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mosfet transistor for cordless drill

Discussion in 'General Electronics Discussion' started by gdc115, Nov 5, 2012.

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  1. gdc115

    gdc115

    3
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    Nov 5, 2012
    Hi, and thanks for looking at my post. I need a recommendation for a mosfet transistor for a cordless drill. The battery voltage is 14.4. The drill motor draws 5 amps initially and then it drops to 3 amps. When the drill motor stalls it draws 30 amps. I have replaced the original mosfet 2 times and have let the magic smoke out of the 2 replacements. The original mosfet was not readable so i couldn't identify it. And should an enhanced mosfet be used.

    Again, thanks for looking,
    Gary
     
  2. duke37

    duke37

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    769
    Jan 9, 2011
    What package was the mosfet in and what were the replacements?
     
  3. gdc115

    gdc115

    3
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    Nov 5, 2012
    The first replacement was this:http://www.radioshack.com/product/index.jsp?productId=2062618. I don't think that one was rated for enough current. The second replacement was from another cordless drill. However there was a diode wired in the circuit that is not in the cordless drill I am trying to fix. The second is too badly damaged to get any numbers so I can ID it. I suspect that the reason the second mosfet failed has something to do with the diode.

    Thank you,
    Gary
     
  4. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    The radioshack fet is a IRF510 in a TO220 package which they say is good for 60V and 3A.

    The IRF640 to IRF645 would do about 15A. There are many others.

    The diode could cause the problem if connected the wrong way round across the motor. It would then present a short circuit.

    When you fit a new fet, try initially in series with a 12V bulb in case there is a fault.
     
  5. gdc115

    gdc115

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    Nov 5, 2012
    I am having trouble understanding what you are saying. The diode was in the drill I took the 2nd mosfet from. The drill I put it in does not have a diode. I assume the diode is used to stop backfeed of the voltage spike that is created when the motor stops. Could this have caused the failure of the 2nd mosfet? If so, what mosfet would you recommend based on the voltage and current draw of the motor? Does an enhanced mosfet have built in voltage spike protection?

    Thank you for your reply,
    Gary
     
  6. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Might be at the motor, or internal to the motor or internal to the original part...

    Yes, it's generally called flyback...

    Possibly...

    Anything is possible on an OEM built part... And when it comes to a mass produced item like a drill it's very possible they would include the diode in the motor or MOSFET as a proprietary part to save part count...

    As for recommendations order it online and get the highest rated you can for the package unless the cost is huge, generally the cost is the same or pennies difference between low rated and high rated parts in the same series... Duke already recommended a series of higher rated ones...
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
    2,809
    Jan 21, 2010
    And if in doubt, add your own flyback diode. It won't hurt.
     
  8. NXP

    NXP

    1
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    Feb 19, 2013
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
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    Jan 21, 2010
    Chris,

    Welcome to Electronics Point.

    Please check your private messages.
     
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