Cheap 1ph 50hz from 60hz 2

[Barry1961]

A customer in the US wants to test machines he builds for overseas where they will be run on 220V, 1ph, 50hz. These are 1/2hp, 1ph, 220V, 50hz, cap start motors.

They are looking for a cheap 1ph, 50hz, 220V supply.

Can you use one phase off a VFD for this?

Any recommendations?

Barry1961

 

[CJCPE]

Some VFDs are made for single phase motors but they are not for cap start and are for variable torque (fan/pump) loads only.

Some 3-phase output VFDs may operate OK with 1-phase loads, but may not be compatable with cap start motor.

Frequency changers are sold that are designed for the purpose you describe. Solid state electronic and rotating types are available.

 

[electricpete]

I don't know how the cap would hold up to the high frequency even for a short time.

Strictly speaking you need to verify the motor insulation is inverter duty but I think usually that’s not a problem.

How does a 3-phase VFD respond to single-phase load and are there special protection considerations? I don't know.


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[itsmoked]

Get a 50Hz 220V bearing generator and run it with a 60Hz 240V motor with a a belt and two sheaves. Make the sheave sizes match the 50-60Hz.

Or get an inverter rated for 60Hz 220V and run it off some batteries.

 

[Barry1961]

The frequency converters I found start around $1500.00(US). I can get a VFD for under $200.00(US).

Has anyone ever tried running a cap start motor from a VFD?

It might be a fun experiment.

Barry1961

 

[CJCPE]

You might want to check into VFDs that are sold as drives for single-phase motors:

http://www.bardac.com/pages/products/ac_optidrive7.html

http://www.minarikdrives.com

 

[Marke]

Hello Barry1961

VFDs are designed to supply three phase only and the output waveform is PWM and is reliant on all three phases to produce the sinusoidal current.
The ouptut of the vfd is 3 wire only (no neutral) so to attempt to operate a single phase you would connect accross two phases.

With a capacitor motor, you would be in major difficluties if you connect to the raw PWM output of the VFD.
I would suggest that if you were to connect a delta primarly, star secondary transformer to the output of the VFD, you may have a chance. The other issue would be that you would need to size the VFD larg enough to supply the start current of the single phase motor (about 6 times the rating of the motor. Ramping up from zero as would normally be the case with a three phase motor would probably not be an option unles you alter the capacitor to suit the applied frequency. - you would probably need a continuously variable capacitor!!
You may also need an additional low pass filter on the output of the transformer to reduce capacitor currents at the carrier frequency.

Bottom line, you would probably be better off with a specific 50Hz output inverter.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[jraef]

I have run cap start 1 phase motors from VFDs, or I should say, tried to. It is a race between the caps popping or the transistors shorting. Usually the caps pop first.

Marke's suggestions MIGHT work, I haven't tried that, but it makes sense. Pay particular attention to his statement about size however. You CANNOT ramp up a cap start motor, the cap is not intended to be in the circuit for more that a second, maybe less. So as he said, the inverter must be sized to supply locked rotor current of that motor. Otherwise it will current limit and may not accellerate the motor to the speed required for the speed switch, and then the cap pops.

Question though, what is the machine application and is speed critical for testing? If it is a short term functional test, the 20% increase in speed may be irrelevant.

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[Barry1961]

Great idea about using the transformer. If a VFD could be used with some kind of filtering it would probably still cost much less than an equivalent adjustable frequency converter. If this can be done with $300 worth of filters it would save $1000 and be more flexible. I guess you would want a very “dumb” VFD if it is going to be fed into a transformer.

The customer wants to have a test that is as close as possible to what it will be at end user. The speed difference would be too much.

Thanks for all the help.

Barry1961