I have 2 battery powered devices (electric shavers) which are rechargeable via AC chargers. The instructions for each device say that the AC chargers must be disconnected when the devices reach full charge (as indicated by a blinking light).

I would like information concerning building a sensor which will turn off the chargers when the devices are fully charged. Better still, I would like such a sensor to permit the devices to be left on the chargers, and then cycle as needed to maintain full charge.

I am a novice, but I have done some minor electronic projects in the past. Can anyone help me?

 

Unless you're noticing a significant heat rise in the batteries when left on, I wouldn't worry about it. I've replaced NiCd batteries in shavers several times and the cells never cost me more than $10.00.

If your shavers have NiMH batteries, the charge circuit should be self terminating as this cell technology is very sensitive to overcharge.

 

http://www.amazon.com/Intermatic-TN800CH-Outlet-Appliance-Operations/dp/B001O9TE9E

they are even cheaper if you shop around.

all you need to know is the duration an average charge takes to complete. Program the time into the timer and bob's your uncle.

 

I expect a system that uses rechargeable batteries to have a reliable charging circuit using the traditional ΔT and/or ΔV charge termination strategies. If it doesn't, I'm not inclined to throw good money after bad by giving it a timer.