Charger for a NiCd rechargeable PP9.

[Nanozeugma]

Afternoon

I recently acquired a piece of battery (only) powered test equipment which uses a PP9 battery.
A *rechargeable* RS NiCd PP9 cell was found inside.
It looks identical to the one still currently offered by RS - stock is now 229-059.

I have no idea of it's antiquity and whether it will still take a charge.
Charging parameters per attached image of label.

Strangely, although RS still offer the battery, there's no sign of a charger.

Does anyone know where I might find a suitable charger (or circuit) to find out whether it is still any good?

Many thanks.

[Bazz4CQJ]

Firstly, what do you already have in terms of low voltage power supply units?
B

[nutteronthebus]

I was looking for one of these for my Roberts 505 radio until I found out the price £50 + ouch . I now have an eveready silver PP9 and it has a plastic case that I will convert to rechargeable when flat but what chemistry I do not know

Merrily give it 120mA (hardly critical) for a while (14 hours). At C/10 (120mA) the battery will self limit and not overcharge in the short (a few days) term. NiCds are like that, unfortunately the modern NiMh types really don't like much overcharge.

I now have an eveready silver PP9 and it has a plastic case that I will convert to rechargeable when flat but what chemistry I do not know

I use a six cell AA holder inside my two, the cells are "eneloop" type. The charger (and four cells) came from John Lewis, additional ones from Amazon. It does take a while to recharge all 12 needed for my Hacker, the charger only takes four.

[paulsherwin]

Two lithium cells will also work well in a PP9 case, giving 8.4V when freshly charged. They don't self discharge much and last for ages if you use something like 18650s. You can take them out and charge them individually when the time comes. Just don't let them run dead flat, and include a fuse.

[Nanozeugma]

Originally Posted by Bazz4CQJ

Firstly, what do you already have in terms of low voltage power supply units?
B

Something I need to acquire, at present none.

[ThePillenwerfer]

This should do it:—

[Bazz4CQJ]

Originally Posted by Nanozeugma

Something I need to acquire, at present none.

Mmm...that complicates things. An old Nicad may well be a deceased Nicad, and if that's true, there would be little point in buying/building a Nicad charger. As Paul points out, if starting a fresh, forget Nicad and go Lithium-ion, or nickel hydride.

Do you have access to a 12volts battery?

B

[broadgage]

A very simple and improvised charging circuit will be fine for an 8.4 volt 1.2 AH battery as illustrated.
A DC supply of about twice the battery voltage and a small lamp in series to limit the charging current.

A 19 volt laptop power supply would suit.
Wire in series with a 12 volt 100ma lamp and a small silicon power diode.
The lamp will confirm correct operation by lighting.
This will give a charge current of a bit less than 100ma which may be continued indefinatly.
A faster charge can be achieved with a higher wattage lamp, but take care then to time-limit the charge.

[emeritus]

The DC supply plus filament lamp to determine the charging current certainly works. I used to use it myself to charge the NiCds the kids used when we had a camper van. However, a chemist colleague at GEC who had worked in their battery research department at Wembley said that, while it was OK for occasional use, charging long term from a smooth DC supply such as a 12V car battery was a good way to ruin them: a dirty DC supply was needed. I recall this being mentioned in the pages of "Wireless World" in the 1980's, where the view was that an ideal NiCd charger for the sealed cells then in use would provide rapidly alternating large current charge, and smaller discharge, cycles. This was to inhibit the formation of dendrites that would otherwise work themselves through the separators and cause short circuits.

A tungsten filament lamp provides a better approximation to a contstant current source than a fixed resistor. When under-run and therefore cooler, its resistance decreases sigificantly and therefore passes a greater current than a fixed resistor would.

[TowerRadio]

I built the Wireless World rapid nicad charger for my young son's radio controlled models(he is now 41).It was quite complex and had different voltage outputs,the problem I had was sourcing a heavy duty switch to select output and a decent transformer( most of the parts I got from work).The PCB came from Combe Martin Electronics(are they still in business?) and had to be bought.Les

[bionicmerlin]

Do you actually need a rechargeable battery. I frequently use an old Megger .That should take a PP9 battery but I use a good quality PP3.
I find that lasts me at least 2 years or longer. Andy