Re: [CAD_CAM_EDM_DRO] Roll-your-own Phase Converter

One thing... Check to make sure your idler motor has BALL BEARINGS. Many
of the older ones have journal (sleeve) bearings. Also, the 'big', slower
motors have 'hu-mung-ous' starting torque (current) pull, as the (big)
rotor inertia is overcome. A large, old 15 hp unit may typically draw
upwards of 120 Amps for a few seconds on startup! (Ask me how I know).


RayHex



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> From: Paul Amaranth <paul@...>
>

<snip>
There seems to be a consensus that lower rpm motors make for better

> phase converters as well; 1750 are better than 3500. I picked up
> an 870 rpm 20 hp monster that probably weighs around 350lb for $10
> a few weeks ago. That one will make a dandy converter to run my
> CNC stuff (as well as the other machinery).
>
> Unless you have a very rare situation where you burn out the windings,
> almost nothing goes wrong with 3 phase motors other than the bearings,
> which are cheap and easy to replace. Buying an old 3 phase motor is
> generally a good bet, although if you wanted to be sure you can always
> check the winding resistances.
>
> Paul