Would a neon bulb work in a multi-meter for circuit protection? - Page 1
Forum section: electronics / testgear

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 26, 2018, 05:04:23 pm
content: I've been thinking a neon tube across the input of a DVM might work as a protection circuit instead of a GDT. They are essentially the same thing. Any opinions? I say this because it would give a visual indication that ac is present in the circuit you are testing as well as providing some limited shunting of voltage spikes in DC applications. It seems it really is just a GDT, but of course, not rated. Just thinking out side the box.

author: james_s
author_rank: Super Contributor
timestamp: March 26, 2018, 06:01:49 pm
content: What happens if you want to measure a voltage higher than about 75V? I don't think a neon bulb is going to offer a whole lot of protection either. When I was a kid I got a NE-2 and did not yet know about the need for current limiting. I poked the leads into the end of an extension cord and plugged it in, *bang*! The bulb turned completely silver-black and bounced off the ceiling, the leads had completely vaporized.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 26, 2018, 11:48:39 pm
content: Rather than trying to put neon bulbs in your meter, it may be time to think about getting a better meter.

author: maginnovision
author_rank: Super Contributor
timestamp: March 27, 2018, 01:04:17 am
content: You probably don't get a neon lit meter with a better meter though. That's the kind of stuff you rely on the makers for.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 27, 2018, 01:05:01 am
content: I keep buyin um they keep breakin. Mostly they get damaged because of operator error. It always seems to involve high voltage which of course one is told not try to measure. I though about this when someone suggested that a neon bulb could be used to detect a kick back from a choke when the magnetic field collapses. Anyway I liked the idea of using this as a high voltage surge suppressor.

author: Brumby
author_rank: Unknown
timestamp: March 27, 2018, 02:06:24 am
content: Yeah .... When you see neons across the mains, there's a reason they have a 100K series resistor in place.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 27, 2018, 02:36:21 am
content: Quote from: joseph nicholas on March 27, 2018, 01:05:01 amI'm curious what specific meters you have bought and broke with your high voltage choke transients? It would be interesting to know what the test setup was that damaged them as well. If you have something documented that was known to damage one of your meters, I could attempt to replicate it. Then, assuming it's not some crazy 121GW, I could apply it to the meters I have and see if it damages any of them. It may give you some idea is there is any meter out there that would survive.

author: Brumby
author_rank: Unknown
timestamp: March 27, 2018, 03:06:36 am
content: ^^^ Now THAT'S an offer I'd encourage the OP to take up! ^^^

author: Fungus
author_rank: Super Contributor
timestamp: March 27, 2018, 06:48:37 am
content: Quote from: joseph nicholas on March 27, 2018, 01:05:01 amYou can get high voltage probes for that.(or just make a resistor divider to divide the voltage by 10 or 100 - which is what high voltage probes are internally)Quote from: joseph nicholas on March 27, 2018, 01:05:01 amIt may work for very short spikes of electricity on small coils but it's not going to work as a general purpose safety device, because...Quote from: blueskull on March 27, 2018, 01:07:01 am...this.There's no current limit so it's going to explode with any sustained current.

author: Fungus
author_rank: Super Contributor
timestamp: March 27, 2018, 06:52:46 am
content: Quote from: joeqsmith on March 27, 2018, 02:36:21 amYep. Are they fancy Fluke meters or are they disposable 830Bs?

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 27, 2018, 10:13:22 am
content: I just buy cheap meters for China like the DT830 only because the postal delivery here is hit and miss. I could buy something used like a Fluke but these aren't all that cutting edge like the Aneg multi meters. What is interesting is what is the difference aside from the obvious between say a neon bulb and a GDT except one is a safety device and one is just an indicator. They both work in similar ways. So... just for fun suppose you tried to swap the GDT for a neon bulb. How would it work? Would it actually ground a low power surge say from a static discharge or not. After all you can get 20 of these things for less that 4 dollars on line. I bet they would work for Joe Smiths grill starter test.

