On Sep 29, 7:27*pm, "DoN. Nichols" wrote:
On 2008-09-29, Vernon wrote:

On Sep 27, 12:38*am, Joseph Gwinn wrote:

* * * * [ ... ]

Buy a VFD to run the mill. *Three phase works very well. *Many VFDs can
be driven from 220 volt single phase, with a derating.

* * * * [ ... ]

I'm still trying to wrap my electrically challenged brain around the
differences / advantages / disadvantages between rotary converters and
VFDs. *As soon as I'm able to articulate an intelligent question I'll
ask one!

* * * * Quick and dirty:

VFD
Pros: * Gives you the ability to vary speed while running over a wide
* * * * range.

* * * * Very efficient compared to a rotary converter.

* * * * Can be set up to accelerate the motor over a programmable time,
* * * * so you don't draw as heavy a current from the wall to get the
* * * * motor up to speed.

* * * * Quiet.

Cons: * Does not like having switching between the motor and the VFD,
* * * * this generates high voltage spikes during the switching, and can
* * * * blow the output transistors.

* * * * So -- rewire the switch on the machine to command
* * * * start/stop/reverse to the VFD's control terminals and you are
* * * * fine for driving a *single* machine at a time. *Best to have a
* * * * separate VFD per machine -- among other things so you can adjust
* * * * the speed of one without affecting the others.

ROTARY Converter
Pros: * Fairly simple to make.

* * * * Can be tuned to minimize current draw and maximize three phase
* * * * quality.

* * * * Can easily run multiple machines (if large enough) because it
* * * * does not care whether you have switches between it and the load
* * * * motors. *The other machines running actually add to the capacity
* * * * of the RPC so you can handle a larger motor on the next machine
* * * * turned on.

* * * * If the idler motor in the RPC is enough larger than the motor in
* * * * the machine, it can handle "plug" reversing (switching to
* * * * reverse while at full speed forward). *If the idler motor is not
* * * * large enough (say the same HP as the machine's motor), attempts
* * * * to plug reverse sometimes result in the RPC reversing instead of
* * * * the machine. This can get exciting if your machine is about to
* * * * hit something (more likely on a lathe than a mill).

Cons: * Wastes power idling when there is no load turned on, so you
* * * * probably want to remember to turn it off.

* * * * Some of that waste power is turned to noise which can be
* * * * annoying (but which will remind you to shut it off when you are
* * * * done -- if you don't banish it to a box outside the house to
* * * * keep the shop quieter. :-)

* * * * Draws a heavy current spike when first starting before you ever
* * * * turn on your machine.

* * * * Depending on the nature of your particular motor, you may need
* * * * to provide additional fan cooling.

* * * * There are probably other things which I have not thought of, but
others may add to the list.

* * * * Enjoy,
* * * * * * * * DoN.

--
*Email: * * | Voice (all times): (703) 938-4564
* * * * (too) near Washington D.C. |http://www.d-and-d.com/dnichols/DoN.html
* * * * * *--- Black Holes are where God is dividing by zero ---

Holy Smokes. You guys are awesome!

Vernon