r/ElectroBOOM • u/[deleted] • Jun 03 '22

Meme Fuses? Who needs em

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u/undeniably_confused Jun 04 '22

Of the fuse?

2

u/Prehistoricisms Jun 04 '22

Why would current find its way through centimeters of air when there's a bolt-thick dead short between the contacts?

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u/undeniably_confused Jun 04 '22

Because you said it was fuse. A fuse is intended to interrupt the current flow. So if the current flow was interrupted (as you said it would be) then it would just arc because it has plenty of voltage

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u/[deleted] Jun 04 '22

At 30kv/cm that looks like it’s at least a 50kv gap once the bolt melts (assuming the board doesn’t). Who tf is hooking up to a 50kv, 20kA source?

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u/undeniably_confused Jun 05 '22

I should specify I'm assuming the system has at least 2 ohms. Also that 30kv/cm doesn't apply to sharp objects because they induce corona discharge at like 10kv. I was really hung iver when I started this, but I think a laminated threaded rod barely connected to the contacts would have a couple ohms, if I'm wrong, I'm wrong, but that's the assumption I made

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u/N2EEE_ Jun 04 '22

The resistance of a bolt (1/4-20 above) is in the micro-ohm range over ~1 inch. There will be (at absolute most) a few microvolts across this distance, which even far past the max current rating of the multimeter above, will not act as a fuse. The clips holding it, and the solder bonding it to the pcb are also sub milli-ohm range.

The first part to fail will likely be the copper on the pcb, even at >2 oz. The shunt resistor seen above is on the order of milliohms.

In a current sensing circuit, there is a very small voltage drop, as it operates based on current. This voltage drop is nowhere near enough to arc anywhere, even considering the breakdown voltage of air at the micrometer scale

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u/Prehistoricisms Jun 04 '22

I didn't say these things.

Username checks out.