Help with a charging circuit needed

Thread Starter

peteec

Joined Nov 16, 2009
1
Hi Everyone,

I have some 7.2V 800mAh Ni-Cd battery pack's,the ones made up by 6xAA's,and i also have a uniross charger that will charge 4X AA or AAA or 1X 9V battery,I'm wondering if i could charge the packs from the 9V output via a resistor,and if so would anyone know what size resistor i would need to use?

Many thanks for any help offered

Great forum btw :)
 

Bernard

Joined Aug 7, 2008
5,228
Read: http://batteryuniversity.com/partone-11.htm If the 9V output, is a true 9V-regulated 9V, use a 1/2 ohm 1/2W resistor till V reaches 8.64V, then switch to 5 ohms for several hours to 8.76V. Probably could just use the 9V battery output for a trickle charge[ not recomender due to possible crystal formation ].
 

Audioguru

Joined Dec 20, 2007
11,251
An old 9V Ni-Cad battery charged at 10mA to 15mA. The current-limiting was built into the charger.
Simply connect your 7.2V battery to it and it will take weeks to fully charge.
 

SgtWookie

Joined Jul 17, 2007
22,201
Actually, a completely discharged 800mAh battery charging with a current of 15mA will take about 53 hours to fully recharge, without any current limiting.

Best to get a charger specifically designed for your 7.2v batteries.
 

Audioguru

Joined Dec 20, 2007
11,251
An old Ni-Cad battery needed 40% longer charging time than calculated because it had poor charging efficiency.
 
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