Can You Discharge a Capacitor Using a Voltmeter?

We've received a lot of comments that many of you discharge run capacitors with a voltmeter. But can you (or should you) really discharge a capacitor with a voltmeter? Bryan tests this method on a turbo mini capacitor and compares it to the capacitor discharge tool he created.

When we tested discharging with a voltmeter, we used the black lead on the common. It took a very long time to reduce the voltage. However, the capacitor discharge tool almost completely discharged the capacitor within 2 seconds.

So, yes, you can discharge a capacitor with a voltmeter, but it will probably take a longer time than other methods.

[rj.parker]

If your digital meter has a LoZ or Low Impedance mode the cap discharge in a LoZ voltage mode will be quick. Normally a high impedance digital meter loads a circuit with an equivalent impedance of ~10 megohm where a low impedance mode, when available, is typically a 3k to 100k ohm load.

[lelandsowards]

You discharged 40V in 10 seconds with a multimeter. At that rate, you will fully discharge the capacitor in 40 seconds, not the "half hour" you mention.

[Gabrielishere]

I'm glad you still showed a multimeter discharging the cap, because all one has to do is have alligator leads handy, hook up the multimeter, and do something else for 15 or 20 minutes, and it works.

[valerietorres]

Thank you for making this video. I had to replace the run capacitor in my AC. Didn't have a discharge tool so I figured the multimeter was better than arching screwdriver. The capacitor was totally uncharged but I am thankful I had this option !

[samersarah]

Thank you for nice video. Is there a formula can use it to get an accurate reading? Second q should position the capacitor vertically or horizontally I saw some duct less mini split is positioned horizontally? Thanks.

[Aldodamnmuch]

Love the video. What gauge wire should I use for the cap discharging tool?

[jkbrown]

The time constant for capacitor discharge/charge is capacitance x resistance. With the rule of thumb, 5 time constants for essentially fully charged/discharged. Assuming some extremes, a 100 mfd capacitor @ 450 v. The time constant with a 20k ohm resistor is 2 s, 5x=10s. 450v on a 20k resistor = 22.5 mA. Not bad, that is an initial power discharge of 10 watts.

[jakebaldwin]

Any quick videos like this one that show the making of that capacitor discharge tool?

[chuckdearruda]

Great job Bryan! Thanks! You made a believer out of me. And this with only 5 MFD. Imagine 40 or 50 MFD.

Added: I stand corrected. This video is a perfect example of how old dogs can learn, correctly, what they thought they already knew.

[TheSwartz]

"Oh, I'll be fine!"

- famous last words ;)

[AlexRamosDrTaz]

Makes perfect sense! And no, I don't think I want to use a screwdriver. That might be OK for lower powered DC devices, though. (I do think that's how I messed up a circuit on a bass distortion pedal once... long story!)

[michaelcostello]

What percentage of capacitors you check will actually have a voltage and why do some not ?

[emanuel_]

Hello Bryan would it be possible to upload a video on how you made your personal discharge tool?

[xradiate]

Why not use the ohm feature of your multimeter and set it to the highest setting ?

[michaeln]

Can you discharge the capacitor using the amperage setting on the multimeter?

[nickg]

couldn't you switch it to ohm meter and dischrge it through the meter?

[Metalhead-life]

What about a meter with Loz function, is that quicker or even possible? I'm pretty sure I read you could use the Loz function to discharge a cap.
I need to solder some new IC's on an led tvs power supply board and figured I should discharge the caps first. 450v caps I believe.

I got a power supply repair kit for my model ps board off shopjimmy cause the ps board was out of stock. Hope it's pretty straight forward, my soldering skills are decent.

Nvrmnd it looks like the LoZ method has been addressed here in the comments already lol

[DanielBerzinskas]

I made a video about this a few years ago, only that I really used an analog meter!
Now, I have supercapacitors (10 F, 5.5V) which needs more current to discharge, and a short-circuit won't work well

[HLiRGiNJR]

Can I still discharge it and use the same capacitor?

[SteveP-vmuc]

I found you today through watching you with MATT. I trust Matt and he trusts you, so I am a new subscriber. I have now watched several of your videos and I have a few questions. It just so happens that one of our daughters is having a new system installed this week and also my parents are having an issue or two. So without a lot of explanation, here are my questions.
Starting with my parents ACHV system. We live in the Tampa Bay area, so hot and humid most of the year. We also have hurricanes and sometimes need alternative power. My father recently bought a portable generator that maxes at 7500 Watts surge. 6000 Watts normal run. He'd like to be able to run the house AC (WITHOUT HEAT), in times of long power outages. He's got a 3.5 ton unit that is 16 seer. I don't remember the brand. I think he could run his AC ONLY if the generator can handle the surge. NOT being a tech or even an electrician, I believe I understand that the capacitor is to give the fan and compressor motors a jolt to start up. His system has a cap on it from the factory, but I don't understand why we do not use a second cap for this surge/boost? Is it feasible? Can a second cap be added to reduce the pull or surge on the incoming power?
I'd also like your opinion on using UV LIGHT to kill and keep mold from growing?

Last Q. Is it true that the air handler and the indoor and outdoor units cannot be mixed as they use to be? My daughters air handler is pretty well plugged and in a inside closet. Very difficult to work on and the entire unit must be removed to pull the fan. She got an estimate and asked what it would cost to put in a new air handler that COULD BE serviced. She was told it is no longer legal to mix units. I realize they would have to be compatible, but that sounds like BS to me. Please advise on all. I truly appreciate it!!