Hi Jinx,

> IIRC, the only way was to rectify the AC and then
> convert the HV DC back to AC at the new frequency.
I think I'll look into this direction.

> All of the rest I can use with a pretty standard SCR
> controller
> (I've a gif of the circuit if you want to take a look)
Yes, please.

> I can imagine a 20krpm router bit run at slow
> speed would not do such a clean job,
But a 76 mm bimetal hole saw fitted on a hand drill ought
to run at 115 RPM for MS, 55 RPM for SS, 170 for Aluminum
and 1800 RPM for wood (according to manufacturer's
datasheet).

Thanks,
Mohit.



----- Original Message ----- 
From: "Jinx" <joecolquitt@clear.net.nz>
To: "Microcontroller discussion list - Public."
<piclist@mit.edu>
Sent: Friday, September 23, 2005 2:38 PM
Subject: Re: [EE] VFD for 1 phase AC motor


>> Is it possible to design a single phase VFD to control
>> speed
>> of motors - 220VAC, 1Ph, 50 Hz, 2kW?  The designs I've
>> found are controllers for 3 phase motors.
>
> Hi Mohit. This topic has been covered before, and at that
> time
> the conclusion was that designing such a circuit is
> fraught with
> difficulties. IIRC, the only way was to rectify the AC and
> then
> convert the HV DC back to AC at the new frequency. I'd
> have
> been interested myself in such a speed control, as all the
> ones
> I've seen have been either 3-phase, expensive, or both.
> Apart
> from tools, I've a few synchronous motors that could use
> VFD
>
>> I've used triac based controllers, but want something
>> with
>> better control
>
> Only my lathe and drill press use synchrounous motors, and
> they are the only ones to use belt selection for speed
> control.
> All of the rest I can use with a pretty standard SCR
> controller
> (I've a gif of the circuit if you want to take a look)
>
> I can't say I've found it lacking in any great respect. It
> has
> feedback to keep the torque up as much as possible, and is
> OK at slower speeds. This particular one doesn't hunt too
> much either. As well as the material you also have bear in
> mind
> the cutting edge. I can imagine a 20krpm router bit run at
> slow
> speed would not do such a clean job, but you probably know
> that anyway
>
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