I have Ni-Mh Batteries that say Standard Charge : 160 MA for 14 hrs.
Now I want to make a charger for it . If I have a 6Volt Transformer
and After Rectifying, what Resistance Should I use to obtain 160 mA @
3V DC?
The easy answer is 19 ohms at two watts. The power line can vary
plus/minus 10% and 19 or 20 ohms is good if cost is the consideration.
Also what else Should I do to ensure that the Current that I give to
the Batteries is clean and Best for the Batteries
The typical technique in cheap battery chargers it to use a
transformer with a lot of magnetic leakage to limit current. The
better way is to add a current limiting circuit.
Also If I fast charge the Batteries (500 mA for 5hrs) what is the
disadvantage ?
The batteries should be designed for fast charging if that is what you
want to do. The disadvantage is usually shorter life. Left
unattended, without automatic circuitry, the cells can overheat and
rupture.
Good NiMh chargers watch the voltage as the cell charges. Great
battery chargers watch the voltage and temperature of the battery. By
monitoring battery voltage, the charger can throttle the charge
according to what the battery can use. NiMH batteries have a
decrease(!) in their voltage when fully charged, good chargers watch
for that and shut off when they see it.
1.2 volts per cell, so you want to charge two cells? Are they a
standard size and can they be separated? Rayovac makes a nice charger
that does AA and AAA NiMH batteries and alkaline. Monitors and shuts
them down as each of four cells charges. Cost in the US is ~$20 and
worth it. Walmart has cheap Quest chargers that cost ~$20 with a set
of four AA batteries included.
See>
http://www.powerstream.com/NiMH.htm
http://www.sensorsmag.com/articles/0303/battery/main.shtml
http://www.extremetech.com/article2/0,3973,1155273,00.asp
Several IC manufacturers have chips designed expressly for charging
batteries.