Nigel Goodwin said:
The entire idea is pretty bizzare? (and wouldn't work very well), you need to study how to charge NiCd and NiMh.
First thing you need is to provide current limiting to the batteries, preferably a constant current charging source. Then you should monitor the voltage across the batteries, looking for a small DROP in voltage - this occurs when they are fully charged, and you then switch to trickle charging. As a further safety measure you monitor the battery temperature, this increases once they are fuly charged, and again such an increase should switch the charger off leaving a trickle current to them.
I think I mentioned that the charging source was 12V 300mA
FYI I have looked at the battery charging manual provided by energiser and they recommend a thermal based system. Although mine isnt exactly as theres I think I can change it around - however I think my system would be even safer as the stage at which thermal is used is right at then end to make it trickle charge. Below is the quote from the manual from Energiser
"Three-Stage—Here a fast charge restores approximately 90 percent of the
discharged capacity, an intermediate timed charge completes the charge and restores
full capacity, then a maintenance charge provides a continuous trickle current to
balance the cells and compensate for self-discharge. The fast charge (with currents in
the 1C range) is typically switched to the intermediate charge using a temperaturesensing
technique, which triggers at the onset of overcharge. The intermediate
charge normally consists of a 0.1C charge for a timed duration selected based on
battery pack configuration. This intermediate-charge replaces the need to fast-charge
deeply into the overcharge region to ensure that the cell has received a full charge.
Three-step charging, such as illustrated in Figure 20, requires greater charger
complexity (to incorporate a second switch point and third charge rate), but reduces
cell exposure to life-limiting overcharge."