Battery self discharge test results

[Lurveleven]

Two months ago I started a test to see how different temperatures influence the self discharge on NiMH batteries. I put 4 batteries in the freezer (-18°C), 4 in the refridgerator (4°C) and 4 in a drawer at room temperature (20°C). I will let the batteries discharge one month more before measuring the capacity, but I did measure the voltage on them the other day and the results was quite interesting (and kind of what I expected, but maybe not such a big difference):
Batteries in drawer: 1.295 V
Batteries in refridgerator: 1.345 V
Batteries in freezer: 1.395 V

The batteries used are all of the same brand and bought at the same time, they are Vanson 2300 mAh batteries.
I measured the voltage on all 4 batteries in each package of batteries and the result was the same for all batteries in each pack, so the result are not a coincidence.

Maybe I will buy a LaCrosse charger to test the capacity, or is there other devices I should concider instead? I was originally going to see how long they would run my TSP, but I now think this may not be a very good way of testing.

Sigbjoern

 

[greenLED]

Cool! For your net round you may stick some in your car. /ubbthreads/images/graemlins/thumbsup.gif

 

[SilverFox]

Hello Sigbjoern,

I have never formally done a self discharge test, but the La Crosse charger does indicate how much charge goes into the cells. I am not sure how accurate that measurement is, but it should give a good indication.

Several people have these chargers so a wide variety of cells could participate in the test. My drawer is a bit warmer than yours (about 22 C) but that should not make that much difference.

Tom

 

[Lurveleven]

I must have misunderstood how the La Crosse worked (next time I will do my homework), I thought it had a discharger that measured how much capacity it could get from a battery, but a measurement of how much it is able to push into a battery will work as well since it shows how much capacity the battery has lost (lets not hope there is a too big difference with my current charger and the La Crosse).

Tom, what do you use for your battery testing? It would be nice to have something that could make discharge graphs, unless this is something that costs a lot of money.

GreenLed, I'm one of those strange people not owning a car (living in a city so doesn't need one that much anyway). It let me spend more money on flashlights /ubbthreads/images/graemlins/grin.gif

Sigbjoern

 

[SilverFox]

Hello Sigbjoern,

The La Crosse charger actually measures both ways. Yesterday I just happened to put some cells in it and noticed that they only took 26 mA to come to full charge. I thought that might be interesting for checking self discharge rates...

My discharge testing is done on a CBA from www.westmountainradio.com . The graphs are done with a $3500 statistical package that I own and use at work called S+. Early on there was some mention that West Mountain Radio was a bit sensitive to publishing full screen shots, so I export the data to my statistical package and produce the graphs from there. This allows me to list more information (Watt Hours and Minutes) and annotate the graphs as needed.

Tom

 

[Lurveleven]

The CBA was quite cheap so maybe I will buy both as is very popular to do here at CPF. Since I have 4 batteries to test on I can put two in the CBA and two in the La Crosse. What accessories should I buy for the CBA?
I have access to a variety of statistical packages at work so that will not be a problem.

Sigbjoern

 

[SilverFox]

Hello Sigbjoern,

Just to remind you that the CBA connects to your PC via a USB cable. The Mac version is not available yet.

I would recommend getting the thermal probe. It has a bit of lag and you have to be careful how you position it, but I think it adds a layer of safety to the testing.

I soldered some #4 copper washers to the wire and hold the battery in a (non conductive) clamp. You may have to make up some connection pieces for different battery pack testing, but those supplies are easily found at your local electronics store.

I think one of the hardest parts of CBA testing is keeping track of all of the data. Of course there also is the hours spent working on high capacity D cells at low current drains... /ubbthreads/images/graemlins/smile.gif

Tom