Charger for a popular small 9-volt battery type 6F22. These batteries are called “Crown”. They are made in nickel-cadmium (NiCd), and environmentally NiMH (NiMH) options. first cheaper, but they have several disadvantages:
- loss of capacity due to incomplete discharge the battery before charging
- smaller capacity compared with the version NiMH
Both battery types allow to save on the purchase of not rechargeable batteries.
- Accumulator charging – 6F22
- for NiMH and NiCd models, 8,4 or 9,6 AT
- Battery protection against overcharging
- alarm work – led indicator
- adjustment of power failure
- power supply – 12 AT
Scheme charger is shown in Figure 1.
transistors T1, T2 and resistors R1, R3 provide current substantially constant during the battery charging cycle, regardless of voltage variations at the terminals of the battery. Resistor R1 sets the current, flowing through the source and the battery. The current source is somewhat dependent on temperature, about -0,3%/° C. I.e, current decreases with increasing temperature transistor structures. However, this accuracy is sufficient in this scheme charger. Diode D1 protects the battery from rapid discharge after the power failure, (without diode discharge current would reach several tens of milliamperes). On the other hand, small discharge current will flow through the potentiometer P1. This variable resistor sets the voltage of the battery, after which the shutter opens IC1A transistors T3 and T4. Opening closes T1 and T3 will stop charging the battery. Then the charger operates in battery mode, the maintenance mode "readiness", charging it with a small current, flowing through the resistor R2 (for R2 = 2 I k – 2 … 3 mA). Opening T4 means the inclusion of the diode D2. He informs, the process is complete charging. D2 also illuminate, If the battery is not connected to a charger. D3 protects the charger from feedback polarization effects. This can damage the integrated circuit CD4001. This chip allows you to monitor the battery voltage 9 At no additional external resistors, such as a comparator. The gate NOR IC1A has no Schmitt trigger. However, practice shows, that disabling battery charging when the voltage, set on the potentiometer P1, It occurs within a few seconds.
The charger has step switch within 3 ÷ 12 The efficiency and power factor 0,3 BUT. power transformer 5 W. If you use the charger, set the source to the maximum range of power.
Assembly and adjustment
The circuit can be assembled on the PCB, shown in Figure 2.
After soldering, check the battery capacity (look at the inscription on its body) and select the charge current on the basis of: battery capacity (expressed in mA) x 0,1. Modern batteries have a capacity of 110 … 150 mA·h depending on the type of (NICd or NIMH) and producer. Therefore, they should be charged shock 11 … 15 mA. The resistor R1 with the value 39 Ohm has been chosen as, to receive the charging current in the range 14 … 15 mA. The final step is to select voltage, after which the battery stops charging. This state will be indicated by LEDs. Depending on, whether the inscription on the battery case, "8.4" or "9.6", we set the charging switch on 10,15 In or 11,6 At a tolerance of less than ± 0,3 AT. The potentiometer is adjusted with the connected battery. Connect the voltmeter to the battery. The best thing, the readings were accurate to two or at least one decimal place. When the battery voltage reaches the 10,15 AT (or 11,6 AT), Turn the potentiometer knob, until the LED. By connecting a small car Lamp 12 AT / 3 … 4 W charged to the battery for several tens of seconds, It will be able to check, Does the charger is properly. If not, adjust the potentiometer setting.