Nicad Battery Charger

[kimbear]

I have 2 battery packs that I would like to replace with Nicads . One pack has 8 "AA" Batteries, the other one has 6 "AA" Batteries does anyone has a cheap and simple charger for these packs, so Im not having to take the batteries out of their holders to charge them ??
As per usual, Im thanking everyone in advance for their help in this matter.

 

[audioguru]

AA size Ni-Cads have not been available for 20 or 30 years. They were replaced by better Ni-MH cells. The Ni-MH cells made in the last 5 years can hold a charge for 1 year and have a much higher capacity than Ni-Cads.

A Ni-Cad or Ni-MH cell is 1.4V when fully charged so a series charger for 8 cells has a voltage of 11.2V, a current limit of 1/10th the cell capacity and a timer for 14 hours (overnight). A 6 cells charger will have a 8.4V voltage.

Many years ago my Ni-Cad cells frequently developed a short. I needed to zap a shorted cell with a high current pulse from a charged high capacity electrolytic capacitor. Ni-MH cell do not develop a short. If you charge a series battery that has one or two shorted cells then the simple charger will over-charge the remaining cells.

 

[Nigel Goodwin]

AA size Ni-Cads have not been available for 20 or 30 years.

Except they are still available now, and always have been (RS list two Panasonic/Sanyo AA ones) - just not as common as NiMh now.

However, NiMh aren't much better than NiCd anyway, we replace hundreds (probably low thousands?) of NiMh every year - and these are all in units with top quality charging circuits. We order them in multiples of 100

As far as I'm aware, prior to Li-Ion, NiCd were always used in cordless power tools, in preference to NiMh which don't work as well under the high loads.

As for replacing non-rechargeable with NiCd/NiMh it was normal to replace 8xAA with 10xNiCd/NiMh to keep the voltage correct. Amateur radio gear often came with a pair of dummy AA batteries that you fitted if you were using normal AA.

 

[kimbear]

Ok, now that we have that out of the way, I have a vintage coinmaster2 metal detector. It has holders for 6 AA Batteries and 8 AA Batteries. I would like to charge these packs in their battery holders, not having to pluck out all the batteries to recharge them.
I havnt bought any batteries for this beast yet, so whatever charger(s) someone comes up with, Ill buy the batteries that match the charger.
So Im looking for a schematic, or be pointed to an existing schematic, please.

 

[Nigel Goodwin]

Add a charging socket that disconnects the batteries from the rest of the circuit (a simple switch on the socket, they are very common), then any decent battery charger for the correct number of cells should be fine.

However, as I pointed out previously, they are a lower voltage - so won't last as long as the original batteries (even fully charged they are partly flat).

 

[kimbear]

Both of the battery holders have a existing socket, allowing easy charging, to the batteries that are all in series in their socket. There are no original batteries in the unit, as it originally took AA batteries in both holders

 

[Nigel Goodwin]

Perhaps something like this then?

https://cpc.farnell.com/unbranded/mw2168/charger-nicd-nimh-battery-pack/dp/BT03388?st=nimh%20battery%20chargers