9 Volt Battery Chargers
Everything I need to know is on the label!
You need to know three things to charge a battery.
VoltageThe voltage the charger outputs in not really that important as long as it is more than the battery voltage. How much more? Enough to overcome the internal resistance of the battery, and push the stated amount of current through the battery.
From Garden State Battery
The most common and reliable method for charging cadmium-based batteries (NiCd and NiMH) is the "Negative Delta V" method. This method senses a fully charged battery by detecting a drop in cell voltage as the battery reaches capacity. This drop is small but noticeable enough to be detected and signal the charger to shut off or to trickle depending on the charger type. Other chargers use "Delta T" or change in temperature sensors to decide when to stop charging. "Delta T" chargers are less reliable and many manufacturers have adopted the "Delta V" or a combination of the two as their preferred method of choice.
Method I'm Choosing
I'm not going to try to detect when the battery is charged. I'm just going to charge my 9V batteries at 11ma for 14 hours just like it says on the label. They might get slightly overcharged, but they will get fully charged. Then I will be able to rule out charger malfunction as a cause of my problems.
Simple 1 Resistor Battery Charger
Constant Current Battery Charger from 2 LED's and a NPN Transistor
9V Battery Charger from 2 NPN Transistors
Adjustable Charge Rate Battery Charger from Op Amp
0 - 160 mA Adjustable Charge Rate Battery Charger
741C Cheat Sheet
Sparks and Flames
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