Re: The tape-O-matic...

Jeff Barlow wrote:

> From: "Jeff Barlow" <barlow@...>
>
> Ah, I see. Oops. Let's hope he waited for the second opinion or that the
> SCR's are beefy and the fuses fast. Anyway, all he needs is a little phase
> order indicator. They must be in the Grainger catalog, somewhere.
>
> Jeff
>
> -----Original Message-----
>
> From: Jon Elson <jmelson@...>
>
> Jeff Barlow wrote:
>
> Not necessarily so. That vintage would likely have an SCR cycloconverter
> for a variable speed spindle drive. The control logic of the cycloconverter
> needs to know the order in which the input phases are coming in to select
> which SCRs to trigger at what time. If the input phase sequence is wrong
> it would be firing SCRs when the phase angle is all wrong, and causing
> conduction when high currents would flow. It shouldn't cause damage
> other than some blown fuses, but it depends on the safety factor built
> into the design.

Well, actually, things aren't that bad, because of new developments in
power semis, and control systems. I've got a 1 Hp variable speed
drive on my mill made by Magnetek, which is absolutely wonderful.
Although it is not rated for it, it works perfectly well on single-phase
240 V input, and drives a 1 HP 3-phase motor from rediculously slow
to too fast, and (with the option module) will take a 0-10 V analog
command signal for variable speed control from the CNC. I got
mine on eBay, it was a dealer's sample, and had all the options, for
about $160. So, as long as his motor is a normal, 3-phase 220 or
440 Volt motor, he could just chop out the antiquated cycloconverter
and put in a modern, 6" cube that will be more flexible and more
reliable, if he has trouble with the existing unit.

If the spindle is DC (not real likely at that vintage) other controls are
available to replace aging power electronics.

Jon