Charging a 7.2 volt 4500mAh ni-mh battery. - RC Groups
Jan 21, 2009, 12:25 PM
Discussion

Charging a 7.2 volt 4500mAh ni-mh battery.

I've got a question here, let me know if I'm right or wrong here.

The battery I'm using is a 7.2 volt 4500mAh ni-mh battery.

If I charge the battery with 9volt and 1A(1000mAh) for 4.5 houres, will it then
be fully charged? Or am I wrong?
 Jan 21, 2009, 12:53 PM characters welcome! Probably not since rechargeable cells typically charge to ~1.4-1.5 volts. That would put the finished charge at well over ten volts for a six-cell 7.2 volt pack. 1.2 volts/cell is the discharged "nominal" rating of those cells. mw
Jan 21, 2009, 01:00 PM
Quote:
 Originally Posted by Mark Wood Probably not since rechargeable cells typically charge to ~1.4-1.5 volts. That would put the finished charge at well over ten volts for a six-cell 7.2 volt pack. 1.2 volts/cell is the discharged "nominal" rating of those cells. mw
So, my time calculations are correct? around 4-5 houres?
 Jan 21, 2009, 04:05 PM Registered User Not really. If you're going to do it by time rather than using a decent charger with proper charge termination you probably need to allow at least another 25% so more like 6 hours at 1A if the battery starts off completely discharged. Steve
 Jan 21, 2009, 04:14 PM Registered User You are correct in thinking that charging at 1 amp will take about 4.5 hours for a standard charger. (Allow a little extra for inefficiencies.) I don't know how it would work using a constant voltage source. Is it worth it? - A battery charger probably costs less than your battery does. - A fully charged battery delivers much, much better power. A nice warm NIMH is the best. - You'll have to sit around, monitoring your battery very closely. How much is your time worth? What if you forget it? Colin
 Jan 21, 2009, 04:43 PM Registered User It's the current that's of concern when charging NiCd or NiMH batteries, not the voltage as long as it's at least 2 volts above the total of 1.55 volts per cell. So, if you want to charge a 7.2 volt pack that has 6 cells; 6 x 1.55 = 9.3 volts. Therefore the voltage output must be at least 9 volts. Now, assuming you're using one of the wall-wart type supplies and not one that's regulated, the open circuit voltage of one that shows 9 volts will probably be closer to 14 volts. You should measure this with a volt meter just to make sure. Also, when using one of these type chargers and charging above .5C you should monitor the pack's temperature very closely. The pack should be fully charged when it's temperature reaches 10*C above ambient. If you're charging at a rate of .1C, or 1/10th the capacity of the pack, then charge it for 14-16 hours. Bill
 Sep 27, 2010, 03:35 PM Registered User Dear Stigern , i've got the answer for you..., you have a 1.0 Ah charger and a 4500 mAh battery ... the best way to charge your battery is: (4500 / 1000) x (25 to 60 / 100) which equals = from 6 hours to maximum 8 hours charging... , and thats how i charge my NiMh , lithum-ion batteries , and i assure you the best performance.... your faithful samishami...