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9V battery charger

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JeanTech

Member
Hi there

I'd like to build a 9V battery charger. Can someone please suggest a circuit diagram and an explanation.

Thanks in advance
 

ericgibbs

Well-Known Member
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Hero999

Banned
I wouldn't recommend using an LM317 to charge a 9V battery because it won't current limit until 1.5A to 3A.

Unless he actually wants a way to power a 9V circuit from the mains, in which case that circuit is perfect.
 

Hero999

Banned
Yes, that will work.

You need to limit the current to a very low level such as C/10 but it'll take a long time to charge. The good thing about using a resistor is that the current will be higher when the battery is flat and the current will drop as it charges.
 

JeanTech

Member
thanks for the help

just to clarify, must the charge current always be 10 times smaller than the battery current and must it always be charged with the same volts as the battery output voltage?
 
Don't mention it. Remember if you need help just post here. Also, you may need to charge the battery using 1.5V higher than the battery, I would just use a 15 volt transformer (because the voltage will vary a bit when the battery's added) Add a 9V regulator to the V+ pin on the battery then your current limiting resistor will be 800 ohms.
 
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