Batteries and Temparature

[skillz21]

Ah.... Turning to the forum once again, because of my own stupidity. So I had this idea for a science project where I have to see how different temperatures affect batteries. I 1 AA battery each in, the sun, the freezer (-19 degrees Celsius), in the fridge (3 degrees Celsius), and one at room temperature.
Long story short, when I actually got to discharging them, I found that the voltage jumps around quite a bit and that this isn't the best project to do for a science assignment. Using ohm's lay I calculated the resistor I used as the load to be around 1.5 ohms.

At this rate of discharge, can someone who knows a bit more about batteries estimate how long it would have taken for the voltage to drop to 0.8 volts under load? Or how batteries would react to temps such as these? As in which batteries would have lasted longer and which ones shorter?

Please help,
Thanks

[danadak]

This might help -


http://www.etf.unssa.rs.ba/~slubura/diplomski_radovi/Zavrsni_rad_MarkoSilj/Literatura/Handbook%20Of%20Batteries%203rd%20Edition.pdf

There are many battery technologies, so book should help. Also online
you can usually get data sheets for the vendors batteries you are using
that will show discharge curves.


Regards, Dana.

[skillz21]

This might help -


http://www.etf.unssa.rs.ba/~slubura/diplomski_radovi/Zavrsni_rad_MarkoSilj/Literatura/Handbook%20Of%20Batteries%203rd%20Edition.pdf


Regards, Dana.

Thanks... it's really long though.... can someone order the four batteries (from earlier) in order of battery life? Just in general?

[sleemanj]

Pages 265 through 268 of that document, assuming you are talking about Alkaline cells.

As to "jumps around a bit" and "calculated the resistor" suggest to me that your testing methodology isn't quite what one would perhaps expect and maybe you would like to describe it.

This sounds like a homework question, while people here will be happy to guide you in your learning, most will refrain from spoon feeding answers.

[skillz21]

Here's how I'm testing it (keep in mind I told you this was a horrible project for me to do). A 1.5v Alkaline battery running through a multimeter (for current) and through the load (resistor). Negative pin of battery then goes to GND of Arduino, positive to A0, for voltage measurement (second multimeter still in the mail  ). I connect the circuit and start a timer when the voltage (on the Arduino, and while the load is connected) drops to 0.8 volts, I stop the timer. At least theoretically.

See, the thing is, the battery goes down to 0.83 or .84 or so, and the goes up to 0.89.... things like that. or just stays at 0.83 for ages and ages, while drawing about 700 or 800 mA.... Not working like I expected.

[sibeen]

You should probably have a peek at the Arrhenius equation.

[sleemanj]

Think about supply voltage stability and noise, namely if you are running this from some "USB" supply or especially have it connected to, your PC usb, that "5v" will

  1. not be exactly 5v (USB could be significantly higher or lower and still be in spec)
  2. not be stable (it can vary within it's spec)
  3. probably have a fair amount of noise on it

these factors will greatly affect your measurements. 

The noise can be, at least ameliorated by averaging a number of samples.  The first two need an alternative solution, either a stable (and known) external analog reference, or by having the Arduino read the actual Vcc at that moment when you make each measurement - as in your other thread about the LM335.

It is unlikely that the cell is "jumping around" in voltage during the discharge (but as it warms up it's not impossible I expect depending on your load), it's more likely a measurement error from one of the above.

Think about what task you can pass to the Arduino...  if you remove the multimeter from the circuit, your setup would be sufficient for you to be able to calculate the capacity of the cell (from it's start voltage to it's terminal voltage whatever you determine that as) because your Arduino can read at any given time the voltage of the cell and the voltage across the load resistor which is across that cell -  exactly the same thing.  Ohm's law applied with the voltage and the resistor value gives you the current, current and the time that current was observed passing for gives you the capacity.  You also now have your multimeter back so can use it to monitor the voltage (and, by Ohm's law, the current too).

[danadak]

Average the Arduino readings, URL ap notes on the topic.


https://www.dropbox.com/s/2h96beh1fbvz4e2/noise_notes.zip?dl=0


Regards, Dana.

[skillz21]

Think about supply voltage stability and noise, namely if you are running this from some "USB" supply or especially have it connected to, your PC usb, that "5v" will

  1. not be exactly 5v (USB could be significantly higher or lower and still be in spec)
  2. not be stable (it can vary within it's spec)
  3. probably have a fair amount of noise on it

these factors will greatly affect your measurements. 

The noise can be, at least ameliorated by averaging a number of samples.  The first two need an alternative solution, either a stable (and known) external analog reference, or by having the Arduino read the actual Vcc at that moment when you make each measurement - as in your other thread about the LM335.

It is unlikely that the cell is "jumping around" in voltage during the discharge (but as it warms up it's not impossible I expect depending on your load), it's more likely a measurement error from one of the above.

Think about what task you can pass to the Arduino...  if you remove the multimeter from the circuit, your setup would be sufficient for you to be able to calculate the capacity of the cell (from it's start voltage to it's terminal voltage whatever you determine that as) because your Arduino can read at any given time the voltage of the cell and the voltage across the load resistor which is across that cell -  exactly the same thing.  Ohm's law applied with the voltage and the resistor value gives you the current, current and the time that current was observed passing for gives you the capacity.  You also now have your multimeter back so can use it to monitor the voltage (and, by Ohm's law, the current too).

Is there some sort of formula I can use to calculate the battery life, without all this testing?

[floobydust]

I suggest to look at battery datasheets. Some give low temperature performance graphs, which can save you some work.

Energizer EN91 AA alkaline battery datasheet   Operating Temp: -18°C to 55°C (-0°F to 130°F)
Energizer L91 AA lithium battery datasheet   Operating Temp: -40°C to 60°C (-40°F to 140°F)


For a science fair project, I think it would be better to do the experiment with rechargeable batteries. This would be relevant for electric cars in cold climates.
You get lower capacity and battery "charge acceptance" goes down drastically with temperature.
Not much data out there on how an electric car with lithium batteries does in cold weather.

[Audioguru]

The 1A of current is too much for an AA alkaline cell and is much too much for the contacts and wires of an AA battery holder. Try 100mA instead.

[skillz21]

Thanks so much for all the great resources and the help! You've helped a lot, Thanks!