9 Volt Battery Chargers

Charge Rate

You need to know three things to charge a battery.

1. Voltage
2. Amperage
3. Time

Voltage

Amperage

• Whatever it says on the label.
• If not, a normal charging rate is the Capacity of the battery C divided by 10 or C/10.

Time

• Whatever it says on the label.
• Long enough to put 44% more power into the battery than it's Charge Capacity
• 14 hours at C/10
• Or you can detect when the battery is charged

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.

• Garden State Battery Battery Types, Tips & Technology http://www.gardenstatebattery.com/contents/en-us/d887.html

• PowerStream Technical Resources for Design Engineers www.powerstream.com/tech.html

• Planet Analog How to design fast charging of high-capacity batteries www.planetanalog.com/features/showArticle.jhtml?articleID=193000473