improvised voltage reference...

[bob prohaska]

Does anybody have a weblink for the temperature coefficient
of voltage for commercial (Energizer) size 357 silver oxide-zinc
button cells? Nominal is 1.55 volts, but knowing the temp effect
is (maybe) important if I\'m stacking up nine or ten of them.

I\'d like to check a trio of inexpensive Radio Shack DVMs for use
in charging relatively-expensive lithium iron phosphate batteries.
On the same battery the three meters report 14.41, 14.51 and 14.58
volts, so they certainly disgree among themselves. I suspect but
can\'t yet prove that the middle one is about 2% higher than actual.

Yes, I probably should buy a good DVM, but the Radio Shack units
are on-hand and except for charging batteries absolute accuracy
isn\'t usually of much importance.

Ten millivolts is plenty good for present purposes. If there\'s a
better/cheaper improvised reference in this range please post!
CR2032 cells are readily available, but voltage details are scarce.

Thanks for reading,

bob prohaska

 

[Peter W.]

Eveready states in their literature that the \"open\" voltage (unloaded) of such a cell is 1.5 to 1.6 volts - as a matter of the specific device in question. Suggesting that the loaded voltage will be lower. They state, typically, at 1.55V for a 1.6V battery. There is also a temperature chart in their literature, but it is applied only to storage and longevity-in-storage.

9 x 1.6 = 14.4, so you are definitely within the range even with the lowest reading given.
Typical accuracy (DC) on an RS meter (today) is +/- 0.5% - as advertised. Meaning some may be better, but should not be worse. As yours are likely older models, +/- 0.5% is likely optimistic.
0.5% x 14.4 = 0.072
Meaning that your range-of-readings should be somewhere between 14.472 and 14.328 for that particular group of nine (9) button cells.

Oh, RIGHT! You are comparing apples (liFe) cells to oranges (ZnAgO). Simple enough: Go to the Manufacturer and get the nominal unloaded and loaded values. Measure with the meters-in-hand. That which is the closest is the benchmark. If the others are consistent, there is your margin-of-error.

Peter Wieck
Melrose Park, PA

 

[legg]

On Wed, 24 Aug 2022 02:24:05 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

Does anybody have a weblink for the temperature coefficient
of voltage for commercial (Energizer) size 357 silver oxide-zinc
button cells? Nominal is 1.55 volts, but knowing the temp effect
is (maybe) important if I\'m stacking up nine or ten of them.

I\'d like to check a trio of inexpensive Radio Shack DVMs for use
in charging relatively-expensive lithium iron phosphate batteries.
On the same battery the three meters report 14.41, 14.51 and 14.58
volts, so they certainly disgree among themselves. I suspect but
can\'t yet prove that the middle one is about 2% higher than actual.

Yes, I probably should buy a good DVM, but the Radio Shack units
are on-hand and except for charging batteries absolute accuracy
isn\'t usually of much importance.

Ten millivolts is plenty good for present purposes. If there\'s a
better/cheaper improvised reference in this range please post!
CR2032 cells are readily available, but voltage details are scarce.

Thanks for reading,

bob prohaska

10mV on a single 3.5V cell is 0.3% - so you\'re going to have to
calibrate SOMETHING, if you intend to provide that accuracy.
One calibrated reference is enough - you can set up cheap meters
to mimic it and calibrate microcontrollers to store correction
factors using it.

Using batteries as a reference is no longer a viable method for
most labs to maintain.

Get one good 6digit calibrated meter. If it\'s built into a data
logger, even better.

RL

 

[ehsjr]

On 8/23/2022 10:24 PM, bob prohaska wrote:

Does anybody have a weblink for the temperature coefficient
of voltage for commercial (Energizer) size 357 silver oxide-zinc
button cells? Nominal is 1.55 volts, but knowing the temp effect
is (maybe) important if I\'m stacking up nine or ten of them.

I\'d like to check a trio of inexpensive Radio Shack DVMs for use
in charging relatively-expensive lithium iron phosphate batteries.
On the same battery the three meters report 14.41, 14.51 and 14.58
volts, so they certainly disgree among themselves. I suspect but
can\'t yet prove that the middle one is about 2% higher than actual.

