[ATM] Re: ATM Digest, Vol 11, Issue 15

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

artbianconi@blast.net wrote:
> That I did not kill myself is an act of good fortune, little else 
> for my primary use was for hot wiring foam cores used in making 
> aircraft wings and the device, which looks much like a cheese 
> cutter, had a bare wire, that was heated from the Variac and thus 
> exposed me to a shock potential.

Art, we're glad you're still with us.  You've got lots to explain 
about composites, so don't electrocute yourself just yet!

Others have covered the ins and outs of variacs, so I don't need to 
restate all of it.  Best to think of the variac as a variable AC 
source, which can be up to full line voltage, and treat it with the 
appropriate respect.  It CAN kill you.

That's why my variac and other components are in a waterproof box. 
Everything is grounded, and it's plugged into a grounded GFI outlet. 
The DC that powers the motor (while dangerous, but much less so) is 
fully isolated in an insulated wire, and is firmly connected with 
cable clamps.  That should remove nearly all of the danger.  I believe 
my toaster is far more dangerous.

> If your intention is to power an ac motor and adjust it's speed, 
> you'd best be advised against that. The speed is fixed as is the 
> RPM. Attempts to reduce the voltage will cause internal temps 
> will eventually destroy the motor. DC motors are the ones best 
> for regulating speed electrically but in the hp range needed to 
> drive a polishing table, they are costly and you will still need 
> pulleys to step the speed down further.

Nope, it's a DC motor.  For anyone interested, here's a great page on 
how to do this:

   http://www.ggls.org/DCPower/

Very simple, and very effective.  Quite a bit of torque at low RPM on 
the turntable.

I'll save the AC motors I have to build some curve generating 
equipment someday......

	Mike

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