How I made a simple static phase converter

How I made a low cost simple static phase converter with wiring diagram and details of the parts I used.

[dc]

This was about the best video I could find on these. At my motor, which just died, I had 240V, 240V, and 200V, that's about a 15% drop. I'm not sure if that's acceptable or if that's what smoked my motor? My static convertor has worked for 20 years, flawlessly; but, now I have to get my Bridgeport motor rewound...

[charlesrpatton]

A patent covering this technique is:
2, 502, 099 March 28, 1950
SINGLE PHASE MOTOR STARTING
By O. Lindfors

The point is that you’re treating the 3-phase motor as a single phase motor and the second phase winding as a start winding. Once it starts ‘rolling’ the winding being treated as a start winding generates BEMF that the potential sensing relay senses and drops out. The patent has more explanation for those interested. One thing to emphasize though, is that now the motor is being used as a single phase, one winding motor and can not reach the full torque and power output that the 3-phase motor can. A continuous ‘run’ capacitor could improve this a bit, but still won’t achieve the level of the 3-phase motor fed with 3 phases.

I have a big, old STAR radial arm saw with a single phase motor that uses this technique as opposed to the simple centrifugal throw out switch used on pretty much any single phase motor of any typical home application with the exception of small desk fan motors using shaded poles for the phase difference to get the rotor rolling or brush motors in vacuum cleaners.

[tapapesh]

The reason you have to wait between starts is to give the bleed resistor time to discharge the start capacitor.

The current going to the start capacitor has a 90 degree phase shift that provides the other "phase" for starting. But, it only provides that while the capacitor is charging. Once charged, it acts like just another AC conductor. So, you have to begin your start sequence with a discharged capacitor.

If you want to restart more quickly, add another normally open switch between the two poles of the capacitor in series with a very low ohm but high wattage resistor to discharge the capacitor more quickly.

Alternatively, you can just short the cap, but you'll get a good be dangerous with dusty conditions or volatile fumes present.

Nice job!

[ToolTalkCanada]

Thanks for the video. May try this on a 5hp 3 phase radial arm saw.

[HaxbyShed]

Hi Chris, this is very useful indeed. I have made a static converter for a small 0.5HP motor and it works but the relay contacts arc too much. I used a (too) small relay and then a potentiometer in the relay coil to adjust the pickup voltage (I've seen several designs like this on YouTube). But because the relay is more an "on/off" relay it does not do well when the voltage is climbing and takes too long to open. Also it's behaviour is a bit erratic and not very predictable. Maybe the relay would last a few weeks or months but soon enough the contacts will burn out or weld. So I've bought the SUPCO APR5 like you but here in the UK there is limited supply of any of these potential relays and it cost me £42 / $52US. All told my static converter is costing me about the same as a cheap inverter - but I don't need speed control on this particular machine and I don't want to rewire the machine switches. Cheers.

[bishopenterprise]

The most likely reason you cannot restart the motor right away is in the potential relay. If it’s design is like the ptc’s for refrigerator compressors then they operate like a positive thermal coefficient. Meaning it has to cool down before restarting. In refrigerators this prevents the compressors windings from meltdown!

[apollorobb]

You should be feeding your Phantom phase with run capacitors . Otherwise your single phasing the motor and thats hard on it as the motor will only be roughly 2/3 of its rating .And the reason it wont immediately restart is the potential relay has a 1-1.5 second restart safety as these are built for HVACR equiptment generally used on single phase semi hermetic compressors .

[tehodoroperez]

I incorporated a three wire magnetic starter between the potential relay and the motor. Am I doing it correctly?

[taylormcnutt]

Why did you go with a static phase converter when you already have a rotary phase converter? Just curious.

[bikefarmtaiwan]

So this is running a three phase motor on single phase 220 . ( which is of course two diametrically opposed sine waves) not really a three phase converter, just a work around .