Hobbie multimeter

[Fungus]

Sure, but if it happens to an experienced David L. Jones, it can happen to anyone.
The only question then is, how expensive the damage is. 

When I let the kids at Arduino club play with motors I get them to put a backwards LED in parallel with the motor so they can learn.

When you turn the motor off you see a flash. That's inductance... 

You can put a long string of LEDs and they'll still flash - the voltage goes as high as needed to find a path. Lesson: Be afraid of inductors.

[joeqsmith]

"Expensive devices will also break, better buy cheap ones to be less annoyed"? 
...
This is my little world. Everything fits into a drawer. 

Indeed.  I dare say of the equipment I own, the higher the cost, the more specialized they are and the easier to damage. 

Where I live, ESD can be a problem.   Recently I suspect I damaged one of those low cost VNAs with ESD while handling it.   A while back I was doing a series on 3-D printed horn antennas, looking at their radiation patterns.   While testing I was not wearing a strap.  I rolled my chair across the plastic floor mat.  Got up and touched the horn (which was grounded through some coax cable).   This event damaged a small amplifier.   I think the IC was under $30, so not the end of the world.

Of course, something like my scopes would cost more to repair.  Because of the custom parts used and their age, may not be repairable.   Normally I wear a strap.

[joeqsmith]

Lesson: Be afraid of inductors.

Of course, we could create high voltage using capacitors as well. 
 
https://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator

[floobydust]

Hobby multimeters can still be dangerous - measuring low voltage on Arduino projects etc. all is well-  but in the blink of an eye you need to repair an appliance, stove/dryer etc. and go taking measurements in the 240VAC world.

Got a DT-830D gift from a Taiwan trade show, wondered if it's better quality than the mainland.
Took it apart and looked at the clearances - could I keep it around in the toolbox as a junker? Use for mains measurements?
How many mm are people thinking is adequate, or do I instead need to make an offering to some deity to keep it safe lol.
So far this thread says yes "she'll be alright" 

[Fungus]

Hobby multimeters can still be dangerous - measuring low voltage on Arduino projects etc. all is well-  but in the blink of an eye you need to repair an appliance, stove/dryer etc. and go taking measurements in the 240VAC world.

YMMV.

Got a DT-830D gift from a Taiwan trade show, wondered if it's better quality than the mainland.
Took it apart and looked at the clearances - could I keep it around in the toolbox as a junker? Use for mains measurements?
How many mm are people thinking is adequate, or do I instead need to make an offering to some deity to keep it safe lol.
So far this thread says yes "she'll be alright" 

I don't know without seeing photos. I know Harbor Freight gives away millions of them in the US and there hasn't been a big lawsuit due to people dying.

If I absolutely had to get a really cheap meter for the people who look at batteries/mains with DT830s I think I'd go with this:

https://zotektools.com/products/zt-s2/

(or the more advanced model: https://zotektools.com/products/zoyizt-s4/ )

It's the poor man's Fluke 113. There's no dial to mess up, just switch on and use. It (tastefully) beeps and flashes a red light at you when the lead is in the current jack, and it feels completely indestructible.

(nb. you switch to current measurement just by moving the lead over to that input - no button press needed, and it only beeps when there's no current flowing so you can use it to watch a current on the bench but you'll never forget to put the lead back afterwards - they thought it through!)

The only downside is you can't measure under 0.8V - that's the cutoff where it starts measuring volts instead of Ohms/continuity.

[Aldo22]

The only downside is you can't measure under 0.8V - that's the cutoff where it starts measuring volts instead of Ohms/continuity.

No mV measurement? Really?
Then you can't recommend it for electronics.
It may be very robust and perhaps well suited for schools or for use in chimpanzee cages, but it's not really cheap (zt-s4)
I don't know why I would buy it.

For a similar price, I would rather take an ANENG ST212 or an AN8008. They can do more.

[Fungus]

No mV measurement? Really?
Then you can't recommend it for electronics.

I didn't.

I said, "If I absolutely had to get a really cheap meter for the people who look at batteries/mains with DT830s".

(although it is a fun meter for poking around PCBs to see what you can find - no need to adjust the dial between volts/ohms/continuity)

PS: I wouldn't recommend a meter for electronics without uA either, which rules out most Flukes.

[Aldo22]

No mV measurement? Really?
Then you can't recommend it for electronics.

I didn't.

Right, I meant in the sense of “it can't be recommended”

I said, "If I absolutely had to get a really cheap meter for the people who look at batteries/mains with DT830s".

That's the point. It's not really cheap.
Maybe there are different prices in different countries, but here, a  ZT-S4 costs US $17.53 on ZOYI Official Store (AE) (I could not find ZT-S2 on AE).
For that, or for very little more, I get a complete, accurate DMM.
I paid US $26.91 for my ZT-225 last August. That's cheap. 

PS: I wouldn't recommend a meter for electronics without uA either, which rules out most Flukes.

 

[Fungus]

That's the point. It's not really cheap.
Maybe there are different prices in different countries, but here, a  ZT-S4 costs US $17.53 on ZOYI Official Store (AE) (I could not find ZT-S2 on AE).

Literally the first hit for "ZT-S2": https://www.aliexpress.com/item/1005003690881213.html


The reason for getting that meter isn't the cheapness though, it's the simplicity (I don't want to say "fool proof" here - there's some ingenious fools out there).

If I want a cheap meter I'd get this one: https://www.eevblog.com/forum/testgear/trashy-meters-redux/

They're 3.5 Euros plus shipping.

