There is confusion here between a self-heating fuse (the common variety) which is designed to melt when the current is excessive and an externally-heated fusible link which melts when the surrounding temperature is too high. For protection against overheating resistors, the latter is needed; it does not need to be able to break a fault current, it merely has to interrupt the normal operating current.
Nobody could ever accuse you of attempting humor.
gm? What's a gm? Transconductance?
130 kilograms of inductor is clearly absurd by about 4 orders of magnitude. A few seconds of mental calculation dismisses the inductor idea. [1]Besides the quantitative absurdity, depletion fets are smaller and cheaper than inductors, and surface mount. DN2530 costs us 43 cents.
Design a better discharge circuit, with values, and we can discuss it.
[1] I'm sort of known for doing math like this standing up at a whiteboard. There are actually tricks, known as "lightning empiricism"Jim Wiliams' 1991 book has a section on that.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
If you have so much energy, design it.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Of course we want lots of red leds lit up when lethal amounts of energy are present.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
You'd need the inductor to saturate late in the exponential discharge to do any good. And the supply voltage isn't constant.
And of course you'd not want to magnetize the core material and mess up the timing of the next discharge.
It's a silly idea.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Hi, John. This topic had led to a long thread, so maybe someone already mentioned it, but if you want something foolproof, make sure your discharge circuit deals with capacitor soakage. That is the annoying problem of discharging an electrolytic capacitor and then having it go back up in voltage after a period of time.
I tested the giant 'lytic for that. After charging to 100v and discharging for 2 seconds, it recovered to about 2 volts.
As received from Mouser, it was millivolts and didn't have a shorting link.
But sure, the discharge circuit should operate forever.
Not that you've noticed. If you were trying to be funny, you didn't make it.
American physics courses don't seem to have been big on System International (SI) units when young Larkin was young and somewhat susceptible to education.
John Larkin is better known for his skills in self-congratulation.
Only for money. I'm perfectly happy with the very limited glory I've already got.
Household mains sockets? You only want warning lights lit when the situation is unusual. If they are lit all the time they become a distraction rather than an attention-getting warning.
No. You need it to come out saturation at the end of the discharge process to get rid of an residual charge faster than the exponential R-C decay will do it. It's going to saturate very rapidly at the start of the discharge process when the initial discharge current is high.
Hi-permeability cores aren't made with magnetic iron. They don't stay magnetised. The process of discharging the capacitors to make them safe isn't a particularly time critical process - they want to be close enough to empty after 200 seconds to keep your safety committee happy, but only time the process will get repeated is during safety trials
That's a remarkably silly objection, even for you. Or were you trying to be funny?
I posted my discharge circuit. It's simple. And the DN2530 pinches off around -2 volts.
When you were in school, didn't they teach you to check your work?
No, I let other people do that.
You need more than -2V for a proper pinch-off. I check my work to my pown standards, not yours.
But you do make it clear that if they don't do it they will end up being accused of being negative and insulting.
And "I'm sort of known for doing math like this standing up at a whiteboard" does look remarkably like self-congratulation.
And your spelling, too.
Most of your posts are coarse insults.
As noted, "lightning empiricism" is handy, and not especially difficult.
I was recently sitting in on a class at CCSF and the prof was lecturing about a circuit. He said "the current is 6 divided by 0.05. Does anbody know what that is? Nobody did, so I said "120" and he said "thank you". None of the maybe 30 kids in the room could do the math in their heads. It's two simple steps.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Examples? They don't flatter you as fulsomely as you'd like, but the insults are mild and fairly refined (like this one).
But no undergraduate wants to fall flat on their faces in front of a professor. And most of them know enough about professors to want to avoid any trap he might have set.
What is your version of safe levels? The NEC says 50 volts or less. What is your definition of a very long time? The NEC used to specify energy storage systems should discharge to 50 volts or less in 5 minutes. I believe this was updated to 50 volts or less in 1 minutes for things like EV chargers and things like that.
If you're final solution is anything more complicated than a NC relay that drops a resistor across the cap bank when the power goes off and a door interlock that does the same, you're reinventing the wheel.
If you want a goofy solution, discharge your cap bank into another cap bank to drop the voltage at a high rate nearly instantaneously, then bleed it off with power resistors. You might be able to play some diodes games to make sure you don't accidentally end up with double the energy blowing up your laser if the discharge circuit faults. Old power packs for studio strobes had all sorts of weird stuff like this going on inside to divide up the energy across smaller or multiple stobe heads.
4800J units were considerd decent sized unit and not unusual. Lookup Speedotron Blackline 4800.
50 volts DC is safe from a shock standpoint, but will still make a gigantic bang if shorted, so I want to ultimately discharge to zero volts.
The customer wants it discharged in under two minutes. They have a serious safety team.
I'm an engineer. I invent things.
What drives the relay coil? What happens if it fails, on or off?
I like goofy.
Slamming caps in parallel is interesting from a circuit theory standpoint, conservation issues, but not practical in my case for lots of reasons.
"Nearly instantaneously" will be the fun part.
Yikes, they have a 9600 joule (they call it a watt/second!) version. A few of those would blind everybody and set the studio on fire.
I worked on a kilojoule discharge thing once, but it used oil caps and was giant. I also did the timing system for a gadget that fires 400 megajoules per shot. I've never been there when it fired. It would be interesting to know how they dischage their caps.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Philips managed that in the 80s
I used some of those giant gold MIL-style 250-watt resistors
like this
I replaced them with planar porcelain-steel thickfilms and that worked fine.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Yeah I've used similar things in the past.
I remember the surge limiter resistors in Philips sets being something like wirewound on a ceramic tube and painted over. 4.7 ohm I think. When they had those fail repeatedly they were changed to something like a cement filled ceramic box which were probably wirewound inside.
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