Post by thread:Speedcontrol using backemf with AC Motor ?

Hi, I4m going to control an small-Power AC/DC Motor. Motor type is german-called "Reihenschlusz-Motor" which means that rotor and field-coils are normaly connected. ------[]-----( O )----- ^Field Coil ^Rotor with brushes I like to controle the speed. I have the possibillity to access the connection between field-coil and rotor. My idea is to generate PWM using an PIC, and measuring the bkemf with the built in A/D. Using the bkemf to determine the speed/load. The Motor Power-consumption is less then .5 Amps continous. Supply -Voltage is rectivied AC aprox. 12 - 25 Volts, 30kHz (!). The Application is to regulate the speed of Model-Railroad-Locos. Does somebody have Ideas, Source, descriptions, suggestions, hints ? Kind regards, Stefan Sczekalla-Waldschmidt.

Stefan.. Having walked a mile in your shoes, I have a few suggestions. Do not use the built in PWM generator. It cannot scale down far enough to provide a suitable motor PWM frequency. Use timer 0 to generate a ramp counter and generate the ramp yourself. The secondary benefit is clear in a moment. The back EMF on a DC motor is a very good indication of speed. The caveat is that when you use PWM to control the power to the motor, the voltage reading on the motor at any randomly chosen time may have nothing to do with the back EMF. Therefore, you should time your reading of the motor voltage to the point just before the on cycle on the PWM output. This way, your motor voltage has settled fairly well into the true back EMF value. Make sure that your overall period is low enough to allow this settling to occur. Best of luck. Chris Eddy Pioneer Microsystems, Inc. Stefan Sczekalla-Waldschmidt wrote: {Quote hidden}> Hi, > > I4m going to control an small-Power AC/DC Motor. > > Motor type is german-called "Reihenschlusz-Motor" which > means that rotor and field-coils are normaly connected. > > ------[]-----( O )----- > > ^Field Coil ^Rotor with brushes > > I like to controle the speed. I have the possibillity to > access the connection between field-coil and rotor. > > My idea is to generate PWM using an PIC, and measuring the > bkemf with the built in A/D. Using the bkemf to determine > the speed/load. > > The Motor Power-consumption is less then .5 Amps continous. Supply > -Voltage is rectivied AC aprox. 12 - 25 Volts, 30kHz (!). > > The Application is to regulate the speed of Model-Railroad-Locos. > > Does somebody have Ideas, Source, descriptions, suggestions, hints ? > > Kind regards, > > Stefan Sczekalla-Waldschmidt.

There is an article in this months (September 1998) edition of Electronics World that describes this method Pete .............................................................................. . Never trust a man who, when left alone in ....... Pete Lynch . . a room with a tea cosy, doesn't try it on ....... Marlow, England . ..........Billy Connolly. ......................... spam_OUTpicTakeThisOuTbeowulf.demon.co.uk .. On Mon, 10 Aug 1998, Chris Eddy wrote: > The back EMF on a DC motor is a very good indication of speed. The > caveat is that when you use PWM to control the power to the motor, the > voltage reading on the motor at any randomly chosen time may have > nothing to do with the back EMF.

PIC development schrieb: > > There is an article in this months (September 1998) edition of > Electronics World that describes this method > > Pete As a (sometimes) lucy man ... I found the september issue of the "electronic world" in the international Book-shop in my Hometown Frankfurt/M. Electronic World charge Germans twice the price than every other european country - grrrummmmmpf ... ;-) Hadn4t already had the time to read the article up to the end, but a glance on it promises new ideas. hoped it would go more into details how to realize it with a PIC kind regards Stefan Sczekalla-Waldschmidt sswKILLspamoikossw.de

