Discharging a Simulated Microwave Oven Capacitor with a DMM

[@colinreid7305]

welcome back. Great information as per usual.

[@joesmith-je3tq]

Thanks. Been playing with other projects and the DMM testing was put on the back burner for a while.

[@ligius3]

Thanks for the video, hopefully this is the first and last time somebody with an audience suggests discharging with a DMM. Most of my non-EE friends have those cheap HF meters. If they heard about this method, it's only a question of time before somebody wants to discharge the socket to make it safer to work on. Maybe slightly safer than trying to measure the current of a socket. Yes, that is a thing people do.

[@leocurious9919]

In the comment of Dave (=EEVblog) here, he says you should not do it? So did he say to do that or not? And if so, why does it sound like he already knows that is a stupid idea?

[@VoeViking]

Would never use a dmm to discharge big caps, Merry Christmas.

[@EEVblog]

The Low Z mode is literally designed for this. Provided of course that you don't exceed the maximum voltage rating of the meter that Joe is doing here. I showed that it's possible, at a pinch, to use the ohms range to work in the same way as the LowZ range if you don't have it, obviously for voltages that don't exceed the maximum input rating. Just a handy tip if you ever need it and don't have a LowZ range or discharge resistor available. Who in their right mind would recommend what Joe is doing here at 2kV?

[@s_s-g4d]

@@EEVblog You have a point, and in your video you explain exactly why and when it's fine, but... Maybe it's not exactly a good analogy, but not all types of microscopes are suitable for hammering every type of nail. Sometimes it works, but since it's not exactly the intended use, the user needs to understand precisely what he's doing and what's expected to happen.

[@joesmith-je3tq]

@@EEVblog Of course if you watched the video, Joe states a few times that they too would never recommend this.

[@NiHaoMike64]

Easy way to discharge a microwave oven capacitor is first short across the diode using a plastic handle screwdriver, then across the cap itself. In the first case, the inductance of the transformer secondary will limit the peak current. Then the direct short is in case there's a bad connection preventing the discharge through the transformer.

[@joesmith-je3tq]

You know, using the secondary and you suggest to limit di/dt doesn't seem like a bad idea. At least with my microwave oven, the filter cap is stuffed way to the back and it is in a fairly tight space. There is no way I am reaching in there with my hand to do anything.

[@francomarianardini681]

thanks Joe!

[@pyromen321]

Your microwave capacitor discharger is much fancier than mine. I have a plastic stick with a half washer glued on the end. If the capacitor’s resistor is broken, I’d immediately know about it in a less fancy way :D

[@joesmith-je3tq]

Using the probes I show with the HV resistors, stress on the caps is greatly limited not to mention there are no weld marks on the parts. Doesn't give the show or sound of a good direct short though.

[@AethericTheorem]

Is there anyway you could do a video showing the inside of compensation network for your HV high bandwidth oscilloscope probe? I know you showed a schematic but seeing it visually how you built inside helps alot as a design aid. Also was wondering where you specifically sourced some of the parts that can't find... Like the end cap and the outside porcelain main insulator

[@joesmith-je3tq]

kzbin.info/www/bejne/oYiylmtmaManrMk

[@joshmyer9]

Are those probe to banana adaptors a standard part? I haven't seen them before, and they're kind of absurd (unless you're testing probes), but they seem like something I'd want to have in my box-o-this-to-that. Searching for them is proving exactly as challenging as you might expect. Happy Holidays to you and yours, thanks for the videos this year!

[@joesmith-je3tq]

Check out Pomonaelectronics, PN# 1809. Digikey and Mouser both carry them.

[@joshmyer9]

@@joesmith-je3tq Thank you!

[@EEVblog]

If anyone is dumb enough to discharge a 2kV 1uF capacitor using the ohms range of their meter, or even with the Low Z range, that greatly exceeds the max rated input voltage specification of the meter, then they deserve to get a blown meter.

[@keitha.9788]

"Hey, I'm making a KZbin Video, trust me....."

[@joesmith-je3tq]

Follow this channel and you will find I have been greatly exceeding the maximum input voltage rating on handheld DMMs for years. I suspect the meters that I have looked at that survive my low voltage transient testing would easily handle this condition. Still, as I stated in the video, this isn't anything I would ever suggest doing.

