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Just being safe Capacitor discharge question

73.199.208.49
Posted on January 12, 2017 at 09:58:54
jk
Audiophile

Posts: 366
Joined: October 4, 1999
 Guys, thanks for looking. I've got to work on my VTL amp and I want to be sure I am being safe.

It appears that the right way to discharge the capacitors is to place a resistor across the terminals. My gut keeps telling me that I should be directing these electrons to ground, not the other terminal. So I'm just being sure. I once touched a charged cap and will never forget it.

 

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RE: Just being safe Capacitor discharge question , posted on January 12, 2017 at 10:01:49
jk
Audiophile

Posts: 366
Joined: October 4, 1999
 Ran out of room before I could say thanks for looking. Like I said I am just trying to be safe. John

 

Discharge across the terminals of the electrolytic cap..... nt., posted on January 12, 2017 at 11:38:23
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
 nt

 

RE: Discharge across the terminals of the electrolytic cap..... nt., posted on January 12, 2017 at 13:51:46
jk
Audiophile

Posts: 366
Joined: October 4, 1999
 Thank you Jea48

 

RE: Discharge across the terminals of the electrolytic cap..... nt., posted on January 12, 2017 at 22:23:58
6bq5
Audiophile

Posts: 4385
Location: SF Bay
Joined: August 16, 2001
 If the amp is built 'Properly' the negative terminal on the cap will be tied to ground - but as JEA suggests across the terminals is BEST - w/o reservation.
Happy Listening

 

RE: Discharge across the terminals of the electrolytic cap..... nt., posted on January 13, 2017 at 11:46:34
jk
Audiophile

Posts: 366
Joined: October 4, 1999
 6bq5, yes but what was bugging me is that the amp is totally isolated, no connection to earth so this is a virtual gnd. I conclude that there must be a potential difference between the terminals on a cap in order for it to discharge. Education is welcome.

 

RE: Discharge across the terminals of the electrolytic cap..... nt., posted on January 14, 2017 at 08:34:46
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
yes but what was bugging me is that the amp is totally isolated, no connection to earth so this is a virtual gnd. I conclude that there must be a potential difference between the terminals on a cap in order for it to discharge. Education is welcome.


Earth ground is not involved. What you are doing is discharging the DC stored energy in the cap by connecting a load, resistor, across the B+ and B- terminals, leads, of the cap.

The cap is connected in parallel with the B+ and B- rails, legs, of the DC power supply. The power supply, where a metal chassis is used, the B- rail of the power supply is connected to the metal chassis. The metal chassis becomes the ground plane for the power supply.

 

RE: Discharge across the terminals of the electrolytic cap..... nt., posted on January 15, 2017 at 17:54:59
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 Think of it this way, in a charged capacitor, there is "charge" accumulated on the plate we think of as the positive terminal. There is a similar "lack of charge" (for want of a better way of saying it and without getting too technical) on the negative terminal. If you were to connect these two terminals directly, there would be an explosive and instantaneous transfer of charge toward an equilibrium state. If you connect the two terminals via a large value resistor (e.g., 270K ohms or so), then the equilibrium state is reached in a more controllable manner over a longer period of time. If you don't provide for that, the charge just sits there and the capacitor is a potential source of a dangerous jolt. Ground has nothing to do with this. The capacitor is a self-contained system.

 

RE: Discharge across the terminals of the electrolytic cap..... nt., posted on January 16, 2017 at 11:26:06
jk
Audiophile

Posts: 366
Joined: October 4, 1999
 Thanks Lew!! That makes great sense. John

 

RE:Thanks Jea nt, posted on January 16, 2017 at 11:27:11
jk
Audiophile

Posts: 366
Joined: October 4, 1999
 no text

 

RE: Just being safe Capacitor discharge question , posted on January 16, 2017 at 20:42:30
AbeCollins
Audiophile

Posts: 46280
Location: USA
Joined: June 22, 2001
Contributor
  Since: February 2, 2002
I would be surprised if there's no bleeder resistor across the cap or somewhere electrically connected across the cap + and - terminals. The bleeder resistor normally discharges the capacitor over time when the amp is powered down. It can also provides some degreee of voltage regulation depending on the value.

You can place a resistor across the capacitor terminals or if you're brave, short the terminals together with a screw driver shaft. Bang! (Wear protective goggles or don't look).



 

RE: Just being safe Capacitor discharge question , posted on January 17, 2017 at 14:19:51
pmaneri@samsontech.com
Manufacturer

Posts: 152
Location: Long Island,NY
Joined: May 22, 2015
 JK-Don't EVER use a screwdriver to discharge a cap. It usually causes internal damage to the foils. That is a bad habit to get into. It will only lead to trouble.

 

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