Ni-Cd Ni-MH Adjustable Constant Current Battery Charger Circuit

This is a Adjustable Constant Current Ni-MH or Ni-Cd battery charger circuit. It can be used to get a constant current power supply. Here is the schematic diagram of the circuit:

This circuit can be adjusted to any value from a few milliamp to about 500mA. The max current is 500mA because it is the limit of the BC140 transistor in the current-limiting part of the circuit.

The input voltage has to be 5.25v above the required output voltage, because of 1.25v across the current-limiting section and Approximately 4v is dropped across the regulator.  The LM317 3-terminal regulator will need to be heatsinked.

the LM series of regulator is suitable for this circuit because they have a voltage differential of 1.25v between “adj” and “out” terminals.

For example, to charge 4 Ni-Cad cells, just connect them to the output and adjust the 500Ω preset until the required charge-current is obtained. The charger will charge 4 Ni-Cad cells at the same current. But, don’t forget to turn off the charger before the cells are fully charged or the battery will be over-charged.

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L200 12V Constant Voltage Battery Charger Circuit

This battery charger is based on L200 regulator IC. L200 is a five pin adjustable voltage and current regulator IC.

This regulator IC is used to keep the charging voltage constant up to maximum charging current. After exceed this limit drop charging voltage and maintaining maximum charging current.

R4 preset is used to control the charging voltage. You can set it to maximum battery voltage.

R2 3W resistor is used to control the maximum charging current (I).

I=0.45/R2 (R2 should be larger than 0.225Ω)

You can adjust “I” up to 2A.

example: when you using 0.47Ω resistor
I=0.45/0.47
I=0.95
I≈1A

L200 PIN Configuration

The L200 design allows some leakage from cells connected while the circuit is not powered. D1 prevents this loss and protects the circuit from reverse polarity.

The L200 needs an input voltage that is at least 2v higher than the output to be able to yield the full rated output. You also need sufficient volts to cover the forward voltage drop of D1. With a 0.6V D1 drop, the input to the L200 needs to be 2.6V higher than the desired output.

You can use 18V 3A transformer and 3A full wave rectifier or bridge rectifier for power supply.

The L200 must be kept sufficiently cool, because it is mounted on suitable heat sink.

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LM3914 12V Battery Monitor Circuit

This bar graph LED battery level indicator circuit is based on LM3914 monolithic IC from National Semiconductor that senses the voltage levels of the battery and drives the 10 light emitting diodes based on the voltage level that is detected.

To calibrate the circuit it must be connected to an adjustable regulated power supply.
Connect an input voltage of 15 volt between the positive and negative poles and adjust the 10K preset until Led 10 lights up. Lower the voltage and in sequence all other Led’s will light up. Check that Led 1 lights up at approximately 10 volts.

This circuit to your own needs by making small modifications. The circuits above is set for ‘DOT’ mode, meaning only one Led at a time will be lit. If you wish to use the ‘BAR’ mode, then connect pin 9 to the positive supply rail, but obviously with increased current consumption.

The LED brightness can be adjusted up- or down by choosing a different value for the 3K9 resistor connected at pin 6 and 7.

You can also change the to monitoring voltage level.

For example, let’s say you wanted to change to 12 – 15 volt,
Remove the R2 resistor and connect 15volt to the input (+ and -) and adjust the 10K potentiometer until Led 10 lights up. Connect  200 Kilo-ohm potentiometer at pin 4 and -. Reconnect a voltage from 12 Volt to the input. Now adjust the 200K potentiometer until Led 1 lights up. When you are satisfied with the adjustment, feel free to exchange the 200K potentiometer with resistors again.(after measuring the resistance from the pot, obviously).

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12V Battery Charge Nominal Discharge (Low) Indicator Circuit

This circuit monitors car battery voltage. It provides an indication of nominal supply voltage as well as low or high voltage.

741 PIN CONFIGURATION

VR1 and VR2 adjust the point at which the red, yellow and yellow, green LEDs are on or off. For example the red LED comes on at 11V, and the green LED at 12V. The yellow LED is on between these values.

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LM317 Battery Charger

According to the battery manufacturers, a battery should be charged with only 1/10 current (in ampere), of its Ah value.

For example, if a battery is of 7Ah value, then it should be charged with 0.7 Ampere current. Charging a battery using this rule, extends the battery life.

LM317 Regulator IC Pin Configuration

BC140 Transistor Pin Configuration

• Charging current is controlled by T1, R1, and R4. VR1 is used to set the charging current.
• As the battery gets charged, the current flowing through the R1 increases. This result in increase in the current and voltage from the LM317.
• When the battery becomes fully charged, charger reduces the charging current to the battery, and the battery is charged in trickle charging mode.
• The input at LM317 should be around 3 volts higher than the output voltage from the LM317. As this IC requires minimum 3-volts for its operation.
• As this IC gets very hot during operation, a good heat sink should be used with this IC.

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This Ni-Cd battery charger is a circuit based on the regulator IC lm317.This circuit is very simple and uses minimum components. By varying value of resistor R1 from 1 ohm to 120 ohms, charging current can be varied from 10 mA to 1.25 A. This circuit functions as a constant current generator.

