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PWM (pulse width modulator) help

Discussion in 'General Electronics Discussion' started by huntern321, May 27, 2013.

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  1. huntern321

    huntern321

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    May 27, 2013
    Hello, I recently bought 2 of these PWMs here, http://www.ebay.com/itm/10A-Pulse-W...697?pt=LH_DefaultDomain_0&hash=item48542d0c31. I planned on using them in a conjunction to control the power going to a small vehicle. At first they appeared to work, but now both seemed to have developed issues. The range of the PWMs has gone from 10%-100% to more like 95%-100%, which is pretty useless for my application. I originally wanted to get a higher current rated PWM, but these were the only ones that shipped in a reasonable about of time. While in their short time of use, I blew their fuses several times, though I never bypassed the fuse with one of a higher rating. I'm very frustrated at this point and have no idea what to do or what is even the problem. This is for a high school project and I would greatly appreciate any insight I could get.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    What voltage and current were you running them at?

    What was the rating of the fuse(s) you blew?

    Did they get hot at any stage?
     
  3. huntern321

    huntern321

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    0
    May 27, 2013
    I was running them with an input of 36 volts and between 5 and 10 amps.

    I blew a few 10 amp fuses

    The heat sinks were fairly hot to the touch.
     
  4. poor mystic

    poor mystic

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    Apr 8, 2011
    Hi :)
    Would you please describe the vehicle.. how heavy is it, and how fast must it accelerate please?
     
  5. huntern321

    huntern321

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    May 27, 2013
    The vehicle is actually quite the frankenstein creation. I took a toboggan and put wheels on it. It has two wheels in the front and one in the back which is powered by. The acceleration is anything we can get from it. There is not real requirement. It's about 30 kg more or less.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,387
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    Jan 21, 2010
    If you blew a 10A fuse then the current was significantly in excess of 10A This may have damaged the mosfets.

    Did you have reversed diodes across the motor? I see no evidence if them in this controller. Without them you may have damaged the mosfets.

    It is possible that this device has two mosfets in parallel. If one has failed short circuit (as they often do) then the motor will essentially always run at full speed. Allowing for resistance of the tracks on the board and the resistance of the failed mosfet, an adjustment range of 95% to 100% does not seem surprising.
     
  7. huntern321

    huntern321

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    May 27, 2013
    The units claimed that they had "reverse polarity protection." Is this what you mean with the question "Did you have reversed diodes across the motor?"
     
  8. davenn

    davenn Moderator

    13,589
    1,870
    Sep 5, 2009
    no, that would be for protection of the motor .....

    the diode Steve is referring to is across the motor and helps to reduce the motor when it stops .... this diode protects other components in the system


    Dave
     
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