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I have found these "bluetooth location stickers" on this website

http://www.sticknfind.com/product/sticknfind

Inside the stickers is a buzzer and a light. I am trying to build something similar, but with no light - just a buzzer - and I am trying to find a battery suitable for use with a piezo buzzer that has a rated current of 3mA.

This company says their stickers use a CR2016 watch battery. The examples that I found of CR2016 batteries seem to have a Nominal voltage: 3V, Nominal capacity: 75mAh,
Standard current: 0.1mA, Continuous current (maximum): 1mA, Pulse current (maximum): 10mA,

The lowest rated current piezo buzzer I could find here http://www.microbuzzer.com/smd-piezo-buzzer has a Rated Current of ≤3mA (second from the top of the list)

Based on this data, is it safe to assume that a battery with a Continuous current (maximum) of 1mA can power a piezo buzzer (and drive circuit) with a rated current of 3mA? Am I missing something here? Wouldn't the buzzer demand more current?

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2 Answers 2

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The battery in question would limit current to the buzzer, per the battery's internal resistance. Thus, the buzzer "demanding" more current is not the constraint, it would only get as much current as the battery is able to supply.

Typical piezo behavior with limited current available (and I just tried this to check) is that the volume of the buzzer starts dropping sharply once the available current reduces below around 30-40% of the "rated" value, but it remains audible (faintly) until well under 5% of rated current.

Also, a piezo buzzer's current demand consists of sharp pulses, much like a capacitor being charged and discharged by a square wave. Thus, the maximum pulse current rating of the battery (10 mA) will come into play, rather than the continuous current rating.

In short:

The buzzer will work fine, it just may not be as loud as it can be. Given that even a tiny piezo buzzer (mine has a minuscule 9 mm diameter) makes an awfully loud sound, this may actually be a good thing.

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  • \$\begingroup\$ Thanks @Anindo, I appreciate that you checked this on your own buzzer! (Could you tell me the name of your buzzer? What is the buzzer's current rating?) Can I just confirm that I have understood correctly? When selecting a battery to power the buzzer, should I be looking at the maximum Pulse Current rating of the battery, instead of the max Continuous Current rating, or are both important? If the piezo buzzer's current demand consists of sharp pulses, will a battery with a max Pulse Current of 5mA, but a max Continuous Current of >1mA be able to power the buzzer? Thanks again! \$\endgroup\$
    – Eddie
    Commented Feb 7, 2013 at 10:26
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    \$\begingroup\$ @Eddie Akaso 5V2MA2KH. I'm in India, here we don't have catalog vendors selling retail - one just goes to a street full of electronic component shops, and buys whatever they happen to have in stock that seems to fit the bill. So my buzzer is some nameless device that I got by asking for "really tiny flat buzzer things", more or less. It has the Akaso etc stamped on it. Oh, and they were around 9 pieces per US$, pretty cheap too :-) \$\endgroup\$
    – Anindo Ghosh
    Commented Feb 7, 2013 at 13:37
  • \$\begingroup\$ Thanks @Anindo. Can I ask you for more information about what you said about the maximum pulse current coming in to play more than the max continuous current? If a battery has a max pulse current of 5mA, but a max continuous current of 0.2mA, will it be able to power a buzzer with a rated current of 3mA? What would you suggest as a safe minimum continuous current? Thanks again! \$\endgroup\$
    – Eddie
    Commented Feb 8, 2013 at 6:29
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    \$\begingroup\$ @Eddie It will work fine, so long as you don't expect ear-shattering sound volume. I have a buzzer working off two paralleled Energizer CR2032 coin cells. \$\endgroup\$
    – Anindo Ghosh
    Commented Feb 8, 2013 at 6:36
  • \$\begingroup\$ Thanks @Anindo. Are there any ways to calculate/estimate by how much the volume will drop, or would this vary from device to device? I have tried contacting buzzer makers, but so far no reply... \$\endgroup\$
    – Eddie
    Commented Feb 8, 2013 at 6:52
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To add to Anindo answer, you can add a big low ESR (tantallum) decoupling capacitor right next to a buzzer to supply it instanteneous current.

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