Charging batteries

"Dry" batteries is a term normally used for the origonal carbon-zinc batteries, and are *NOT* rechargeable. And alkaline batteries are also *NOT* rechargeable (except for the Renewal(TM) type). I do not think that crocodile clips will fit.....

Need to know a LOT more about the batteries. If they're nicad or nimh, you can probably get away with charging at C/10. Use a high voltage supply in series with an appropriate light bulb. Select the light bulb for approximately what you need. Won't be perfect, but works. mike

NOT a good idea: 1) too much voltage can cause over-charging and might cause damage, and 2) light bulbs have a fairly low resistance, which could result in too much current. The open-circuit voltage of the supply used for charging should be set to the highest voltage that the particular cell chemistry supports: NiCd runs from 1.20V to 1.35V; Li-ion runs from 4.1V to 4.2V; NiMh is about 1.2V. Either pick a resistor for C/10 rate based on "discharged" cell voltage near 80 percent of charged rating, or make a "constant current" limiter with a JFET and resistor. BEST, is to use a charger made for the cells; they are made to optimize charging time and protectionof the cells.

What you say is partially correct. You can certainly choose a voltage and light bulb that overcharges the batteries. The objective is NOT to do that. A light bulb makes a perfectly good positive TC resistor and a current source that is rather invariant over a reasonable voltage range, depending on the source voltage and bulb selection. If you select the voltage and light bulb correctly, it works just fine. It's plenty good for battery charging at approximately C/10 for nicads and NiMH. I am partial to #382 bulbs because they're small. YOu get 35ma give or take charging current. Parallel as many as you need.

DO NOT GUESS. MEASURE THE CHARGE CURRENT.

If you have wildly varying charge current requiremets, you can put the bulbs inside the device and the external voltage source. mike