Ni-MH Ni-Cd Adjustable Constant Current Charger— 1 Comment ↓

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:

PARTS LISTR1 100ΩVR1 500Ω PresetC1 0.1µFC2 0.01µFD1 1N4001Q1 BC140IC1 LM317

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.

the Circuit

The LM317 is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5A over an output-voltage range of 1.25 V to 37 V. It is exceptionally easy to use and requires only two external resistors, R2

’ and R2”  (R2= R2’+

R2”) to set the output voltage. Furthermore, both line and load regulation is better than standard fixed regulators. In addition to having higher performance than fixed regulators, this device includes on-chip current limiting thermal overload protection, and safe-operating-area protection. All overload protection remains fully functional, even if the ADJUST terminal is disconnected. By connecting a fixed resistor, R1  the ADJUST and OUTPUT terminals, the LM317 can function as a precision current regulator. An optional output capacitor can be added to improve transient response.

Schematic Diagram using LM317 & other Parts (Click to Enlarge)

 

The ADJUST terminal can be bypassed to achieve very high ripple-rejection ratios, which are difficult to achieve with standard three-terminal regulators. A capacitor of

small value should be connected across the input pin of LM317 and ground, particularly if the regulator is not in close proximity to the power-supply filter capacitor.

Homemade 12V Sealed-Lead-Acid Battery Charger

We need 14.2V to proper charge a 12V sealed-lead-acid (SLA) batteries (like batteries in your car, computer UPS power supply, emergency light, etc). Too high a voltage will damage the batteries and too low the batteries will never get charged.

I use an old Acer laptop charger as the DC input source which gives about 19V. The homemade charger reduces the 19V to a stable 14.2V.

The charger composes LM317 voltage regulator, NPN transistor, capacitors and resistors. By setting the resistor R3 (refer to circuit below) to 830 ohm I was able to get 14.2V of output. If you want to charge a 6V SLA battery you can try to set R3 to ~ 120 ohm to output 7.1V.

The output voltage can be calculated using the formula: 1.2 x (R1 + R2 + R3) / R1

REMINDERS:(1) LM317 gets warm during charging so it needs to be mounted on heat sink.(2) Never set the output more than 14.2V to charge 12V SLA battery. (3) The charger is meant for SLA batteries only.(4) Use cautiously and at your own risk.

ADJUSTABLE CURRENT SOURCE Circuit

The HIP5600 can supply a 450 A (20%) constant current.It makes use of the internal bias network.

See Figure 27 for bias current versus input voltage.With the addition of a potentiometer and a 10 F capacitor theHIP5600 will provide a constant current source. IOUT is givenby Equation 13 in Figure 16.

FIGURE 16. ADJUSTABLE CURRENT SOURCE

1.5A ADJUSTABLE CURRENT SOURCE Circuit

The LM317 is an adjustable 3−terminal positive voltage regulatorcapable of supplying in excess of 1.5 A over an output voltagerange of 1.2 V to 37 V. This voltage regulator is exceptionallyeasy to use and requires only two external resistors to set theoutput voltage. Further, it employs internal current limiting,thermal shutdown and safe area compensation, making itessentially blow−out proof.

The LM317 serves a wide variety of applications includinglocal, on card regulation. This device can also be used tomake a programmable output regulator, or by connecting a fixedresistor between the adjustment and output, the LM317 can beused as a precision current regulator.Features-Output Current in Excess of 1.5 A-Output Adjustable between 1.2 V and 37 V-Internal Thermal Overload Protection-Internal Short Circuit Current Limiting Constant with Temperature-Output Transistor Safe−Area Compensation-Floating Operation for High Voltage Applications-Available in Surface Mount D2PAK−3, and Standard 3−LeadTransistor Package-Eliminates Stocking many Fixed Voltages-Pb−Free Packages are Available