RPC question .....

[Eddyde]

I'd be curious if you ever measured the voltage drop on the generated leg while starting the lathe and closing the clutch?

I don't think I measured the voltage at the peak of start-up, only the inrush current. But I did test the running voltage and current under various conditions. I don't recall seeing the voltage drop, at start-up, being mentioned as a significant factor when I researched my design. However, there is undoubtedly more that I don't know than know, about this subject...

Here is a link to my build thread, there is an analysis of the voltage and current, there.

Rotary Phase Converter Rebuild / Build

Looks nice Ed, old Mr. Snyder would be blown away I'm sure :cool:

www.hobby-machinist.com

 

[rabler]

@Eddyde 10% is commonly accepted tolerance for 3 phase, and is mentioned by someone for the purposes of balancing caps in your thread.
Here's a snippet for your consideration: "A voltage unbalance of 3.5% can produce a 25% or greater increase in motor temperature." That's based on continuous use, not startup transients, but the idea still is relevant. You just get more complicated to analyze the impact of startup issues. But temperature is generally accepted as a significant factor in motor longevity, so the simple "it works" isn't always the complete story. Best would be to measure the temperature of the motor windings (not the case), and a lot of higher end 3 phase motors have a thermostat option for this.

This is more critical for 3phase motors run under continous load (pumps, fans, conveyors), but I cringe when I see some youtubers waiting 30 seconds or more for the RPC driven motor to kick up to speed, sometimes with lights dimmed all that time.

 

[Chipper5783]

Back 40 years ago, I bought a 5hp RPC for my 5hp lathe. It is 2 speed machine, 3 hp or 5 hp - I’d only get a couple starts on the 5hp setting before tripping the RPC overload. I just ran it on 3hp, quieter anyway. However the 5 hp air compressor had no problem.

So the 5hp RPC may work, but marginal.

 

[Eddyde]

Thanks for the link, there is always so much more to learn when it comes to this stuff. I don't seem have any overheating problems and I've had the system working for over 4 years now, I've even had the lathe running for many hours continuously, when using it to tumble parts. I think got it balanced a little better than 10%. My wife even uses the RPC as our washer is a 3 phase commercial machine, salvaged from a coin-op laundromat.

For entertainment. see this guys sketchy Youtube build, skip to 16:40 for the best part, That's no NEMA rated enclosure! lol