Clarke PC40 Static Converter query?

[Philip MajorParticipant @philipmajor52482]

Hi all, for many many years I successfully used an old Static converter to power my 3 phase machines, considering its age i decided it was time to move it on, as I thought it was getting cranky.

So I bought a Clarke PC40 converter from machine mart. The machine has 3 switch to provide range 0.5 , 1.0 and 2.0 hp therefore up to 3.5 hp

I don't have any machine motor greater than 1.5hp, most 1.0 hp.

The issue, to run my 1.5hp Lathe I need to 2.5 hp setting, miller bothe vertical and horizontal similar, however my surface grinder (Jones and Shipman 540) doesn't like any setting except full 3.5 and not happy with that!

Experiences with this converter, and or advice appreciated

[Philip MajorParticipant @philipmajor52482]

Experience of using the Clarke PC40

[not done it yetParticipant @notdoneityet]

Too late now, I suppose, but my advice would have been to convert your motors to delta configuration and buy 5 or 6 VFDs. So many programmable benefits.

[Clive FosterParticipant @clivefoster55965]

A quick look at the PC40 circuit diagram suggests that it doesn't have an automatically switched start boost capacitor to generate extra phase shift during the run-up from stationary to around half or three quarters speed. Without this capacitor run up performance will be all over the place and highly dependant on load.

Bottom line is you will need to use a higher power setting than the motors actual power to get it going. As a result the motor will end up running with more capacitance than desirable for the quoted power. So the motor may well be very unhappy due to excessive phase shift.

Best cure is to permanently connect a decently powerful idler or pilot motor to make a low rent crypto rotary converter. 4 hp should do it best but anything between 2 hp and 5 hp will be an improvement. Set the switches so it starts up and runs smoothly and use the machine controls as per normal once the converter is running.

Back in pre (affordable) VFD days I made a fair few static converters for folk using whatever components I could get for not too many £ and ended up with a healthy respect for how tricky it could be to get one going well. Towards the end I settled on an effective and near bullet proof design with automatic start boost and no switches for finger poken and fiddling. Usually decent when configured for a range from 3/4 to 2 hp. But sometimes a motor just didn't want to play. No way on earth that I'd care to go true commercial with a product range.

Clive

[Philip MajorParticipant @philipmajor52482]

Hi Clive, thanks for this, once again I have learned you get what you pay for.

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