Thanks Jinx,

Just the sort of thing I was looking for, I am controlling the air input for
a furnace so I would like to run down to say 10% before I stop and by the
looks of things this circuit looks like it should do it. I don't expect a
small 50w motor will mind stepping  around too much. If I feel real keen I
might write some code to pwm a sine wave but I expect the binary control
will do fine for a start.

regards

Lee



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jinx
Sent: Wednesday, 27 February 2002 11:20 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: AC Motor Control


> For 0 to 100 %  speed variation you need a frequency variator
> and not a dimmer

Hi Vasile, I was going to suggest that but it seemed like a lot
of work for just a fan. You're right that a synchronous motor will
not be successfully controlled over a wide range with power
chopping. Perhaps you'd like to comment on this circuit, which
rectifies the AC mains to DC that the PIC can then apply to the
motor

o/p transistors are BU508Ds or similar (700V 8A). Resistors
"a" to "d" might not need not be there and "e" and "f" could
possibly be replaced with 10n caps. Snubber across the motor
is 100 ohms + 100n

I was helped a while ago with this circuit by Roman and Peter Peres

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