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Cheap AC motor speed controllers?

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John Swift:
Hi Rich

the universal motor works on either a DC or AC supply
http://en.wikipedia.org/wiki/Universal_motor

you will need to use an over size variac transformer to ensure you don't overload the winding
at low speeds

the ebay controller should work but going by the pictures of the minimal components on the  PCB and the lack of an control IC 
I expect its more of a lamp dimmer
( like figure 4 - http://sound.westhost.com/lamps/dimmers.html )

I would not expect the ebay speed control  has any way to compensate for changes in mechanical load on the motor
but may be OK for use with the biax tool

as an example this speed control circuit -  http://www.aaroncake.net/circuits/acmotcon.asp
has a feedback circuit to measure the motor current and compensate for variations in load
the voltdrop across R13 is a measure of the motor current
to run of 240V some component values will need changing

another example - http://www.velleman.co.uk/manuals/k2636.pdf


    John

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