I have not seen the Clark converter but do have two differing ways of running my machinery. The lathe has a three HP motor that is not dual wired to run 240v or 440v so that runs off a Transwave static converter of around 4.5HP capacity at the 400 volts.

My Bridgeport mill was originally wired to run off the same Transwave kit but was never happy and would stop after a short run time. This was changed to a digital inverter drive (a cheap Chinese one for around £90) the motor was changed delta to star or the other way around and runs perfectly. I did not do the wiring, that was done by a friend who knows what he is doing.

What I am saying is these things are not a plug and play, most ordinary household electricians have no idea on the three phase wiring .

The Clarke converter is a static phase converter, which AFAIK is not ideal for a lathe. The third phase is provided by a phase shift capacitor, the value of which is controlled by the switches on the front of the panel. The ideal capacitor setting will depend on the motor load, which on a lathe will not be constant. Have you tried all settings?

Also if the contactor is not holding in, then it could be that the control circuit is being fed from the "artificial" phase. The Clarke manual does cover this.

On my chipmaster I went for a VFD installation, which works like a dream, but it did require ripping out the exsiting control wiring and replacing with the low voltage DC VFD controls. Also critical here was that the original 1963 motor was not dual voltage, so I run the 415V motor with a 240V VFD uing a 29Hz base frequency setting. This was using the technique described at https://www.inverterdrive.com/HowTo/240V-Supply-to-a-400V-AC-Motor/

You have a choice of start and run capacitors. Are the switches set for your motor HP ? there is an ammeter measuring your single phase current does this show any thing? It should show a huge current when the inverter is powered (30A+?) then settle back to the running current (10-15A?).

here is a circuit diagram of it if its not in your documentation :- www.clarkeservice.co.uk/manuals2/pc20_60.pdf

Frank

Adding decent size pilot motor to make the static converter into a rotary converter always improves things. Whether it improves them enough to fix the problem is a different matter and impossible to judge without trying out. A common cause of control gear problems with converters, both static and rotary although statics are much more sensitive, is running the contactor coils via the generated phase. The generated phase is very unstable in both voltage and phase during run up. Often the variations are sufficient to cause the contactors to drop out during run up or even a short time after things should have settled down. The control gear must run via the mains supplied phases.

Sometimes the whole darn machine is sensitive to converter phase connection for no known reason. A friend has a Bridgeport connected to a Transwave rotary converter which will reliably run on only one specific order of phase connections. Wrong order = usually or sometimes runs. I had to switch the control gear transformer connections around so the contactors were happy with the same connections as the motor was. Shop gremlins playing I guess.

Over the years I've probably done over 20 static and rotary phase converter installs or sort outs. Mostly they go OK but the 4 or 5 that didn't were very hard work. One refused point blank to co-operate. That was the first time I ever used a modern VFD. Instant fan. Given the relatively small price differential converters are no longer worth the potential hassle if you do have a stubborn machine.

Clive

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Has the control panel got a transformer in it.?

If so are there various tappings for incoming voltage. Maybe connect for a lower voltage on the primary winding.

Also possible is to change the contactor and control circuit to one of a 240v rating. You could then feed the control circuit side only with a 240v supply and getting that side working without the motor connected.

However, remember that you will have 2 separate feeds to the machine so care must be exercised when working upon it. This could be best done with a master for both converter and control voltage circuit.

Nick

Hi, This is quite interesting as it seems to be similar to whats happening with my Bridgeport (Pancake Motor) and my Transwave.

I would value any comments or advice please as my new projects are on hold until i get up and running.

thanks and Regards Vince