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Looking for a motor speed control circuit.

Can anyone please point me to a web page that has the
schematic of a speed control circuit with these features ?

1. It should be analog, not microprocessor-based. No
tachometer.

2. The motor will be a mains-operated brushed DC type of
1 or 2 hp, with a separate field winding. The load will be
fairly constant, but speed should not be greatly affected
by mains voltage fluctuations.

3. It doesn't have to be super-precise, but should be
somewhat more sophisticated and precise than a typical
drill speed control with an SCR plus four or five passive
components.

4. It should have a good starting torque as the load will
be permanently coupled.

5. Speed control range should be roughly from one-third to
two-thirds of the full rated speed.

6. If possible, I'd like to avoid dedicated speed control
ICs even if they're analog.

I'll probably be able to adapt a good general design to my
particular requirements. I'm not entirely clueless about
the theory, but rather long out of touch with practical
designing. I have searched with Google, but the two dozen
or so results I checked did not have what I need. Thanks
in advance for any help.
 
Can anyone please point me to a web page that has the
schematic of a speed control ,,,
1. It should be analog, not microprocessor-based. No
tachometer.

For a DC motor of 1-2 horsepower, you might want to consider
the simple and rugged autotransformer; just rectify the AC and
feed it to the motor.

Assuming you have a 180V DC rating, a 20A autotransformer
and suitable 120V branch circuit could do ya; it'll cost more
than a commercial DC motor control, but eBay or craigslist
can solve that problem.
 
R

Rich Grise

Jan 1, 1970
0
Can anyone please point me to a web page that has the schematic of a speed
control circuit with these features ?

1. It should be analog, not microprocessor-based. No tachometer.

2. The motor will be a mains-operated brushed DC type of 1 or 2 hp, with a
separate field winding. The load will be fairly constant, but speed should
not be greatly affected by mains voltage fluctuations.

3. It doesn't have to be super-precise, but should be somewhat more
sophisticated and precise than a typical drill speed control with an SCR
plus four or five passive components.

4. It should have a good starting torque as the load will be permanently
coupled.

5. Speed control range should be roughly from one-third to two-thirds of
the full rated speed.

6. If possible, I'd like to avoid dedicated speed control ICs even if
they're analog.

I'll probably be able to adapt a good general design to my particular
requirements. I'm not entirely clueless about the theory, but rather long
out of touch with practical designing. I have searched with Google, but
the two dozen or so results I checked did not have what I need. Thanks in
advance for any help.


Try a web search on "pulse-width modulation" "motor speed control", and
whatnot.

I once built an astable with a pot in the middle, so I could dial the
duty cycle from about 5% to about 95%. I only ran a little bitty 12V,
150 mA motor, but that could be easily scaled up to a few KW, if you're
handy with high-current stuff.

I would recommend against a variac, because when you reduce a motor's
voltage, the torque decreases dramatically. With PWM, you get full
torque all the way down to 0 RPM.

Good Luck!
Rich
 
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