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    Discharging Pas quad cap

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    poconoman

    Posts : 106
    Join date : 2013-01-17

    Discharging Pas quad cap

    Post by poconoman on Tue Feb 12, 2013 11:20 pm

    Before I do any work, what's the best way to discharge the quad cap and/or all caps?

    Thanks

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Discharging Pas quad cap

    Post by peterh on Wed Feb 13, 2013 3:10 am

    Have a multimeter ready, and a resistor 500-2000 ohm a little larger so it's convenient
    to handle.

    Then measure the voltage on the cap ( any of the + connections). With that value in mind
    then replace the multimeter with your resistor, one lead to the cap one lead to ground
    (any ground). Hold it for 10s, then repeat measurement. When you are down under 10V
    you are safe to work.

    Alternatives:
    One could create a "boxed" resistor with clip-on cables for the purpose. Or one could equip all amps with a "bleeder" of some 100kohm that will discharge in a few minutes.

    poconoman

    Posts : 106
    Join date : 2013-01-17

    Re: Discharging Pas quad cap

    Post by poconoman on Wed Feb 13, 2013 10:13 am

    Thanks for your help! This sounds easy enough! About the ground. An unplugged Pas or ST70 chassis is fine? If not, what's the best way? Also, what setting on the multimeter?

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Discharging Pas quad cap

    Post by peterh on Wed Feb 13, 2013 11:57 am

    poconoman wrote:Thanks for your help! This sounds easy enough! About the ground. An unplugged Pas or ST70 chassis is fine? If not, what's the best way? Also, what setting on the multimeter?
    the chassis _is_ the ground, any metal part will do(providing you get contact).
    You might be able to hear/observe a small flash when the resistor makes the first contact.

    when using a auto-ranging multimeter then it's easy. Other wise use the range
    applicable for the highest voltage you expect ( >300V DC )

    I remember that i used an old Simpson where i had mounted 100kohm across the
    leads, this was used solely to discharge caps at a workshop i worked in.That way
    one had regular testpins to poke around with and at the same time could see the voltage
    (falling ).

    poconoman

    Posts : 106
    Join date : 2013-01-17

    Re: Discharging Pas quad cap

    Post by poconoman on Wed Feb 13, 2013 12:46 pm

    Had a hunch the chassis is good. Just wanted to make sure.

    I guess I get the resister at Radio Shack?


    poconoman

    Posts : 106
    Join date : 2013-01-17

    Re: Discharging Pas quad cap

    Post by poconoman on Wed Feb 13, 2013 3:21 pm

    Got a 1 meg at 1 / 2 watt. Good?

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Discharging Pas quad cap

    Post by peterh on Wed Feb 13, 2013 3:40 pm

    poconoman wrote:Got a 1 meg at 1 / 2 watt. Good?

    one: it's physsically small ( your fingers will be close to cap voltage)
    a 2w is larger and easier to grab without risking "zaps"

    two: 1 mohm will draw 0.3mA, it will take ages to discharge
    1kohm will draw 0.3A initially ans in a few seconds discharge
    anywhere between 1k and 10k will do.

    poconoman

    Posts : 106
    Join date : 2013-01-17

    Re: Discharging Pas quad cap

    Post by poconoman on Wed Feb 13, 2013 4:41 pm

    peterh wrote:
    poconoman wrote:Got a 1 meg at 1 / 2 watt. Good?

    one: it's physsically small ( your fingers will be close to cap voltage)
    a 2w is larger and easier to grab without risking "zaps"

    two: 1 mohm will draw 0.3mA, it will take ages to discharge
    1kohm will draw 0.3A initially ans in a few seconds discharge
    anywhere between 1k and 10k will do.

    Ok, back to the shack. I have the receipt so I'm fine.

    1K-10K at 2W. Got it.

    poconoman

    Posts : 106
    Join date : 2013-01-17

    Re: Discharging Pas quad cap

    Post by poconoman on Wed Feb 13, 2013 5:36 pm

    peterh wrote:
    poconoman wrote:Got a 1 meg at 1 / 2 watt. Good?

    one: it's physsically small ( your fingers will be close to cap voltage)
    a 2w is larger and easier to grab without risking "zaps"

    two: 1 mohm will draw 0.3mA, it will take ages to discharge
    1kohm will draw 0.3A initially ans in a few seconds discharge
    anywhere between 1k and 10k will do.

    I found some 3W at 5.6K. Good?

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Discharging Pas quad cap

    Post by peterh on Thu Feb 14, 2013 4:28 am

    poconoman wrote:
    peterh wrote:
    poconoman wrote:Got a 1 meg at 1 / 2 watt. Good?

    one: it's physsically small ( your fingers will be close to cap voltage)
    a 2w is larger and easier to grab without risking "zaps"

    two: 1 mohm will draw 0.3mA, it will take ages to discharge
    1kohm will draw 0.3A initially ans in a few seconds discharge
    anywhere between 1k and 10k will do.

    I found some 3W at 5.6K. Good?

    That's ok. Be careful!

    poconoman

    Posts : 106
    Join date : 2013-01-17

    Re: Discharging Pas quad cap

    Post by poconoman on Thu Feb 14, 2013 10:43 am

    Thanks for all your help! I'll be careful.

    poconoman

    Posts : 106
    Join date : 2013-01-17

    Re: Discharging Pas quad cap

    Post by poconoman on Thu Feb 14, 2013 12:07 pm

    Another thought. Does it matter which lead on the resistor goes on the cap and the other on the ground?

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Discharging Pas quad cap

    Post by peterh on Thu Feb 14, 2013 4:21 pm

    poconoman wrote:Another thought. Does it matter which lead on the resistor goes on the cap and the other on the ground?

    No. A resistor is "symmetric" and non-polarized.

    poconoman

    Posts : 106
    Join date : 2013-01-17

    Re: Discharging Pas quad cap

    Post by poconoman on Thu Feb 14, 2013 4:41 pm

    Again, thank you. You've been fantastic! Very Happy

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