A brief discussion on the stepless voltage regulation charging circuit of 18650 battery pack 3.7v

　　1. Stepless voltage regulation (current) charger

　　A commercially available fan speed regulator (firebox thermostat) is connected in series to the primary stage of the rectifier transformer, and the purpose of stepless voltage regulation can be achieved by adjusting the input power frequency voltage. Although the output waveform is not good, practice has proved that it is feasible.

　　When charging, as long as the charging current is adjusted to meet the requirements, the voltage will definitely be appropriate. (Except the battery itself is faulty).

　　Only when the battery polarity is connected correctly, the relay will close and connect the charging circuit.

　　When the remaining power of the battery is too low, or when charging the battery below 12V, the charger needs to be connected to the mains power and press AN to help start. The 100Ω resistor maintains J pull-in. The contact capacity of the relay should be greater than. 10A (double contacts used in parallel).

　　There are three 1Ω resistors (=0.333Ω) in series in the negative circuit, which are used to form a voltage difference to detect the current. The higher the output voltage and the greater the current, the greater the voltage drop. The ammeter is actually a voltmeter, but the setting value is the current number. I use a cheap 91L16300V small square meter. I remove the 220k voltage-reducing resistor connected in series in the meter and re-set the calibration value.

　　The figure below is the basic circuit of a stepless voltage regulation charger. During production, the capacity of the rectifier transformer, secondary voltage, rectifier diode, etc. can be selected according to needs.

　　Charging current selection: 4~6Ah, choose below 500mA; 7~15Ah. Choose 800mA-1.5A; choose 2A above 15Ah.

　　2. High-frequency and efficient charger

　　High-frequency charger, small in size, light in weight, fast in charging, and has no obvious memory effect on the battery.

　　The left side of the dotted line in the figure below. It is a ready-made and discarded 60W energy-saving fluorescent lamp electronic ballast circuit. The printed circuit board is very small and can be used in its entirety. Connect the output wires at both ends of the lamp to the primary of the modified color TV switching transformer.

　　When the switching transformer is remodeled, the primary and inter-stage insulation should be kept intact (the remaining windings in the primary layer should be ignored), all secondary windings should be removed, and the number of turns in each group should be recorded in order to calculate the number of volts per turn, generally each turn. It is 0.46V~0.60V, and then use enameled wire of about 0-7mm to rewind the number of voltage turns you need. Take a few more heads in the middle. When the estimation is inaccurate, you can use it according to the situation. Winding volt selection: half-wave rectification, charged bottle voltage V (nominal) × 2.5. For example: nominal 12V battery × 2.5, equal to 30V (AC). Full wave rectification is halved.

　　1HB is a small loop transformer with positive and negative feedback. If it is difficult to start at light load (no output), its L1 can be wound by 1 to 2 turns.

　　When the charging current exceeds 1A, V1 and V2 will become a little hot. Remove them and add appropriate heat sinks, set them up in another position, and then connect them to the original circuit board with wires.

　　On the right side of the dotted line, the rectification and charging output circuit. Set ZK to facilitate conversion when charging 6V and 12V batteries. The contact capacity of ZK should be greater than 5A, and try to operate it quietly (before powering on).

　　Rectifier D1 must use high-frequency diodes, ordinary power-frequency diodes or rectifier bridges, which have slow recovery speed, large loss, serious heat and damage (used in discarded VCDs and digital machine power boards).

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