On 03/26/2013 05:58 AM, Scott Dorsey wrote:
In article , jim beam wrote:
On 03/25/2013 05:57 PM, Jamie wrote:
jim beam wrote:

Another way to do this, is to have an inductor on board with the
speed control circuit. You would PWM that inductor in series to a filter
cap
on the output which will then give you a clean variable DC. THe inductor
will be doing all variable voltages.

ok, as i understand it, and as i said to scott earlier, this is a
problem because it mungs low speed motor start and low speed torque.

Not really, it's feeding the motor with variable DC from that integrator
stage.

i understand that - and variable voltage is the problem. the secondary
[bordering on primary in some applications] advantage of pwm is low
speed start and torque. if a motor starts at low dc voltage, not only
is the start speed inconsistent, it has little torque. pwm can start a
motor slower and at much higher torque. it's a big deal.


It's not much different than a big rheostat in terms of starting
torque. It's just more expensive and less reliable and quieter.
--scott



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