Pulse Width Modulation Speed Control

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?
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Bob La Londe wrote:

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
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A vfd controller can be (many can be) used on single phase as well. Martin
Jon Elson wrote:

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On Tue, 30 Dec 2008 13:41:36 -0700, Bob La Londe wrote:

http://curtisinst.com/index.cfm?fuseaction Νatasheets.dspListDS&CatID=1
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http://www.techbriefs.com/component/content/article/2453
Electrical engineers use j for the square root of -1 in the Q (quadrature) axis because i is current intensity.
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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.
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    Most drills are brush type motors -- AC/DC, not AC induction motors.
    For the brush type, they work fairly well.
    For induction motors, they work very poorly at frequencies much off from the design frequency (60 Hz US, 50 Hz UK -- both are close enough so they can be used mostly interchangeably as long as there is enough iron in the motor to handle the slightly lower frequency.
    For a VFD (frequency synthesis via PWM) to work well, you want a true three phase motor.
    Enjoy,         DoN.
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Bob La Londe writes:

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.
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On Wed, 31 Dec 2008 03:30:50 -0600, Richard J Kinch

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.
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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.
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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
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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.
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WB
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On Wed, 31 Dec 2008 14:43:09 -0500, "Wild_Bill"

The Maximizer really did deliver claimed performance. The problem was a really kludgy temperature-sensing sub-circuit. PWM control is now integral to most trolling motors.

I think the introduction of switchers in PC (personal computer) supplies was about in that time frame more or less.

Ayup. Aerospace was doing that in the '60s. Detroit was doing it before that,without electronics: the venerable electromechanical voltage regulator was a switcher.
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Don Foreman wrote:

Millions of the 3524 family of ICs were used in PC, XT, AT & ATX power supplies. Of hundreds of dead computer power supplies I've looked at, I have only found a few bad ICs. Most computer power supply failures were bad fans, high ESR electrolytics, or shorted switching transistors. I used to salvage the requlators, but now I just pull the bad parts off the PC boards and stuff them into banana boxes till I need parts.
NTE has the NTE1720 in a pinch.
http://www.nteinc.com/specs/1700to1799/pdf/nte1720.pdf
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On Thu, 01 Jan 2009 01:40:14 -0500, "Michael A. Terrell"

One of my sons is a silicon peddler repping ST. Nuff said? <G>
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Don Foreman wrote:

Where is the challenge in that? Anyway, Silicon has really small pedals. :)
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haha. What did all the junk "do"?
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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.
Bob Swinney
Bob La Londe writes:

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.
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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.
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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

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