Single phase or Inverter

This topic has 7 replies, 6 voices, and was last updated 31 January 2011 at 18:18 by John Olsen.

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30 January 2011 at 19:21 #63316
Peter Simpson 2
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@petersimpson2
Hi Guy’s

I have just aquired a nice Meddings powered hacksaw which has a 3 phase, dual voltage motor. I’m not sure if I should install an inverter as I have on my lathe and milling machine of change the switch gear to single phase. An inverter on a mechanical saw seams a little over the top. what do think ?

Best regards

Peter
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30 January 2011 at 19:21 #5389
Peter Simpson 2
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@petersimpson2
Powered Hacksaw
30 January 2011 at 20:43 #63319
Peter G. Shaw
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@peterg-shaw75338
Hi,

I understand that it is possible to use the same inverter for a number of machines by using a system of switching. After all, if you are a lone worker, you can only (safely) use one machine at once.

Regards,

Peter G. Shaw
30 January 2011 at 22:17 #63320
John Stevenson 1
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@johnstevenson1
Peter, seeing as a power hacksaw only needs a limited amount of power what about converting the existing 3 phase motor to run on single phase using a capacitor on the dead leg.

True it will be derated but I’m sure that it will be powerful enough.

All it will cost to find out is to rob a capacitor out of a scrap florry essence tube.

John S.
30 January 2011 at 22:18 #63321
John Haine
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@johnhaine32865
Um, I don’t think fluorescent tubes have capacitors do they? Inductors, yes.
30 January 2011 at 22:59 #63322
John Olsen
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@johnolsen79199
The flourescents will have a capacitor too but I don’t think it would be up to the job.You want something more like you find on a motor, and it want to be continuously rated too.

If you set the three phase motor up to run on single phase, you will get , in theory, about 2/3 of the power. Practically, what you will get is in my experience more than enough. I have an 18 inch shaper, one setup that I have tried with that limited it to a quarter of the nominal horsepower, eg 3/4 hp out of a 3 hp motor. You would be surprised how big a cut you could still take. I more usually run that machine with a single phase set up, without the starting capacitor. This means giving the pulley a suitable kick at the right moment. Running like that, eg nominally about 2/3 of the original power, it has taken a cut of 0.250 thou across a piece of cast iron bar. So lack of power is not usually a problem.

regards

John
31 January 2011 at 09:16 #63327
KWIL
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@kwil
Do you really mean 1/4 thou?
31 January 2011 at 18:18 #63356
John Olsen
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@johnolsen79199
Hi Kwil, ooops, I should engage brain first shouldn’t I. No that should have been 250 thou or 1/4 of an inch. The machine took that cut in its stride without the slightest sign of distress. I am not sure how much more it could take, it gets expensive finding it enough metal to feed it at those sort of cut sizes. Very handy when a big slab of metal needs cleaning up, and leaves a much nicer finish than a milling machine.

regards

John
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