Vermes
Advanced Member level 4
Transformer from UPS 300W (EVER), giving the voltage of 15,6V was used in this device. Graetz bridge KBPC 25A was also used, instead of capacitors 2 x 2200uF, 3300uF + 3300uF + 4700uF = 11300uF were used. After the bridge, preventive 10A fuse (less ones were not enough after the screwdriver load). Instead of transistor 2N3055, solid KD502 Tesla was used. There is an automatic thermal fuse 2A at the output, which can be bridged by a switch in the front of the housing, after plug in the cordless screwdriver. Bridging switch is turned on only when connecting the screwdriver.
The board was made of paper-phenolic laminate, made by thermotransfer method on iron “upside down” in a vise.
Elements such as the bridge, KD502 and 7812 were screwed to a big radiator, which is cooled with a ventilator. A ceramic pad for TO-3, covered with paste with improved thermal conductivity was installed under KD502.
The ventilator has two modes:
- automatic mode – normally, the ventilator is not running – it turns on after reaching dangerously high temperature of the radiator. Its rotations are dependent on the height of the temperature, controlled in a simple manner by thermistor 10k. For improved conductivity, the thermistor is screwed by a profiled copper plate and covered with a thick thermo-conductive paste.
- manual mode – the thermistor is bridged by a switch and the ventilator is running all the time at maximum speed.
The air sucked from the front, goes to the radiator fins, then warmed up comes out through ventilator holes on the bottom and top of the housing, which is standing on tall, rubber legs.
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Link to original thread (attachment) – Zasilacz 13,6V dużej mocy, czyli nowe życie dla wkrętarki aku