# Nicad and NiMH Battery Charger by IC LM317T

Here is circuit diagram of the Nicad Battery Charger. It use IC LM317T ( Hot IC) Control Current less 300mA, Size battery 2.4V,4.8V,9.6V.It Low cost circuit.
This is a NiCAD battery charger circuit. High-quality, Not necessary to have a full charge and cut, Because this circuit charges with constant current and voltage regulated. But this circuit is not difficult and cheap.

The basic principles of a NiCAD Battery charging. There are a number of ways, as follows.
1. A constant current.

The Nicad battery can provide current 500mA-hr charge rate that is 1/10 of the current capacity. Therefore should be charged with a constant current 50mA for 10 hours, but actually want to charge for 14-16 hours because when near full current to charge less. So lasts longer.
– In the NiCAD battery charger for fast charging current to about 100mA charging rate for 3-5 hours. But it has the disadvantage of charging, when the battery is fully charged, it must be removed, otherwise the chemical substances in the battery will be very hot and damage.
– But a slow charger will not do, because it can withstand heat.

2.A constant voltage or Fixed voltage regulator
The NiCAD battery, each battery has a voltage 1.2V, when it is fully charged voltage 1.25-1.3V. Therefore, we are charging a battery, the plus the voltage additive, such as 4 pieces, then the charging voltage 1.2×4 = 4.8V. But the charge like this, at first, a very high current flow. So, the voltage between NiCAD battery charger and very different, may have caused overheating and damage.

3. The Current and Constant voltage.
Like this charging, devices little more than the two first, but high quality. The safest way, and the battery the voltage is required by the specifications. When fully charged, the charger can be left in, because there is no current flow, Because the the voltage between the battery as well.
– I so chose the charging current and Constant voltage.

A constant current.
I am using LM317 as a constant current. Determined by the R6. In the circuit be defined output current (Iout) is about 50mA. If you want to current different from this, you can find out the R6. = 1.25V / Iout
this circuit is designed for charging multiple pieces. So it can select multiple the voltage levels is S1.
– 3.1V be applied to 2 battery (2.4)
– 5.5V be applied to 4 battery (4.8V)
– 10.3V be applied to 6 battery (9.6V)

Which we use Q1(TIP31),Q2(C1815) And other equipment. Included circuit is maintained at a constant voltage. LED1 is used for the power on. T1 transformer size is 300mA.
The other parts please look in the figure circuit.

How to build. Friends can place the part in perforated board. Because this circuit has a few devices. You should check diagram well before use charge battery. Good luck.

Update:
Now I add The copper PCB layout as Figure 2 and the components layout as Figure 3.
though this circuit very old or very ancient, But still useful.
However, if this error please tell me.

Figure 2 The actual-size of Single-sided Copper PCB layout
At 200 pixel per inchs.

Figure 3 the components layout.

## 5 thoughts on “Nicad and NiMH Battery Charger by IC LM317T”

1. Leon says:

I am a big fan of your site, but that last time there are more and more errors (mistakes) in your circuitry. these charger circuits take the cake on that…..

LM317T Contant current and NiCd charger circuits;

A lot of errors damn!
circuit 2 ; + therminal of C1 bufferelco should be connected to the both cathodes of D1 and D2. Then the center tap CT should be connected to GND..

circuit 3 ; R6 and R7 should be connected to GND and not to the +….current flows out of the base of the PNP transistor Q2

circuit 3 with LM317 ; the diode D2 is shorted…take a look the line after the one that connects D1 with D2 should be removed.So that the tap 0V (center tap) is connected to the elco C1. next resistors are forgotten at the switch S1 5,5V and 10,3V settings…the are non now….so output is about 3V nou.
And the LM317 with resistor as current source take up 3V + 1.25V +(300mA x 5 Ohm) is 4.25V+1.5V=5.75V drop….so the batt get NOTHING and will not charge! That LM317T circuit should be placed between the buffer elco C1 and transistor Q1. So to charge even the 9.6V batt. the raw voltage at the rectifier sould al least be 10.3V+5.75V=16.05V
trafo 9V gives only squar root of 2×9 = 1.414=12.72V !!! So the trafo must at least be 12V AC.

2. Leon says:
3. Jack says:

Re: Nicad Battery Charger by IC LM317T.
Nicad/NiMh batteries require approx 1.65V/cell for charging. So for 2 cells you require close to 3.3V at the battery. Then you need about 1.5V for the LM317 to work as per spec. So the input voltage to the LM317 should be 3.3+1.5 = 4.8V. Then remove R7 which messes up the whole circuit.
The Vref in the LM317 is 1.25V. So if you want 50mA then 1.25V/.05A = 25 Ohms. 24.9 Ohms for R6 is close to that. With 27 Ohms you get near enough 46mA. Next is the “4.8V” which I am assuming is for 4 cells i.e. 6.6V and for 8 cells is 13.2V at the battery terminal. Your reference is 3.1 at the base of Q2. So in place of R3 you need 820 Ohms; in the line marked 5.5V you need a resistor 2400 Ohms and in the one marked 10.3V you need 5600 Ohms.
This will make the circuit work forever and perfectly. By the way instead of all those parts Q1, Q2 etc why not use another LM317 with biasing resistors to give you the voltages as follows: 4.8V; 6.6+1.5 = 8.1V and 13.2+1.5=14.7V. less parts and more robust. The reference voltage in the LM317 is much better that the Zener diode and the base-emitter junction you presently have.
and yes Leon is right: the trfo diodes are shorted. u need to remove the line from D1 to GND and I did not calculate the input voltage to the circuit.

4. By the way, I think 27 Ohms is correct because the LM317 also supplies some current which I did not take into consideration. The reference voltage made up of the ZD1 and the Vbe of Q2 is good enough for a battery charger. However, if you put the voltage feedback lines from S2 instead of some internal voltage then you have better control of the battery voltages, and you do not need S1. So your feedback resistors will be 96 Ohms instead of R3; and the other two resistors will be nearest value to 1694 Ohms and the one for 13.2V will be nearest value 4.9K Ohms.

5. J.Richert says:

Is the schematic now updated with the corrections?