Solid State Fuse

Two, some, not many, simple, uncomplicated...

it's not hard to understand the goals.

John Plot the VI curve for the load and for the poly, if they cross at one point, then the system is monostable will RESET without removing the power. If they cross at 2 or more points then the system is bi-stabe and can hang up as you describe. But for the load lines to cross at 2 points, one has to exhibit a negative resistance region. Does the poly exhibit a negative resistance region? I don't think that it does... like an incandescent light bulb, the resistance changes but it never goes negative.

Mark

I think if both the load and the poly are positive resistances then

Good suggestion. A quick search led to a NASA webpage, and they talk about it a little there.

The idea of splicing isn't important, a ground in the circuit is quite alright.

The objective, on a good day, would be to remove the offending short before our small batteries are drained or wire insulation melts.

Heat dissipation is a primary concern, RF corona effects are another. Shorts are unlikely, but no one could predict what events can take place. Short and long blasts of gases at 1000 F are a real hazard.. might not happen, but as likely could.

I will assume you were about to say "the system will not hang up" or words to that effect!

Anyway, I *have* had systems where this happens. It had a negative voltage convertor, and other switch mode supplies in it. I guess these must have presented the negative resistance load which you describe.

Thinking about it, amost *all* circuits with switch mode supplies probably have negative resistance, since they draw less current the more voltage you feed them with.

Sweet mother of Jesus, he's serious. I wouldn't let you within 300 yards of a lit match, never mind a rocket...

There will be threadlocker. Thanks though.

I love how cheeky everyone is.. mind you it's better than being a jerk outright.

Mr. Pete. I think about this stuff all the time. I'm in conversations with 10 and up to 50 project members daily.

And many a circuit jock pops in, sure as anything that they are the first one to ever think of something.

Project wide, it's more my concern than anyone else's, which is the way I would have it.

If you understand what's involved with the match and treat it with due respect, it's safe to use.

Au contraire, when all is said and done, safety will be designed and tested in... this is no 'experiment', it's a very deliberate effort.

"if you understand what's involved with the match"

That's just it; you haven't demonstrated that you understand much relating to electronics.

"it's a very deliberate effort"

I've seen your deliberate efforts. Just warn people in a 400 mile radius OK?

For an incandescent, more voltage always makes more current, at least until it burns out. For the polyfuse, more voltage makes less current in the active region, approaching a constant-power/constant-temperature mode, so there's incremental negative resistance, like a tunnel diode but a lot slower. As you point out, it must have a negative resistance region to be bistable.

So, is it possible to make an oscillator from a polyfuse?

John

Have you spoken with the likes of the Surrey micro-satellite group? Don't have a link on hand sorry (will look later though) but they're probably handy being UK also. Or folk like Microsat

Ken

My circuit is simple and it has 10 essential parts, plus a few convenience parts, like an LED indicator.

yep, they do. thats why an input filter can make a stable smps oscillate. Likewise driving a smps with a smps can cause problems - Fred Lee's crowd at VPEC have written dozens, if not hundreds, of papers on this particular subject.

Cheers Terry

The rocket part of it is being handled by people who are experts in that aspect, and everything happens with a view to safety first, and then success.

There is a review process to get permission to launch something, and we will be in the middle of a desert probably. I think some kind of horizontal excursion is out of the question, as the rocket will be equipped to recognize attitude with substantial reserve resources, and made to cancel the flight in any such event.. and at any time... despite my confidence in my immediate group, I remain convinced that the more critical control funcitions are going to work precisely because I'm the fall guy for the works, no matter who designs which parts.

Serious rocketeers always think first about safety of others.

Also, rocketry is a subject unto itself. A casual observer would have little idea of physical operation and what goes into development.

The basic process is a simple execution of events based on sensing. What I'm adding to it is failsafe operation, and some calling of the tune for the band.

These guys are very clever. Some RF, some software, analog, digital, math, physics, and then most are very strong in technical electronics.

It stands to be a significant achievment in both global networking and amateur rocketry, and could influence future directions in satellite deployment methods.

Ok, 400 miles, will do.

"Frank Bemelman" "Phil Allison"

An important point is to fit the device in series with any LC filter components that feed the tweeter so when it trips and goes high R, the LC filter is still loaded by the low impedance of tweeter and NOT high one of the device.

This is to avoid the LC filter turning into a series tuned circuit, presenting a very low impedance to the drive amp at and near resonance and simultaneously boosting the voltage level delivered to the device and exceeding it ratings.

....... Phil

I have no idea if this will work for you - this just allows the poly to reset if it opens by insuring no current through it when the relay drops out. You need a delayed on relay for a 2 part solution.

Vcc-----+----POLY-----+----- N/O | | ^------------ To Circuit +----- N/C | ^--------+----[DelayRly]---Gnd

I don't know if either the poly or your circuit can take the possible "abuse" this might cause. (A "bolted" short comes to mind ...)

Ed