author: Gyro
author_rank: Super Contributor
timestamp: March 27, 2018, 10:26:52 am
content: The real differences are:- Electrode area - GDTs are designed for Arc discharge, much higher current density and different electrode materials. Neons only for glow discharge, much more fragile (as has been indicated previously), they cannot withstand Arc discharge, or even the 'Abnormal glow discharge region'- Gas composition and pressure are different resulting in:...-Different breakdown voltage. Neons break down at 70-90V. GDTs are typically specified at 230V (telecom), 1kV etc.They really are very different beasts.Edit: Neons would probably work for static but no more.

author: Fungus
author_rank: Super Contributor
timestamp: March 27, 2018, 10:46:18 am
content: Quote from: joseph nicholas on March 27, 2018, 10:13:22 amBetter!(a GDT is designed to handle several amps, a neon bulb isn't)

author: Brumby
author_rank: Unknown
timestamp: March 27, 2018, 10:49:44 am
content: This is the prime difference:Quote from: Gyro on March 27, 2018, 10:26:52 amA 90V breakdown voltage is pretty useless if you want to measure 120V.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 27, 2018, 12:48:17 pm
content: Quote from: joseph nicholas on March 27, 2018, 10:13:22 amSo when I suggest buying a better meter, you would rather buy cheap ones and keep replacing them. I assume that has not worked out so well for you and replacing meters has become too costly. Rather than buy a better class of meter, you want to try to modify one with a $0.10 neon bulb to save money. For now, let's forget about the cost and Darwin awards.One thing about a GDT, they will not stop conducting until the current drops to basically nothing. You put DC across it and if the tube fires it will basically short out the supply. The MOV will act more like a zener. You could put a MOV in series with a GDT to get the reset and higher voltages. I've tested a meter that was designed like this. One thing I have yet to test is a handhel meter where they have placed a clamping device (GDT, MOV or neon buld) directly across the inputs. There is always a PTC or something there to limit the current. Even with the cheap ANENG meters you mention.The ANENG meter is a bit special in that they actually do have a clamp right across the inputs. It's called the rotary switch. You may feel these meters are cutting edge. I say they have set back the front end designs to the stone ages..The grill starter is a very short high voltage transient. Everything is done and over in under 10ns. The peak current is much lower than the standards call for. Hard to say if the neon bulb would do anything for it or not. Same for putting a MOV across it.You are damaging your meters with some sort of magnetic choke field collapse. I suspect this transient will have a longer decay, slower rise time, potentially much higher energy and a much lower peak voltage. I mention this because it sounds like you may feel that if it survives the grill starter, it would survive what ever you are doing. This may not be true.Show me what the setup that damaged your 830 and I will get a couple of 830s, attempt to replicate your test, install a neon bulb in the second meter and see if it then survives. If it does, we will try the piezo grill starter. If it survives that, I will use the ESD gun I designed. If all of that survives, we can try the other generators. Maybe finish the job with that half cycle simulator. This is what happens to a light bulb when placed across it. Second video talks about MOVs and GDTs.https://youtu.be/ms5OIBnQ_ig?t=17https://youtu.be/wYCGnYglRjY

author: Fungus
author_rank: Super Contributor
timestamp: March 27, 2018, 01:32:11 pm
content: Quote from: joseph nicholas on March 27, 2018, 10:13:22 amGet a Fluke 101. They cost under $50, delivered. You'll have great difficulty zapping one of those.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 27, 2018, 02:44:05 pm
content: Thanks for all the answers. My question definitely got answered and more. To Joe's inquiry, I though it would be fun to measure the discharge from my stove top electric igniter. I had a 10x1M series of resistors in a DYI probe but I forgot to use this instead I just hooked it up with a normal probe. Well needless to say it blew the meter. These meters come to me in various states of non function to begin with. One works on ac voltage but the low ohms range does not, or one works like it should but the buzzer does not. Well you know the story. I just tell the seller the problem and he refunds my money.The last meter I got I decided to go with the Bside ADM08A because it had a CATIII rating. Very pleasantly surprised because everything worked except one of the probs was a bit wonky, just needed to have the contacts adjusted. It cost 20 bucks. No auto ranging, but who cares. Instead of using it I tried to sell it. Nobody was interested, they just brought out their Flukes to show what they already had. Flukes are the standard here in Mexico.I really wanted the Aneng, and ordered a few of them, but they never seem to make it here. The Bside did only because certain Chinese sellers send things over 20 dollars in a different way not through the gov postal system. I choose the Bside because it was the closest thing to the Aneng I could get with a CATIII rating. I opened it up and it has proper fuses and even a tantalum cap not an el cheapo but not the DT830 either.

