shaded pole motor control
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From: George Herold on 1 Jul 2010 09:18 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.
From: Jeroen Belleman on 1 Jul 2010 16:23 On 07/01/2010 07:49 PM, Fred Abse wrote: > On Tue, 29 Jun 2010 17:00:03 -0500, ontherails wrote: > >> 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. >[...] > AKA Magnetic Amplifier, or Saturable Reactor. > Not the same thing! In a saturable reactor, a DC current saturates the core of an inductor, reducing its inductance. In the arrangement described above, there is no DC magnetization, and the core does not saturate. Jeroen Belleman
From: Phil Hobbs on 1 Jul 2010 18:29 On 7/1/2010 1:49 PM, Fred Abse wrote: > On Tue, 29 Jun 2010 17:00:03 -0500, ontherails wrote: > >> 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. > > > AKA Magnetic Amplifier, or Saturable Reactor. > That's not a mag amp. Mag amps use DC to control AC. 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 1 Jul 2010 18:53 On Thu, 01 Jul 2010 18:29:27 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >On 7/1/2010 1:49 PM, Fred Abse wrote: >> On Tue, 29 Jun 2010 17:00:03 -0500, ontherails wrote: >> >>> 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. >> >> >> AKA Magnetic Amplifier, or Saturable Reactor. >> > >That's not a mag amp. And it's not saturating. John
From: Martin Riddle on 1 Jul 2010 21:47
"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:117q26pnvab6cvrbj61d6cg2rf37li83fp(a)4ax.com... > On Thu, 01 Jul 2010 18:29:27 -0400, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >>On 7/1/2010 1:49 PM, Fred Abse wrote: >>> On Tue, 29 Jun 2010 17:00:03 -0500, ontherails wrote: >>> >>>> 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. >>> >>> >>> AKA Magnetic Amplifier, or Saturable Reactor. >>> >> >>That's not a mag amp. > > And it's not saturating. > One way to control speed is to add series resistance. The technique varies the impedance seen looking into the primary of the transformer. Cheers |