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Simple stall over current 12v dc motor protection?

Discussion in 'Sensors and Actuators' started by supak111, Nov 10, 2015.

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  1. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    Hey guys, are there any simple circuits out there that can protect a motor from stall over current? I run a 12v dc gear motor from a battery and sometimes something jambs up the motor and I would like some circuit that can sense the motor has stop and automatically turn OFF the power to the motor.

    Currently I'm just using a PTC fuse do protect it but they are slow, on average they take about 10-15 seconds of over current before the PTC fuse stops the current from hating the motor.
     
  2. Alec_t

    Alec_t

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    Have you tried a slow-blow fuse?
    Whatever you use will be a compromise, since it will have to allow the motor to get up to speed from a stopped/stall state.
     
  3. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Yea a mechanical fuse isn't really suitable, this happens a lot so I would be replacing fuses all the time. Has to be some kind of smart system that can tell if the motor uses more then say 500ma for more then 3 sec to just turn OFF and perhaps reset back on in 10+ or so seconds later.
     
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I'm thinking of a system with a bit more brains. Instead of simply monitoring for stall current how about a system that monitors both motor current and RPM? This way the circuit can differentiate between a stall and startup current.

    As with many things these days this is an easy job for a μC.

    Chris
     
    Arouse1973 likes this.
  5. Minder

    Minder

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    Apr 24, 2015
    You just need a small correctly rated circuit breaker, these do not operate immediately but have a small time delay to allow for inrush.
    M.
     
    Arouse1973 likes this.
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Now this logic is all wrong! Why make things simple?! :p

    Chris
     
  7. Colin Mitchell

    Colin Mitchell

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    Simply detect the brush noise from the motor to turn off the supply.
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Now THIS is really scary! When I suggested testing for RPM I was thinking along the same line! :eek: Has the Earth stopped turning on its axis????! :p

    Chris
     
  9. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    I just looked up mini circuit breakers and I guess they do have them and they're automatic :), I had no idea. This would be perfect as its small, cheap $.70 (model OP-01C), and automatic, but I can't seem to find the ones under 2.5A. (PS never mind ,it has a trip time of 5-20sec at 200% current, wont do the job.)

    How would I detect brush noise, and have lack of noise turn off the circuit? Sounds like a complicated circuit for someone that is a newbee
     
    Last edited: Nov 13, 2015
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I typically post spiced (computer simulated) circuits. Unfortunately none of my three spice programs will simulate commutator noise. Since I never actually bench test anything I post on EP and since I don't have your motor I can only give you tips of how I would attempt this.

    One of the neat functions of a 555 Timer chip is called "Missing Pulse Detector". The 555's output pin can drive a relay coil who's contacts are in series with the motor.

    Alternatively you can rectify and filter the noise spikes to create a DC average voltage to drive a transistor base which controls the relay.

    Chris
     
  11. dorke

    dorke

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    Jun 20, 2015
    What is the operating current of your motor?
    At what current do you wish to "disconnect the motor" and how fast?
    You can put a simple current limit in series with your motor,
    may do the job of protecting the motor...
     
  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes that should work too but he'll need a short delay to ignore the current limit upon startup of the motor. Not a big deal though. ;)

    Chris
     
  13. Minder

    Minder

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    Apr 24, 2015
    Have you tried a self resetable PTC fuse?
    M.
     
  14. Martaine2005

    Martaine2005

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    May 12, 2015
    Minder, Post #1

    Martin
     
    Minder likes this.
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Marty, sometimes you amaze me. Whenever I think you've burned out your brain beyond repair you catch stuff like this.

    You make your uncle proud! :)

    Uncle Chris
     
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  16. Martaine2005

    Martaine2005

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    Aww, uncle Chris, thank you.
    I think the reason I noticed that was because I wasn't on the "grapes"!
    Still plenty of time though!:p

    Marty
     
    Arouse1973 likes this.
  17. Alec_t

    Alec_t

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    How about this?
    The current trip is adjustable. The higher the stall current the shorter the delay before the trip.
    Automatically resets after a further delay when current drops. R3,C2 determine the delays.
    MotorShutOff.PNG
     

    Attached Files:

    Arouse1973 and CDRIVE like this.
  18. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Ah dats
    Alec, nice design but I think a manual reset would be safer. Ouch!

    Chris
     
  19. Alec_t

    Alec_t

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    Jul 7, 2015
    You're probably right. Add a latch to keep the tripped state?
     
  20. Alec_t

    Alec_t

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    Jul 7, 2015
    Here you go:
    MotorShutOff2.PNG
     

    Attached Files:

    CDRIVE likes this.
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