[Aldo22]

Literally the first hit for "ZT-S2"

AE price comparisons without looking at shipping cost are useless.
That's $16.07 shipped. Not cheap for what it is.

ANENG ST212 DC/AC clamp meter also does (almost) everything automatically (I don't like that btw.), has a mV range and no A input at all (-> clamp up to 400A, but not accurate below 500mA), NCV, zero line, temp, frequency, capacitance, dual display etc.
There is even less that can go wrong.   
$22.97 shipped.

However, current measurement is also unsuitable for electronics. It is good for cars etc.

[Fungus]

AE price comparisons without looking at shipping cost are useless.

I don't know what shipping costs are in your region and it was just the first hit after you said you couldn't find one. Maybe there's a cheaper option.

PS: Don't judge "value" by feature set or until you used one.

[joeqsmith]

The only downside is you can't measure under 0.8V - that's the cutoff where it starts measuring volts instead of Ohms/continuity.

No mV measurement? Really?
Then you can't recommend it for electronics.
It may be very robust and perhaps well suited for schools or for use in chimpanzee cages, but it's not really cheap (zt-s4)
I don't know why I would buy it.

For a similar price, I would rather take an ANENG ST212 or an AN8008. They can do more.

Who is the real chimpanzee here?

Electronics is a broad subject.  My advice is buy the tools you need.   

[shapirus]

Dave made a video once where he was cycling some device with his power supply and damaged it.

Interesting video. 
What can I learn from it?

That even the little 5V coil inside a relay can destroy things if you're not careful.

It had nothing to do with the coil in that case. The damaged channel was shorted via the relay's contacts.

[EEVblog]

Indeed.  I dare say of the equipment I own, the higher the cost, the more specialized they are and the easier to damage. 

That's generally a deliberate design decision.
Try and find a high count bench meter that is as robust as a $50 hand held meter.
And it's not because it's bench. The hand held Gossen 6.5 digit 30M is only CAT II rated for example.

[joeqsmith]

Indeed.  I dare say of the equipment I own, the higher the cost, the more specialized they are and the easier to damage. 

That's generally a deliberate design decision.
Try and find a high count bench meter that is as robust as a $50 hand held meter.
And it's not because it's bench. The hand held Gossen 6.5 digit 30M is only CAT II rated for example.

I wasn't thinking about meters so much as my scope, VNA and SA. 

Meter wise, if we learned anything from those tests, its that more case does not insure more robust.  That $50 Fluke 101 is one of the most robust products I have looked at.  It's hard to find any handheld no matter the price, that will compete with it.   

I may bitch about Gossen's stupidity for not shielding the Ultra but I think their front end is pretty much bullet proof as well. 
 

[joeqsmith]

Dave made a video once where he was cycling some device with his power supply and damaged it.

Interesting video. 
What can I learn from it?

That even the little 5V coil inside a relay can destroy things if you're not careful.

It had nothing to do with the coil in that case. The damaged channel was shorted via the relay's contacts.

Sounds like you dug into it.   I watched the video and it sounds like Dave never found the root cause.   He stated that he was using the relay to short CH1 but had no video of it.  If we assume that is correct, did he have enough lead inductance to cause it or is there some sort of sneak path on the other channel driving the coil and the BEMF caused it?   I had used some crap power supplies for work once that would go up in smoke during radiated susceptibility testing.   The RF would cause the supply to go unstable and the output would swing high enough to trip the crowbar which could not handle the power and would short.   Is there enough crap from switching the relay that could have caused it?  What were your thoughts about the root cause?

 

[shapirus]

It had nothing to do with the coil in that case. The damaged channel was shorted via the relay's contacts.

Sounds like you dug into it.   I watched the video and it sounds like Dave never found the root cause.   He stated that he was using the relay to short CH1 but had no video of it. If we assume that is correct, did he have enough lead inductance to cause it or is there some sort of sneak path on the other channel driving the coil and the BEMF caused it?   I had used some crap power supplies for work once that would go up in smoke during radiated susceptibility testing.   The RF would cause the supply to go unstable and the output would swing high enough to trip the crowbar which could not handle the power and would short.   Is there enough crap from switching the relay that could have caused it?  What were your thoughts about the root cause?

Yeah I watched the entire video. At the end of it Dave demonstrated the exact same arrangement that he had in place when CH1 went dead and he could not reproduce the issue after the successful repair. He could not reproduce it when he randomly shorted bare ends of the leads directly by hand, either. The current regulation circuitry in the PSU consistently did its job and dropped the output voltage respectively every time the output was shorted.

What was the root cause of the pass transistor failing short initially? I have no idea other than a dodgy transistor (maybe partially damaged with ESD when it was hand-soldered at the factory?)
What else could it be? The rest of the components remained the same, nothing else was broken. I don't think it was inductive kickback, either, as there are some protection diodes there close to the pass transistor that are supposed to (I don't know how they're connected, but what else can it be) clamp any overvoltage on the pass transistor's terminals.
Was there something radiated by the coil onto the contacts that could cause issues? That sounds too fantastic to me, but I can't disregard it entirely as I do not know everything :).

p.s. I've been wondering about the BJT that was getting hot when the blown pass transistor was letting current through when it was supposed to be off. What is its purpose? It's apparently placed after the pass transistor, so can it be there to create load across the output terminals to quickly bleed off any residual charge when the pass transistor is being turned off or partially off? Does that make sense?