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Measuring discharge length safely — Parallax Forums

Measuring discharge length safely

ArchiverArchiver Posts: 46,084
edited 2002-06-28 23:40 in General Discussion
Hi All,

I want to measure the length of a capacitor discharge pulse. The cap is
charged to 75V. What is the best method? I mean to physically hook it up.
Can I just use a resistor large enough to drop the voltage to what the Stamp
can handle? Klunky, but will it work?

Thanks,

Jonathan

www.madlabs.info

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2002-06-27 18:25
    Hi Jonathan,

    Be sure to use a voltage divider made of 2 resistors, let's say 1K and 15K
    in serie, from the + of the capacitor, 15K, 1K, - of the capacitor. You
    measure accross the 1K resistor.
    The voltage would be 75 x 1K /( 15K + 1K ) = 4.6875 V. This could be
    acceptable.
    Double check with a multimeter first !

    Hope this helps...

    Phil.
    Original Message
    From: "Jonathan Peakall" <jpeakall@m...>
    To: <basicstamps@yahoogroups.com>
    Sent: Thursday, June 27, 2002 2:50 PM
    Subject: [noparse][[/noparse]basicstamps] Measuring discharge length safely


    > Hi All,
    >
    > I want to measure the length of a capacitor discharge pulse. The cap is
    > charged to 75V. What is the best method? I mean to physically hook it up.
    > Can I just use a resistor large enough to drop the voltage to what the
    Stamp
    > can handle? Klunky, but will it work?
    >
    > Thanks,
    >
    > Jonathan
    >
    > www.madlabs.info
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2002-06-28 21:53
    Jon:
    I was wondering if you could further elaborate on "I want to measure the length
    of a capacitor discharge pulse". What exactly are you trying to figure out or
    do? Find a value for a capacitor? If you know an emf value and a resistor you
    can calculate how long it would take to discharge the capacitor. I don't
    remember the formula off hand but i'm sure you can find it in a physics book. If
    you were going to somehow interface 75 volts to a stamp I wouldn't take any
    chances and do everything through an optoisolator.
    -=Randy Knutson

    Jonathan Peakall <jpeakall@m...> wrote: Hi All,

    I want to measure the length of a capacitor discharge pulse. The cap is
    charged to 75V. What is the best method? I mean to physically hook it up.
    Can I just use a resistor large enough to drop the voltage to what the Stamp
    can handle? Klunky, but will it work?

    Thanks,

    Jonathan

    www.madlabs.info


    To UNSUBSCRIBE, just send mail to:
    basicstamps-unsubscribe@yahoogroups.com
    from the same email address that you subscribed. Text in the Subject and Body of
    the message will be ignored.


    Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/



    Do You Yahoo!?
    Sign-up for Video Highlights of 2002 FIFA World Cup

    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2002-06-28 23:40
    Randy,

    I have a coil gun (shoots metal projectiles). You can see it at
    www.madlabs.info Calculating the discharge length of the capacitors is
    difficult, because the inductance is changing as the projectile enters the
    coil, and capacitor discharge rates with different cap arrays make a
    difference and so on. I don't have a storage scope, so...

    Just got some optoisolators today, and that is the plan. Any circuit
    suggestions? I'm good at building, not so great at design.

    Regards,

    Jonathan Peakall
    >
    > Jon:
    > I was wondering if you could further elaborate on "I want to measure the
    length of a capacitor discharge pulse". What exactly are you trying to
    figure out or do? Find a value for a capacitor? If you know an emf value and
    a resistor you can calculate how long it would take to discharge the
    capacitor. I don't remember the formula off hand but i'm sure you can find
    it in a physics book. If you were going to somehow interface 75 volts to a
    stamp I wouldn't take any chances and do everything through an optoisolator.
    > -=Randy Knutson
    >
    > Jonathan Peakall <jpeakall@m...> wrote: Hi All,
    >
    > I want to measure the length of a capacitor discharge pulse. The cap is
    > charged to 75V. What is the best method? I mean to physically hook it up.
    > Can I just use a resistor large enough to drop the voltage to what the
    Stamp
    > can handle? Klunky, but will it work?
    >
    > Thanks,
    >
    > Jonathan
    >
    > www.madlabs.info
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
    >
    >
    >
    > Do You Yahoo!?
    > Sign-up for Video Highlights of 2002 FIFA World Cup
    >
    > [noparse][[/noparse]Non-text portions of this message have been removed]
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
    >
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