PWM - Mosfet/motor introducing noise


Closed Thread
Results 1 to 12 of 12
  1. #1
    Join Date
    Jun 2005
    Location
    Wisconsin
    Posts
    382

    Default PWM - Mosfet/motor introducing noise

    I'm building a prop controller for Halloween. The circuit I've designed has two relays controlled via transistors and a PWM motor controller via a mosfet.

    The mosfet gate is tied to the pic via a 1K resistor. The motor and relays all have a 1N4001 tied between 12V and common. I’m using the same 12V supply for the motor, relays, and the rest of the circuit (5V regulator to the circuitry). The PWM controlled Fet is connected to a windshield wiper motor from a car.

    The issue I'm running into is when the motor is run I am seeing spikes on the power buss.

    Any thoughts on how to correct this issue without dramatically changing the design? I could drop optos in and use a separate power supplies but that would require a ton of rework.

  2. #2
    Join Date
    Nov 2003
    Location
    Wellton, U.S.A.
    Posts
    5,924


    Did you find this post helpful? Yes | No

    Default

    Are the spikes on the 5 volt buss? What do you have in the way of capacitors before and after the the 5 v regulator?
    Dave
    Always wear safety glasses while programming.

  3. #3
    Join Date
    Jun 2005
    Location
    Wisconsin
    Posts
    382


    Did you find this post helpful? Yes | No

    Default

    Here is a working schematic.

    I'm sharing a common between the 12V and 5V rail. I haven't looked at the 5V rail yet.
    Attached Images Attached Images

  4. #4
    Join Date
    Nov 2003
    Location
    Wellton, U.S.A.
    Posts
    5,924


    Did you find this post helpful? Yes | No

    Default

    Try a 4700 or greater cap across the motor leads?
    Dave
    Always wear safety glasses while programming.

  5. #5
    Join Date
    Jun 2005
    Location
    Wisconsin
    Posts
    382


    Did you find this post helpful? Yes | No

    Default

    I tried a 2200K, no change.

    Here are some scope shots of the 5V and 12V rails with the motor running.
    5V = motor controller2 sml
    12V = motor controller 12sml

    2ms/div, 1V/div (x10 probes)
    Attached Images Attached Images   
    Last edited by DynamoBen; - 17th October 2007 at 04:32.

  6. #6
    Join Date
    Jun 2005
    Location
    Wisconsin
    Posts
    382


    Did you find this post helpful? Yes | No

    Default

    After some thought I may just leave things as they are. To get it perfect will require a major redesign which I don't have time for. At this point I'm not sure that this will be a big deal. Agreed?
    Last edited by DynamoBen; - 17th October 2007 at 04:31.

  7. #7
    Join Date
    May 2004
    Location
    NW France
    Posts
    3,611


    Did you find this post helpful? Yes | No

    Default

    Hi,

    First ...

    Your diode parallelled to the mosfet must be paralleled to the MOTOR ... that will GREATLY limit the spikes ( 1N400x seems a bit Weak for this kind of motor ... try better 1N540x or a fast recovery TO220 model )

    Now,

    1) place a low ESR 1000µF or + capacitor as close as possible to the motor ... to lower the 12v power source impedance. ( by the way, I'm saying the mosfet could be placed close to the motor ...and the diode between motor terminals ...)

    2) place a .1µF on your motor terminals

    3) place a 10nF between each motor terminal and motor frame which has to be connected to circuit ground.

    4) you can place a core coil ( 1mH range "big value" ) in series beetween 12 v and your 5v reg input

    Alain
    Last edited by Acetronics2; - 17th October 2007 at 10:01.
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  8. #8
    Join Date
    Jun 2005
    Location
    Wisconsin
    Posts
    382


    Did you find this post helpful? Yes | No

    Default

    Your diode parallelled to the mosfet must be paralleled to the MOTOR ... that will GREATLY limit the spikes ( 1N400x seems a bit Weak for this kind of motor ... try better 1N540x or a fast recovery TO220 model )
    The schematic isn't correct in this case, the diode seems to be drawn wrong. However I will try moving the diode up to the motor. I will try to located a different diode...

