I have a 110W solar panel that I use to charge some LiFePO4 battery packs. The panel delivers 18-20V, so I have a DC buck converter between the panels and the batteries to bring the voltage down to 14.8V. To avoid having the batteries feed the buck converter when there is no feed from the solar panel, I put some diodes on the output side of the converter.
Initially I had two MUR460 diodes in parallel, but they got so hot that plastic case for the terminal block they were connected to melted.
According to the data sheet for the MUR460 diodes, they should be able to withstand a 4A average constant current, so two diodes was within the limits for the ~7A that a 110W panel should be able to deliver when the voltage is bucked down to 14.8V.
Due to the heat issue I replaced the two parallel diodes with three parallel, expecting that heat should no longer be an issue.
Those three parallel diodes still get very hot, not enough to melt the terminal block insulation, but still too hot to touch.
I will of course replace them with other diodes with a higher current rating, but I'm still curious: what am I missing here?
Are these diodes perhaps off-spec/bad, or is there something else that would explain why they get extremely hot? Did I just pick* the wrong kind of diodes, these are meant for high frequency switching, so are they perhaps not good for a constant forward DC current?
I would have thought that 3x diodes rated for 4A each should easily be able to carry a 6-7A forward current without producing a lot of heat.
*= the reason I picked those diodes was just that I happened to have a strip of them lying around in a drawer
Update: based on the advice in the answers and comments, I changed to a MBR3045CT schottky diode in TO220 packaging, and attached that to a heat sink. No more heat problems…