Page 2 of 3 FirstFirst 123 LastLast
Results 14 to 26 of 32
  1. #14
    Join Date
    Jun 2011
    Location
    Houston area
    Posts
    1,493
    I just use my tongue. It's kinda like checking a 9 volt battery except it sometimes tingles a bit more.

    Naw, not really. I use an old Crastman screwdriver. Craftsmans work better than Kleins for some odd reason..
    The picture in my avatar is of the Houston Ship Channel and was taken from my backyard. I like to sit outside and slap mosquitos while watching countless supertankers, barges and cargo ships of every shape and size carry all sorts of deadly toxins to and fro. It's really beautiful at times.....just don't eat the three eyed fish....

    `. .` .>(((>

    `... `. .` .>(((>

    .` .>(((>

    LMAOSHMSFOAIDMT

  2. #15
    Join Date
    Nov 2011
    Location
    Gerald, MO
    Posts
    67
    a screwdriver

  3. #16
    Join Date
    May 2006
    Location
    Northern California
    Posts
    70
    Quote Originally Posted by Cooked View Post
    I just use my tongue. It's kinda like checking a 9 volt battery except it sometimes tingles a bit more.

    Naw, not really. I use an old Crastman screwdriver. Craftsmans work better than Kleins for some odd reason..
    I picked up a used service van a few years ago it was traded in by a retired hvac tech, he left about 50 caps and a few relays. The dealer asked if I wanted the caps and stuff that were left behind. After I agreed he then says that he caught his detail guy putting his tongue on the end of the caps.

  4. #17
    Join Date
    Feb 2006
    Location
    USA
    Posts
    4,367
    Quote Originally Posted by smoke View Post

    I have never seen a Run Cap hold a charge after the circuit has been de-energized.
    me either . . . until 2 weeks ago

  5. #18
    Join Date
    Nov 2011
    Location
    vancouver island canada
    Posts
    8
    You can use a screw driver but it really loads up the capacitor ie: high current and may damage it. a 20k 5watt resistor sounds fixed to me. I would go with the specified tool if I were doing it.

    Ryan

  6. #19
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    4,663
    I'd go with a 0 ohm resister. AKA, screwdriver.

    Unless you dealing with something big.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  7. #20
    Join Date
    Nov 2011
    Location
    Camp Verde, AZ
    Posts
    4

    Confused

    An way to discharge a cap is to connect to a volt metered _

  8. #21
    no

  9. #22
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,718
    First, a meter should not be used to discharge a capacitor, unless you like buying new meters often.

    Second, capacitors will hold a charge depending on how it is placed in a circuit.

    The reason a run cap doesn't hold a charge is because the motor windings discharge it very quickly. It does have low resistance, but it also has greater mass to dissipate the charge via heat.

    Unless it is placed in the circuit as a trickle charge capacitor. That is why there is a resistor on those aswell. To discharge the cap before a tech touches it. If you don't believe me, wire in a trickle circuit without a resistor across the terminals. Allow it to run, then pull the disconnect and check the voltage across the cap terminals.

    A start cap uses the bleed resistor for two reasons. One, to protect the potential relay from welding it's contacts, and two to save a tech from getting shocked.

    Yes, you need a 20kΩ 5watt minimum resistor.
    Theory... higher wattage resistors can dissipate heat better. That is pretty much what you're asking it to do, in order to discharge the cap.

    Typical caps are 370v when charging.

    Ohms law tells us E/R = I, and IE = P.

    So, when charging at 370V/20000Ω we get < 0.0185A. (charging is by reactance which is lower or < resistance of the resistor)
    When discharging to line voltage at 230V
    we get 230V * 0.0185A = 4.255W

    Using a screwdriver to discharge a cap is a good idea. Not so much for the equipment, but for you. I would much rather eat up a screwdriver or cap than get shocked. In most cases, the cap should be discharged before you have time to touch it. If it's not wired properly or an issue with the circuit, it could hold a charge. I don't know any tech that carries a 20kΩ resistor in his/her pocket. So a screwdriver is a good sacrificial alternative.
    Last edited by mgenius33; 11-30-2011 at 09:40 PM.
    "The only true wisdom is in knowing you know nothing" Socrates

  10. #23
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,718
    The charging part of that last post is wrong. Was just going off the top of my head.
    "The only true wisdom is in knowing you know nothing" Socrates

  11. #24
    Join Date
    Oct 2004
    Location
    Texas
    Posts
    1,172
    Notice the arc flash when you short the cap. For your start relay it will experience that arc flash on every start up if your start cap does not have the resistor. As for discharging when wanting drain the energy then short it or bleed it (speaking of capacitors in residential or small electric motor applications),NOT VFDs.
    Saddle Up!

  12. #25
    Join Date
    Oct 2011
    Location
    Hendersonville, Tennessee
    Posts
    30
    I don't know anyone who carries around a 20k ohm resistor either. Definitely use a screwdriver. Your teachers just tell you that because they have to give you the most professional methods available.

  13. #26
    Join Date
    Jul 2009
    Location
    Northern area between Alantic and Pacific
    Posts
    107
    How big the cap is,if small charge inside I just use screwdriver.

Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event