    1) place a low ESR 1000µF or + capacitor as close as possible to the motor ... to lower the 12v power source impedance. ( by the way, I'm saying the mosfet could be placed close to the motor ...and the diode between motor terminals ...)
    The mosfet can't be moved. I don't know if I have a low ESR cap. I can dig through my parts bin. Anything specific I should be looking for?

    2) place a .1µF on your motor terminals
    Is this in addition to the above cap?

    3) place a 10nF between each motor terminal and motor frame which has to be connected to circuit ground.
    Will try.

    4) you can place a core coil ( 1mH range "big value" ) in series beetween 12 v and your 5v reg input
    I don't have anything like this lying around.

  9. #9
    Join Date
    May 2004
    Location
    NW France
    Posts
    3,611


    Did you find this post helpful? Yes | No

    Default

    QUOTE=DynamoBen

    The mosfet can't be moved. I don't know if I have a low ESR cap. I can dig through my parts bin. Anything specific I should be looking for?

    > IF I tell you BC Components (ex. Philips ) Series 136 ... ESR <= 22 mOhms ( Milli ...yes ! )


    Is this in addition to the above cap?

    > The .1µF capacitor must be soldered ON the motor terminals ...


    Will try.

    > The 10nF are also necessary.


    I don't have anything like this lying around.

    > Not compulsory, yes ...but highly recommended !!!

    Alain
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  10. #10
    Join Date
    Jun 2005
    Location
    Wisconsin
    Posts
    382


    Did you find this post helpful? Yes | No

    Default

    This seems to be what you are describing.

    http://www.kronosrobotics.com/an142/GAN142.htm
    Last edited by DynamoBen; - 17th October 2007 at 22:38.

  11. #11
    Join Date
    May 2004
    Location
    NW France
    Posts
    3,611


    Did you find this post helpful? Yes | No

    Wink

    Quote Originally Posted by DynamoBen View Post
    This seems to be what you are describing.

    http://www.kronosrobotics.com/an142/GAN142.htm
    Hi, Ben

    Yes ... that's a nice tutorial ... but some tips still missing !!! ( diode, low esr cap, inductor ...)

    note here, in this example, motors can be reversed ... so, the diode can't be placed on the motor terminals, but close to the "reversing commutator" ( relay, transistors bridge ...)

    Alain
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  12. #12
    Join Date
    Jun 2005
    Location
    Wisconsin
    Posts
    382


    Did you find this post helpful? Yes | No

    Default

    1N400x seems a bit Weak for this kind of motor ... try better 1N540x
    I picked up a 1N5406 at Radio Shack last night.


    1) place a low ESR 1000µF or + capacitor as close as possible to the motor ... to lower the 12v power source impedance.
    I was unable to locate a low esr cap, so this one can't be done.

    place a .1µF on your motor terminals
    done

    place a 10nF between each motor terminal and motor frame which has to be connected to circuit ground.
    done, frame of motor is connected to common

    you can place a core coil ( 1mH range "big value" ) in series beetween 12 v and your 5v reg input
    Still no luck locating a coil.

    In the end my "issue" still exists. *sigh*

Similar Threads

  1. Half-bridge PWM with a 16F684 ?
    By Byte_Butcher in forum General
    Replies: 7
    Last Post: - 17th January 2010, 23:18
  2. Variable PWM PIC18F2431
    By trr1985 in forum mel PIC BASIC Pro
    Replies: 7
    Last Post: - 12th June 2009, 07:03
  3. PWM: Vernacular/Function (Newbee)
    By TerryN in forum mel PIC BASIC Pro
    Replies: 2
    Last Post: - 3rd July 2008, 17:58
  4. PWM setting PIC16F887
    By Gevo in forum mel PIC BASIC Pro
    Replies: 6
    Last Post: - 12th June 2008, 08:24
  5. Tidying Up PWM Routine
    By Tissy in forum mel PIC BASIC Pro
    Replies: 4
    Last Post: - 21st February 2005, 01:26

Members who have read this thread : 1

You do not have permission to view the list of names.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts