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I'm trying to make a little buzzer for my bike to sound occasionally to warn off bears. I have a 12V buzzer from Radio Shack (Cat. No. 273-065) and was wondering if I could run it off of 18V directly (2x9V Transistor Batteries series) for 1-2 second bursts, or if I should run through a lm317 which I worry might use more energy than the protection it provides. Are piezo elements relatively rugged when used like this?

Note: I can directly run the buzzer off 9V, with OK results, but I imagine 12V (or 18V) should be much louder.

Thanks!

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  • \$\begingroup\$ bike = bicycle or motorcycle? \$\endgroup\$ – Federico Russo May 29 '12 at 7:29
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Devices have voltage ratings for a reason. Usually a higher voltage will damage the device. Look at the datasheet and see what the real maximum operating voltage of this device is. Perhaps 18 V is OK, but unless it explicitly says so for a "12 V" buzzer, you should not assume it is.

Keep in mind that anything rated for "12 V" operation intended for end consumers (not engineers that actually understand voltage specs) is most likely designed to work or at least not blow up with 12 V car power. Even without spikes, that is actually more like 13.6 V when the engine is running, so it is quite likely this buzzer can handle 14 V.

18 V is more of a stretch. If this is a piezo buzzer (you didn't provide a link), the higher vibration amplitude could damage something. Eventually the higher power could cause overheating and damage something that way, but that is unlikely to be a problem with infrequent bursts lasting only 2 seconds.

The correct answer is to get a 12 V battery. Unfortunately those are not as widely available as 9 V batteries. Another OK answer is to run it from a single 9 V battery. Try it, it might be loud enough. You can also do what Coder suggested, although it will use the batteries less efficiently. Find a resistor so that you end up with about 12 V accross the buzzer. Put a capacitor accross the buzzer to keep the voltage roughly constant, else you will still exceed the voltage spec some of the time.

Another possible solution is to not worry about bears. You didn't fill in much in your profile (remember, that's really a courtesy for us, it's not for you). Your mug shot implies Africa, but there are no bears there. Maybe you live in place where there are brown bears or polar bears, but if it's just black bears this seems paranoid.

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You should provide a link to the product so that we can have a look at it. A datasheet would be great. I couldn't find the product you mention on the RS website. Not that it makes much difference, when I looked at a different buzzer the product summary just says 6-16V, 65mA, 3200Hz. That's it. "Tech specs", where you should find more information, has literally nothing, unless you find "supported languages: English" useful. Don't use RadioShack as a supplier if you're serious about electronics. DigiKey for instance offers very good selection tools, and has datasheets for all of its products.

Like Olin says specs have their reason. If the product would work at 18V and produce a louder sound, they wouldn't hide this from you, on the contrary, trust me.
Since it's an active buzzer it has an oscillator inside. Manufacturers usually don't tell you anything about that, I've never seen a schematic of a buzzer's internals. The only thing you can guess is that it will use a couple of cheap components, an oscillator for a piezo is a simple.

enter image description here

I found these schematics in a Murata catalog, where they show them as examples of externally driven circuits. Doesn't mean that they did it this way, though it's possible.

The left circuit uses a couple of discrete transistors, and if you ignore the piezo for a moment this may well work at 18V. Small signal transistors are often rated at minimum 30V. The question is: what will the piezo do at this voltage? I imagine the piezoelectric ceramic mounted on the brass diaphragm may crack.
The right circuit uses a logic IC, probably a CD4000 series. Those are often specified for up to 18V recommended operating conditions, so that may work as well, but again the piezo may be the problem.

Don't do it. It the datasheet says up to 12V then expect problems if you don't follow that.

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My last answer was inadequate so I have decided to try again.

To put it simply: Yes. You can. But it is not a good idea. It will work but having more voltage than what is recommended will decrease the life time of you buzzer, drastically. It is advised (to get the longest lifetime out of your buzzer) to use the recommended voltage.

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  • \$\begingroup\$ In many cases, operating a power-handling device continuously at the highest voltage where it would operate successfully would cause it to eventually suffer damage from overheating. Devices which are rated for continuous operation may thus, in practice, often be operated somewhat above specified voltage for short periods of time. The problem is that manufacturers don't often specify how far above the spec voltage is "somewhat", nor do they specify the duration of a "short" period of time. For quick-and-dirty one-off projects, it's sometimes easier to push specs, hope for the best, and... \$\endgroup\$ – supercat Jun 12 '12 at 21:52
  • \$\begingroup\$ ...be prepared to replace things that break, than to try to engineer a perfect solution that complies with every specification. Of course, such an approach should only be employed if the end-user is willing to tolerate unexpected failures, and the cost of dealing with such failures is expected to be less than the cost of proper engineering. \$\endgroup\$ – supercat Jun 12 '12 at 21:55

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