shaded pole motor control
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From: Phil Hobbs on 2 Jul 2010 14:48 On 7/2/2010 11:41 AM, Fred Abse wrote: > On Thu, 01 Jul 2010 18:29:27 -0400, Phil Hobbs wrote: > >> That's not a mag amp. Mag amps use DC to control AC. > > By definition? Seems a bit narrow. > > It's still controlling current using another current in a magnetic device. > If you want to redefine what "magnetic amplifier" means, go ahead. That just isn't what it means to the rest of the world. (Not that the rest of the world cares too much about mag amps at this point.) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: John Larkin on 2 Jul 2010 16:05 On Fri, 02 Jul 2010 08:41:12 -0700, Fred Abse <excretatauris(a)invalid.invalid> wrote: >On Thu, 01 Jul 2010 18:29:27 -0400, Phil Hobbs wrote: > >> That's not a mag amp. Mag amps use DC to control AC. > >By definition? Seems a bit narrow. > >It's still controlling current using another current in a magnetic device. Amplifiers amplify, which means using a small signal to control a bigger signal. A magnetic amplifier does the amplification magnetically. A regular transformer, operating as such, is not a magamp. John
From: JosephKK on 3 Jul 2010 12:01 On Thu, 1 Jul 2010 06:18:49 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On Jul 1, 7:06 am, "JosephKK"<quiettechb...(a)yahoo.com> wrote: >> On Tue, 29 Jun 2010 17:00:03 -0500, "ontherails" >> >> >> >> >> >> <peter.elbro(a)n_o_s_p_a_m.btinternet.com> wrote: >> >> >>Does anyone have experience with speed control of a small shaded pole >> >>motor about 25W, with a ghastly PF of about 0.36 ?. >> >> >> This drives the water circulation pump in an experimental setup much too >> >>hard, and the churning >> >>measurably heats the water. >> >> >>I thought a variable frequency inverter might be nice, but wondered how >> >>sinusoidal it would need to be. I doubt that a simple phase shift let-it- >> >>slip-more controller, would be good enough. Works for fans up to a point. >> >> >>Rather than suck it and see, I thought I'd politely probe the brains of >> >>the experts first. >> >> >>All the best >> >>Ian Macmillan >> >> >Use my variable inductance controller. Carry out this simple experiment to >> >see how it works. Get a 100VA transformer, something like 240V to 40V. Put >> >the 240V windings in series with the motor and connect to the mains - >> >nothing happens. Short the 40V windings - motor runs at nearly full speed >> >but you are still working with AC. >> >> >Put a bridge rectifier on the 40V windings and short the DC output. Motor >> >runs at nearly the full speed it did before but now you are working with >> >DC. Put a transistor (I normally use a darlington - TIP121 for a 40V >> >secondary and add simple control electronics. You can normally get up to >> >about 90% full speed. >> >> >Approximately 10% losses occur in the transformer, bridge rectifier and >> >darlington. This could be reduced by using a higher voltage secondary and a >> >MOSFET when the losses could be 5% or lower. The control electronics side >> >is isolated by the transformer so you are working with low voltage DC. >> >> >Have fun experimenting but beware of the 240V on the transformer. >> >Peter >> >> Gosh that is only about 40 years old. Over 75 if you count tubes.- Hide quoted text - >> >> - Show quoted text - > >You make it sound like an old design is not as good as something more >recent. I'd never heard of this so it is 'new' to me. > >George H. It is not so much as saying old is good, but that i find it disingenuous to represent it as a new circuit / discovery.
