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Model Forum / Radio Controlled / Land Models / April 2004Charging Question ?
My Slow charger's output is 0.86va and the Battery is 1400mah. So how long do i charge it for ? And how do i work this stuff out ? Thanx in advance ;-) Zardos -- The all singing all dancing Crap of the world ! > My Slow charger's output is 0.86va and the Battery is 1400mah. > > So how long do i charge it for ? > > And how do i work this stuff out ? You forgot what the voltage on your battery is, but roughly speaking these are the calculations. I will assume that you have a 7.2V pack. 0.86va = 0.86W (which is really small by the way). watt hours of your battery = 7.2V x 1.4A = 10Wh Assume inefficiency of about 40 per cent. Therefore total watt hours required to charge battery = 10 x 140 per cent. = 14Wh Therefore time required to charge your battery = 14Wh/0.86W ~= 16 hours. However, don't worry about overcharging it. With this little current, it's safe to leave the battery charging permanently as trickle current. Regards, Waleed. >You forgot what the voltage on your battery is, but roughly speaking these >are the calculations. I will assume that you have a 7.2V pack. Sorry i forgot to say, but yeah you're right they're 7.2 pack I have a bigger one to, which i've been trying to work out, its a 1700mah, so...... >watt hours of your battery = 7.2V x 1.4A > = 10Wh 7.2 x 1.7A =12Wh >Assume inefficiency of about 40 per cent. >Therefore total watt hours required to charge battery = 10 x 140 per cent. > = 14Wh not sure about this bit ? 12 x 140 per cent 16Wh ? >Therefore time required to charge your battery = 14Wh/0.86W ~= 16 hours. 16Wh/0.86W = 18 hours Is that right ? Thanks again :-) Zardos -- The all singing all dancing Crap of the world ! If you want to remove the efficiency assumption in the equations below, just measure the charging current with an ammeter. Then your charging time will be: (charging time) = (battery capacity) / (charging current) e.g. (charging time) = 1400 mah / 100 ma = 14 hours. BRW >> My Slow charger's output is 0.86va and the Battery is 1400mah. >> [quoted text clipped - 23 lines] > >Waleed. > If you want to remove the efficiency assumption in the equations > below, just measure the charging current with an ammeter. Then your [quoted text clipped - 3 lines] > > e.g. (charging time) = 1400 mah / 100 ma = 14 hours. ... except that part of the inefficiency is within the cells, in the way they accept current, and you can't measure that. As already posted: with a 10+ hour charger, it's perfectly safe to leave the cells on for quite a bit longer (50% more?) than the calculated charge time. Jonny |
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