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PICList Thread
'Speedcontrol using backemf with AC Motor ?'
1998\08\10@054833 by Stefan Sczekalla-Waldschmidt

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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.

1998\08\10@191155 by Chris Eddy

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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}

1998\08\11@150846 by PIC development

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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_OUTpicTakeThisOuTspambeowulf.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.

1998\08\12@052903 by Stefan Sczekalla-Waldschmidt

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PIC development schrieb:
>
> There is an article in this months (September 1998) edition of
> Electronics World that describes this method
>
> Pete

Hi Pete,

I4m living in Germany and have no acces to the Electronics World.
It would be very nice if you could copy the article and send it
to me by fax. my Fax is +49 69 97 57 07 25.
( ? scan + E-Mail ? )

Kind regards

       Stefan Sczekalla-Waldschmidt
       .....sswKILLspamspam@spam@oikossw.de

1998\08\13@100115 by Stefan Sczekalla-Waldschmidt

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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
       sswspamKILLspamoikossw.de

1998\08\18@215628 by Larry G. Nelson Sr.

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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}

Larry G. Nelson Sr.
.....L.NelsonKILLspamspam.....ieee.org
http://www.ultranet.com/~nr

1998\08\19@053849 by Stefan Sczekalla-Waldschmidt

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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_OUTspamTakeThisOuToikossw.de

1998\08\19@065537 by fmccay

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----------
> From: Stefan Sczekalla-Waldschmidt <sswspamspam_OUTOIKOSSW.DE>
>
> What is the meaning of the abbreviaton "RTV".
>
> kind regards
>
>         Stefan Sczekalla-Waldschmidt
>         @spam@sswKILLspamspamoikossw.de


RTV stands for "Room Temperature Vulcanizing."
Vulcanizing is a process that heats rubber with sulfur or a sulfur compound
to help stabilize and harden it.

Regards,        -Fred McCay
               KILLspamfmccayKILLspamspamgis.net

1998\08\31@213130 by Larry G. Nelson Sr.

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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.
spamBeGoneL.NelsonspamBeGonespamieee.org
http://www.ultranet.com/~nr


'Speedcontrol using backemf with AC Motor ?'
1998\09\01@111717 by Andy Kunz
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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
==================================================================

1998\09\01@115635 by goflo

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Devcon has a product called Flexane, a polyurethane synthetic rubber.
Durometer adjustable per curing process. Expensive, but good stuff.

Regards, Jack

Andy Kunz wrote:

> There are also RTV's which produce alcohols instead.  I believe these are
> electronics-grade ones, as the acetic acid can start corrosion.

1998\09\01@150158 by Engineering Department

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< 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
TakeThisOuTImageLogicEraseMEspamspam_OUTibm.net

1998\09\02@070105 by Morgan Olsson

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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}

/  Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \
\  mrtEraseMEspam.....iname.com, ph: +46 (0)414 70741; fax +46 (0)414 70331    /

1998\09\02@073942 by wwl

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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 / EraseMEwwlspamnetcomuk.co.uk  _/ L_/
_/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

1998\09\02@093616 by Engineering Department

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<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
RemoveMEImageLogicEraseMEspamEraseMEibm.net

1998\09\02@095249 by Andy Kunz

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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}

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\02@140741 by goflo

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media4.hypernet.com/~DEVCON/ENGCOAT/devcon.html

Morgan Olsson wrote:
{Quote hidden}

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