author: janoc
author_rank: Super Contributor
timestamp: March 27, 2018, 03:13:50 pm
content: Quote from: joseph nicholas on March 27, 2018, 02:44:05 pmIf you trust a CAT III rating on $20 meter not being fake (i.e. the meter didn't see an actual test lab even from the plane that brought it into the country) and use it for measuring anything high-voltage or high energy ...QuoteAnd you think someone would buy a used Chinese special that costs $20 new?Fluke has kinda religious following among many people but the fact is that their meters are of excellent quality andsafe. People don't buy them just to have a $500 toy to show off but because they have only one life. If you are poking the probes into anything connected to mains or high voltage, I would strongly suggest you actually follow their example - doesn't need to be a Fluke, there are plenty of good quality brand name meters in all price brackets on the market (Agilent/Keysight, Amprobe, Brymen, etc).And if you are breaking so many meters (even cheapo ones), I would strongly advise to step back and look at what you are doing - and why the meters are breaking. That isnotnormal.Seriously, you are asking for a Darwin award with your attitude. Not to mention that if you have saved all that money you have wasted on crap meters you could have probably bought that Fluke already.

author: james_s
author_rank: Super Contributor
timestamp: March 27, 2018, 04:46:28 pm
content: I bought a Fluke years ago based on their reputation and I'm still using the same meter, it has never had any problems. There's a reason everyone has them, and you've demonstrated why, these cheap meters are mostly crap and by now you have probably spent enough on junk meters to pay for a used Fluke. There are other good meters out there too but none of these no-name Chinese ones are any good, and certainly they don't hold their value like a Fluke, Agilent, etc.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 27, 2018, 05:25:19 pm
content: Quote from: joseph nicholas on March 27, 2018, 02:44:05 pmAs I now understand, you have damaged at least one with and electric stove igniter and others with some BEMF transient. I am not too surprised by the stove igniter damaging one but am still interested in knowing more about the BEMF transients you first mentioned.I have seen a few people post besides yourself who wanted to "measure" the output of an igniter. Again realize that the whole event is over in just a few ns. Even if it repeats every few ms, the duty cycle would be so small, I am not sure what you would expect to see beyond a dead meter. I did have someone write to me once how their analog meter could measure ns events.Again, forgetting the safety risks and Darwin awards, I did run a few of those cutting edge ANENG meters. Their poor design (using the switch for a spark gap) allow them to survive fairly well with my tests. However, I test at VERY low energy levels compared with a CAT III environment. Something goes wrong there, you won't be limited to 10-20 Joules. Just something to consider. It may be possible to get one to survive some basic transients like I run . Why anyone would ever attempt it beyond for educational or entertainment purposes is beyond me. This video shows the final changes I had made after destroying four of them. Again, I would NEVER suggest modifying a handheld meter because of the risks involved.https://youtu.be/EkQ6CCj7jmU?list=PLZSS2ajxhiQDdiope9HBA8uOD1SbLP5XC

