Big Clive did a tear down of a Piezoelectric Aquarium air pump. I want to know is the piezo actually flexing at 50Hz. Or is something else going on. I don't know the capacitance of the piezo, but If I were to make a WAG, I'd say 8000pf to 30,000pf. That said the tuning (?) inductor is 150uH, nowhere near enough to tune down to 50Hz. Anyone care to enlighten me.
Thank you, Mikek
No tuning or resonance, the disk is flexing at 50 Hz mains frequency.
One minute gives you 3000 cycles at 50 Hz. The given 0.45 l/min is then
150ul/cycle or 150mm^3/cycle.The disk is maybe 30 mm diameter which is 700 mm^2 so it would have to move 0.2 mm or +/- 0.1 mm every cycle.
Double that to allow for losses and it still seems very reasonable.
Fun to play with these disks - I don't know why there aren't piezo electric relays (or maybe there are?), once moved they take very little power to hold.
Cheers
-- Clive (not that one)
Why would the 150uh inductor with 47 milliohms of reactance (50hz) be there?
Mikek
At a guess, along with the 10 nF capacitor it helps to stop mains electrical noise from making it acoustically noisy.
It's probably not an optimal design, but a design using parts which were at the time available for minimal cost.
Cheers
-- Clive
That was another thought I had, 50 Hz about 2 watts on the driver, why was it very, very quiet, no 50 hz?
Mikek
It that based on how much water it has to push through a one-way valve? Because that valve has to open and shut, which involves some back-flow, perhaps significant with such a small displacement. How is the valve constructed, is it just a ball on a seat?
Clifford Heath.
Well, this is a bit outside my area, but it's a small pump, not a bass reflex cabinet. I guess you're not going to couple much 50 Hz energy to the air. Press one against your ear and you'd hear it.
Cheers
-- Clive
It is an aquarium AIR pump. Click on the link, he's shows the valves. It rubber with a hole in one end and a cut on the other end. Positive pressure blows the flaps open on the cut end, but a negative pressure seals them shut.
Mikek
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The rubber flap *is* the valve. When air pushes on it, it opens. When the air pushes back it closes.
Lawn mowers use a flap in the gasket to create a flap valve so the vacuum p ulses of the engine pull the gas up from the tank. When this valve starts to leak the valve will have back flow leakage and if the tank isn't nearly full it won't start. If you prime it enough it will start and continue to run, but may stop before the tank is empty.
-- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
Apologies for not reading carefully. The air flaps still take some finite amount of air to open and close, even if they don't leak as well, that still affects efficiency.
Clifford Heath.
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You mean like in every diode ever built? Nothing is perfect. Why are you worried about something so unimportant?
-- Rick C. + Get 1,000 miles of free Supercharging + Tesla referral code - https://ts.la/richard11209
Worried? Not me. Just interested in the (in-)efficiency and the reasons for it. It's a very small displacement - like a diode trying to rectify a very small signal, it doesn't always work very well. Apparently well enough, though.
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syou worried about something so unimportant?
Seems to me to work just fine. I think your knowledge of the valve you see m to think is "inefficient" works just fine. I have no idea what your metr ic for "working well" is. Every check valve has back flow. This one seems to be pretty well suited for moving air.
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He did a couple of videos on different brands which had nearly identical guts. The L was also in series with a cap, both in parallel to the element. Their Fres was ~13 kHz IIRC.
Clive said he could hear the pump humming, not whining.
Clive opined that the L and C were there to keep line spikes and other noise away from the piezo element, not to tune to its resonant frequency, which makes sense.
Mark L. Fergerson
But then what is this pulsating air stream from the pump if not coupling?
Best regards, Piotr
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The air stream doesn't couple to the outside, it in fact, is buffered and s moothed by the capacitor like chamber that is mentioned in the video just s o it doesn't couple to the outside air. I suspect they also want to mainta in a steady pressure on the aerator so water doesn't come into the unit.
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OK, all this was interesting to me, at job I once had we bonded a 2" x Approx 1/16" round PVZT8 piezo to 1/16" plate. And found resonance at ~660kHZ. Before bonding they were about 1.2K. Actually we ran it at anti resonance. Being my only experience, I was a bit surprised to see a piezo run without being tuned and so far from a resonant frequency. When the company closed, I bought a lot of the parts. So, I have bunch of Piezos, what other fun projects can I do? I wonder how they would compare to a geophone? Plop a weight on the center and clamp to the outer rim. I think I have some 4" square pieces.
Mikek
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