[@FISHERMAN33RUS]

I have discharged the condenser of the microwave owen with my ut71e by mistake. It was in V mode at that moment. Of course now it's shows the weather on Mars, but question is try to fix or not to fix equipment is not standing now days, to fix is the only answer. Of course i am beginner in electronics, and this mistake is typical, same as voltage measurements in current mode. You can short caps for ex in some PC power supply, during voltage measurements if do not track the trace in advance or discharge them first and can get same result. Ok, as you always said "puppy is probably dead" but hopefully i am alive, and i am thinking that beginners should have an opportunity for mistake, at least 1 time 😂

[@h7qvi]

Should use transorbs for the diode clamps

[@drkastenbrot]

not quite as clean of a curve, you really dont want any leakage over the operational band

[@Scorry]

Double glasses - checked. Using the same little lazy trick when I don't want to wear cumbersome dentist's glasses.

[@hightttech]

I repaired CRT monitors for decades, they store a nasty "SNAP", and i've NEVER heard of any tech discharging caps and CRTs with a DMM 😂. Must be a DIY thing. And I was shocked to learn from Joe's narrative that death by microvave oven electrocution is a THING. Darwin Awards anyboby?

[@leocurious9919]

Really not Darwin. Just look at all the safety warnings absolutely everywhere for every fart. And then there are actually deadly things and they have the same kind of warnings. How are random people supposed to know that one warning is more a suggestion and the other is about more or less certain death?

[@rustlebruxz0013]

I think a lot of injuries from microwaves is due to people using the transformers to create high voltage to burn interesting patterns into wood. There are pictures of some really horrible injuries on the web.

[@MaxPivovarov]

In my opinion, your results do not contradict Dave's statements. In this case, the allowable voltage threshold for this class of multimeters was simply exceeded. And frankly, the audience Dave made that video for definitely shouldn't be dealing with such equipment-not just with cheap multimeters, but in general!

[@s_s-g4d]

I think that developing a habit to use any DMM to discharge any capacitors is a bad idea, because, well, it's generally a bad habit to systematically rely on undocumented behavior.

[@MaxPivovarov]

@@s_s-g4d The main habit every electronics enthusiast should have is to think with their head before sticking their hands or multimeter probes anywhere.

[@joesmith-je3tq]

It was never a goal to contradict Dave's statements but rather build upon them. I can't speak for Dave's entire audience but I obviously watched their video and worked on such equipment. Granted, I would never make a suggestion about using the DMM in this way (which I stated a few times during the video), I wouldn't be surprised to hear about others following Dave's lead. And because I am not adverse to testing meters beyond their limits, here we are....

[@MaxPivovarov]

@@joesmith-je3tq This was by no means an accusation against you. I generally agree that discharging capacitors with a multimeter may not be the best practice, especially if you don't fully understand what you're doing. However, it doesn't contradict the multimeter's specifications (as long as you stay within the device's rated limits). I usually use a dedicated discharge probe similar to yours, but a few times "in the field," I've had to use a multimeter to discharge capacitors in power supply units.

[@joesmith-je3tq]

@@MaxPivovarov As I mentioned and demonstrated in the video, and Dave mentioned as well, not all meters are the same. Some meters will not use surge rated resistors, PTCs, MOVs or GDTs. I've seen them with jelly bean resistors only to limit the current, similar to the free HF meters. Let's assume you are correct and the topic is beyond the majority of Dave's audience. Personally, I would never opening the doors by making such a suggestion because it assumes the audience understands not only what you are presenting, but also the inner workings of their particular equipment. Suggesting the only caveat is that your DMM not survive seems unprofessional.

[@GadgetReviewVideos]

Hey Joe, I think I have two or three microwave caps if you want one for future videos. The one I am looking at now is a Samsung 2100W VAC 1.05uF with diode sitting on the shelf. Shoot me an email with a addy or PO Box and I’ll add it to my next UPs drop-off.

[@joesmith-je3tq]

Thanks for the offer but I am not sure if a standard microwave oven capacitor would like the repeated high dV/dT that a test like this would expose them to. This is a good application for film capacitors.