Joe wrote:
> I use the Silicon Chip VFD
>=20
> http://www.siliconchip.com.au/Issue/2012/April/1.5kW+Induction+Motor+Spe
> ed+Controller%2C+Pt.1
>=20
> with a single-phase scrollsaw which has an internal fan. For longish
> periods of use at slower speeds I add external fan cooling. It may turn
> out that a fan will be needed with the clock motor, assuming it has
> useable torque at 100Hz.

Nice circuit, in some ways overkill but looks not too difficult to make.

Wondering if there's a simpler method of doubling the frequency. Thought ca=
me to=20
mind of a full wave rectifier followed by a DC blocking cap. See sketch par=
t way=20
down this page http://www.edaboard.com/thread256733.html. In context they a=
re=20
talking about 100MHz not 100Hz, though principal should be the same. Bad at=
tempt=20
at drawing the double freq waveform, but you get the jist of things from th=
e circuit.

Voltage will be much reduced, and probably not too symetrical. May need a s=
tep up=20
transformer. Nice if the resistors can be omitted or selected to waste mini=
mal=20
power. Maybe the cap value could selected to resonate with the inductance o=
f the=20
motor at 2x input freq, with the hope of improving the shape of the wavefor=
m and=20
efficiency.


--=20
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