Seems to me this sort of technology would be very affective for any type of motor. Anybody know a good source for one for 110 AC motors? A rheostat type works if its go brushes, but so many motors these days are brushless. Also, because pulse width is always deliverying full voltage (less reaction time of the circuit) it is not as hard on your motor.
I know that Minn Kota introduced it on DC electric trolling motors years ago. How about for AC and/or generic for DC motors?
Shaded-pole motors (up to 1/10th HP or so) can be controlled to some extent this way, but the torque curve on them is really weird, so you need closed-loop speed control. that means an RPM sensor on the motor. Motors that have a start winding and switch, or those with a run capacitor, do not work well at variable speed.
For real speed control, a 3-phase motor and a VFD is the way to go.
Jon
There was a circuit years ago using Triacs to control speed on AC motors, like drills. Was a pulse width modulation and you only gave the max part of the sine wave to the motor. Texas Instruments has a lot of speed and power control chips for AC motors. Most of the major appliances and HVAC vendors use them.
This is how the common industrial DC motor speed controllers work, and have for many years. Minn Kota may have been the first to apply it to trolling motors, and good for them, but surely they're not the innovators of the principle.
That was the MinnKota "Maximizer". When mine quit working, I was told that the design was so proprietary the authorized service places had no schematics -- they had to be returned to factory for service. Screw that, I wanted to go fishing. After tracing the circuitboard, I understood why it was so secret: if I'd designed that piece of crap I'd certainly want it to be a secret! I fixed it simply by snipping out a bunch of unnecessary stuff. It was based on the 3524 chip, introduced by Silicon General in the mid-70's and subsequently offered by several vendors. Nothing wrong with that, but the "designer" of the Maximizer was clearly clueless, a tinker and hacker. This chip is now on "lifetime buy" status from National Semiconductor but is still active at ST Semi.
Why are there questions re. closed loop servo controllers? I can think of nothing I would ever use wherby the speed feedback of the rotating shaft would be necessary.
This is how the common industrial DC motor speed controllers work, and have for many years. Minn Kota may have been the first to apply it to trolling motors, and good for them, but surely they're not the innovators of the principle.
I haven't seen drive motor tach feedback on any circuits smaller than industrial DC drives in the 20-60+ HP range, Robert.
Most small variable speed drives don't use tach feedback, as it's not required in most applications, and would definitely raise the cost of production.
Variable speed is a separate function than precision speed control. Armature speed sensing can be accomplished with sense/regulate circuits instead of external signal inputs from a tach.
nothing I would ever use
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
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.
I wondered about the Maximizer marketing hype, Don. It seemed that they were really spreading it on thick.
Chopping the power supplied to the load has become a common method of efficiency in many devices today, but back then, not that many devices were being introduced into the consumer market.
Linear speed regulation was often wasteful of power in many applications, but chopping has has been the solution to almost eliminate inefficiency.
What about inductive kicks with that approach in a motor controller, Bill? Are they not a problem to the semiconductors, or are they dealt with in the circuitry?
-- Ed Huntress
There are often diodes used with SCRs, Ed. I don't know about different quadrant-type controllers that may actually utilize any back-EMF for useful purposes, but I suspect that there are.
many of the Minarik controllers support tach feedback as well as reverse EMF feedback - the cheap harbor freight type controllers don't, but the better ones from other sources do as well
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.
very common on treadmill controllers
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.
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
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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