Design Article
The impact of high pulse drain on CR2032 coin-cell battery capacity
Kjartan Furset, Strategic Applications Manager, Nordic Semiconductor, and Peter Hoffman, Staff Technology Engineer, Energizer
1/2/2012 12:41 PM EST
Coin-cell batteries are often used to power portable devices, including wireless ones, but there is little available information into how they perform in high-rate, pulsed applications, in contrast to relatively steady-state load situations.
This article shows how the high-peak, short-duration pulsed loads–which typical of, but not exclusive to, ultralow-power wireless applications–affect Energizer CR2032 coin-cell batteries. It also examines how your design and operation affects the battery life time you can expect in your application. [Note: the CR2032 type is one of the most commonly used coin cells in the very large, sometimes bewildering universe of such cells.]
To read this article by two experts on these batteries and low-power wireless applications, which is presented as a pdf document, click here.
About the authors
Kjartan Furset is Strategic Applications Manager at Nordic Semiconductor; Peter Hoffman is a Staff Technology Engineer at Energizer.
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mema
1/3/2012 6:36 AM EST
Why do you classify ZigBee as a 5-50+ mA technology? (Low Power)
While describing Ble/Ants as less than 1mA technology (Ultra Low Power)?
We do a lot of work with 802.15.4 and protocols based on this (ZB and others). We also do a lot of work with Ble. We do not see this differences in the technologies themselves.
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kcooley
1/4/2012 8:27 AM EST
Here at buildmyproduct.com we've built several low power devices using coin cell batterys. Most product designs still require more energy to work of the desired life of the product. We've run vibrating motors from coin cells, but only for a couple of weeks before the battery voltage is too low to power the microcontroller properly. Better choices are rechargable lithium batteries, coil cell alkaline or zinc, or even AAAA batteries.
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psi123
1/4/2012 11:23 AM EST
They do not have to be tested all the time.
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jeremybirch
1/4/2012 12:00 PM EST
I am probably missing something here, but if the issue here is pulse current drain on the battery due to intermittent high current use, then surely most of the issues go away if there is a capacitor in parallel with the battery in some way? This way the pulse current comes from the capacitor (which has a much lower IR) and the battery has a long time to top the capacitor back up before the next pulse.
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bcarso
1/4/2012 1:00 PM EST
You're not missing anything! It's astonishing that the authors don't even mention capacitors in parallel to improve performance, which is a time-honored strategy. I speak from personal experience, having determined optimal strategies for coil cell use in certain wristwatches, ones that use electromechanical displays.
Brad Wood
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zeeglen
1/4/2012 6:36 PM EST
I think the intent of the article is to show the response of the cell alone, not how to compensate. Yes, a capacitor would certainly help; that would be good information in a follow-on article.
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glen.herrmannsfeldt
1/4/2012 6:09 PM EST
A reasonable-sized capacitor would help for very short pulses, but as the pulse length increases (at constant average current) the needed capacitor will eventually be too big. Well, one has to do the experiment to find where that point is.
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Mac_H
1/4/2012 6:27 PM EST
These are results from one specific brand of batteries - it is worth remembering that it can change dramatically for different brands. We ran some tests and found that more complex battery packs with internal temperature sensors were even *faking* safety-critical data - the manufacturer had saved money by simply removing the temperature sensor and faking the results!
The graphs (and photos of the internal teardown) are here: http://bit.ly/tCTPVC
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bcarso
1/4/2012 8:57 PM EST
Coin Cells and Peak Current Draw
Texas Instruments
Mathias Jensen
White Paper
September 2010
This is worth checking out. I can't post the link directly but it was also an EETimes featured article --- a Google search ought to be productive. Note that it discusses both capacitor optimization and differences among battery manufacturers.
Brad Wood
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mema
1/5/2012 11:22 AM EST
The TI link is:
http://www.ti.com/lit/wp/swra349/swra349.pdf
Using a capacitor in parallel is useful. However, remember that you have different states in Ble. The duty cycle is not the same in all states, which means that you have to make sure that you capacitor is properly loaded in cases several TX/RX activities are done at short intervals. So a smaller TX/RX current is also an advantage there.
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studleylee
1/5/2012 12:14 PM EST
Good reference info guys. thanks to authors and commentators. -Lee
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ThermalHunter
1/5/2012 1:36 PM EST
In the early 90's I worked for a company where long life (5 yrs at room temp, 2 years at -20C) was manditory from CR2430 coin cells in a high pulse\low average current regime. We developed a custom test which emulated the pused operation and so could predict battery lifetime. There were large (2:1 - 3:1) variations between manufacturers for the "same" battery. The discharge curves were like fingerprints; it was clear which "brands" were mearly OEM versions from other manufacturers.
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