Trying to refresh my knowledge I was design and construct a fixed unregulated power supply 12V/5A using parts that I have around. Parts are 150VA/12V toroid, an 25A rectifier bridge in KBPC case and 20 electrolytic capacitors 1000μF/35V each. Trying to calculate a plate heatsink for the rectifier, I test my construction with an ohmic load (a tungsten lamp rated 55W/12V) and monitoring the rectifier case temperature I find the temperature rise abnormal and I cut the power around 100oC, then I remove the capacitor bank, and get temperature again
This is the graph
I can not explain the reason of this difference in temperature rise. I used another rectifier but no deference even using a 35A one.
The maximum current during charging period is calculated about 33A but it lasts just 1,8ms and with a duty cycle 0.22 the total dissipation is about 6.6W in total. In no load condition, there is no consumption by the capacitors.