I did this with small DC motors and it works well. Be sure to not use RTV near the motor or you will have problems. The RTV out gasses silicides and will cause glassivation on the brushes in the presence of an arc so the noise will increase and you will have control problems. At 07:04 PM 8/10/98 -0400, you wrote: {Quote hidden}>Stefan.. > >Having walked a mile in your shoes, I have a few suggestions. > >Do not use the built in PWM generator. It cannot scale down far enough >to provide a suitable motor PWM frequency. Use timer 0 to generate a >ramp counter and generate the ramp yourself. The secondary benefit is >clear in a moment. > >The back EMF on a DC motor is a very good indication of speed. The >caveat is that when you use PWM to control the power to the motor, the >voltage reading on the motor at any randomly chosen time may have >nothing to do with the back EMF. Therefore, you should time your >reading of the motor voltage to the point just before the on cycle on >the PWM output. This way, your motor voltage has settled fairly well >into the true back EMF value. Make sure that your overall period is low >enough to allow this settling to occur. > >Best of luck. > >Chris Eddy >Pioneer Microsystems, Inc. > >Stefan Sczekalla-Waldschmidt wrote: > >> Hi, >> >> I4m going to control an small-Power AC/DC Motor. >> >> Motor type is german-called "Reihenschlusz-Motor" which >> means that rotor and field-coils are normaly connected. >> >> ------[]-----( O )----- >> >> ^Field Coil ^Rotor with brushes >> >> I like to controle the speed. I have the possibillity to >> access the connection between field-coil and rotor. >> >> My idea is to generate PWM using an PIC, and measuring the >> bkemf with the built in A/D. Using the bkemf to determine >> the speed/load. >> >> The Motor Power-consumption is less then .5 Amps continous. Supply >> -Voltage is rectivied AC aprox. 12 - 25 Volts, 30kHz (!). >> >> The Application is to regulate the speed of Model-Railroad-Locos. >> >> Does somebody have Ideas, Source, descriptions, suggestions, hints ? >> >> Kind regards, >> >> Stefan Sczekalla-Waldschmidt. > > Larry G. Nelson Sr. .....L.NelsonKILLspam.....ieee.org http://www.ultranet.com/~nr

Larry G. Nelson Sr. schrieb: > > I did this with small DC motors and it works well. Be sure to not use RTV > near the motor or you will have problems. The RTV out gasses silicides and > will cause glassivation on the brushes in the presence of an arc so the > noise will increase and you will have control problems. > What is the meaning of the abbreviaton "RTV". kind regards Stefan Sczekalla-Waldschmidt EraseMEsswspam_OUTTakeThisOuToikossw.de

Room Temperature Vulcanizing. It is a type of liquid rubber or caulking compound. There are electronic rated formulations as well as a type commonly used for sealing around a bathtub enclosure. As it cures it smells like vinegar as the acetic acid is driven off. Many people use this to seal electronics against moisture but the problem occurs in the presence of an arc so the material should never be used near components that have electrical contacts like relays or DC motors. At 11:44 AM 8/19/98 +0100, you wrote: {Quote hidden}>Larry G. Nelson Sr. schrieb: >> >> I did this with small DC motors and it works well. Be sure to not use RTV >> near the motor or you will have problems. The RTV out gasses silicides and >> will cause glassivation on the brushes in the presence of an arc so the >> noise will increase and you will have control problems. >> > >What is the meaning of the abbreviaton "RTV". > >kind regards > > Stefan Sczekalla-Waldschmidt > RemoveMEsswTakeThisOuToikossw.de > > Larry G. Nelson Sr. spamBeGoneL.NelsonspamBeGoneieee.org http://www.ultranet.com/~nr

At 04:29 PM 8/31/98 -0400, you wrote: >Room Temperature Vulcanizing. It is a type of liquid rubber or caulking >compound. There are electronic rated formulations as well as a type >commonly used for sealing around a bathtub enclosure. As it cures it smells >like vinegar as the acetic acid is driven off. Many people use this to seal There are also RTV's which produce alcohols instead. I believe these are electronics-grade ones, as the acetic acid can start corrosion. Andy ================================================================== Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA ==================================================================

