phase convertors

[fireryan]

I was doing some reading on three phase and single phase today. It talked about how u could use a phase convertor to get 3phase out of single phase. Can anyone explain how this works and is this the only way to do it?

 

[Jraef]

I was doing some reading on three phase and single phase today. It talked about how u could use a phase convertor to get 3phase out of single phase. Can anyone explain how this works and is this the only way to do it?

Only way???
Well, you need SOMETHING to convert 1 phase to 3 phase, and that something, whatever it was, would then be a "phase converter" no? So the question probably is, is there more than one type of phase converter? That answer is Yes.

• Static Phase Converter (SPC), which is done with some basic electronics and capacitors. Sometimes called an "Add-a-Phase" unit.
• Rotary Phase Converter (RPC), which uses a 1 phase motor to spin a 3 phase motor, then uses the 3 phase motor to "add-in" that 3rd phase
• Variable Frequency Drive (VFD), which converts the 1 phase power to DC, then reconverts it (inverts) back to pseudo AC.
• Electronic Phase Converter (EPC), which is a simplified form of a converter/inverter similar to a VFD, but without the speed variation ability

Did I miss anything?

 

[winnie]

[*]Rotary Phase Converter (RPC), which uses a 1 phase motor to spin a 3 phase motor, then uses the 3 phase motor to "add-in" that 3rd phase

You can subdivide Rotary Phase Converters into various different classes.

For example, a single three phase induction motor with two terminals driven by a single phase source will generate the third phase, without any other motors involved.

Or you can have motor-generator systems similar to your description.

-Jon

 

[gar]

090217-2117 EST

The vast majority of low cost rotary phase converters are made with a single 3 phase induction motor, and balancing capacitors. The capacitors are useful for starting, but are also necessary for successful production of an adequate 3 phase output under load. Note: in this single motor application that about 1/3 of the load power is a direct pass thru. Not so if output is isolated from the input supply as it would be in a motor-generator combination.

I have always thought it would be useful to try a 3 phase synchronous motor for this purpose. However, it would likely be more expensive. I have looked, but not seen any surplus motors that are small enough for a typical application. There are many applications where 3 phase CNC or manual machines are used in areas where 3 phase power is not available. Home garages for example. Most of these applications require a 5 to 30 HP capability.

.

 

[Rick Christopherson]

• Static Phase Converter (SPC), which is done with some basic electronics and capacitors. Sometimes called an "Add-a-Phase" unit.

A static converter (well at least the store-bought type) is nothing more than a motor starter, and once the motor is up to speed, the converter drops out completely and the motor is left to single-phase. I have heard of only one company that offers an option for balancing capacitors for their static converter. It is commonly stated that a static converter will provide 2/3 the motor power, but I am pretty sure this is incorrect, but it has been repeated so much (even by me in the past) that it is considered true by default. In retrospect, I think it is more like 50%.

• Rotary Phase Converter (RPC), which uses a 1 phase motor to spin a 3 phase motor, then uses the 3 phase motor to "add-in" that 3rd phase

This is called a pony motor converter, and in my opinion is a waste of two good motors, and it is only marginally more effective than the motor starter of a static converter. Unlike a generator, there is no field winding (or permanent magnets) in the idler motor. If you put a meter on the generated leg while a load was present, you wouldn't find much of any power generation, but enough to get your tool motor started. If you put balancing capacitors on, it would bring the power up to a more usable level.

 

[Jraef]

A static converter (well at least the store-bought type) is nothing more than a motor starter, and once the motor is up to speed, the converter drops out completely and the motor is left to single-phase. I have heard of only one company that offers an option for balancing capacitors for their static converter. It is commonly stated that a static converter will provide 2/3 the motor power, but I am pretty sure this is incorrect, but it has been repeated so much (even by me in the past) that it is considered true by default. In retrospect, I think it is more like 50%.
This is called a pony motor converter, and in my opinion is a waste of two good motors, and it is only marginally more effective than the motor starter of a static converter. Unlike a generator, there is no field winding (or permanent magnets) in the idler motor. If you put a meter on the generated leg while a load was present, you wouldn't find much of any power generation, but enough to get your tool motor started. If you put balancing capacitors on, it would bring the power up to a more usable level.

I hadn't intended to provide, nor did the OP ask for, all the gory details of every type and sub-type. There are several versions of just about every type I listed above, what you are describing are the details on just some of the variations. I would not categorize them all that way, but what you say is certainly true of some of them.