Need to know how to build a charger!

[tj107us]

I need to know how to build a charger for a 3.6v 300mAh battery. I need the schematics for the charger for the battery.


If anyone has it send it to me please!
Thanks Jacob

 

[audioguru]

First you must and we must find out which type of battery. A lithium battery will blow-up or catch on fire if charged with a Ni-Cad or Ni-MH charger.

If the battery is Ni-Cad or Mi-MH then it is easy to charge slowly. You didn't say anything about how long you want it to take to reach a full charge.

 

[tj107us]

It is a nickel cadmium battery that goes in a telephone. How long will it need to charge, it don't matter 4-6 hours.

 

[audioguru]

You want to charge your Ni-Cad battery at a fairly fast rate. Therefore your charger must have extra circuitry to detect the amount of charge remaining in the battery and to limit overcharge:
"Overcharge current must be limited to 1/20th of the battery's ma/hr rating" (Energizer's Ni-Cad Applications Manual).

Considerations:
1) It is nearly impossible to detect how much charge remains in a Ni-Cad battery. Therefore a discharge cycle is used in fast chargers, and each cell is discharged to about 0.9V each.
2) A regulated charging current and a timer are used in some fast battery chargers.
3) A temperature sensor and a pressure sensor are also used to cutoff charging when excessive.
4) A battery charger IC (Maxim) can be used to detect when a Ni-Cad battery is fully charged instead of a timer. Temperature and pressure sensors and a timer are still used as backups in case the IC misses detecting full charge.

Search Google for Ni-Cad Battery Fast Charger and you might find a circuit.

I just use a regulated voltage (sometimes just an unregulater wall-wart adapter) and a resistor to slowly charge my Ni-Cad and Ni-MH batteries. A cell is 0.9V when discharged by its work and rises to 1.45V when fully charged. I select the resistor and voltage source so that the charge current is about 1/10th the battery's ma/hr rating for most of the charge and the current reduces to about 1/40th when the battery is fully charged. It takes overnight (12 hrs) but the trickle-charge current can be left on indefinitely without damage, and the circuit is simple and cheap.