< Jack writes> >Devcon has a product called Flexane, a polyurethane synthetic rubber. >Durometer adjustable per curing process. Expensive, but good stuff. We use Flexane 94 (15250) to pot non-PIC electronics. A split mold dipped in liquid floor wax and clamshelled around the electronics with a DB25 sticking out at the seam produces a very clean result. Just slap on a label, no case is necessary. The circuits we've potted are typically 0 - 3 VDC at about 20KHz -- we've seen no problems after 5 years use. One of these days I'll try it with a 4 MHz PIC and see how that holds up. However I'd be nervous about potting a RF circuit (1 -- I don't know much about RF, 2 -- I assume anything that's opaque and black has some carbon in it somewhere <g>). Cheers, Win Wiencke Image Logic Corporation TakeThisOuTImageLogicEraseMEspam_OUTibm.net

At 13:27 1998-08-31 -0400, you wrote: >< Jack writes> >>Devcon has a product called Flexane, a polyurethane synthetic rubber. >>Durometer adjustable per curing process. Expensive, but good stuff. Sounds interesting. What is max operating temp for this Flexane? Is it available in Europe? Thanks in advance /Morgan {Quote hidden}>We use Flexane 94 (15250) to pot non-PIC electronics. >A split mold dipped in liquid floor wax and clamshelled >around the electronics with a DB25 sticking out at the seam >produces a very clean result. Just slap on a label, no case >is necessary. > >The circuits we've potted are typically 0 - 3 VDC at about >20KHz -- we've seen no problems after 5 years use. > >One of these days I'll try it with a 4 MHz PIC and see how that >holds up. However I'd be nervous about potting a RF circuit >(1 -- I don't know much about RF, 2 -- I assume anything that's >opaque and black has some carbon in it somewhere <g>). > >Cheers, > >Win Wiencke >Image Logic Corporation >RemoveMEImageLogicTakeThisOuTibm.net > > / Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \ \ mrtEraseME.....iname.com, ph: +46 (0)414 70741; fax +46 (0)414 70331 /

On Mon, 31 Aug 1998 13:27:02 -0400, you wrote: >< Jack writes> >>Devcon has a product called Flexane, a polyurethane synthetic rubber. >>Durometer adjustable per curing process. Expensive, but good stuff. > > >We use Flexane 94 (15250) to pot non-PIC electronics. >A split mold dipped in liquid floor wax and clamshelled >around the electronics with a DB25 sticking out at the seam >produces a very clean result. Just slap on a label, no case >is necessary. > >The circuits we've potted are typically 0 - 3 VDC at about >20KHz -- we've seen no problems after 5 years use. > >One of these days I'll try it with a 4 MHz PIC and see how that >holds up. However I'd be nervous about potting a RF circuit >(1 -- I don't know much about RF, 2 -- I assume anything that's >opaque and black has some carbon in it somewhere <g>). No carbon, but potting RF stuff can seriously de-tune due to differing dielectric properties. ____ ____ _/ L_/ Mike Harrison / White Wing Logic / EraseMEwwlnetcomuk.co.uk _/ L_/ _/ W_/ Hardware & Software design / PCB Design / Consultancy _/ W_/ /_W_/ Industrial / Computer Peripherals / Hazardous Area /_W_/

