9 volt alkaline battery

Discussion in 'Electronic Basics' started by fashazee, Feb 6, 2006.

1. fashazeeGuest

Hello,

Technically speaking, at what voltage is a loaded 9 V alkaline battery

Mike

2. BobGGuest

===================
6.6V? (1.1V/cell x 6 cells)

3. ChrisGuest

Hi, Mike. When consumer batteries are rated for A-h (amp-hours), they
are typically given a constant load, and are considered dead when the
output voltage reaches 60% of specified voltage (in the case of a 9V
transistor battery, that would be 5.4V)

Of course, any battery is _really_ dead by the time it reaches 60% of
rated voltage. I'd consider a 9V battery with a 25mA load very dead by
the time it got to 7V or so. Once the output voltage slides below 80%
of nominal, it's got one foot in the grave.

Good luck
Chris

4. Phil AllisonGuest

"fashazee"

** When whatever it is powering ceases to function properly.

........ Phil

5. Don KlipsteinGuest

I just got a look at: http://data.energizer.com/PDFs/522.pdf

Looks to me there is a bit of a "knee" in the discharge curve with the
"center of the knee" at 7 to 7.2 volts (1.1667-1.2 volts per cell), but
the "knee" only stands out a little. With intermittent duty and a
constant resistance load, the time to 5V is about 50% longer than the time
to 7V.
The constant current discharge curves show mAH about or slightly more
than 7/6 as great when discharged to 4.8 volts as at discharge to 6 volts.

Meanwhile, as for what voltage to design something to work at with this
battery? Since the datasheet has constant resistance and constant current
hours-to-specified voltage curves (as a function of resistance or current)
only for 6 and 4.8 volts, I would design something using this battery to
keep working at least until the voltage decreases to 6 volts.
Although I think it's OK for a product using this battery to work but
not quite meet its specifications below 7.2 volts, I believe that a
product designed to use this battery should work reasonably at least down
to 6 volts.

Meanwhile, in general design of products using alkaline batteries: I
believe they need to work well with NiCd and NiMH that are typically 1.2
volts per cell, and considered discharged at 1.1 volts per cell *or less*.
So I believe a product needs to work well at 1.1 volts per cell.

- Don Klipstein ()

6. Phil AllisonGuest

"Don Klipstein" :

( snip agreed stuff)

** There is no need to assume that a Ni-Cd or NiMH battery ( made to
replace the 9 volt single use size) will have only 6 cells - 7 cell
examples of both have been available for a long time and more recently 8
cell ones too. These have nominal 8.4 and 9.6 volt ratings as opposed to
7.2 for the old 6 cell ones.

Also, where an item uses a 9 volt single use battery and no mention is made
in the handbook of suitability of use with rechargeables, owners are not
wise to assume it is safe to do so.

A NiCd cell ( and many NiMH too now) can deliver a dangerously large current
if shorted or reverse connected and the item concerned must be designed to
cope with this without damage if the use of rechargeables is allowed.

........ Phil

7. David L. JonesGuest

Energizer specify the capcity of their 9V alkaline to a discharge
voltage of 4.8V
This makes sense as alkaline batteries are typically physically
constructed of 6 "AAAA" batteries in series, and single AAA/AA/C/D
cells are specs to be "dead" at 0.8V. So 0.8V x 6 = 4.8V
So in theory, to use all the available capacity of a 9V battery, a
device should be designed to operate down to 4.8V. Not many devices are
though, they will die at a much higher voltage and hence won't use all
the capacity of the battery.

Dave

9. Rich GriseGuest

When it won't operate the thing it's powering any more.

Cheers!
Rich