Post by thread:[EE] RE: Synchronous AC Motor Speed Control?

Tag added ... > Based on some searching around, synchronous AC motor seemed to be the most > plausible. There are 4 leads. The original circuit has two of them shorted together, > then switches AC power to one of the remaining leads to make the motor move. The > direction depends on which lead is energized. > > Naturally the motor hasn't any marking on it, so I'm guessing. If there's another > type that it might be, I'm open to more investigation! This sounds rather like the model railway engines I deal with that run on AC. One armature brush is connected to the AC source. The other armature brush is connected to the centre tap of the field winding The two ends of the field winding are connected, one at a time to the other side of the AC source, depending on which direction you want the motor to run. I believe this is also the basis of the so-called "universal motor" that has been used in power tools for a long time, and will run on AC or DC. -- Scanned by iCritical.

On Sun, Apr 22, 2012 at 12:31 PM, <spam_OUTalan.b.pearceTakeThisOuTstfc.ac.uk> wrote: > Tag added ... Thank you, been awhile since I missed that! > This sounds rather like the model railway engines I deal with that run on AC. > > One armature brush is connected to the AC source. > > The other armature brush is connected to the centre tap of the field winding > > The two ends of the field winding are connected, one at a time to the other side of the AC source, depending on which direction you want the motor to run. > > I believe this is also the basis of the so-called "universal motor" that has been used in power tools for a long time, and will run on AC or DC. Interesting. Mine has two green wires, a yellow, and a white. The two greens enter the PCB next to each other and connect to the same trace (ie they're shorted together). The white and yellow are separate. I can make the motor spin by connecting one leg of AC to the green wires, then to either the white or the yellow. The white and yellow wire seem to have a 44uF cap across them. There's also a higher power resistor around there, but I'm having a bit of trouble figuring out where it goes. Suppose I tried feeding power to green(s) and yellow. Would I potentially cause any damage if I shorted white to green or white to yellow? Thanks! Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams

> Interesting. Mine has two green wires, a yellow, and a white. The two greens enter > the PCB next to each other and connect to the same trace (ie they're shorted > together). The white and yellow are separate. I can make the motor spin by > connecting one leg of AC to the green wires, then to either the white or the yellow. > > The white and yellow wire seem to have a 44uF cap across them. There's also a higher > power resistor around there, but I'm having a bit of trouble figuring out where it > goes. > > Suppose I tried feeding power to green(s) and yellow. Would I potentially cause any > damage if I shorted white to green or white to yellow? Ah, so it is a capacitor run motor (as distinct from a capacitor start motor, where a centrifugal switch opens the capacitor circuit one the motor is up to speed, typically used on a saw bench and the like). -- Scanned by iCritical.

On Tue, Apr 24, 2012 at 4:27 AM, <.....alan.b.pearceKILLspam@spam@stfc.ac.uk> wrote: > Ah, so it is a capacitor run motor (as distinct from a capacitor start motor, where a centrifugal switch opens the capacitor circuit one the motor is up to speed, typically used on a saw bench and the like). I did a bit of searching around for "capacitor run synchronous motor", but mostly found much larger units (rated in HP). Mine is about the size of an espresso mug. Presumably if I took out the cap things wouldn't run well (or at all). Because of that I'm considering leaving the existing board in place and just tagging some leads on to it. That way the current configuration of caps and resistors stays in place. I'm still confused as to how they manage to get 2 speeds out of it. If indeed something is shorting, then there really are only two options. Assuming AC connected to the green and white wires, the yellow wire could either be shorted to white (shorting out the run cap), or to green (basically then connecting the cap directly across the AC line. Thoughts? Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams

Could you post a photo of the motor somewhere? On Tue, Apr 24, 2012 at 9:08 PM, Josh Koffman <joshybearKILLspamgmail.com> wrote: {Quote hidden}> On Tue, Apr 24, 2012 at 4:27 AM, <.....alan.b.pearceKILLspam.....stfc.ac.uk> wrote: >> Ah, so it is a capacitor run motor (as distinct from a capacitor start motor, where a centrifugal switch opens the capacitor circuit one the motor is up to speed, typically used on a saw bench and the like). > > I did a bit of searching around for "capacitor run synchronous motor", > but mostly found much larger units (rated in HP). Mine is about the > size of an espresso mug. > > Presumably if I took out the cap things wouldn't run well (or at all). > Because of that I'm considering leaving the existing board in place > and just tagging some leads on to it. That way the current > configuration of caps and resistors stays in place. > > I'm still confused as to how they manage to get 2 speeds out of it. If > indeed something is shorting, then there really are only two options. > Assuming AC connected to the green and white wires, the yellow wire > could either be shorted to white (shorting out the run cap), or to > green (basically then connecting the cap directly across the AC line. > > Thoughts? > > Josh > -- > A common mistake that people make when trying to design something > completely foolproof is to underestimate the ingenuity of complete > fools. > -Douglas Adams > >

