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i Have 5 x 250V 100A VE can mppts in parallel. the temperatures are running quite high - 1 of them at60 degC - is this normal. What could be causing this.
3x strings of 370w panels - 5 in series
so under 30A short circuit current
235V open circuit voltage (brochure)
5 panels in series with 235V OC will go easily above 250V at lower temperatures (below 5°C).
That can damage the MPPT.
I presume each controller has the 3x5 array that you mentioned? 5.5KW per MPPT controller?
If you consult the datasheet, the 250/100 has a Maximum efficiency of 99%, so at least 1% is lost as heat.
1% of 5.5KW is 55W lost in heat. I reality, especially at almost full power, the controller efficiency is likely to be between 98% - 99%. So it is probably losing ~80W in heat.
I roughly estimate the heatsink specification of the 250/100 to be ~0.4°C/W @25°C ambient temperature, ie. the heatsink temperature will rise by 0.4°C above ambient for each Watt of heat put into it if the ambient temperature is 25°C.
So if the heatsink is having to get rid of 80W of heat, it's temperature will rise by 32°C above ambient temperature if the ambient temperature is 25°C. 32+25 =57°C
If the ambient temperature is higher then the temperature gradiant is less and the heatink cannot shed its heat as easily, so it will get hotter.
The above are rough estimates, but do give us ballpark figures.
Thank you - excellent answer. If i am correct -this then means that the MPPT is functioning correctly but the high temperatures will probably shorten its operating life. So we need to reduce the ambient temperature as much as possible?
