EEVblog 1655 - Multimeter TIP: Discharge Capacitors using ANY meter

[EEVblog]

You can use almost any multimeter to safely discharge high voltage capacitor banks WITHOUT a LowZ function.

[David Aurora]

Yeah... nah.

I really don't feel good about this "using ANY meter" title. Or the whole idea in general to be honest.

We've all seen the ass blown out of meters that were used in the wrong modes. And whether or not they SHOULD be able to withstand it ain't the question here. There are too many different meters out there (not to mention meters that may already have damage the user isn't aware of). And then of course there's the question of what each meter tolerates when switching through functions live because whether or not people should, someone is DEFINITELY going to keep the leads connected and turn the dial. Or forget to turn it back and power something back on in ohms mode.

It'd be one thing if you had been using it as a trick to bleed off 5 or 10 volts before using an LCR meter or something, no argument there that this could be handy in a pinch, but using a few hundred volts in the demo seems like a bad suggestion to throw out there to people who might not know the potential pitfalls. In less than a minute you could have just explained the right way to do it. Or in half the time of this video you could've explained that and even gone into calculating discharge times and power ratings of bleed resistors and the whole 9 yards.

It just strikes me as bad practice overall, and given how simple it is to do it the right way I don't see a reason to reinvent the wheel on this one.

[JPortici]

Youtube gives me translated title+description, i hate that crap, i've probably unsubscribed to every channel that does that.

[Kleinstein]

The PTC current limit at high voltage gives quite some stress to the voltage clamp, especially if this are only BJT Base-emitter junctions. When could this could be only some 1.5 K from the PTC and thus up to 100 mA from 150 V and more from 300 or even 400 V. The meter should survive this at least a few times, but it could still be one of the weaker spots. DMMs with a blown ohms part are not that rare.

If one has a good alternative available, but not stress the meter. Repeated stress to this level may still cause small damage that can add up.

[Per Hansson]

When you use this trick to destroy the input protection of your UNI-T UT61E
(European TÜV Rheinland GS version with extra input protection) I have this thread that will show you how to fix it:
https://www.eevblog.com/forum/repair/uni-t-ut61e-diode-mode-repair/
 

[Ranayna]

Youtube gives me translated title+description, i hate that crap, i've probably unsubscribed to every channel that does that.

Can individual channels even do something about Youtubes automatic translation?
Feels like shooting the messenger if that is your reason to unsubscribe.

AFAIK there is a setting to disable this for you. I remember this happening to me as well.

[armandine2]

The PTC current limit at high voltage gives quite some stress to the voltage clamp, especially if this are only BJT Base-emitter junctions. When could this could be only some 1.5 K from the PTC and thus up to 100 mA from 150 V and more from 300 or even 400 V. The meter should survive this at least a few times, but it could still be one of the weaker spots. DMMs with a blown ohms part are not that rare.

If one has a good alternative available, but not stress the meter. Repeated stress to this level may still cause small damage that can add up.

...may still cause damage

.....umm, I wonder if any one will take up that "may" and test it?

[Kleinstein]

One could do the testing with a separate setup, of 2 BJTs as zener clamp and some current pulses (may not even need a high voltage and PTC). It is known that stressing BJTs to zener mode can make the transistors more noisy. So low noise amplifier should avoid this mode. It is a bit unclear if there is also increasing leakage and not just noise when used as an amplifier.

[JPortici]

Youtube gives me translated title+description, i hate that crap, i've probably unsubscribed to every channel that does that.

Can individual channels even do something about Youtubes automatic translation?

It is enabled by the content creator on a per-video basis

[Ranayna]

Youtube gives me translated title+description, i hate that crap, i've probably unsubscribed to every channel that does that.

Can individual channels even do something about Youtubes automatic translation?

It is enabled by the content creator on a per-video basis

YT seems to honor my browsers language setting. Which is set to prefer english. My work browser didn't even have german installed.
If i add german and switch the preference, the title of the video is indeed automatically translated. But the audio is still not. Might be my browser (a castrated version of chromium) or a YT A/B Test.
Now that i am thinking about it, the automatic translation of video titles might actually have been the reason why i switched the browser language to always prefer english years ago. I might have confused that with a setting in the Google/YT account. The german sites i use most still default to german, since most are not even bi-lingual.

I don't know how much control the creator has about this.

[EEVblog]

Ok, I don't want to keep getting email for the next 10 years, so I've updated and re-released the video to show disconnecting the probes before switching.

[JPortici]

I don't know how much control the creator has about this.

