[TheForge] Fwd: Shop tools & layount (3-phase converter)

[Steve Smith]

Well said. A couple of comments:

xlch58@swbell.net wrote:

> Three phase motors are much more efficient 
> than single phase motors, but only when powered by real three phase 
> power.    I know someone here has stated that a three phase motor 
> running off of a  rotary converter drew less current than the single 
> phase that it replaced, but that is probably due to the fact that since 
> three phase motors are almost always intended for industry, they tend to 
> be better made and more efficient to begin with and you probably aren't 
> pulling anywhere near nameplate hp.   

I should have given more detail. This was a test setup in a university 
lab allowing adding a measured load to the motor. Greater efficiency was 
achieved when the converter was precisely tuned to match the load, which 
would not be achievable across a broad range of loads.

> There are a lot of 
> disadvantages to running three phase motors on single phase.  The only 
> advantages are:  You can bump stop three phase motors, and often 
> inductrial equipment comes with integral three phase motors that can't 
> be easily replaced with standard single phase.

And if you're a good scrounge, they're lots cheaper than single phase 
motors.

> 3) Rotary Converter.....
 > This does not produce true three phase, it
> produces quasi unbalanced two phase with a hinky power factor.  

Charles, I'm not sure what you mean here. Sure, the third leg isn't 
quite as good as the others, it's voltage may sag a little even with 
capacitor tuning, but the phases of the legs are all locked in to the 
correct angles. The idler motor ensures this. I'm probably not following 
what you mean.

Steve Smith