7.2V battery charger

[zodiak]

Hello All,

I have a project that uses 6 AAA 1.2V rechargeable batteries to make 7.2V. I would like to charge the batteries without removing them from where they are, so I would like to charge the full 7.2V battery pack. What would be the best and simplest way to do that - I'm ok with charging times up to 10h.

- I have several 4 AAA chargers at home, any suggested modification to one of these?

- 7.2V is quite common in the RC world. If I go to an RC shop and get a 7.2V charger from there, is there any possibility that could do it?

- Any other idea?

Many thanks,
Cheers,
Rui

 

[audioguru]

A simple charger that is only a timer must match the mAh rating of the battery cells.
According to Energizer's datasheets, their old obsolete Ni-Cad AAA cells had a capacity of only 220mAh and were charged at 22mA for 14 hours.
Their new Ni-MH AAA cells have a capacity of 850mAh and are charged at 85mA for 14 hours.

If you use a fast charger then it must match the chemistry of the cells.

 

[zodiak]

thank you for the quick reply, but it's still not clear how I can solve my problem.

As I mentioned, I have a 7.2V pack made up of 6 AAA NiMH rechargeable batteries. I would like to be able to charge the whole pack, without removing the individual batteries and placing them in the charger. The common chargers for those batteries charge 4 batteries at a time.

May I simply connect my 6 cell pack to a 4 cell charger and wait longer for it to charge?

 

[audioguru]

May I simply connect my 6 cell pack to a 4 cell charger and wait longer for it to charge?

Four Ni-MH cells in series are about 5.6V when fully charged. If the charger is simply a current-limited timer then its output voltage is probably 6V.
Six Ni-MH cells in series are about 8.4V when fully charged. If the charger is simply a current-limited timer then its output voltage is probably 9.0V.
Therefore six cells in series won't even begin to charge from a 6V four-cells charger.