Homebrew PCBs

I am thinking of changing the circuit/code in Microchips app note AN958 
to slow the motor down/

Bob H

On 5/1/2010 10:24 PM, Slavko Kocjancic wrote:
> ... and little more.
> For now in small laminators I see just smal synchronous motor, and in
> one big one I see squirel cage shaded pole motor. As all of these are
> frequency dependent the regulation is not so easy. Pwm wil not work.
> These motors need sinevave signal of changing frequency. Even worse. If
> we lower frequency then we MUST lower the voltage too or we will burn
> that motor. When frequency is turned up the voltage is turned up too. -
> the power must stay same. In low frequency the indictance has less
> influence than pure resistance and in high frequency the inductance have
> more impact. But going high is not good idea for that's motors as they
> in most cases doesn't have good lamination and high frequency eddy
> current's will heat up the core.
>
> The easy way to go trought that problems is to put on/off circuit and
> this should triger in zerro crossing or overheat will be here again.
> Let's just pass 50 periodes of AC and after that block 50 periodes and
> we have 50% slower transfer. The simple 555 and zero crossing
> photocoupler with triac can do that. Just don't go way below 50 cycles
> of on period.
>
>
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