Charger Heat sink assembly
The heat sink for power elements can be realized in several ways and limits in practice the charge and discharge features of the Universal charger (with the fan cooler). The heatsink dimension shall not exceed 130x70x30mm in order to be right fitted on the charger case. The figure shows the drilling plan for the heatsink, compatible with the PCB assembly. To be noted that the most critical process from the heat dissipation point of view is the discharge that deliver on te heatsink the power of the cell pack voltage multiplied for the discharge current, while the charge dissipate only the power of the difference between the power supply and the battery pack voltage multiplied for the charge current. For example, the discharge of 4 LiPo elements at 20 Amps will delivery a power of 3.7V*4*20=296W when the charge of the same batteries at 4 Amps with 20V power supply will delivery about (20-3.7*4)*4=20.8W.
The power elements must be secured to the heatsink with M3 stainless steel screws. Starting from the left we have the two discharge mosfets in case TO-247 (IRFP044 or IRFP260), then the two charge mosfets in case TO-220 (IRF9540 or IRF 9530), then the schottky diode (MBR1645) in TO-220 case. The power mosfets will be fastened DIRECTLY on the heatsink with a thermal conductive paste (VERY small tickness) and the power diode will be fastened using a isolation kit because it must be electrically isolated from the heatsink. On the heatsink will be present the battery voltage: take VERY care to not make accidental short circuit with other charger parts. Take very care also on the fastening (very tight) of the power elements on the heatsink using a proper screwdriver.
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