Yes, I probably should buy a good DVM, but the Radio Shack units
are on-hand and except for charging batteries absolute accuracy
isn\'t usually of much importance.

Ten millivolts is plenty good for present purposes. If there\'s a
better/cheaper improvised reference in this range please post!
CR2032 cells are readily available, but voltage details are scarce.

Thanks for reading,

bob prohaska

You want a precision that is doomed by the technique you
intend to use - stacking cells. Instead, build a voltage
reference using a single IC: ADR01 available from Digikey
https://www.digikey.com/en/products/detail/analog-devices-inc/ADR01AUJZ-REEL7/996117
It provides 10V output at +/- point one percent (.1%)

Calibrate your meters to that.

Ed

 

[amdx]

On 8/23/2022 9:24 PM, bob prohaska wrote:

Does anybody have a weblink for the temperature coefficient
of voltage for commercial (Energizer) size 357 silver oxide-zinc
button cells? Nominal is 1.55 volts, but knowing the temp effect
is (maybe) important if I\'m stacking up nine or ten of them.

I\'d like to check a trio of inexpensive Radio Shack DVMs for use
in charging relatively-expensive lithium iron phosphate batteries.
On the same battery the three meters report 14.41, 14.51 and 14.58
volts, so they certainly disgree among themselves. I suspect but
can\'t yet prove that the middle one is about 2% higher than actual.

Yes, I probably should buy a good DVM, but the Radio Shack units
are on-hand and except for charging batteries absolute accuracy
isn\'t usually of much importance.

Ten millivolts is plenty good for present purposes. If there\'s a
better/cheaper improvised reference in this range please post!
CR2032 cells are readily available, but voltage details are scarce.

Thanks for reading,

bob prohaska

Aliexpress, Ebay and Amazon have some for under $10, and more for under $20.

https://tinyurl.com/2ajs395b

https://www.google.com/search?q=5+volt+reference&client=firefox-b-1-d&sxsrf=ALiCzsa702yEJPZb4SzokD4GXJ1Jimyrjw:1661422961250&source=lnms&tbm=shop&sa=X&ved=2ahUKEwiA7rTr4uH5AhXOoWoFHb3PDVkQ_AUoAXoECAEQAw&biw=1472&bih=657&dpr=1.3

 

[Jeff Liebermann]

On Wed, 24 Aug 2022 02:24:05 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

Does anybody have a weblink for the temperature coefficient
of voltage for commercial (Energizer) size 357 silver oxide-zinc
button cells? Nominal is 1.55 volts, but knowing the temp effect
is (maybe) important if I\'m stacking up nine or ten of them.

Bad idea. If a silver oxide battery goes below 30% charge, there will
be about a 100mv step increase in terminal voltage:
<http://members.iinet.net.au/~fotoplot/accbatcc.htm>
<http://members.iinet.net.au/~fotoplot/dis.jpg>

I\'ve seen the step in my cheap Chinese digital calipers, where I need
to re-zero the indicator when the cell voltage crosses the transition.
Of course, the alkaline batteries are somewhat worse, where I need to
re-zero the calipers nearly every time I use them.
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Thu, 25 Aug 2022 11:48:56 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

If a silver oxide battery goes below 30% charge, there will
be about a 100mv step increase in terminal voltage:
http://members.iinet.net.au/~fotoplot/accbatcc.htm
http://members.iinet.net.au/~fotoplot/dis.jpg

Oops. That should be \"goes below 70% charge\". I\'m accustomed to
capacity being state of charge (SoC), not state of discharge.

--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Wed, 24 Aug 2022 02:24:05 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

Ten millivolts is plenty good for present purposes. If there\'s a
better/cheaper improvised reference in this range please post!
CR2032 cells are readily available, but voltage details are scarce.

There are ready to use voltage reference PCB\'s available.
<https://www.adafruit.com/product/2200>
<https://www.amazon.com/Voltage-Reference-Source-Output-Precision/dp/B07WMYN32C>
<https://www.amazon.com/Reference-Precision-Resistance-Calibrating-Multimeter/dp/B0B6FK8Z1D>
<https://www.ebay.com/itm/393398250363>
<https://www.aliexpress.com/wholesale?SearchText=precision+voltage+reference>
<https://www.aliexpress.com/item/2251832677587870.html>
etc...

--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558