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 27, 2018, 06:54:00 pm
content: As I now understand, you have damaged at least one with and electric stove igniter and others with some BEMF transient. I am not too surprised by the stove igniter damaging one but am still interested in knowing more about the BEMF transients you first mentioned.I have seen a few people post besides yourself who wanted to "measure" the output of an igniter. Again realize that the whole event is over in just a few ns. Even if it repeats every few ms, the duty cycle would be so small, I am not sure what you would expect to see beyond a dead meter. I did have someone write to me once how their analog meter could measure ns events.Again, forgetting the safety risks and Darwin awards, I did run a few of those cutting edge ANENG meters. Their poor design (using the switch for a spark gap) allow them to survive fairly well with my tests. However, I test at VERY low energy levels compared with a CAT III environment. Something goes wrong there, you won't be limited to 10-20 Joules. Just something to consider. It may be possible to get one to survive some basic transients like I run . Why anyone would ever attempt it beyond for educational or entertainment purposes is beyond me. This video shows the final changes I had made after destroying four of them. Again, I would NEVER suggest modifying a handheld meter because of the risks involved.https://youtu.be/EkQ6CCj7jmU?list=PLZSS2ajxhiQDdiope9HBA8uOD1SbLP5XCI watch your videos and like your work.I modify my meters all the time because it just seems like a good way to learn. I have a DT 9205A, not a bad device if it was in good working order but unfortunately some of the capacitance function did not work out of the box. I took it apart and got a schematic for it and traced the problem down to one of the two op-amps it uses to do the measurement. I ordered a replacement ic, I think its a LM324 and when it comes I'm going to replace it and see if it was the problem. Seems like a great way to work on your diagnostic skills, soldering smd components and reading schematics. I was scratching my head trying to understand why there were 3 potentiometers and what they did. One was to adjust the voltage reading (AC and DC), the other two I don't know. It had a place for an led but it came unpopulated. So I added it in. Except for the capacitance function I ended up with a something I can use, it beeps on continuity and flashes an led.As to safety: I have used all my meters even the cheapest junk to measure the 123v ac in my house. No problem. I measure microwave oven transformers with a 10x`s resistance probe I made for a few dollars. Works great, and now I have the confidence to measure old CRT flyback transformers safely. No need to buy expensive things to check high voltage. Just make them yourself and satisfy your curiosity.

author: Fungus
author_rank: Super Contributor
timestamp: March 28, 2018, 06:13:16 am
content: Quote from: joseph nicholas on March 27, 2018, 06:54:00 pmI don't doubt that almost any meter will measure mains if you follow procedure and do it perfectly."Safety" is there for when you mess up: We all have bad days.I invite you to connect one of your junk meters to the mains and turn the range selector through the resistance and diode test ranges. Just for curiosity's sake.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 28, 2018, 08:21:59 am
content: QuoteI think it is better to find a safer hobby, like jump from a plane during a hurricane with a DIY parachute made from C-grade Chinese T-shirts. Or what about Russian Roulette, use a .22 those bullets are small and cheap so it can not be dangerous....Aneng cutting edge ? More like cutting costs.No problem making things your self, if you know what you are doing. And you have not a single clue about what you are doing.QuoteThinking out of the box has nothing to do with it, you are not thinking at all.Testing things is fun and educational but not this way

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2018, 10:12:23 am
content: Quote from: joseph nicholas on March 27, 2018, 06:54:00 pmGlad you enjoy them.I also have modified several handheld meters when making these videos. These meters get clearly marked and should never be used outside of my controlled tests.I've made a few of my own probes as well. When I first started testing these meters, I received a few comments how it was unsafe and stupid to use my Tektronix probe to monitor the waveforms. These nut jobs were coming out of the woodwork. I would still use that probe for these tests had I not exceeded its rating and did not want to risk damaging it. The scope probe I use now is home made. It works fairly well. Cost/performance wise, I think it would have been better to get a used high voltage probe but as a electronics hobbyist, I enjoy designing and making things.For low frequency, I used to cobble up HV resistors every time I needed to measure something with a meter. It was not until recently that I finally constructed an attenuator just for this purpose. This one contains two HRC fuses, several HV resistors and a GDT. It's balanced so there is no polarity and the current is limited in both legs. The whole thing is potted. It's designed so even with a double fault, the meter should survive when using it. Someone complained how it cost too much. Then there were people asking if it was safe to use.It seems you are avoiding posting details about your BEMF transient that you first mentioned damaging your meter. I assume you did not make this up and it really happened. So is it a case where you just did not document what it was you were doing at the time? Any chance you could reconstruct the setup from memory or describe it.https://youtu.be/kWOe803atvghttps://youtu.be/bj_YndfA4Qs

