Re: HP 22 rechargeable batteries Message #3 Posted by Andrés C. Rodríguez (Argentina) on 3 July 2008, 10:41 p.m., in response to message #2 by Eric Smith
If possible, recharge the batteries outside the calculator, avoiding risks of damage to the delicate and difficult-to-replace ICs.
If you feel so inclined, look in the MoHPC archives for postings from Norm (a.k.a. Captain Zener), who proposed the technique of soldering a certain Zener diode inside the calculator. Such diode will provide quite a degree of protection against possible overvoltages while charging the batteries inside the calculator.
The overvoltages will appear and will damage the ICs if the regulating behaviour of the batteries is not present, even briefly. That will happen if contact between the batteries and the calculator is not perfect (movement, oxide, corrosion, dirt are possible causes for imperfect contact). Also overvoltage may occur if batteries become bad over their lifespan.
|