From: ontherails on 11 Jul 2010 14:31 >On Tue, 29 Jun 2010 17:00:03 -0500, "ontherails" ><peter.elbro(a)n_o_s_p_a_m.btinternet.com> wrote: > >>> >>>Does anyone have experience with speed control of a small shaded pole >>>motor about 25W, with a ghastly PF of about 0.36 ?. >>> >>> This drives the water circulation pump in an experimental setup much too >>>hard, and the churning >>>measurably heats the water. >>> >>>I thought a variable frequency inverter might be nice, but wondered how >>>sinusoidal it would need to be. I doubt that a simple phase shift let-it- >>>slip-more controller, would be good enough. Works for fans up to a point. >>> >>>Rather than suck it and see, I thought I'd politely probe the brains of >>>the experts first. >>> >>>All the best >>>Ian Macmillan >>> >>> >>> >>> >>Use my variable inductance controller. Carry out this simple experiment to >>see how it works. Get a 100VA transformer, something like 240V to 40V. Put >>the 240V windings in series with the motor and connect to the mains - >>nothing happens. Short the 40V windings - motor runs at nearly full speed >>but you are still working with AC. >> >>Put a bridge rectifier on the 40V windings and short the DC output. Motor >>runs at nearly the full speed it did before but now you are working with >>DC. Put a transistor (I normally use a darlington - TIP121 for a 40V >>secondary and add simple control electronics. You can normally get up to >>about 90% full speed. >> >>Approximately 10% losses occur in the transformer, bridge rectifier and >>darlington. This could be reduced by using a higher voltage secondary and a >>MOSFET when the losses could be 5% or lower. The control electronics side >>is isolated by the transformer so you are working with low voltage DC. >> >>Have fun experimenting but beware of the 240V on the transformer. >>Peter >> >> >> >> >>--------------------------------------- >>Posted through http://www.Electronics-Related.com > >Interesting! What kind of (stable) speed range can you get? > > ...Jim Thompson >-- >| James E.Thompson, CTO | mens | >| Analog Innovations, Inc. | et | >| Analog/Mixed-Signal ASIC's and Discrete Systems | manus | >| Phoenix, Arizona 85048 Skype: Contacts Only | | >| Voice:(480)460-2350 Fax: Available upon request | Brass Rat | >| E-mail Icon at http://www.analog-innovations.com | 1962 | > >Obama: A reincarnation of Nixon, narcissistically posing in > politically-correct black-face, but with fewer scruples. > The range of speeds is zero to about 90-95%. The speed isn't stable as shaded pole motors have very poor regulation versus load and there is no feedback. However, you could add a tacho feedback and get a very stable speed up to the torque capability of the motor for that speed. Interesting comments about mag amps. My original design dates back to my B.Sc project in 1973 where I wanted to stabilize a voltage of a cathode ray oscilloscope as part of a bigger project. The object was to provide a stable voltage to the CRO despite fluctuating mains voltages. The original design was to have been a saturable reactor but I accidentally found I could control the voltage dropped across the primary by varying the current in the secondary. I call it variable inductance controller as the inductance of a primary winding is very high with an open circuit secondary but very low (leakage inductance) with it shorted. Also, very little power seems to be dissipated in the transformer indicating it is operating as an inductor rather than a resistor. What it is doing is transforming the resistive value on the secondary by the square of the turns ratio. Today I use them as ceiling vent fan controllers with a thermistor (15k at 25C) connected collector to base of the darlington transistor base and a variable resistor (10k) connected base to emitter. That makes a very simple automatic room temperature controller for the summer. The very high Hfe of the darlington (1,000-3,000) removes most of the effect of increasing secondary voltage as the temperature drops and keeps the control point almost constant. Peter --------------------------------------- Posted through http://www.Electronics-Related.com
From: Jim Thompson on 12 Jul 2010 22:17