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 28, 2018, 10:43:52 am
content: I guess there was some miscommunication. I actually just made the same error I did with the stove igniter. I was messing around with microwave oven transformers and didn't read the or believe the manual about not measuring voltages above 1kv.I only actually ruined 2 meters by measuring high voltage. Both times the meter just squeaked and I think it cooked the cob. After seeing how these meters cant protect themselves I constructed my 10M probe and use it for everything above 1kv.Your video on constructing a balanced attenuator was very educational. I have started buying resistors to construct one of my own design. I plan on using a larger enclosure and not potting it up in case it needs modification or I want to change something. Putting it in a large enclosure with added creapage distances will add to the protection I believe.Adios

author: janoc
author_rank: Super Contributor
timestamp: March 28, 2018, 10:55:47 am
content: Quote from: joseph nicholas on March 28, 2018, 10:43:52 amHoly molly dude ...You do realize that MOTs generate like 5kV and quite a few amps? And you have attempted to "measure" this using one of these crap meters, without a proper high voltage probe?You really do have a death wish. Why do the clueless people get so attracted to all the most dangerous stuff that one can find in a household today

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2018, 11:16:42 am
content: Quote from: janoc on March 28, 2018, 10:55:47 amLet me just take the wife's microwave oven apart and make a funny video about it. You have adults making videos targeted to curious children showing MOTs. Seems like this is the expected outcome.http://newyork.cbslocal.com/2016/04/20/teen-electrocuted-youtube/

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2018, 11:40:23 am
content: Quote from: joseph nicholas on March 28, 2018, 10:43:52 amThe potting makes it heavy but it's sealed and I have zero concern of it if breaking down. The box is about the size of a meter. The fuses and HV resistors are fairly large. Yes, I could have made it without potting it. It has Teflon spacers in it and most likely would survive anything I would ever throw at it with no potting, as is. It's just one more added step. IMO, this is a better approach to making HV measurements than adding the neon bulb assuming that it is done correctly. Unlike a standard HV low frequency probe with a common ground, I like that this attenuator limits the current through other potential faults but to each their own.

author: Fungus
author_rank: Super Contributor
timestamp: March 28, 2018, 12:11:18 pm
content: Quote from: blueskull on March 28, 2018, 11:57:24 amIt takes a special kind of eyebrow to survive that.

author: HKJ
author_rank: Super Contributor
timestamp: March 28, 2018, 12:24:31 pm
content: Quote from: blueskull on March 28, 2018, 07:10:40 amThe part about "filled" is not always true, i.e. they are ceramic, but not filled.Quote from: blueskull on March 28, 2018, 07:10:40 amHow do you plug in the small power supplies and chargers? They sometimes use glass fuses and often 10mm instead of 20mm fuses.

author: janoc
author_rank: Super Contributor
timestamp: March 28, 2018, 01:02:03 pm
content: Quote from: Fungus on March 28, 2018, 12:11:18 pmAnd also an actual EE degree and knowledge about what one is doing. His videos are funny and he looks like a fool that is constantly asking to get killed but he knows very well what he is doing.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 28, 2018, 04:21:46 pm
content: The potting makes it heavy but it's sealed and I have zero concern of it if breaking down. The box is about the size of a meter. The fuses and HV resistors are fairly large. Yes, I could have made it without potting it. It has Teflon spacers in it and most likely would survive anything I would ever throw at it with no potting, as is. It's just one more added step. IMO, this is a better approach to making HV measurements than adding the neon bulb assuming that it is done correctly. Unlike a standard HV low frequency probe with a common ground, I like that this attenuator limits the current through other potential faults but to each their own.Of course potting up something is safer but spending all that time and effort on construction then not being able to fix it when it stops functioning for any reason is not the way if would do it. I'd like to tweak it in case stray capacitance or something else caused by putting potting compound around a device happens. If you plan to sell it then it would need the compound.I've seen videos where people complained of stray inductances when making HV oscilloscope probes, but of course you know about that from your high voltage scope probes.

author: tkamiya
author_rank: Super Contributor
timestamp: March 28, 2018, 04:37:39 pm
content: I am not sure if any meter is hardened enough to survive what OT is doing.Microwave oven transformer is, at minimum, 2K volts, usually more. I'm so glad he is still "here" to tell us about it.There are two rules that I always go by.1) know what kind of voltage I am expecting and select the range accordingly.2) if that is unknown, go from the highest.A lot of inexpensive meter and test leads say withstand 1000 volts but they usually don't. Using these will require such technique as powering the machine down and bleed any stored energy. Use allegator clip and afix the probes. Then turn on the power, fully expecting something might blow. If you start an arch, insulator can melt, wires break, and have enough force to launch itself and land on your hand, if you are too close.Please, please.... stay safe.

author: HKJ
author_rank: Super Contributor
timestamp: March 28, 2018, 04:46:43 pm
content: Quote from: tkamiya on March 28, 2018, 04:37:39 pmHow do you know that? 1000V is not that much, it first get bad when you add the CAT rating and what type of voltage they requires for a 1000V rating (CAT IV 1000V must handle 12000V).

