I have about 100+ 20v (18v NiCd/NiMH & Li-Ion) packs that all charge to 19.5 - 20.5v but I suspect some of them don't have such good holding capacity. I also have many hundreds (possibly thousands) of individual NiCd and Li-ion cells that I'd like to check as well.

Doing the packs one by one isnt' such a big deal, but doing the individuals will be a major PITA and lots of time. Any ideas on how to speed this up? Also, will I be able to determin the MAH of the battery (say it's printed 2600MaH new, but only gives 1200 - vs a 2600 new battery that has been worn down that lost some capacity - can these be told apart?)

I'm trying to figure the best way to do this with what I have on hand. I will buy equipment to do this as I've been getting about 50-80 packs a week, sometimes more.

I understand if I charge to full, then put a load on it (IDK what kind of load to apply for 18-20v that would be constant) and run for 20 mins - check V, run 20 mins, check v, run for 20 mins, check V, etc until I hit the low point of say 3.0-3.2v per cell. It'd be nice to have a volt meter that would beep when it hits the calculated low voltage (and maybe turn off load), real nice with built in stopwatch.

Is there any software that has this setup, USB connection and then just add a load?

Any suggestions on how to set up this testing process is appreciated.

 

hi RR,
An Arduino MEGA has a number of ADC inputs, IIRC at least 16.
The 19V thru 20.5V could be reduced to a level suitable for ADC by using resistive dividers.
The program would monitor the 16 ADC inputs versus Time, with some method of switch Off the CC load at the Vmin point.
You would require 16, CC loads, these could be MOSFET's configured as CC.

On demand, read out from the Arduino the stored battery discharge data, using serial in a USB converter to a PC.

It is assumed the batteries will be fully charged prior to the life discharge test.

E

 

I built a unit to do what you require many years ago. It was based round an electronic counter module that Maplin used to sell. The load was a simple constant current circuit. (Mine was switchable between 0.5 amps and 1 amp.) There was switchable voltage detector that cut off in multiples of 1 volt. (I decided 1 volt per cell was a suitable cut off voltage for discharging.) A button was pressed to start the discharge and the counter then incremented every second when the discharge current was 1 amp. (Every 2 seconds when the discharge current was 0.5 amps.) When the voltage detector detected the selected cut off voltage the the load switched off and the counter stopped incrementing. The counter display then then read the capacity in amp seconds. If I was doing it today I would use a small microcontroller which had a bult in ADC to detect the cut off voltage, swtch the load on and off, and display the discharge time. You could remove the need for a display by connecting it to a PC via a serial to USB converter.

Les.

 

You really need to monitor individual cell voltages, rather than the overall stack voltage, otherwise you risk depleting cells below their rated minimum voltage. For lithium cells without protection ICs that could be nasty.

 

Hi Alec,
I missed the point that Li-ion packs were included. I have never worked out if the protection circuit in packs for power tools shuts of the output from the pack or just sends a signal to the tool so that it can stop drainibg the pack any further.

Les.