Electronics > Projects, Designs, and Technical Stuff
DMM Lead Arc getting voltage from power strip
bdunham7:
--- Quote from: DW1961 on July 26, 2020, 04:52:09 am ---
"Our products are equipped with professional voltage and current fuses. In case of misoperation and exceeding the maximum voltage/current range, the fuse will be blown first, and then the circuit board will be destroyed."
--- End quote ---
Oh dear. A teardown should be interesting.
coppercone2:
I have seen non obviously destructive sparks (high end meter must have had the protection circuit work) when contact was made with probes on the probe/board junction when using a DMM on voltages higher then its rating on the correct mode (i.e. 2kv). I think maybe it made LESSER sparks near the upper limit of its range.
obviously a mistake (similar equipment but they raised the voltage level between models that had near identical circuit topology/components)
Gyro:
--- Quote from: DW1961 on July 26, 2020, 04:52:09 am ---
--- Quote from: helius on July 25, 2020, 10:24:17 pm ---The "wire with a little bead on it" is a K-type thermocouple wire. It is designed for high-temperature use and isn't going to just melt (although the heatshrink could).
If your meter only reads AC amps using the clamp, it is unlikely to have any fuse.
--- End quote ---
Just got this back from teh Amazon merchant:
"I received this replay back fro the seller on Amazon, for what it's worth. He is saying it has both current and voltage fuses in it:
"Our products are equipped with professional voltage and current fuses. In case of misoperation and exceeding the maximum voltage/current range, the fuse will be blown first, and then the circuit board will be destroyed."
F-it! I can tear it apart and see if it really does?! It might be interesting. If it has fuses, I'm assuming it has a way to change them. I'll ask the merchant.
--- End quote ---
Yep, they're talking complete bollocks. ::)
DMMs use VDRs and PTC thermistors for voltage ranges, and those only come into play when it is subjected to gross overload.
It will be using a current transformer for the current jaws (hence AC only), but it's easy to clamp the high impedance current output - actually a fuse opening on the output [Ed: of the] transformer would turn it into a very high internal voltage source!
I'd return it as defective - only do a teardown if you don't have to break any seals and hide the serial number. Try to find one that isn't manufactured by "RockSeed" ;)
P.S. A reputable supplier would apologise for melting the end of your probe, scaring the life out of you, and ask you to return it for urgent investigation - not burble on about its mythical fuses.
tooki:
--- Quote from: DW1961 on July 25, 2020, 08:10:23 pm ---
I was checking voltage at a power strip and had an arc that partially melted the tip of my lead (It put a little melt point on it). I may have inadvertently had it on DC voltage. Would that cause an arc, or just an out of range signal on the LED? It's a good way to ruin leads, so I don't want to repeat that if possible.
--- End quote ---
Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).
helius:
--- Quote from: tooki on July 26, 2020, 12:37:08 pm ---Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).
--- End quote ---
This is the most likely answer :-+
I've had this happen when probing the starter socket of a fluorescent desk lamp. Any time you measure terminals that are close together (and the wires in a power strip can be much closer than is evident from the outside) this can happen. It's good to learn how to use the probe tip insulators if you measure such things. :-BROKE
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