On Sun, 11 Jul 2010 13:31:25 -0500, "ontherails" <peter.elbro(a)n_o_s_p_a_m.n_o_s_p_a_m.btinternet.com> wrote: >>On Tue, 29 Jun 2010 17:00:03 -0500, "ontherails" >><peter.elbro(a)n_o_s_p_a_m.btinternet.com> wrote: >> >>>> >>>>Does anyone have experience with speed control of a small shaded pole >>>>motor about 25W, with a ghastly PF of about 0.36 ?. >>>> >>>> This drives the water circulation pump in an experimental setup much >too >>>>hard, and the churning >>>>measurably heats the water. >>>> >>>>I thought a variable frequency inverter might be nice, but wondered how >>>>sinusoidal it would need to be. I doubt that a simple phase shift >let-it- >>>>slip-more controller, would be good enough. Works for fans up to a >point. >>>> >>>>Rather than suck it and see, I thought I'd politely probe the brains of >>>>the experts first. >>>> >>>>All the best >>>>Ian Macmillan >>>> >>>> >>>> >>>> >>>Use my variable inductance controller. Carry out this simple experiment >to >>>see how it works. Get a 100VA transformer, something like 240V to 40V. >Put >>>the 240V windings in series with the motor and connect to the mains - >>>nothing happens. Short the 40V windings - motor runs at nearly full >speed >>>but you are still working with AC. >>> >>>Put a bridge rectifier on the 40V windings and short the DC output. >Motor >>>runs at nearly the full speed it did before but now you are working with >>>DC. Put a transistor (I normally use a darlington - TIP121 for a 40V >>>secondary and add simple control electronics. You can normally get up to >>>about 90% full speed. >>> >>>Approximately 10% losses occur in the transformer, bridge rectifier and >>>darlington. This could be reduced by using a higher voltage secondary and >a >>>MOSFET when the losses could be 5% or lower. The control electronics >side >>>is isolated by the transformer so you are working with low voltage DC. >>> >>>Have fun experimenting but beware of the 240V on the transformer. >>>Peter >>> >>> >>> >>> >>>--------------------------------------- >>>Posted through http://www.Electronics-Related.com >> >>Interesting! What kind of (stable) speed range can you get? >> >> ...Jim Thompson >>-- >>| James E.Thompson, CTO | mens | >>| Analog Innovations, Inc. | et | >>| Analog/Mixed-Signal ASIC's and Discrete Systems | manus | >>| Phoenix, Arizona 85048 Skype: Contacts Only | | >>| Voice:(480)460-2350 Fax: Available upon request | Brass Rat | >>| E-mail Icon at http://www.analog-innovations.com | 1962 | >> >>Obama: A reincarnation of Nixon, narcissistically posing in >> politically-correct black-face, but with fewer scruples. >> > >The range of speeds is zero to about 90-95%. The speed isn't stable as >shaded pole motors have very poor regulation versus load and there is no >feedback. However, you could add a tacho feedback and get a very stable >speed up to the torque capability of the motor for that speed. > >Interesting comments about mag amps. My original design dates back to my >B.Sc project in 1973 where I wanted to stabilize a voltage of a cathode ray >oscilloscope as part of a bigger project. The object was to provide a >stable voltage to the CRO despite fluctuating mains voltages. The original >design was to have been a saturable reactor but I accidentally found I >could control the voltage dropped across the primary by varying the current >in the secondary. > >I call it variable inductance controller as the inductance of a primary >winding is very high with an open circuit secondary but very low (leakage >inductance) with it shorted. Also, very little power seems to be dissipated >in the transformer indicating it is operating as an inductor rather than a >resistor. What it is doing is transforming the resistive value on the >secondary by the square of the turns ratio. > >Today I use them as ceiling vent fan controllers with a thermistor (15k at >25C) connected collector to base of the darlington transistor base and a >variable resistor (10k) connected base to emitter. That makes a very simple >automatic room temperature controller for the summer. The very high Hfe of >the darlington (1,000-3,000) removes most of the effect of increasing >secondary voltage as the temperature drops and keeps the control point >almost constant. > >Peter > > >--------------------------------------- >Posted through http://www.Electronics-Related.com Have you accidentally created a method to dim incandescent's without all the RFI that TRIAC's create ?:-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Obama isn't going to raise your taxes...it's Bush' fault: Not re- newing the Bush tax cuts will increase the bottom tier rate by 50% |