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 28, 2018, 04:50:49 pm
content: Quote from: tkamiya on March 28, 2018, 04:37:39 pmWhen I did this the transformer was out of the microwave. I put the meter on the ground, used alligator clips to attach it and stood back away so no problem. There is a way to do it safely. People with children should encourage their kids to not experiment with high voltage unless supervised.

author: Vtile
author_rank: Super Contributor
timestamp: March 28, 2018, 05:29:06 pm
content: Neon bulbs were used even in top end meters back in the day, but they were used just before the input amplifier after the input resistor network.

author: janoc
author_rank: Super Contributor
timestamp: March 28, 2018, 06:07:18 pm
content: Quote from: HKJ on March 28, 2018, 04:46:43 pm1000V is not that much but do you actually trust the "rating" written on a $20 meter from China that doesn't have proper input protection and has never been tested? The same about the probe cables.And we are talking about a microwave oven trafo that can deliver significant current at that voltage, not a "soft" supply where the voltage collapses immediately should any insulation arc through.If he was doing it with a properly constructed meter it would have likely survived (but even then it is a very stupid thing to do, IMO!), but a $20 cheapie? Fluke has a good video of what happens at a slightest mistake (like selecting a wrong range) and that is "only" some 770V (that the meter is actually 'rated' for):https://youtu.be/OEoazQ1zuUM?t=354Now imagine you were anywhere near that or holding the probes. That is the famous DT830 variant but the Aneng and similar meters in this price range are not really any better.

author: janoc
author_rank: Super Contributor
timestamp: March 28, 2018, 06:14:37 pm
content: Quote from: joseph nicholas on March 28, 2018, 04:50:49 pmAnd what the heck did you actually expect to measure there? You don't believe people that that transformer outputs about 2kV (which is then doubled to about 5kV when the magnetron is connected to it)?Children definitely shouldn't experiment with high voltage, that I agree with. But I think you shouldn't neither because you have done the above without a proper high voltage probe (I wouldn't trust a bunch of resistors in series soldered together for this - all it takes is a bit of moisture or grime for the HV to shoot through over their surface!) and using a totally inadequate meter. And when the first one died, you tried it several more times, for good measure. You certainly don't sound like someone either qualified or knowing what they are doing to tinker with something like that.Do yourself a favor and stop before you end up in a hospital (or worse).

author: HKJ
author_rank: Super Contributor
timestamp: March 28, 2018, 06:26:21 pm
content: Quote from: janoc on March 28, 2018, 06:07:18 pmI do basically trust that they can withstand 1000V (I test a lot of stuff with a few thousand volt), but I doubt the CAT rating and in some cases also the longevity of the probes.Quote from: janoc on March 28, 2018, 06:07:18 pmThe protection in the cheap meters will usual handle 250VAC especially when it is fused at not too high levels, but using them in distribution or industrial settings is a very bad idea.

author: janoc
author_rank: Super Contributor
timestamp: March 28, 2018, 06:37:53 pm
content: Quote from: HKJ on March 28, 2018, 06:26:21 pmYou are fairly optimistic - I believe Dave has tested a few cheap meters with his megger and some have arced through at such voltages already.Quote from: HKJ on March 28, 2018, 06:26:21 pmOf course, as is poking a microwave transformer. That's a pretty high voltage, high energy setup.And those cheap meters will blow up even at 250VAC when set to the wrong range (e.g. current or ohms) - that's what the video was about. That crappy glass fuse (which some don't even have) is not much protection in such situation.

author: HKJ
author_rank: Super Contributor
timestamp: March 28, 2018, 06:48:57 pm
content: Quote from: janoc on March 28, 2018, 06:37:53 pmI said the probe can handle 1000V and the meter 250VACQuote from: janoc on March 28, 2018, 06:37:53 pmAny meter with a small PTC will usual handle 250VAC (That is most cheap meters), glass fuses can usual also handle 250VAC, but they may pulverizer and they are not guaranteed to handle high current (i.e. kA or even 100's of A).A microwave is high voltage, but the current is not that high. Power is limited to between 1kW and 2kW. Of course this is more than enough to fry a meter protected for 250VAC (Even though it is marked CAT III 600V as some of them are).

