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connecting a VSD/VFD to an AC compressor

I was wondering about using a Variable Speed AC Drive for two air conditioners.

One is a window unit, with rotary compressor that uses single phase with a capacitor to phase shift and three wires to the motor. Can this be made to run as a three phase motor without the cap? As far as I'm aware "inverter" (hvac-speak for VFD drive) aren't available for window units, in spite of their higher efficiency.

The second is a mini-split with a three phase motor that does have an inverter style drive and ramps between 2 amps and 10 amps when heating or cooling. (from a hardware perspective cooling is the default valve position)

My mini-split has control issues and they want more for a replacement board than a new unit costs, and they ain't cheap.... When it chooses to work it works very well, but generally the controller starts sending the outside unit conflicting heat-cool/set-point commands with rapid fire succession, and I haven't been able to find the cause except to say it seems to be humidity related.

Both units are 230 VAC.

Commercially available VSD's are reasonably priced and will go from single to three phase, and I kinda like the idea of designing my own thermostat that will ramp the VSD depending on temperature.

AND the big question (I've installed a lot of VSD's in industry in pharmaceutical manufacturing) how do I know, preferably before wrecking the hardware, that the motor is turning in the right direction. SOP in industry is to look at the motor, but with a sealed compressor that isn't an option. (and there doesn't appear to be a convention anywhere that I'm aware of for which phase is A-B-C.. Do motor wire colors offer a clue?).

Reply to
default
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Having little knowledge other than when you slow down a motor with a VFD, more heat is produced. My experience is these sealed motor/compressor units already run hot, I wouldn't want to add any more heat. My one data point, is with the electric motor rewind industry, years ago it came out with a higher temperature insulation for motors used with VFD. Mikek

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Reply to
amdx

With the older VFD the motors would run hot. They often depend on the speed of the motor to use the internal fan blades to cool the motor. As the motor slows down the motor runs hotter. Some of the newer VFDs use a different power scheme to help this out. Some even have a setting for an internal fan, or external cooling of the motor.

Where I worked they burnt out 2 of the 30 HP motors whena VFD was put on them. I told them to add an external fan to cool the motor and whenthat was done the motor never failed again.

I don't know so much about the compressor part of the Air Conditioner, but of then the air handler fan is ramped up and down. This seems mainly just so they can get a better efficency number to put on the unit.

Reply to
Ralph Mowery

The single phase motor cannot be run as a three phase motor because it is a two phase motor. There are only two windings, not three as in a three phase motor so changing connections cannot make it a three phase machine. Single phase motors that do not use a run capacitor have a really lousy power factor when lightly loaded, it gets better when fully loaded.. These motors can be made more efficient by lowering the voltage when lightly loaded and there used to be for sale a device that does this. There still may be I just can't remember the name. Single phase motors with a run cap have a better power factor but it still can be improved. The main advantage for making the motor more efficient is just to reduce heat in the windings. You won't save any money. Is the cap in your unit switched out of the circuit when the motor is up to speed? If it is then I would suspect that the motor is running pretty much fully loaded and there is not much you can do that is economically feasible. Eric

Reply to
etpm

For a piston type compressor rotation direction is not important but for a scroll type it is. If it's a scroll and is not performing then change the direction.

Reply to
Rheilly Phoull

Can it run in the wrong direction long enough (say a few minutes) without damage, to determine if it is cooling?

Reply to
default

"These motors can be made more efficient by lowering the voltage when lightly loaded and there used to be for sale a device that does this. There still may be I just can't remember the name."

Aren't you referring to the NASA attributed "power factor corrector?"

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I have one on a window fan and one for my well-pump.

I did something like that with a large 48" belt driven commercial cooling fan. The original motor used 5.7 amps, the replacement (split phase capacitor type) I got for it used 3.2 amps and I could shave a little more by reducing the voltage (had an ammeter on it and would turn down the voltage until the current started climbing again).

The voltage control was from a schematic I found in one of the "Encyclopedia of Electronic Circuits" -Marcus. It was originally intended as an AC voltage regulator for commercial theater projectors and used a pair of SCR's to regulate the voltage. (just slightly more complicated than a lamp dimmer)

Reply to
default

I wouldn't like to say since there are probably models that would but anecdotally it would seem there are some that may displace a seal. I would google for specific info id in that situation.

Reply to
Rheilly Phoull

Potential relays energize windings and capacitors using back electromotive forces (which is efficient).

Reply to
bruce2bowser

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