Would a neon bulb work in a multi-meter for circuit protection?

[janoc]

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. 

Holy 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

[joeqsmith]

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. 

Holy 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 - the HV capacitor in a microwave alone stores enough energy to kill you on the spot. Why do the clueless people get so attracted to all the most dangerous stuff that one can find in a household today

Let 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/

[joeqsmith]

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. 

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.     

[Fungus]

That Persian Canadian's video should serve the purpose well enough. But one must know not everyone can touch a falling Jacob's ladder and live to tell the tale.

It takes a special kind of eyebrow to survive that.

[HKJ]

More and more Chinese meters are replacing glass fuses with ceramic filled ones, though not HRC rated, they should contain the arc safely even if directly connected across mains.

The part about "filled" is not always true, i.e. they are ceramic, but not filled.

And yes, there are mains connected devices using glass fuses, but you don't hold them in your hands when you plug in the power.

How do you plug in the small power supplies and chargers? They sometimes use glass fuses and often 10mm instead of 20mm fuses.

[janoc]

That Persian Canadian's video should serve the purpose well enough. But one must know not everyone can touch a falling Jacob's ladder and live to tell the tale.

It takes a special kind of eyebrow to survive that.

And 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.

[joseph nicholas]

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.     
[/quote]

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.

[tkamiya]

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.

[HKJ]

A lot of inexpensive meter and test leads say withstand 1000 volts but they usually don't.

How 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).

[joseph nicholas]

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.

When 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.

[Vtile]

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. 

[janoc]

A lot of inexpensive meter and test leads say withstand 1000 volts but they usually don't.

How 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).

1000V 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=354

Now 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.

[janoc]

When 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.

And 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).

[HKJ]

1000V 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.

I 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.

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=354
Now 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.

The 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.

[janoc]

1000V 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.

I 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.

You are fairly optimistic - I believe Dave has tested a few cheap meters with his megger and some have arced through at such voltages already.

The 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.

Of 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.

[HKJ]

You are fairly optimistic - I believe Dave has tested a few cheap meters with his megger and some have arced through at such voltages already.

I said the probe can handle 1000V and the meter 250VAC

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.

Any 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).

[james_s]

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.

[rsjsouza]

When 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.

Although 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).

[joeqsmith]

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.

Normally, 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.

[joeqsmith]

More and more Chinese meters are replacing glass fuses with ceramic filled ones, though not HRC rated, they should contain the arc safely even if directly connected across mains.

The part about "filled" is not always true, i.e. they are ceramic, but not filled.

I 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.

[joeqsmith]

I 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.

Jeez. I should be glad every time I smashed a fuse for curiosity I got some filler. So now they are making "ceramic" fuses without filler?

I 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.