discharging caps

The customer specified 200 seconds. They are a government organization that has a very pickey safety review team.

I want it really dead in well under 200 seconds, below 1 volt.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

People would notice if that were shorted.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I'm active on the NSW IEEE section committee. That puts me in contact IEEE members (including professors and lecturers) at the local universities. Maquarie and UTS figure largely at the moment, but Western Sydney (where my late wife was was a distinguished professor) is also pretty active . The University of NSW has gone quiet for now. I got to see their quantum computer up close once, but that was through the Royal Society of NSW - I got dragged in when my wife got to be a fellow of the Royal Society of London (which is a much bigger deal) but I've not done much with them since she died.

The quantum computer tour was sort of funny - I went around with the then chair of Royal Australian Chemical Society of which I'm also a life member (if never a very active one) whom I'd met earlier.

Like I said, your judgement in such matters isn't great. Rowan Atkinson gave up a masters in electronics at Cambridge to pursue a career in comedy. I did have some involvement in student theatre at the University of Melbourne, and was sort of okay, but nowhere near good enough to take it seriously.

Quicker is safer.

Yes, you have to set the boost conversion output voltage accordingly.

Also, I used to have halogen lamps in my bicycle headlights for many years and when the NiCd started to fade (it did a lot in hilly terrain) there would be an undervoltage. They still lasted nearly forever. I did

Another iteration of the halogen bulb urban myth.

The halide recycling loop is pretty cool, keeping the bulb envelope clean.

That’s all it does, though. Tungsten is lost preferentially from the hot spots, which get hotter as this proceeds, but is redeposited rather uniformly as crystals. There’s no healing of the hot spots.

The long filament life comes from the high gas pressure, which slows down tungsten vapor diffusion from the hot spots, which greatly enhances redeposition there.

The high pressure requires a very strong envelope that doesn’t melt easily. If it were as big as a normal bulb, it would be an explosion hazard and the convection loss would be horrible.

The halogen mechanism makes it possible to use a small envelope without it turning black early in the filament’s life.

Cheers

Phil Hobbs

So it's a bunch of modules which you have glommed together.

The 0.2F of capacitance is a lot of smaller capacitors in parallel.

You are trying to design in safety as an after-thought.

If you put a discharge circuit into each module and broadcast a "discharge" signal to all the modules, the problem would be a lot easier to solve.

This looks more like a dumb newbie afterthought question, with the usual dumb newbie fault of insufficient background information, released incidentally half-way down the thread.

Not if the energy were dissipated making the internals of a couple of big resistors several hundred degrees warmer for a few minutes.

That isn't noisy or flashy. Capacitors don't change shape much when they discharge. The wiring around big inductors can move. Big transformers hum if the windings aren't impregnated, so making the discharge curve critically damped with an inductor might call for extra care.

True, but innocent people are killed all the time, traffic, wars, etc and I'm sure that dwarfs the number wrongly executed. Anyway if you're dead you can't regret it.

Personally, I'd rather press the 'off' switch than spend years in gaol.

I dunno, been locked up for so long... makes you stronger.

And of course nobody can give a wrongly imprisoned person the years back, or take away the suffering and degradation. There are good arguments against capital punishment, but that isn’t one of them.

Cheers

Phil Hobbs

Six, 30mF 200v each, in parallel. The caps are bigger than beer cans.

It's not my design, but I thought I should try to keep people from being killed.

There are no "modules", and complex safety schemes can fail and kill people.

It's a discussion group, not a lecture platform.

You might introduce an interesting topic some day too. In full detail.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Did I remember to say "shorted" ?

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Always a good idea. You are still trying to design in safety as an after thought, but at least it is somebody else's fault

So can simple ones. The idea is to keep as simple as is practical, but excessively simple schemes have their own risks.

Putting a discharger on each capacitor might not be a bad idea. At least it keeps each discharge current loop as compact as possible,and if one of six fails, at least the other five won't be a menace.

It shouldn't ever go up in flames. There were liquid filled capacitors when I started in the business, but if the liquid was a halo-carbon they didn't burn - they put out fires. Some of the chloro-carbon fluids were pretty nasty but the fluoro-carbons weren't as bad.

And a series inductor could let you make the discharge path critically damped, which does offer faster decay.

Even one inductor per 30mF capacitor is going to need big inductors, but one big inductor per beer can - a toroid that was dropped over each capacitor - might allow neat packaging, if probably not the packaging that was originally intended,

A good thought. Pity you took so long to make it clear what the problem was.

But the more detail you put in up-front, the better the discussion

I'm applying for a provisional patent on a neater way of making a non-progressively wound toroidal inductor. Obviously I can't talk about that until the provisional patent has been registered.

I've certainly posted the occasional detailed question here in the past, but I'm retired - whether I like it or not - and that does means that I don't get introduced to other peoples interesting problems all that often.

If I've done the sums right, that's a capacitor bank bigger than six beer cans storing about the same energy as one AAA cell!

Yes, I used to operate capacitor banks of maybe 2-4 times that physical size charged to 1kV and discharged via a spark gap through a marine sparker for seismic work. Long time ago before H&S was a thing.

I got one of the giant caps. It says that it's 30,000 uF but it measures 50,000. So we'll have 4000 joules with four in parallel at

I think it's normal for elecs to have more initial capacitance than the nameplate value.

One of the more depressing things about electrolytic capacitors is the need to reform them by keeping the rated voltage across them for a day or so if they have been unused for a while.

The actual electrolyte is a layer of aluminium oxide on the electrode surface, and that diffuses away slowly if the capacitor is stored uncharged. In extreme cases you have apply the reforming voltage through a big resistor because the thinned down layer can no longer stand off the rated voltage. With the big resistor you can measure the reforming current as the process proceeds.

Obviously the initial capacitance is higher than the rated capacitance. That may have contributed to your initial 50mF - a +50% tolerance only get you up to 45mF

I reformed a couple of electroltics many years ago when I bought some military surplus electrolytics for my home built hi-fi. I didn't bother to monitor the current.

I'm sure you didn't mean that!

I'm thinking that they overdo the capacitance to account for later-on drying out or some electro-chemical effects, to ensure the guaranteed minimum c over the (short) specified lifetime.

Caps are tricky parts.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics