Searching for AC Inverters

What's it driving?

I have five 24000 BTU Air conditioners that are rated at 230V 60Hz 20 amps 3.5KV They were ship to me with the wrong Hz

James

How strange that this was rated off topic. (I voted it back to on topic.) It is an essential question. It is impossible to supply a reasonable answer without knowing what is to be powered. Converting the input to DC at some voltage to feed an inverter is simple, and if the load is not large, there are many inverters available that are dirt cheap -- a small fraction of the price of a VFD, for example.

I agree with the question, Whats it driving ?

I have seen motor-generator configurations used to convert 60Hz to 25Hz, for railroad use. So if you are driving a load that could flat-line an electronic convertor, consider rotating machines.

Consider using a 1ph AC Drive. Allen Bradley mfg's a 1Ph output with 1ph or 3ph input, 230-575VAC 50/60 Hz. The drive will give you the 60Hz 230V 1Ph output, You will need 1 drive for each A/C unit. They are really inexpensive, and can be programmed to power up to your load in 2 seconds, this will also ramp up, so eliminates across line starting= energy efficiency and reduced wear on A/C units.

Almost any VFD can be suitable. Motor-generators are a bit obsolete but also can be used.

I agree with Jim, your best bet will be to use a single phase VFD (Variable Frequency Drive) with each unit. MoGens were suggested but, they are relatively inefficient, noisy and will need to be oversized to handle the inrush current that occurs when your compressors fire up.

Most VFDs have a soft start feature, which ramps the voltage/frequency up gradually, eliminating the inrush current when the compressors fire up. On top of being much more efficient than a MoGen, VFDs are also easier on the compressor motors, during start up, so they will last longer.

The price of VFDs has really come down recently, so they are quite affordable. A new VFD can probably be had for much cheaper than even a used MoGen setup.

I think that to look at converting is fraught with danger re using rated output, starting and also the control electronics.

I agree with Grey Haired Old Goat, get the correct unit for your existing power supply (GA)

I believe that the motor speed inverter replies may not be considering the entire unit but are reflecting the motor control only, there will be inherent sensors and control electronics that are not designed for use on a noisy PWM output.

I agree that a VFD will work. It is the best approach for a motor. For other loads, if you can locate a double conversion UPS. You mentioned an inverter. If you get both a rectifier (could be just a battery charger) and an inverter and connect them via a DC bus, this will work. Be sure the inverter generates the quality of sine wave you require (some just put out square waves). Lighting inverters can work too if you do not require a perfect sine wave. Good luck.

Is there any possibility that the AC system will still work on 50 Hz mains? Check with the manufacturer. It might save you alot of time and effort.

Bill

I have voted all of you who suggested VFDs as being ff-topic. You did not read the original post correctly.

He has SINGLE PHASE MOTORS and a 3 PHASE SUPPLY, not 3-phase motors and a 1-phase supply. All of the VFDs suggested, i.e. Allen Bradley etc., are for the latter scenario. The take a 1-phase supply and create a 3-phase output to run a 3-phase motor. You CANNOT use these on single phase motors.

There are 1-phase in, 1-phase out VFDs available, but it is dangerous to apply them to just any single phase motor without knowing very specific details of what TYPE of single phase motor it is. You can only apply 1-phase VFDs to PSC (Permanent Split Capacitor) type 1-phase motors. All other types will result in the destruction of the VFD, motor or both.

I also voted the response (sorry, can't read the name while typing a response myself) which stated that there is more to it than just the motor; that is absolutely correct. You cannot assume that anything other than motors will work on the output of a VFD.

Also as someone else suggested, it is likely less expensive to insist on getting the correct version re-sent.

JRaef,

AB Powerflex 4M is a Single Phase AC Drive 240VAC output up to 2.2kw

Input voltage of 120-240 Single phase.

http://www.ab.com/en/epub/catalogs/36265/1323285/2531069/tab3.html

I see where you might think that these drives can be used on 1-phase motors, Allen Bradley's website information is VERY sloppy in that regard. It implies that the drive can be used for single phase motors, but the website never actually says it, and that is an incorrect implication. If you download the brochure, it clearly states on page 2 that the OUTPUT is always 3 phase, meaning it can only be used on 3 phase motors. It does not say that anywhere on the website. So you are forgiven...

A-B Powerflex 4M brochure

If I had to guess, I'd say that A-B website was designed by some marketing grunt who had no dea what he/she was writing about. Again, very sloppily done and misleading, not what A-B is known for but I guess it's a different world now.

I stand corrected. I agree with you on all counts.

Thanks

Jim