Pulse Width Modulation Speed Control

I've seen motor drive circuits that support tach beedback Bill, but I don't have any imformation or experience regarding speed regulation that indicates
the differences in performance between a drive with tach feedback and without (for any particular model).
Most of us can be grateful that the majority of drives operate well without tach feedback, since matching a tach to a particular drive, and then having the space to utilize them, would complicate a lot of the used (or surplus) drive purchases.
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WB
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On Wed, 31 Dec 2008 13:27:06 -0500, "Wild_Bill"

very common on treadmill controllers
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I've only had a few treadmills apart, Clare, but now that you mention it, I've seen optical detectors on the walking belt motor armature shaft before. I wasn't making the association from tach to detector. The use of a detector and a perforated/segmented plastic disk are probably cheaper than an actual tach generator. Runout or alignment on a segmented disk isn't a serious problem.
Also, there have been detectors on the incline motors, for a positioning purpose, not for speed feedback.
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On Wed, 31 Dec 2008 18:06:19 -0500, "Wild_Bill"

That mechaism IS an optical tachometer.
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Robert Swinney wrote:

Funny you should say that - I'm in the process of using just such. I'm putting an independent feed on my lathe. I'm using a DC motor, servo amp, & tach feedback. The usefulness here to to be able to run very low speeds for fine feed at low spindle speed, without bogging down the motor. Bogging down is exactly what it does without feedback.
Bob
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PWM is a common method used for a lot of different types of electrical devices (tools, machines), Bob.
The home shop type SCR speed controls that many HSMs use, such a KB Electronics use a much higher component count for speed control and regulation, than say, a generic variable speed device like a triac router variable speed device.
The typical basic AC universal motor variable speed circuit may use about 6 actual components.. triac, diac, capacitor (or 2), resistor (or 2) and a speed pot/switch. This circuit may allow the user to change the operating speed, but has no control over the speed regulation at a selected speed. A KB DC variable speed control with speed regulation may have closer to 80 components not including the internal circuitry of the ICs.
Speed control for single phase AC induction motors involves more functions than chopping the AC supply power. Oriental Motors of Japan has variable speed modules with speed regulation for their small (up to about 1/8 HP) PSC permanent split capacitor AC motors.
There are other speed control and regulation modules for single phase AC motors, but they aren't common, so the use of DC motors is often an easier/cheaper choice.
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Wild Bill sez:
"There are other speed control and regulation modules for single phase AC motors, but they aren't common, so the use of DC motors is often an easier/cheaper choice."
God didn't mean for induction motors to have speed control or else he'd a made Tesla a Baptist.
Bob Swinney
PWM is a common method used for a lot of different types of electrical devices (tools, machines), Bob.
The home shop type SCR speed controls that many HSMs use, such a KB Electronics use a much higher component count for speed control and regulation, than say, a generic variable speed device like a triac router variable speed device.
The typical basic AC universal motor variable speed circuit may use about 6 actual components.. triac, diac, capacitor (or 2), resistor (or 2) and a speed pot/switch. This circuit may allow the user to change the operating speed, but has no control over the speed regulation at a selected speed. A KB DC variable speed control with speed regulation may have closer to 80 components not including the internal circuitry of the ICs.
Speed control for single phase AC induction motors involves more functions than chopping the AC supply power. Oriental Motors of Japan has variable speed modules with speed regulation for their small (up to about 1/8 HP) PSC permanent split capacitor AC motors.
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WB
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