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logic level mosfet VS. relay — Parallax Forums

logic level mosfet VS. relay

ArchiverArchiver Posts: 46,084
edited 2004-02-24 01:49 in General Discussion
In another thread, a logic level mosfet, like an IRL520 is
recommended instead of a relay. Is a logic level mosfet much faster
than a relay?

I am currently using a transistor and relay to control on/off for a
drill. Same setup for forward and reverse. Would it be beneficial
to switch to a mosfet?

I have switched drills. I am now using a 6VDC cordless drill.

Thanks,
Frank

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2004-02-23 02:35
    A logic level MOSFET is indeed much faster than a relay, by a factor of 100
    or so. From memory, a typical relay may take 5 to 10 mS to close.

    If turn on and turn off speed is not a concern, as I think is the case for a
    drill motor, the transistor relay combination is just fine in my opinion.

    ken
    In another thread, a logic level mosfet, like an IRL520 is
    recommended instead of a relay. Is a logic level mosfet much faster
    than a relay?

    I am currently using a transistor and relay to control on/off for a
    drill. Same setup for forward and reverse. Would it be beneficial
    to switch to a mosfet?

    I have switched drills. I am now using a 6VDC cordless drill.

    Thanks,
    Frank


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2004-02-23 03:00
    Ken,

    Starting is no problem. I modified my code so I wouldn't overshoot
    my destination. I stop prematurely and inch up on the desired
    measurement.

    I may try the MosFet or switch to a DC Motor controller.

    Thanks for the info!

    Take care,
    Frank



    --- In basicstamps@yahoogroups.com, smartdim@a... wrote:
    > A logic level MOSFET is indeed much faster than a relay, by a
    factor of 100
    > or so. From memory, a typical relay may take 5 to 10 mS to close.
    >
    > If turn on and turn off speed is not a concern, as I think is the
    case for a
    > drill motor, the transistor relay combination is just fine in my
    opinion.
    >
    > ken
    >
    >
    > In another thread, a logic level mosfet, like an IRL520 is
    > recommended instead of a relay. Is a logic level mosfet much
    faster
    > than a relay?
    >
    > I am currently using a transistor and relay to control on/off for a
    > drill. Same setup for forward and reverse. Would it be beneficial
    > to switch to a mosfet?
    >
    > I have switched drills. I am now using a 6VDC cordless drill.
    >
    > Thanks,
    > Frank
    >
    >
    > [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2004-02-23 12:10
    Hi Frank,
    The MOSFET has a much faster switching time. I would imagine that unless you
    are using the drills in a robot for motion that the relay will work fine. When
    the DC motor starts, stops and runs it generates lots of electrical noise.
    The relay will isolate that from your control circuit. Im not sure what
    protection the MOSFET will need to drive a DC motor.
    The pullin time of the relay (5 to 100 ms.) is usually not a concern if you
    are still drilling. The motor will take as much time to come up to speed so
    turning it on 5 ms faster may sound good, but, like the EPA mileage ratings on
    new cars, is not going to buy you much.

    Hope this helps,
    Alan Bradford
    Plasma Technologies

    In a message dated 2/22/2004 9:07:09 PM Eastern Standard Time,
    franksmith512@y... writes:
    In another thread, a logic level mosfet, like an IRL520 is
    recommended instead of a relay. Is a logic level mosfet much faster
    than a relay?

    I am currently using a transistor and relay to control on/off for a
    drill. Same setup for forward and reverse. Would it be beneficial
    to switch to a mosfet?

    I have switched drills. I am now using a 6VDC cordless drill.

    Thanks,
    Frank


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2004-02-24 01:49
    Thanks for your reply Alan! It is appreciated.


    --- In basicstamps@yahoogroups.com, plasmastamp@a... wrote:
    > Hi Frank,
    > The MOSFET has a much faster switching time. I would imagine that
    unless you
    > are using the drills in a robot for motion that the relay will work
    fine. When
    > the DC motor starts, stops and runs it generates lots of electrical
    noise.
    > The relay will isolate that from your control circuit. Im not sure
    what
    > protection the MOSFET will need to drive a DC motor.
    > The pullin time of the relay (5 to 100 ms.) is usually not a
    concern if you
    > are still drilling. The motor will take as much time to come up to
    speed so
    > turning it on 5 ms faster may sound good, but, like the EPA mileage
    ratings on
    > new cars, is not going to buy you much.
    >
    > Hope this helps,
    > Alan Bradford
    > Plasma Technologies
    >
    > In a message dated 2/22/2004 9:07:09 PM Eastern Standard Time,
    > franksmith512@y... writes:
    > In another thread, a logic level mosfet, like an IRL520 is
    > recommended instead of a relay. Is a logic level mosfet much
    faster
    > than a relay?
    >
    > I am currently using a transistor and relay to control on/off for a
    > drill. Same setup for forward and reverse. Would it be beneficial
    > to switch to a mosfet?
    >
    > I have switched drills. I am now using a 6VDC cordless drill.
    >
    > Thanks,
    > Frank
    >
    >
    > [noparse][[/noparse]Non-text portions of this message have been removed]
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