Battery charging circuit

Brian Carpenter

I have a load that requires around 7 volts to run.· I am using an 8,4 volt battery(1100 mah).· I have a charging jack also.· I would like to make the load operate off the battery unless the is a walwart plugged into the charging jack, at which time i want the load to run off the walwart and also charge the battery.· If the switch is in the off position, i them want the battery to charge.· The walwart is a 9 volt unregulated transformer and the load is abot 150ma.· The attached is a circuit that a friend of mine helped me with.· it does not work.· i toasted the walwart.· The theory, he told me, was that the resitor would trickle charge the battery and the the diode lets the juice from the battery get to the load.· Toasted· a diode in a different attempt.· Either way,· i got to figure out a way to charge the battery and also sometimes run the load from the walwart.· Can anyone point me in the right direction?

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It's Only A Stupid Question If You Have Not Googled It First!!

Post Edited (altitudeap) : 5/16/2006 3:42:16 AM GMT

kjennejohn

To all intents and purposes the diode is a short, bypassing the resistor, and the wall wart's input gets dropped .2V to .7V (depends on the diode) before crashing through the battery to the load. Something more fragile keeps blowing before the battery, otherwise you'd be washing battery juice off the ceiling and walls. The diode may be too small in wattage value to survive initial current surge. Try something like a 1N4000 or larger (1N4001, -4002, etc.). BUT first change this circuit.

Maybe someone else can provide a proper diagram of what you need.

Good luck with your project.
kenjj

Chris Savage

Here is a page of existing Battery Charging Circuits...Perhaps you will find one in there that can help you.

http://www.discovercircuits.com/B/batt-chrg.htm

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Chris Savage
Parallax Tech Support
csavage@parallax.com