VFD with a difference

[Piero]

It could be a problem with the potential relay sticking. These are used to turn on extra capacitors for the boost voltage that gives the motor an initial kick to get it spinning.
The relay failed on mine but after fitting the pony motor I realised it wasn't required anymore. The small pony motor is not under load so it spins up without boost capacitors. Then because this is already running and creating the missing 3rd phase it easily starts the lathe motor with ease even in top speed range and high gear selected.
Its turned out to be a very simple reliable setup. You'll notice i have VA meters on all three legs so I can make sure the phases are balanced within 20 volts. Some jobs I'm running the lathe almost continuously for 3 hours and neither motor gets hot.

I dont think mine has the booster

I am quite sure off it

I've had it apart in the past and have never seen a relay or a timed relay that some have

Mine is just the transformer and a load off caps

I have a photo off the internals on my home pc

I am at my workshop right now

 

[Fazerruss]

Does anyone have any useful links on converting a static phase converter to a rotary phase converter

How would you size the dummy motor ???

Its really easy. All you do is connect a motor to the same output as used for the machine you are running. I went a step further and fitted the VA meters so I can see the voltage and current draw for each leg. This allows me to fine tune the output with the "hp switch" to get the motor to run smooth. The smoother and quieter means its input voltage is correct ballanced. ( all the hp switch does is connect extract capacitors to boost the voltage on the missing leg)

Pony Motor size isn't crucial. Something around half the hp of the lathe motor. This is mine.




I read a good book on motors before doing all this ( can't remember the name of it) and one interesting phenomenon is the more motors you have running helps smooth out the voltage. Every spinning motor acts as a flywheel and the inertia of the spinning pony motor helps with surge in demand from the machine motor. (The pony motor is acting as a generator for the 3rd missing leg)

 

[Memmeddu]

Just fit a pony motor to your static then you will have a true rotary phase converter.

I have the same lathe and motor. It works perfectly View attachment 522849View attachment 522850

My lathe is slightly bigger than yours, but it has not a Norton box or feed bar

 

[Piero]

I am quite liking the idea of a 230v input 380v 3 phase output VFD. as mentioned further up in this post.

I was unaware they did such things

I am currently trying to find a quality manufactured one as all of my VFds are Invertex at the moment, Shneider or Mitsubishi would be good options ( I don't know if they do them) as I don't care much for cheap VFds