<Thread fragments are> <Jack writes in part> >>>Devcon has a product called Flexane, a polyurethane synthetic rubber. >>>Durometer adjustable per curing process. Expensive, but good stuff. <Win comments in part> >>We use Flexane 94 (15250) to pot non-PIC electronics. >>A split mold dipped in liquid floor wax and clamshelled >>around the electronics with a DB25 sticking out at the seam >>produces a very clean result. Just slap on a label, no case >>is necessary. <Morgan Olsson writes> : >Sounds interesting. >What is max operating temp for this Flexane? >Is it available in Europe? Here's what information I have: Flexane 94 Liquid (this stuff comes in all sorts of viscosity's) #15250 ITW Devcon 30 Endicott Street Danvers, MA 01923 USA 01 (508) 777-1100 Operating temperature maximum: dry: 180 degrees F wet (I have no idea what "wet" means): 120 degrees F Dielectric Strength (ASTM D 149): 350 volts/mil Cure Shrinkage (ASTM D 2556): 0.0004 in./in. Cured Hardness: 97 Shore A scale Tensile Strength ASTM D 412: 2800 psi I don't know if this is available in Europe, I get it from an industrial plastics vendor and I gather it is used for resurfacing conveyors and the like that are subject to a great deal of abrasion. Cheers, Win Wiencke Image Logic Corporation RemoveMEImageLogicEraseMEEraseMEibm.net

I use 3M #280 to pot my ESC's. They are PIC-based, waterproof, and run in harsh environments w/o problems. See http://www.users.fast.net/~montana/root.html and follow the link for Products to see a picture. Andy At 11:39 AM 9/2/98 GMT, you wrote: {Quote hidden}>On Mon, 31 Aug 1998 13:27:02 -0400, you wrote: > >>< Jack writes> >>>Devcon has a product called Flexane, a polyurethane synthetic rubber. >>>Durometer adjustable per curing process. Expensive, but good stuff. >> >> >>We use Flexane 94 (15250) to pot non-PIC electronics. >>A split mold dipped in liquid floor wax and clamshelled >>around the electronics with a DB25 sticking out at the seam >>produces a very clean result. Just slap on a label, no case >>is necessary. >> >>The circuits we've potted are typically 0 - 3 VDC at about >>20KHz -- we've seen no problems after 5 years use. >> >>One of these days I'll try it with a 4 MHz PIC and see how that >>holds up. However I'd be nervous about potting a RF circuit >>(1 -- I don't know much about RF, 2 -- I assume anything that's >>opaque and black has some carbon in it somewhere <g>). >No carbon, but potting RF stuff can seriously de-tune due to differing >dielectric properties. > ____ ____ > _/ L_/ Mike Harrison / White Wing Logic / RemoveMEwwlspam_OUTKILLspamnetcomuk.co.uk _/ L_/ > _/ W_/ Hardware & Software design / PCB Design / Consultancy _/ W_/ >/_W_/ Industrial / Computer Peripherals / Hazardous Area /_W_/ > > ================================================================== Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA ==================================================================

media4.hypernet.com/~DEVCON/ENGCOAT/devcon.html Morgan Olsson wrote: {Quote hidden}> > At 13:27 1998-08-31 -0400, you wrote: > >< Jack writes> > >>Devcon has a product called Flexane, a polyurethane synthetic rubber. > >>Durometer adjustable per curing process. Expensive, but good stuff. > > Sounds interesting. > What is max operating temp for this Flexane? > Is it available in Europe? > Thanks in advance > /Morgan > > >We use Flexane 94 (15250) to pot non-PIC electronics. > >A split mold dipped in liquid floor wax and clamshelled > >around the electronics with a DB25 sticking out at the seam > >produces a very clean result. Just slap on a label, no case > >is necessary. > > > >The circuits we've potted are typically 0 - 3 VDC at about > >20KHz -- we've seen no problems after 5 years use. > > > >One of these days I'll try it with a 4 MHz PIC and see how that > >holds up. However I'd be nervous about potting a RF circuit > >(1 -- I don't know much about RF, 2 -- I assume anything that's > >opaque and black has some carbon in it somewhere <g>). > > > >Cheers, > > > >Win Wiencke > >Image Logic Corporation > >RemoveMEImageLogicTakeThisOuTspamibm.net > > > > > / Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \ > \ EraseMEmrtspamspamBeGoneiname.com, ph: +46 (0)414 70741; fax +46 (0)414 70331 /