Wtd: small 3 phase inverter

Gavin Oseman and others sell that size quite often on the homeworkshop.org.uk

I have a small collection, rescued over the years from industrial surplus, various makes, though all except one (Hitachi) are 3 phase input fwir.

What do you plan to drive with it ?...

Regards,

Chris

It's a pillar drill with a 1 HP star/delta motor. In the past I've re-jigged the input stage of 415/415 inverters into voltage doublers so that they work from 230 single phase, but the mid-point of the DC buss capacitors needs to be accessible so it needs a bit of poking around. Dave

Thanks Mark, I'll have a look

For 1hp, I would use at least a 1Kva inverter, preferably 2, just to be on the safe side.

The voltage doubler is s neat idea, though the input bridge diodes may need to be derated. Same for the filter caps, as the rippple current will be much, much higher than for a 3ph bridge configuration.

The way I got round the problem here was to build a 500v DC 10A psu, to drive the inverter directly into the 3ph input. It wouldn't work on those inverters with transformers for the low voltage supplies, but most seem to use switchers on the input these days. Some of the 3ph units will drop out complaining about phase failure if you drive them from

1ph, but driving them from dc seems to get round that problem. Would suggest that they use dc rail ripple to detect phase failure.

A 500v psu is not too difficult to build. An industrial 240 to 110v 10A isolation transformer with the secondary in series with the mains to produce around 360 v ac, into a screw down 25A bridge, with a couple of big electrolytics in series (from and old ups and with balancing resistors) for smoothing. A series resistor on the ac side and 3 pos power switch for soft start completes the job. Of course, very non standard connector on the output for safety and circuit breaker on the mains input. Have been using this for several years now, driving at one stage a 7.5hp motor for testing, so seems to deliver enough grunt.

Can post a schematic and pics if it would be helpfull...

Regards,

Chris

With the voltage doublers the buss caps needed increasing and the inverter derating, but the approach has worked in several different applications and no problems with the diodes thus far.

I've had some success with simply putting 415 single phase into a 3 phase inverter and increasing the buss cap but I think an external 500V DC PSU would be a bit too scary!

I was a bit suspicious of the 1HP motor rating on the pillar drill so I've just looked at it again - it's a badly-stamped 1/2 HP. Now I can't decide whether to buy an inverter or to just add a couple of capacitors and bodge a 3rd phase.

Dave