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PIEZO - Sanity Check before spending money/time

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LAN_403

Sun Jan 14 2007, 03:36PM

Banned on April 7, 2007
Registered Member #277 Joined: Fri Mar 03 2006, 10:15AM
Location: Florida
Posts: 157

Some of you have been nice enough to correspond with me in another thread about my quest to find the most efficient method of converting HV sparks jumping a gap... into constant LV. I've tested many different methods and currently am using a buck converter to keep a large cap charged that in turn drives small loads like LEDS, small motors, and on occassion a fuel cell, but still searching for THE best efficiency method. I'm considering testing Piezo conversion by 1) allowing the spark to directly impact a Piezo element (or via a shield) generating some temperature/mechancial change, or 2) spark energizes a solinoid that strikes the Piezo element, or 3) spark energizes an audio speaker (making the diaphram move) which in turn impacts a lever that then impacts the piezo (similar to the solinoid idea), or 4) Spark energizes one style of Piezo element causing it to flex... which is mechanically connected to a 2nd Piezo element that receives the mechancial stress and generates V/ma. Interested to hear from those who know about Piezo if any of the above are worth testing effort and cost... or if Piezo simply isn't suited for this application. Below are pix of my collector array, spark gap and buck converter. Thanks in advance. CM

Bjørn

Sun Jan 14 2007, 06:50PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

There is a company selling piezo electric converters, they mention an efficiency of up to 90% as possible. It is two elements bonded together driven by AC at the resonant frequency.

Try searching "Oxford Electric Bell" for some ideas. You would want your voltage to stay high to be as efficient as possible.

You need to start with measuring the power output (current at different voltages) from your collector, without knowing that you don't know enough to judge your efficiency and you are left to try things at random instead of testing the most promising things first.

Bored Chemist

Sun Jan 14 2007, 07:30PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

There are some interesting aspects of piezo transformers that make me wonder why we don't see them more often. The sort described here

seems typical and is used as a step up system. There's no reason why they are not reversible.
BTW, if you are getting sparks you are wasting power. Do you have any sort of data on the effective output impedance of your collector array?

Sun Jan 14 2007, 09:10PM

Banned on April 7, 2007
Registered Member #277 Joined: Fri Mar 03 2006, 10:15AM
Location: Florida
Posts: 157

Thanks much for the piezo urls. Gotta admit I've had a rough time trying to measure the HV collector output due to three things, 1) my apparent lack of experience measuring HV, 2) I distroyed my only Oscope and quite a few meters trying, 3) seems whenever I attach any type measuring device to the collector side of the circuit through resistors, even small value resistors, all HV collection, or almost all, stops. The only signal remaining is the signal from radio stations which I am not interested in. My previous patents are in RF and shape memory alloy... so I remain in a HV learning curve for now. I'm sure the collector output can be measured, but months ago I got frustrated destoying so many meters, obviously not doing it correctly. Impedance of my system, I have no idea. The only guestimate of collector output is based on spark gap distances, some days/nights the sparks jump only a short gap, other days 1/2 inch and some days nearly a full inch, it changes constantly with the ion density, humidity, barometric pressure and the price of tea in China. Quite a while ago I hired a technical guy to come with his equipment and measure the output of a few of my collectors on a balloon, but even he ended up saying his was a wild guess (he was trying to measure the V and Amps of the spark itself). Possibly if there is an experienced 4hv.org member near Pensacola Florida, he/she can contact me and come by the test site and make the measurements, could be fun. CM

thedatastream

Mon Jan 15 2007, 08:20AM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

Piezo transformers can be very effiecient, I've worked with them before for an LCD backlight.
You have to drive them on or around (typ Â± 5kHz) their resonant frequency to get the best out of them.
IIRC, the ones I used were 28V input, 1500V output. You may well be able to drive them backwards.

Here is a good application note from Linear Technology on Piezo transformers -

,C1,C1003,C1042,C1035,D4170
Don't know of this is any good either -

James

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