To see LM 317 pin configuration

Construction is fairly simple and it can be constructed on a veroboard or tag board. As a general rulle all Ni-Cd batteries should be charged at the maximum charging current of 1/10 ampere-hour rating of the battery. This should never be exceeded. Exact charging current can be set by using a potentiometer or a preset in place of R1 and putting an ammeter or multimeter in series with the load. As the maximum input voltage to IC is 40V, input voltage should always remain less. Proposed circuit is suitable for charging four cells in series. But the maxmum number that can be charged  will depend on input DC voltage o regulator.

This circuit is vary rugged and reliable. Output current is virtually independent of load and can be controlled very precisely. Almost any type of Ni-Cd battery can be charged. IC should be fitted with heatsink (LM317T is plastic package of LM317K with same rating but costs only half as much). Typical specifications for a Ni-Cd cell are as follow:

• Nominal 1.2V Full charge 1.4V.
• Charging time max. 12 hrs.
• Discharge rate on storage is 0.014V/24 hrs.
• Totally discharged cell recovers fully on 12hrs charging
• Electrolyte seepage does not affect performance.Wipe cell with dry cloth.

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Many a time the outdoor audio or video recording becomes imperfect due to a ‘dying’ battery. If the battery voltage is less than 9V for a 12V recorder, the output during playback will not be of a good quality due to variations in the motor speed.

Many car owners take their battery for granted, rarely giving it the maintenance required. As the winter nights advance the demands made on this vital power source increase. Combined with the inevitable aging process and diminishing ability to store a charge for a  long period, this makes the requirement of a simple aid to monitor battery voltage continuously obvious.

The indicator was therefor designed to forestall any incipient failure by providing ‘at a glance’ information on battery state with three coloured LEDs.
Green indicating a battery voltage adequate for normal use,
Yellow that the voltage was fairly low and
red that the cell was dead.

When the battery is in top condition, its output voltage will be around 13V and, of course, even higher if recently charged. This potential is applied via D8 through R4, D7 and R5 to the base of Q2. This turns Q2 on, causing D6 to illuminate via R3. At this time Q2 effectively places a short circuit across the rest of circuit via D6, preventing D2 and D3 from emitting light.

As the battery voltage becomes lower,Q2 begins to turn off as the threshold of D7 is reached.This allows D2 to conduct as Q1 has all the time to be turned on via R1, D1 and R2. (D5 increases the voltage required for turning on D2 when T2 is on.) The current thus drawn via R3 precludes D3 from illuminating as the potential across it and D4 is not above the zener level.

Eventually, at still lower battery voltage, Q1 will turn off in the same way as Q2, allowing potential at the junction of D2, D3 and D6 to rise in excess of 5V zener level of D4 which begins to pass current and illuminates D3.

Zener diodes may be selected for other switching points and / or battery voltages.


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12 Volts Lead Acid Battery Charger Circuit

Except for use as a normal Batter Charger, this circuit is perfect to ‘constant-charge’ a 12-Volt Lead-Acid Battery, like the one in your flight box, and keep it in optimum charged condition. This circuit is not recommended for GEL-TYPE batteries since it draws to much current.

The above circuit is a precision voltage source, and contains a temperature sensor with a negative temperature coëficient. Meaning, whenever the surrounding or battery temperature increases the voltage will automatically decrease. Temperature coëficient for this circuit is -8mV per °Celcius. A normal transistor (Q1) is used as a temperature sensor.
This Battery Charger is centered around the LM350 integrated, 3-amp, adjustable stabilizer IC. Output voltage can be adjusted with P1 between 13.5 and 14.5 volt. T2 was added to prevent battery discharge via R1 if no power present. P1 can adjust the output voltage between 13.5 and 14.5 volts. R4’s value can be adjusted to accommodate a bit larger or smaller window. D1 is a large power-diode, 100V PRV @ 3 amp. Bigger is best but I don’t recommend going smaller.

LM 350 Regulator IC

The LM350’s ‘adjust’ pin will try to keep the voltage drop between its pin and the output pin at a constant value of 1.25V. So there is a constant current flow through R1. Q1 act here as a temperature sensor with the help of components P1/R3/R4 who more or less control the base of Q1. Since the emitter/base connection of Q1, just like any other semiconductor, contains a temperature coëficient of -2mV/°C, the output voltage will also show a negative temperature coëficient. That one is only a factor of 4 larger, because of the variation of the emitter/basis of Q1 multiplied by the division factor of P1/R3/R4. Which results in approximately -8mV/°C. To prevent that sensor Q1 is warmed up by its own current draw, I recommend adding a cooling rib of sorts.
(If you wish to compensate for the battery-temperature itself, then Q1 should be mounted as close on the battery as possible)
The red led (D2) indicates the presence of input power.

Depending on what type of transistor you use for Q1, the pads on the circuit board may not fit exactly (in case of the BD140).
Caution: Adjust the voltage of capacitor C1 according to the input voltage. Example, if your input voltage will be 24 volt, your C1 should be able to carry at least 50V.

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