Battery/cell tester

I’m using slightly used AA and AAA alkaline batteries from entrance door locks among other things to run LED lights, blackout lights, Xmas lights etc. Most run for many hours which extracts the mostly unused energy which is normally just thrown away long before they become truly flat.

I found my Tandy electronic project kit a few years ago. Never tested it to see if it still works but this might be a good excuse.

Mark Gray

Isn't loading the battery while testing (less than 1 second should be enough) to see the 'operating' voltage. An old battery can easily show fx. 1.4V unloaded, but as soon as you draw just a little current, the voltage drops very fast way under usable level. A Joule Thief of course draw the rest of the 'juice' out of such a battery :-)

Zeedijk Mike

That's good. I doubt you need to dwell for 5 sec though. Probably a millisecond would do it, long enough to take a reading do some sums etc.

Mike Page

I made myself an Arduino based battery tester (total over-kill) that tests the battery at 3 load levels for 5 sec each, 0mA, 50mA and 100mA . It shows the voltage as a graph on a small O-Led display (again total over-kill) The "project" never came off the bread board, so all parts (well the Arduino and the display) have since been reused. Fun little project though.

Zeedijk Mike

Shame you didn't go on to mod the first tester to make it more accurate... ;)

Pete Kay

I have an old Maxell battery checker from the 90s, which is much larger, has 4 positive terminal positions and a short probe lead to touch the negative end. These are marked UM-1/2/3, UM-4/5, 1.55V (listing various SR/G values such as SR44) and 6.2V 4SR44(G13). There is also a separate 2-pin 9V terminal. The display has two graphs, one for Dry Battery (red/yellow/green zones) and one for Silver Oxide (red/green zones). Surprisingly, it's well calibrated as a fresh Alkaline or watch battery will go right to the edge of the green zone, whereas a battery that has just stopped working (e.g. from a TV remote) will usually move the needle to the boundary between the red and yellow. Obviously not as effective with Ni-MH's which go to the middle of the green zone at nearly any charge state above being flat.

Seán Byrne

I have often thought about making a better version that measures open circuit voltage and internal impedance, displaying O/C V and S/C I - as you'd get with a meter but without the current drain, dependence on good leads and knowledge of the meter current shunt. But it's not quite exciting enough and I'm rubbish at mechanical design.

Mike Page

So if you remove the 1200 ohm resistor and put in a 770 ohm resistor on the 1.5 volt side, the old meter would work better. Also I'd drop the 8.2k ohm resistor to 7.7k ohm for the 9 volt side.

Belgrath

The issues with an unpowered tester like this are:- 1) The load can significantly drain the battery being tested. 2) It isn’t very accurate (as demonstrated in the video). 3) It doesn’t measure the actual battery voltage. I much prefer battery powered testers because they don’t have the drain/accuracy issues, and some also display the actual battery voltage on an LCD.

Gadgetman

Could one of these be converted into a Whoofler tester?

Ymir the Frost Giant

I remember doing similar with a 160 in 1 electronic project kit from Tandy, but it was way less portable :)

Tim Grainger

It is a factor in both directions. It has to be factored into the design.

Big Clive

I hacked one of these with a LDR photocell in series when I was a kid so I had a crude light sensor. Walking around pretending I was getting radioactivity readings. :)

Wim

Somehow I had it in my head that 9-volt batteries had a low internal resistance and could supply relatively high current. Heck, I based a whole project around that idea. I guess not!

Circuitmike

What happens if you treat the 9V resistors as a parallel load to the coil? My Kirchoff's Law skills are crusty and slow, but it seems like it may be a factor. Update - it's about 30 uA difference. Carry on.

Be-Ankh-Ah