Author Topic: Can you use low impedance volt measurement to discharge capacitors  (Read 1852 times)

0 Members and 1 Guest are viewing this topic.

Offline Skippy

  • Contributor
  • Posts: 39
Just watched Dave's Agilent multimeter review. I see it's got a low impedance volt measurement input.

Could you use it to discharge  filter capacitors in power supplies? So, you've got 300V in your cap, you attach the probes, it's got 10k impedance across it, and you can watch the power drain out? Or would your multimeter melt? Or am I a numpty in some other way?
 

Offline Excavatoree

  • Frequent Contributor
  • **
  • Posts: 836
  • Country: us
  • Country: us
Re: Can you use low impedance volt measurement to discharge capacitors
« Reply #1 on: April 11, 2013, 01:36:10 pm »
In SOME cases, you might get away with it,  but honestly, why risk an expensive meter when a cheap resistor (chosen correctly) is the best way to do it?

 

alm

  • Guest
Re: Can you use low impedance volt measurement to discharge capacitors
« Reply #2 on: April 11, 2013, 03:03:13 pm »
The low impedance mode is not very resistive at high voltages. The Agilent U1272/1273A, for example, is specified as having a 2 kohm input impedance in lowZ mode on the 1000 V range. 1000 V across 2 kohm would dissipate 500 W, not going to happen. So there is something like a PTC in series that goes up in resistance as the current through it increases. It is designed to discharge the stray capacitance of wiring, I would not rely on it dissipating the energy from a large cap. It might very well go high resistance and stop discharging the cap.
 

Offline ddavidebor

  • Super Contributor
  • ***
  • Posts: 1134
  • Country: it
  • Country: it
    • Fermium LABS website
Can you use low impedance volt measurement to discharge capacitors
« Reply #3 on: April 11, 2013, 03:38:46 pm »
In SOME cases, you might get away with it,  but honestly, why risk an expensive meter when a cheap resistor (chosen correctly) is the best way to do it?
+1
Davide Bortolami,
Fermium LABS srl
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf