EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: 6SN7WGTB on March 26, 2022, 02:20:24 pm
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I've just had a curious experience, the short version of which is that I traced the anomaly to an excessive battery voltage.
The device in Q required a 1.5V battery supply - and given its age (1970) predates any fancypants cell chemistry.
I had however used an AA Energizer Li cell.
Now, the Energizer spec would suggest that is OK when basically open circuit - see diagram.
However, I always test on load and I got a steady 1.737V with 88mA - this certainly does NOT meet spec. Several cells from two different batches tested the same.
Not sure I'm too happy with some multi-cell devices I have (e.g. 4 x AA , 6V 'nominal') getting 6.8V...
Anyone come across this and/or thoughts?
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Just found this chart on the Energizer website, which appears to contradict the above 'Discharge Profile' - the above asserting that 10mA discharge will produce a ca. 1.5V output over the bulk of the capacity of the cell, whereas below suggests many service hours above 1.5V.
Am a bit puzzled.
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Are you measuring voltage and current simultaneously or are you measuring one and then the other? What is the open circuit voltage of the cell?
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What you're seeing is normal and within spec. From the Energizer FAQ:
What is a normal open circuit voltage for an L91? {AA}
"The normal open circuit voltage for an L91 (https://data.energizer.com/pdfs/l91.pdf) is higher than that of alkaline and ranges from 1.75-1.8V. This should not pose a problem in devices since the voltage drops once the battery is under load."
Will the higher open circuit voltage damage my device?
"No. Numerous devices have been tested and third-party device engineers have certified that the higher open circuit voltage of the L91 is not an issue in devices."
If you are using one of these lithium for a reference battery 1.50V then I'd add an LDO like replacements for PX625 1.35V mercury battery.
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Just found this chart on the Energizer website, which appears to contradict the above 'Discharge Profile' - the above asserting that 10mA discharge will produce a ca. 1.5V output over the bulk of the capacity of the cell, whereas below suggests many service hours above 1.5V.
Am a bit puzzled.
They're both useless baloney. The V/I characteristics of the Energizer Lithium AA cells are very dependent on cell temperature and any characterization that ignores that is useless. At room temperature or a bit warmer, they will put out quite a bit of current at well over 1.5V.
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"However, I always test on load and I got a steady 1.737V with 88mA"
So it is NOT dropping under load!