Accumulator rectifier with adjustable current

Vermes · Apr 22, 2012

Assumptions:

smooth regulation of charge current (adjustable PWM approximately 20Hz)
cutting off the charging when set voltage exceeded
after the charging is cut off, reloading after previous reduction below a set threshold (desulfurization mode)
operation in temperature range from -10 to +30 degrees Celsius
lack of forced air flow
resistance to rain
adapted to 6V and 12V accumulators
no microprocessors/displays
low cost
design in KiCAD
charging current min 4A

Design:
Assumptions were met in the second version of SCH and PCB, the first version had no PWM current regulation.

Implementation:
Transistor has heat sink, because the following elements heat up:

Principle of operation:

PWM regulator – there is a triangular signal at the generator output and it is compared to the potentiometer voltage on the comparator. In that way you get a rectangle with adjustable filling.
voltage measurement system – the reference voltage source is TL431, it is compared to the accumulator current voltage on the comparator (with hysteresis)
executing system – N mosfer transistor – controlled by galvanic isolated inferface – cuts off „+” to the accumulator

Behavior of the system – the algorithm of operation:

after turning on a discharged accumulator, the rectifier loads like any other, except that you can set the average current (average because the PWM 20Hz is visible on the ammeter – you can see the hand vibrations)
when the accumulator is loaded and threshold 15,2V is exceeded – the system cuts off the charging
then the behavior of the system depends on the accumulator state: the system waits until the voltage on clamps drops below approximately 14V. In fully efficient accumulators after fully charging the voltage from drops quite slowly from 15V – even for a minute. In a sulphated accumulator, voltage on terminals drops very quickly – within a few-dozen seconds
when the voltage drops below 14V, the system again switches the charging and when the system loads itself >15,2V, it turns off again. Such subsequent charging takes a few seconds, depending on the set charging current
„loading”/”pause” cycles are repeated until the rectifier is turned off. The charged and/or accumulator state can be judged by estimating the ratio of „loading”/”pause” time. Such cycles cause a few seconds recharging the accumulators every few tens seconds
pulse current (PWM) and a slight gassing of the accumulator: it is to stimulate the crystals to dissolve

Link to original thread (useful attachment) – Prostownik akumulatorowy z regulacją prądu