On Wed, Apr 25, 2012 at 12:05 AM, Sean Breheny <EraseMEshb7spam_OUTTakeThisOuTcornell.edu> wrote: > Could you post a photo of the motor somewhere? This should be a couple of pics of the motor: https://picasaweb.google.com/116550046901469534071/Motor?authkey=Gv1sRgCN7krb6okfuFWA The ruler in the first picture is 6" in length. Hope that helps! Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams

The drive hub looks like it might be a ribbon drive assembly. I have seen those built with two flat motors in the assembly that are mechanically connected. That may sound inefficient but if the part is outsourced the part is bid to a spec and implementation is cost driven. On 4/26/2012 4:51 PM, Josh Koffman wrote: > On Wed, Apr 25, 2012 at 12:05 AM, Sean Breheny<shb7spam_OUTcornell.edu> wrote: >> Could you post a photo of the motor somewhere? > This should be a couple of pics of the motor: > > https://picasaweb.google.com/116550046901469534071/Motor?authkey=Gv1sRgCN7krb6okfuFWA > > The ruler in the first picture is 6" in length. > > Hope that helps! > > Josh -- John Ferrell W8CCW “During times of universal deceit, Telling the TRUTH becomes a revolutionary act” George Orwell

Varying the speed could be as simple as triac phase control of the AC input to your motor. Is there a triac or scr/bridge on the old controller? When the voltage is dropped, there is more slipage in the magnetic field, so the motor spins slower. I think what you may have is a normal capacitor run INDUCTION motor. Can you feel any cogging of magnetic poles when no power is applied? If you spin the rotor by hand, do you get anything out of the input leads? If not, its more likely and simple induction motor, as commonly used for fans, garage door openers, etc. Borrow or buy a 'fan speed control' commonly used for ceiling fans to see if the motor slows down smoothly. A fan dimmer is just like a like light dimmer, except that the pot starts out at max voltage instead of minimum, and often has a trimpot adjustment to set the minimum speed to something other than zero output.

On Thu, Apr 26, 2012 at 5:16 PM, John Ferrell <@spam@jferrell13KILLspamtriad.rr.com> wrote: > The drive hub looks like it might be a ribbon drive assembly. I have > seen those built with two flat motors in the assembly that are > mechanically connected. That may sound inefficient but if the part is > outsourced the part is bid to a spec and implementation is cost driven. Hi John, I'm not entirely sure I understand what you're talking about. Is it the metal bit on the output shaft? The top of that connects with an arm that moves the door, and there's a plastic flag in the middle for an optical interrupter. I've wondered if the metal part itself is some sort of safety clutch in case someone pushes on the door. I haven't figured that out yet though. Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams

On Thu, Apr 26, 2012 at 7:35 PM, Robert Rolf <KILLspamRobert.RolfKILLspamualberta.ca> wrote: > Varying the speed could be as simple as triac phase control of the AC input > to your motor. > Is there a triac or scr/bridge on the old controller? Well, I took another look at what I thought was a transistor and it turns out it is a BT139 triac. So that's interesting, in now we have a better idea of how they're doing it, but I'm not super interested in implementing full phase control in my circuit. I wonder if there's a way to cheat and get two speed control without going full on phase control. > When the voltage is dropped, there is more slipage in the magnetic field, > so the motor spins slower. > > I think what you may have is a normal capacitor run INDUCTION motor. > Can you feel any cogging of magnetic poles when no power is applied? > If you spin the rotor by hand, do you get anything out of the input leads? > If not, its more likely and simple induction motor, as commonly used for > fans, garage door openers, etc. This motor feels like it's got a gearbox internally, which means I can't spin the motor sadly. > Borrow or buy a 'fan speed control' commonly used for ceiling fans to see > if the > motor slows down smoothly. A fan dimmer is just like a like light dimmer, > except that the pot starts out at max voltage instead of minimum, > and often has a trimpot adjustment to set the minimum speed to > something other than zero output. Unfortunately this motor runs on roughly 18VAC, which makes it a bit harder to find a fan control for. Good thought though! Thanks! Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams