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2018, 08:42:34 pm
content: A microwave transformer typically puts out about 500mA at 2kV when then feeds a voltage doubler. Despite the magnetic shunts that limit the current, it would not surprise me if it can deliver more than that into a short. Either way it's rather academic as it's easily enough to be lethal and/or blow up a meter.

author: rsjsouza
author_rank: Super Contributor
timestamp: March 28, 2018, 09:40:27 pm
content: Quote from: joseph nicholas on March 28, 2018, 04:50:49 pmAlthough a hard fault to ground on the secondary will increase thermal losses on the transformer, it will still output a significant fraction of the 1000VA (2kV/.5A) - it will not go easy on a DMM that happens to be on the way, especially if you depend on its quality (or the lack thereof).That said, in my experience with the levels you are working, only poorly maintained or super low-quality DMMs like the ones you have been using will effectively be in danger of ejecting matter outside of their enclosure - I would be either behind a shield or at a very conservative distance. Anything with a decent enclosure (or even the rubber holster) will help contain the bang. Any issues with the voltage range or accidentally leaving the switch on the mA range (fused) of the DT830 will potentially be less consequential than plugging such voltage to the 10A unfused terminal.That only talks about damage to the equipment and not to the most significant element in the room - YOU.If you look at Joe's latest video about the Fluke 87V, you will see how it can withstand 1.6kV continuous DC on its voltage range without any perceptible change in its characteristics. However, this is a well built DMM with a very decent enclosure - I don't think it would survive a 2kV jolt as gracefully as it did, but I also don't think you would be at risk of it exploding in your hand/face as well.Taking this into consideration, I think Fungus' suggestion about the Fluke 101 is excellent, but unfortunately you are already having issues with either Aduana México ó Correos de México with cheaper Anengs - imagine what they would do to a Fluke!(I know very well what it is to deal with similar corrupt systems).

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2018, 10:56:10 pm
content: Quote from: joseph nicholas on March 28, 2018, 04:21:46 pmNormally, when I think of hand held meters, I think DC to KHzish bandwidth. The stray capacitance is not so much of a problem assuming good construction practices. The scope probe is another mater. There I am wanting to measure into the MHz and everything comes into play. That large HV probe was a fun little project to design and construct but required a lot more hair pulling than the attenuator.I get what you are saying about wanting to repair things and not wanting to spend a lot of time and effort on them. It's just a different mindset. Typically I want my designs to survive for my lifetime so I take my time with them. That's also why you see the high end components being used inside many of my projects. This attenuator was no exception and why the costs were so high. If it ever does fail, I should be fairly impressed with what ever it was that I did...There are various encapsulants available. The potting I used for the attenuator is reenterable and could be removed without too much problem.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2018, 11:03:22 pm
content: Quote from: HKJ on March 28, 2018, 12:24:31 pmI had recently tried to get a member here to open up a ceramic fuse on a cheap meter for this vary reason. I was showing how you can have name brand fuses that are ceramic and certified but not be HRC.The glass ones are always fun to dispose of but I like the tiny ones used on the ANENG meters. Those are so small, they can arc across the fuse with little effort. I tried some of these on my half cycle genertor and managed to crack the ceramic on one of them.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 29, 2018, 12:56:27 am
content: Quote from: blueskull on March 28, 2018, 11:29:52 pmI am not sure if that is new or not. The vast majority of the ones I have cut apart (even low voltage ceramics) have been filled. This includes what appears to be some counterfeit SIBA fuses. The tiny ceramic fuses used in the ANENG meters that I have looked at have not been filled.