PiezoElectric Spark Ignitor

Piezoelectric Transducers (PZTs) shrink in size for one polarity, and grow in size for the other. They are reciprocal devices, so if you squeeze them, they will produce the polarity that would ordinarily shrink them, and if you stretch them, they will produce the other polarity.

Since the sparkers are just stacks of PZT material they work the same way. When the striker smacks the stack, it squeezes it, and that makes it produce a mostly DC pulse of rather high voltage. Since PZTs are really just ceramic capacitors, if you squeeze the stack, and short it to zero, when you release the squeeze, they will produce a voltage in the opposite direction.

If you put a diode (in the correct direction), and a capacitor, in series with the sparker, the capacitor will accept charge every time you click the sparker, and you will have a manual HV generator. You can use this to power flea sized HV devices, such as IR viewer tubes, Geiger-Muller tubes, and neon lamps.

Since the pulse is unipolar, you can eliminate the diode by just using a spark gap, but you will reduce the maximum voltage your supply can achieve by the breakdown voltage of the gap.

-Chuck

"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...

The output is a few thousand volts but at very low current. A LED is out of the question as it is a very poor impedance match. You will probably get a weak flash off of the neon lamps you mentioned. If the output is not grounded, there is usually some residual voltage across the piezo so be wary of shocks. The crystal is rather tiny and thus has very little energy. Energy is probably a tenth of the barbecue spark lighters.

I use a barbecue lighter to do a do a insulation breakdown test on some of our high voltage arc lamp cables. Since the piezo is driving a capacitive load, it will store a hefty charge in the cable capacitance. If there is no apparent arcing at the electrodes (everything has been built and potted correctly), we short the piezo and look at the size of the spark which is a gauge of the remaining voltage. Not very precise but it does weed out bad assemblies in manufacture before they get built into the larger system. Oppie

I read in alt.binaries.schematics.electronic that "Watson A.Name - \"Watt Sun, the Dark Remover\"" wrote (in ) about 'PiezoElectric Spark Ignitor', on Mon, 5 Sep 2005:

Yes. They are like cobras; no matter how carefully you handle one, it'll bite you eventually.

Only if you add long lead-out wires. Otherwise it's short pulse. Think of it as a 10 nF capacitor you charge by bending it.

You can make a capacitive divider, using a bit of window glass and some foil for the HV cap at the top.

It would zap up to 1000 in series!

If you use one 230 V neon, with 250 k+ series resistor, you get a bright flash. Probably not the same if you use two 120 V neons in series, because the series resistor is MUCH lower in value.

Yes, the crystals are very stiff.

You were wondering if anyone has been shocked by these... When I was a kid we used to use them to zap each other. Especially on the earlobe. It was hilarious. It didn't really hurt that bad either. More of a build up of fear of shock than an actual pain from the shock.

Jeff

"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message news: snipped-for-privacy@corp.supernews.com...

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I already have a manual HV generator. ;-) I think you mean a manual HV DC generator. The problem I have is that the diode has to be rated at several kV, maybe 10kV or more. Same for the cap and whatever else is connected to it. It's not like connecting a mechanical generator where the voltges are 'only' a hundred volts. And I surmise that connecting a dozen 1N4007 rectifier diodes in series isn't a good idea because they may have too much capacitance and leakage that's more than the total current from the piezo. Like the piezo is dealing with less than a milliamp, and at 10kV, ten megohms isn't enough resistance, more than a gigohm is more like it.

tubes,

One click isn't a lot of current. I would have to have some kind of cam affair to crank and drive the clicker at more than a click every few seconds. I think the usefulness of rectifying and filtering the pulese isn't really much good; like someone said, they're way too high an impedance. The pulses should be used as pulses, to their best advantage.

achieve

I think there is some amount of reverse voltage, no matter how low it is. But I'll never know as long as I don't have any HV probe or other HV pulse measuring devices.

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Snakes! I _hate_ snakes! Thanks for the good (experiential?) info.

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A bit of window glass? According to my ref manual the dielectric constant of glass is 7.5, so I guess the idea is to get a reasonable amount of capacitance in a small package. But I could just use a couple plates spaced far enough apart to prevent arcing. But what should I be using for the capacitances and ratio? Should I try for 100:1 divider, or 50:1? 100 pF for the HV cap and 10,000 pF for the low? Or more for both, or less for both? I may be able to find a few low value, high voltage capacitors in my junk box, or from an old TV set. I wonder if a

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I've seen some healthy sparks jump from my finger to a rail when shuffling across a carper on a very dry day. But it's more of a surprise than a shock to one not epxecting it. It's not all that bad.

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I've been shocked by them several times..intentionaly.. It feels like a little pin-prick,and is gone just as quick. They do make some hot arcs tho.. Try zapping your thumb,while looking at the hot arc ;-) (okay,so i'm easily amused.)

On Tue, 6 Sep 2005 18:20:33 -0700, "Watson A.Name - \"Watt Sun, the Dark Remover\"" Gave us:

Nope. A diode string is perfectly acceptable, but they should be fairly fast.

Nope. Potential is all that is needed to conduct through diodes, even a string of them. You overcome the junctions, and they conduct.

It is likely even higher than 10kV.

Sure is. What it is not, is of a high duration. Into a current sink, the voltage will clamp a bit too.

Think of it like a bouncing basketball. You press it, and it responds by exhibiting a voltage. AS the pressure is released, it returns to rest potential of zero. Both are as close to identical as it gets as long as the mechanical actions both follow the same timelines. Mechanical force translates directly into electromotive force. Release returns to zero, and stretch exhibits opposite polarity EMF.