> Borrow or buy a 'fan speed control' commonly used for ceiling fans to see > > if the > > motor slows down smoothly. A fan dimmer is just like a like light dimmer, > > except that the pot starts out at max voltage instead of minimum, > > and often has a trimpot adjustment to set the minimum speed to > > something other than zero output. > > Unfortunately this motor runs on roughly 18VAC, which makes it a bit > harder to find a fan control for. Good thought though! > What do you have for AC supply now? If you have a center tapped transformer, and only want two speeds, use a relay to switch between using the full output, and half of it. Phase control is phase control A fan dimmer will work at 18VAC. You just won't get the full range of control. You won't get to 100% output because the R/C for the diac is too long at low supply voltage. If that is a problem (80% max) you can fix that by reducing the value of the C disharging into the diac to fire the triac (since you'd have a harder time replacing the pot with 1/5 the value). The alternative is to put the fan dimmer on the input to the transformer that is currently supplying the motor, but most dimmers can't handle the inductance of an unloaded transformer very well. The usual issue is lack of holding current at low values of output, which you can 'fake out' by using a 3W christmas light bulb or equivalent. This also gives you a motor power level indication.

On Fri, Apr 27, 2012 at 6:06 PM, Robert Rolf <RemoveMERobert.RolfTakeThisOuTualberta.ca> wrote: > What do you have for AC supply now? > If you have a center tapped transformer, and only want two speeds, > use a relay to switch between using the full output, and half of it. The unit is powered by an AC wall wart. {Quote hidden}> Phase control is phase control A fan dimmer will work at 18VAC. > You just won't get the full range of control. You won't get to 100% output > because the R/C for the diac is too long at low supply voltage. > If that is a problem (80% max) you can fix that by reducing > the value of the C disharging into the diac to fire the triac (since you'd > have a harder > time replacing the pot with 1/5 the value). > > The alternative is to put the fan dimmer on the input to the transformer > that is > currently supplying the motor, but most dimmers can't handle the inductance > of an unloaded transformer very well. The usual issue is lack of holding > current > at low values of output, which you can 'fake out' by using a 3W christmas > light bulb or equivalent. This also gives you a motor power level > indication. What would happen if I tried the old "reduce your soldering iron temp" trick and put a diode in line? I'd be cutting off one half of the AC cycle, but I get the feeling this won't work quite as well as I'm hoping... Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams

On Sun, Apr 29, 2012 at 4:16 AM, Robert Rolf <spamBeGoneRobert.RolfspamBeGoneualberta.ca> wrote: >> What would happen if I tried the old "reduce your soldering iron temp" >> trick and put a diode in line? I'd be cutting off one half of the AC >> cycle, but I get the feeling this won't work quite as well as I'm >> hoping... > > He would burn out the motor if he used a diode. > It would not spin. It would get very hot. That's what I figured. Oh well, it was worth the ask! Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams

Josh Koffman writes: > On Sun, Apr 29, 2012 at 4:16 AM, Robert Rolf <TakeThisOuTRobert.RolfEraseMEspam_OUTualberta.ca> > wrote: > >> What would happen if I tried the old "reduce your soldering iron temp" > >> trick and put a diode in line? I'd be cutting off one half of the AC > >> cycle, but I get the feeling this won't work quite as well as I'm > >> hoping... > > > > He would burn out the motor if he used a diode. > > It would not spin. It would get very hot. That is actually the way one can apply an electronic break to an AC motor if one needs to stop one quickly. There is a man who has invented a quick stop device to stop a table saw blade when it contacts something it shouldn't like your fingers. He says it puts a quick pulse of DC on the motor and then kills the power to it. Marti

> > > That is actually the way one can apply an electronic > break to an AC motor if one needs to stop one quickly. > > There is a man who has invented a quick stop device to > stop a table saw blade when it contacts something it shouldn't > like your fingers. He says it puts a quick pulse of DC on the > motor and then kills the power to it. > > That method wouldn't work fast enough, even with a massive DC pulse. The youtube demo of 'saw stop' shows that it uses a mechanical claw to block the blade instantly. DC method would allow the blade to rotate enough to do damage (back EMF only works with MOTION). http://www.youtube.com/watch?v=cTUOhYcw4ZY jump to 1:40 to see how it works, and why the claw has to be replaced every trigger. Small price to pay to not lose part of a hand to a blade, but not inexpensive

