a variable resistor to control speed like fan control, provided the motor is a very low capacity one?

Converting to three phase and then using VFD seems to be an overkill.

 

[Andreb]

Maybe something like these.

http://www.anaconsystems.com/text/ps.html

http://www.directindustry.com/prod/...erter-for-single-phase-motor-5698-272247.html

 

[sreid]

Follow itsmoked's advice. We get this question all the time and there is simply no practical way to control the speed of a single phase induction motor.

Small single phase fan motors that can be speed controlled are special purpose induction motors designed for high slip. It would be uncommon to find this kind of motor at 2.2 kW.

 

[jraef]

You need to know more details about your 1 phase motor. If it is what is called a PSC (Permanent Split Capacitor) type, you can use the VFDs described above. If not, you may be "S.O.L." as itsmoked said. The reason is, most 1 phase motors use capacitors in order to make them start and a speed switch that takes them out of the circuit when they are no longer needed. If you lower the speed, the speed switch closes again and you damage the capacitors AND the VFD.

There are "universal" motors such as itsmoked mentioned, also "Shaded Pole" motor designs that can be controlled via resistors or rheostats, but they are of limited use and about a 99% chance of not being used in your blower.

So if your motor is not PSC, your choices would be to swap it out with a PSC version (if that works out mechanically) and use one of those 1 phase VFDs, or swap it out with a 3 phase motor and use a more standard off-the-shelf VFD to convert your 1 phase source to 3 phase for the motor. That is a common practice now because most VFDs 3HP and under will accept 1 phase input without derating.

 

[itsmoked]

The only other alternative I see is to run your motor at its designed speed and bleed the gas out from in front of your test area/device so that you effectively lose velocity/pressure the same way you would with slowing the motor. You can run the bleed back to the blower input. You can control all this by looking at the output pressure and adjusting the bypass valve/leuver.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Tmoose]

Would throttling the discharge work?

 

[LionelHutz]

Throttling should work, unless the blower is a constant displacement type.

 

[Javier72]

You can use somethig like this:

http://www.kelvin.es/producto.php?idioma=en&id=70

 

[itsmoked]

Have you ever used one of those Javier? What do they do with the centrifigul switch?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Kiljoy]

Allen-Bradley and several other drive manufacturers make a single phase drive. Smaller 3 phase drives are also able to be run single phase. Haven't you ever seen the drive demo kits that the salesmen bring in that plug into the wall outlet?

These guys all have single phase drives:
AB Powerflex 4 & 40
Yaskawa CIMR-VU
WEG CFW08

 

[Kiljoy]

Maybe that's the other way around. Some 3 phase drives can run a single phase motor? Anyway, they make them for single phase.

 

[itsmoked]

You are backwards. The sales guys are showing you 3phase VFDs running on single phase. This is what I suggested to the OP.

Single phase motors are very different from 3Ph motors. They have switches in them!!!!!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

LOL,
Every time this subject comes up, someone jumps on this; it's probably the most common misconception out there. The vast majority of drive salesmen don't bother to explain their demo case to people (or don't understand it themselves) so they leave with the customers thinking they just demonstrated a drive for a 1 phase motor.

As Keith said, those demos are showing a 3 phase drive and motor, fed from a 1 phase source. You CANNOT use any drive made by Allen Bradley, Yaskawa or Weg on a 1 phase motor.

 

[Kiljoy]

Based on the large single phase selection in the drives catalogs, there seems to be a market for them. Who or what application are they targeting??

 

[dcasto]

switch to a dc motor. Or, put a louver on the inlet.

 

[jraef]

Again Kiljoy, you are misinterpreting the "large single phase selection" in most drives catalogs as being for 1 phase MOTORS, which they are NOT. They are drives that can be fed from a 1 phase source, but the OUTPUT IS 3 PHASE.

There are only a small number of manufacturers who offer a 1 phase VFD for a 1 phase motor. Invertek out of the UK is by far the largest, and their drives are brand labeled by several other people in the US such as Bardac and Anacon (one of the ones shown in the links above posted by Andreb). There are 3 or 4 small manufacturers specializing in the HVAC industry for bathroom fans, but the applications are extremely limited because they can only be used on PSC and Shaded Pole motors, which are a small percentage of 1 phase motor applications to begin with.

Interestingly funny side note.
The other link put up by Andreb shows a Flygt VFD that says "for 1 phase motors". But if you go to Flygt's website there is no info available. That drive name (on the image) is registered to Bell and Gossett, Link a different division of ITT. They show the drive in their info, but CLEARLY state that the drive is ONLY for 3 phase motors! So even the marketing dept. of a manufacturer can't keep it straight!