Thread: Rotary Phase Converters!

Don't know if this helps
3 Three Phase Power Converter Australia converts single phase to three phase

Originally Posted by Lappa

Don't know if this helps
3 Three Phase Power Converter Australia converts single phase to three phase

2-4k aud Thats what makes me feel it must be possible but.

The transformer in your circuit steps up to 380Vac, which is applied between 2 phases of the motor. 380Vac is common for a lot of motors as it is the 3ph terminal voltage for 22OVac single phase systems which are common in much of the world. 415Vac 3ph relates to our older spec 240Vac single phase systems, We are now officially 230Vac single phase (Active to Neutral) which would correspond to around 395Vac phase to phase on a 3ph system.

The motor in the circuit diagram is not the motor in the machine you want to power, it is a 'pony' motor in the converter unit. Your machine motor operates from the output terminals of the circuit.

The system uses a contactor system to stop and start the motor, that is the relay system shown near the transformer, and the momentary acting switches around it. Pressing the start switch allows current to flow through the contactor coil, which closes the active, neutral, and aux contactor contacts. Once the aux contacts are closed, they supply an alternative current path for the contactor coil, and keep it engaged when the start switch is released. Pressing the stop switch interupts the coil current causing the three sets of contacts to open, withdrawing power from the motor. Also, if the power fails, the contactor coil is deenergised and the contacts release and will not engage again until the start switch is pressed with power restored, i.e. the system cannot automatically restart on restoration of power supply, possibly endangering people in the area.

There is a group of capacitors arranged between the phase terminals of the motor, these in combination with the motor windings produce phase shifts to create a pseudo 3phase voltage for the motor. There are a couple of capacitor networks beyond the motor which are switched with another contactor. Not sure exactly what they are doing, but it will either be to provide additional phase shift to get the motor started, or to trim the capacitance used to balance the motor phase voltages with variation in load.

Overall, the system operates with one supplied phase being fed to the load motor, and two additional phases being generated within the motor by induction. This type of unit has been used for a long time, but has an inherent problem in that the value of the capacitors installed needs to be adjusted to match the load. This has been a sticking point for a long time, as to have the units operate reliably and safely, the operators had to monitor the phase angles and voltages and try to adjust the capacitance values by switch capacitors in and out as required. Switching the capacitors was an issue because it required heavy duty high voltage switches or contactors.

In the last ten years or so, a NZ company has developed a solid state switching module which can provide the monitoring and capacitor switching to make the concept more viable. However that module is about the price of a reasonable VFD for motors of similar ratings. The capacitors used tend to be large and expensive, and need to be at least 600Vac types. You stil need a 240-380/415 single phase transformer that can handle the entire system, say at least 2KVA for a 2HP load motor. The transformers can sometimes be found second hand, generally operating in reverse and taking 415V or 380V and stepping down to 240 to provide an isolated supply for ancilliaries in a large machine, but they are still big, heavy and expensive.

Have you passed on information about the motors in the lathe and mill, some motors can be converted to operate at 240V 3ph simply by rearranging the connections in the terminal box on the motor. Or alternatively, there are 240V single phase to 415V 3ph VFD's available at a cost about 3 times that of a 240V to 240V or 415V to 415V unit. The added benefits of VFD include variable speed without belt swapping, or a wider speed range with belt swapping, soft starting, easy motor reversing, braking to a stop and others.

Hope this helps you with your quest. Sorry for bring up the dreaded VFD's, but really I would look a fool if I encourage you to drop a couple of thousand into making a RPC, only to have you discover that you could have done the job with a $600 VFD.

There is a 4KW/5.5HP RPC listed on ebay here for $1800 BIN at the current time in case you are interested.

I have had 3 Phase Converter running off our 240 supply for about 4 years. I sourced the bits and pieces, mainly from Ebay, and got a fellow Forumite to put it all together. The most expensive bit is the transformer. It has to go from 240 to 415 to feed into the "pony" motor. Thankfully I had a welder that was the donor for the 5Kva transformer. Eurotec (New Zealand) supplied a little black box to get it all to work. The system runs a 5 Hp "pony" motor that can support a machine of 5 Hp. In practice my Panel Saw has a 5.5 Hp motor on the main shaft and a separate 1 Hp on the Scriber. So in use I am using 6.5 Hp. I queried this with Eurotec and they assured me everything would be fine.
Well after using it regularly over the last 4 years or so, it has never missed a beat!! The only comment I would make with my set up is that the 3 legs of 3 Phase are within 25 volts of each other which hasn't been a problem, but if you were plugging in a machine that had electronic switching you would need a filter because the out put of the converter is "dirty", meaning the voltage can fluctuate causing damage to the electronics. By doing the "manufacturing" of the converter myself and the Forumite it cost me about $1200. Why did I go this way instead of VFD? The idea of an electronic circuits delivering 415, 3 Phase just doesn't give me the confidence that it will be reliable over a long time.

Originally Posted by chambezio

Why did I go this way instead of VFD? The idea of an electronic circuits delivering 415, 3 Phase just doesn't give me the confidence that it will be reliable over a long time.

415V controlled electronically is not that big of an ask and is standard protocol in industry.
The lab gear we used at work from the 1980s onwards was up to 20kV+.
All controlled and delivered with volt level stability by electronic circuits for over 30 years.
The only reason one of the bits of gear died was because it was hit by a lightening strike.
What surprised us was that most of the electronics actually kept working even after the lightening strike and it was more of the analog components that had problems.
All of the other gear was still working when it was decommission a few years back.