Ni-cad Checker

One of my projects has been a computer controlled Nicad checker. This will charge and discharge up to 7 Ni-cads measuring the volts, amps and temp of each cell every 10 Secs. This is then displayed in a graph from which you can work out which cell is better from others or finding out if there is a defective cell in a pack. Unfortunately is was made to work on a BBC computer. I would have liked to convert it to work on a PC but I do not have enough knowledge of the PC to be able to do this. If you want any more information on this then please contact me.

Download PCB details

The Hardware

Voltage leads connected to the cells

Inside the box

Single cell rig

Close up

How the cells are mounted

These are the charge and discharge cycles from an evenly matched set of cells. Notice the traces of the cells are very close together indicating a well matched set of cells. On the left hand chart the single line that starts about halfway up the chart is the temp trace, notice how it ramps up at the end of the charge as the cells reach there peak. On the discharge chart the temp trace starts at the 1.25 volt mark and then disappears out the top of the chart as the cells heat up during discharge.

These chart above are the charge and discharge cycles of two different packs, notice how very spread out the traces are. The left hand one is the charge, notice how some of the cells have started off at a very high voltage, over 2 volts per cell in some cases. As the cells charge up they do start to come into line but are still very spread out. The effect of the drop in volts at the start of charge can play havoc with delta peak charge detectors. This also indicates that the cells are only fit for the recycle bin. On the discharge chart on the right notice how the cell traces start to spread out very early on in the discharge compared to the trace of the good cells above it. Under heavy discharge the voltage of this pack would be a lot lower than the good pack above.