We made a power supply (actually advanced amplifier) for a nano-positioner. That is a piezo stack driven device (1 inch x 3 inches @ 80 wafers, seriesed).

The amp peaks at 800 V p-p. The stack causes the stylus tool to move

This device can take a spinning pin in a lathe, and cut a square shaft out while the lathe is spinning. The machines are used to cut raw contact lenses for thoroughbred horses.

The control program learns and makes up for all backlashes, etc.

The stacks are several thousand dollars each, and they have shorting wires on them, just like HV caps.

So, presumably, one could compress that stack to 0.5 mm, and see a nearly 400V pulse on the wire.

You need some very high value resistors seriesed together. Like ten

Multiply your waveform x 10 after any probe multiplications, of course. I would use a 100V or higher probe.

HV scope probes are several hundred buckaroos... at least the good ones are.

the sensation of the spark is less than the kick from the spring.

I'd imagine that too, there could be some harmoonics in there too.

there's not enough current there to damage a led. probably not enough to light one either,

you could try a flourescent tube too.

those things don't last real long, maybe a couple of thousand operations and then they're kaput.

Bye. Jasen

I read in alt.binaries.schematics.electronic that "Watson A.Name - \"Watt Sun, the Dark Remover\"" wrote (in ) about 'PiezoElectric Spark Ignitor', on Tue, 6 Sep 2005:

Not primarily; it's to get a cheap bit of dielectric that will undoubtedly stand as many kV as the piezo will offer it.

The GLASS is the spacer!

What will you scope input stand, and display reasonably? Many these days don't display much over 50 V p-p. Assume 10 kV, rather than the likely

Don't.

On Thu, 8 Sep 2005 00:42:55 +1200, Jasen Betts Gave us:

You must have had a "dead" one then. I have had some that pack quite a bite. They do wear out as the pile accumulates fractures.

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So I guess that implies that the current is so low that it's not affecting the nerves that much. Eh? Besides, the spark is confined to a small local area, right around the end of the thumb or finger. I guess that if it were over a wider area, the effects would be more noticeable (to put it mildly). :-P

But the main stumbling block it seems is getting such a high voltage to do something useful. I think about how to handle it with instruments or add it to a circuit, and I come up with the problem of really high voltage and leakage current problems, and preventing destruction of the rest of the circuit.

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Thanks for the flourescent [sic] tube idea, I hadn't thought about that yet.

I did think about the fact that these are disposable lighters and that the ignitor may be designed for a limited lifetime. One thing's for certain: the strong little spring and plastic shaft make it hard on the fingers after just a few strokes, so it will have to be put into something more amenable to being squeezed.

Only 10pF (see below). I've twisted 1.3" (30mm) of 24 gauge solid tightly and it's about a pF and a half. So for 10pF I'd need about ten inches, but the problem is that it doesn't have thick enough insulation. If I could get some 10kV insulated solid wire, I'd guess a foot or two would give me ten pF. I'm thinking that I could use a center conductor and its dielectric from a piece of solid RG-58/U, if I wasn't so lazy as to not want to strip the jacket and shield off it.

But I rummaged arpund in the junk box and found several 2, 3, and 4kV ceramic disks of cvarious values in the 27 to 270pF range. Later I'm gonna sit down with the calculator and come up with a few that will add up to ten pF in series.

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Max is 20V/cm times 8cm so it'll handle 120V P-P AC. It's an old scope, from back in the days when toobs were still around and B+ was a couple hundred volts. So it should be okay with a 100:1 divider.

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I think the probe has 10pF(?) It's an old probe from a Heathkit scope. I think that 10pF value may be only on the 10:1 range. I'll have to see if I have a Heathkit manual with more info.

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Like I was saying above, I think I can scrounge up enough 3 or 4kV caps to put several in series, and get the capacitance down to 10pF or so. These are usually tested to twice their rated value, so if two 3kVs are in series, they should be able to handle over 10kV, not that they would ever have to, tho.

One thing I may have a problem with is the single pulse of the output. The ol' scope may not be able to display a single pulse bright enough if it's a very fast pulse. Since the piezo element is mechanical I would expect the pulse to be in the range of greater than 100uS, assuming that the snap of the spark is in the audible range.

On Thu, 8 Sep 2005 03:14:35 -0700, "Watson A.Name - \"Watt Sun, the Dark Remover\"" Gave us:

We used to make HV pre-emphasis caps for our feedback loops from a strip of FR4 with copper tape on both sides. Once we figured out how much we needed, we incorporated it into the PCB itself. Works great.

We got about 10pF from about a half sq in from two separated but internal layers (plates).

snip

The ones in cigarette lighters just barely give a tingle (for me anyway). Electric acupuncture pens using these are sold in the Orient. Good for waking oneself when coffee doesn't do it.

On Thu, 8 Sep 2005 03:14:35 -0700, "Watson A.Name - \"Watt Sun, the Dark Remover\"" Gave us:

You can buy 15kV wire that has teflon insulation that is no thicker jacketed than normal wire, so your numbers should be the same.

Try "rubadue" wire for HV applications.

SPC or "silver plated copper" is the best. Easy to solder, whereas the TPC stuff doesn't take solder well.

Also, mil surplus stores. It doesn't have to have a thick sheath to have a high withstand voltage. They typically have some nice spools of wire around.

Another way is to rope coil form the two wire "plates" and place a sheet of "nomex" paper between the two flat coil forms. It has a very high volts per mil withstand, and is made for the purpose. That will increase the withstand potential as long as the paper extends outward far enough to make the creepage distance high.