On Mon, Apr 30, 2012 at 11:46 AM, Robert Rolf <RemoveMERobert.RolfTakeThisOuTualberta.ca>wrote: {Quote hidden}> > > > > > That is actually the way one can apply an electronic > > break to an AC motor if one needs to stop one quickly. > > > > There is a man who has invented a quick stop device to > > stop a table saw blade when it contacts something it shouldn't > > like your fingers. He says it puts a quick pulse of DC on the > > motor and then kills the power to it. > > > > That method wouldn't work fast enough, even with a massive DC pulse. > The youtube demo of 'saw stop' shows that it uses a mechanical claw to > block > the blade instantly. DC method would allow the blade to rotate enough to do > damage (back EMF only works with MOTION). > > http://www.youtube.com/watch?v=cTUOhYcw4ZY > jump to 1:40 to see how it works, and why the claw has to be replaced every > trigger. > Small price to pay to not lose part of a hand to a blade, but not > inexpensive. >

> The youtube demo of 'saw stop' shows that it uses a mechanical claw to > > block the blade instantly. DC method would allow the blade to rotate > enough to do > > damage (back EMF only works with MOTION). > > > > http://www.youtube.com/watch?v=cTUOhYcw4ZY > > jump to 1:40 to see how it works, and why the claw has to be replaced > every > > trigger. > > Small price to pay to not lose part of a hand to a blade, but not > > inexpensive. > > --

> > > > Having used a SawStop, I personally _hate_ them. > > > > Ummm, why? They appear to work exactly as advertised. > > > Yep, exactly as advertised. It will take a $200 module and crash it into your $50 blade, destroying both, the instant the blade touches anything even remotely conductive. Slightly damp wood? BANG. A piece of circuit board with a trace on it? BANG. Carbon fiber composite? BANG. A piece of plywood with a staple in the edge? BANG. After the fourth time, I bought a $200 cheapo saw that I could actually USE.. -Denn

On Mon, Apr 30, 2012 at 6:12 PM, Denny Esterline <desterlineEraseME.....gmail.com>wrote: > > > > > > > Having used a SawStop, I personally _hate_ them. > > > > > > > Ummm, why? They appear to work exactly as advertised. > > > Yep, exactly as advertised. It will take a $200 module and crash it into > your $50 blade, destroying both, the instant the blade touches anything > even remotely conductive. Slightly damp wood? BANG. A piece of circuit > board with a trace on it? BANG. Carbon fiber composite? BANG. A piece of > plywood with a staple in the edge? BANG. > > After the fourth time, I bought a $200 cheapo saw that I could actually > USE. Thank you for that valuable user feedback. I had been considering a purchase of this saw, but I can see that would be a costly mistake

{Quote hidden}> > > > > > > > > Having used a SawStop, I personally _hate_ them. > > > > > > > > > > Ummm, why? They appear to work exactly as advertised. > > > > > > Yep, exactly as advertised. It will take a $200 module and crash it into > > your $50 blade, destroying both, the instant the blade touches anything > > even remotely conductive. Slightly damp wood? BANG. A piece of circuit > > board with a trace on it? BANG. Carbon fiber composite? BANG. A piece of > > plywood with a staple in the edge? BANG. > > > > After the fourth time, I bought a $200 cheapo saw that I could actually > > USE. > > > Thank you for that valuable user feedback. > I had been considering a purchase of this saw, but I can see that would be > a costly mistake. > -- > Don't get me wrong, it WILL save your fingers. And in the right environment it may be wholly worthwhile, perhaps a cabinet shop or something where the materials being cut are well controlled. But I tend to use a saw in a lot of ways that would make a product liability lawyer wince, so it definitely is not for me. Mount a fence on at an angle to the blade and use it to mold cove -yep. Put on a metal cutting abrasive blade and slot 1/4" wall box tubing - yep. Bolt a pulley on instead of the blade and run another contraption -done that too. :-) None of the above with a SawStop... -Denn

On Thu, May 3, 2012 at 9:10 AM, Electron <EraseMEelectron2k4infinito.it> wrote: > At 20.46 2012.04.30, you wrote: > >http://www.youtube.com/watch?v=cTUOhYcw4ZY > > wow.. but how does the system "understand" that it's meat and not wood? > There's a couple of possibilities for the underlying mechanism, but basically it puts a static charge on the blade or between the blade and the other metal parts. When it sees that charge change because of something conductive... Mechanically, it has a fairly stiff compression spring tied down with some thin wire/foil tape and it dumps a large cap through it to burn the wire when they want to fire. It has a TI MSP430 dsp chip in it... -Denn