Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

... 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.