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Quick piezo question

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Quick piezo question

Unread postAuthor: limbeh » Tue Oct 06, 2009 9:41 am

Hi guys,


As part of a school project (NOT spudgunning related), I need to modify a standard cheap BBQ lighter Image to light directly by electric current (ie bypassing the piezo). This will be done by hooking the thing up to an electronic circuit of power source, capacitors, switch, etc.

The electronics is no problem, but what I don't know is the current / voltage that such a lighter would require.

Anyone has any suggestions? I'm a flaming pragmatist, any simpler way to electrically light a flame is very welcome.

Thanks.
Limbeh
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 06, 2009 9:57 am

This type of ignitor depends on the physical striking of the quartz to generate a spark. If you want it battery operated, rip the flash circuit out of a disposable camera, there are plenty of tutorials if you search a bit.
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Unread postAuthor: limbeh » Tue Oct 06, 2009 10:25 am

@JSR: The electronics aren't a problem, we've been doing that for a long time, but we need to plan the circuit around the lighter.

The "Sparkers Reference" tutorial mentions a voltage of 300V-1000V. For a typical cheap lighter like the one i posted an image of, would the voltage be closer to 1000 or 300? If its closer to 300, I could possibly use one of those old camera capacitors......

Thanks.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 06, 2009 10:32 am

limbeh wrote:For a typical cheap lighter like the one i posted an image of, would the voltage be closer to 1000 or 300? If its closer to 300, I could possibly use one of those old camera capacitors


As far as I know the lighter you posted above has the same piezo ignitor as cigarette lighters, which have a piece of mineral that is struck by a spring loaded hammer when you click it which generates the voltage for the spark. No idea what that voltage is though.

With a camera flash you have the circuit ready made, that's the most practical option in my opinion.
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Unread postAuthor: john bunsenburner » Tue Oct 06, 2009 10:38 am

Look at it this way. What ever the voltage of the lighter you will be using a camera curcuit will do the job regardless.
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Unread postAuthor: rp181 » Tue Oct 06, 2009 10:49 am

You will need a arcing voltage, so 1000 is cutting it close, higher is better.
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Unread postAuthor: limbeh » Wed Oct 07, 2009 4:14 am

@rp181: the higher the better. That's good......

thanks so much ppl!
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Unread postAuthor: jimmy101 » Wed Oct 07, 2009 10:31 am

Do it the same way the photoflash board does.

You don't need the 300V cap, or the ~1Meg resistor.

The flash board has a "10KV" high voltage transformer on it. That's the voltage that "ignites" the flash tube. Just use that in place of the piezo. The HV transformer is powered by 300V from a specialized cap that is, IIRC, about 0.02uF. (It isn't powered by the big photocap.)

1KV probably won't be enough, 2KV might be but it will be inconsistent and you'll need very sharp electrodes for the spark to jump. 5KV will generally work. 10KV would be even better.

It takes at least a couple tenths of a millijoule to ignite butane in air. For consistent sparking a millijoule or two would be better. If the cap on the photoboard is 0.02uF and charged to 300V that's about 0.9J. You might want to double up the small cap.
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Unread postAuthor: Technician1002 » Wed Oct 07, 2009 12:29 pm

More info is below on using a flash trigger transformer;

There is a device called a trigger transformer that will take the 150 volt pulse and convert it into a 4000 volt pulse. The 4000 volt pulse will be more than enough to start the lightning leader in the tube, but where do we get 150 volts? How about a voltage divider across the 300 volt supply? Charge a 0.1 µF capacitor with the slowly rising 300 volt supply divided in two and then bang - discharge it with a microsecond pulse from a SCR.


Info with some schematics for an aircraft strobe is included on the page. Unlike a camera flash, this is an auto flashing circuit, but the trigger is the same. It runs off a timer in the strobelight and off shutter contacts in a camera.

http://www.piteraq.dk/flight/strobe.html

The schematic shown will fry a small camera flashtube. It can't handle the heat of a full power flash every 5 seconds.
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Unread postAuthor: jimmy101 » Wed Oct 07, 2009 1:15 pm

The disposable photoflash boards can be hacked to operate at ~0.2Hz and probably as fast as 1Hz. You have to drop the capacitance of the photocap (or set the hack to trigger at considerably less than 300V) so you are dissipating less energy in the tube.

The trigger part of the circuit shouldn't have any problem running at say a couple hundred hertz indefinitely.
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Unread postAuthor: limbeh » Thu Oct 08, 2009 4:01 am

Wow. Thanks for all the advice.

I'll update you on the progress.
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