Seeing the EEVBLAB right now

Though currently it's still under control of the creator.
https://support.google.com/youtube/answer/15569972

[joeqsmith]

As you mention, not all meters are the same.   Maybe it have a surge rated resistor in series with the PTC.  Cheap meters I have looked at use a 5mm PTC with no series resistor.

I can see the wannabe home tech, repairing their microwave oven and thinking, I saw Dave recommend this so I'm just going to discharge the 1uF 2kV cap with my cheapo meter and cheap test leads.     

While you do mention it could damage your meter, from a safety standpoint, I use a homemade chickenstick.  These have some HV resistors.  Note the LED.  Turns off at about 10V.   

[joeqsmith]

Thinking about that, the 121GW has a low input.  It seems that the traces and switch contacts do not have a lot of clearance for that function.  It should be fine at the 400 or so volts from a typical PFC stage but I am not sure how it would handle the microwaves 2kV.   The two 121s I evaluated were already obsoleted at the time they were sent out.  It's possible that the newer PCBs addressed this. 

[axantas]

Youtube gives me translated title+description, i hate that crap, i've probably unsubscribed to every channel that does that.

Can individual channels even do something about Youtubes automatic translation?
Feels like shooting the messenger if that is your reason to unsubscribe.

AFAIK there is a setting to disable this for you. I remember this happening to me as well.

This is a strange new phenomenon. I prefer to hear Dave's explanation and not that artificial lady. The translation sounds rather silly - like Teleshopping. 
But: Thank you Dave, valuable information. 

[Geoff-AU]

Yeah... nah.

<snip>

It just strikes me as bad practice overall, and given how simple it is to do it the right way I don't see a reason to reinvent the wheel on this one.

Agreed.  Teaching people it's OK to abuse their equipment is poor form.

I will continue to use a resistor.

[David Hess]

There are some old multimeters that I might trust to discharge a capacitor because I know how good their ohms converter protection is, but I would not risk my modern inscrutable $300 multimeter for this.

I was not able to watch the video because it always comes up in a foreign language.  This is becoming more common but this was the first one on a channel that I care about.

[EEVblog]

I don't know how much control the creator has about this.

Seeing the EEVBLAB right now

Though currently it's still under control of the creator.
https://support.google.com/youtube/answer/15569972

I have turned off automatic dubbing. I presume this applies channel-wide.
EEVblog2 does not have the option yet.

[EEVblog]

I was not able to watch the video because it always comes up in a foreign language.  This is becoming more common but this was the first one on a channel that I care about.

Click the Settings wheel thingo and choose the language.

[JPortici]

I don't know how much control the creator has about this.

Seeing the EEVBLAB right now

Though currently it's still under control of the creator.
https://support.google.com/youtube/answer/15569972

I have turned off automatic dubbing. I presume this applies channel-wide.
EEVblog2 does not have the option yet.

Thanks!
I started seeing this on other channels as well. Hope they will be as receptive, because it's not only the titles, but it's the voice that i find really disturbing. Also hilariously wrong at all times.
Thankfully there is an extension for firefox -> https://addons.mozilla.org/en-US/firefox/addon/youtube-anti-translate/ works better than setting your profile / system locale because that doesn't even solve the problem. Set locale to english? my favourite german videos are in english. My favourite italian videos (well, none, but beside the point) are now in english. Good job google. maybe it's going to be added as a patch to revanced as well, fingers crossed

If anything, this forced me to finally check out odysee but eevblog is the only channel there

[golden_labels]

There is an on-topic update about discharging capacitors through a DMM in another thread.

[David Hess]

I was not able to watch the video because it always comes up in a foreign language.  This is becoming more common but this was the first one on a channel that I care about.

Click the Settings wheel thingo and choose the language.

Unfortunately that does not work for me because I do not watch Youtube videos through streaming, and Youtube does not associate language setting with the session cookie.

[JPortici]

EEVblog2 does not have the option yet.

Now it does

[EEVblog]

EEVblog2 does not have the option yet.

Now it does

So it does, they must have just enabled it.
Now disabled channel-wide.

[David Hess]

One could do the testing with a separate setup, of 2 BJTs as zener clamp and some current pulses (may not even need a high voltage and PTC). It is known that stressing BJTs to zener mode can make the transistors more noisy. So low noise amplifier should avoid this mode. It is a bit unclear if there is also increasing leakage and not just noise when used as an amplifier.

The noise goes up because the hfe falls, which increases the input bias current increasing the input current noise.

I tested the base-emitter junction of a 2N3906, and there was no increase in the leakage at 3 volts of about 20 picoamps after driving the junction into breakdown with 5 milliamps for an extended time.