Passively cooled controllers in high ambient temperatures

mcgivor

Been going through the usual March April hot period, the last two weeks have been 40-42°C ( 104-108°F ) both my controllers are passively cooled 60A units, passing ~40A maximum, the heatsink temperatures run in the regon of 70°C ( 158°F) the Schneider begins to regulate it's current at 40°C, the Morningstar at 70°C. Although I'm not using near the maximum capacity of the controllers the derate is probably not too much of an issue but my thoughts are that it would be better if they were a little cooler, for the sake of the electronics.

With the Schneider I use the remote temperature sensor, which is now redundant with LFP batteries, to control a 120 mm.computer fan mounted on the heatsink set to 36°C, the Morningstar has the same fan, but with its own solar module as a power source and control, only runs when needed. The heatsink temperatures are kept at ambient whatever it may be.which is well below what they would be without active cooling.

For those operating close to maximum current with passively cooled controllers in still air, derating it's something to consider when ambient temperatures begin to climb.....summer is just around the corner for those in the northern hemisphere.

BB.

Using the old engineering that "aging" life of "almost anything" is cut by 1/2 for every 10C (18F) rise in temperature.

So, if you ca reduce temperature from 70C to 40C, that is (2)^3 = 8x longer "aging" life

Of course, you now have added a fan which has its own ~10,000 to 50,000 hour life (depending on bearing/bushing type, construction--remember 1 year~8,766 hours). So, you do have the "issue" of having fans failing every ~1-4 years (and the noise of a fan(s)).

Another major factor for shortening life, is thermal cycling. For example, A jet engine can go over 40,000 hours between major overhaul:

https://www.rolls-royce.com/products-and-services/civil-aerospace/airlines/rb211-535e4.aspx#section-technology

I don't know if the story is real or not, but some 50+ years ago, the store I heard was jet engines had a 10,000 hour TBO (time between overhaul). And an airline found an engine that had slipped through the TBO paperwork and was found to be still operating reliably at 40,000+ hours--That created a whole new way of looking at jet engine life--Cycle life, not just hours.

I had a friend that used this information to create a service for privately owned turboprop and jets--Basically every 10 (or ~20?) hours, the pilot would set a particular engine RPM and such, at altitude, and send in a postcard with the resulting data (Exhaust gas temperature, fuel flow, etc.). He would enter the data into a computer (this was the early 1970's, before the Internet/personal computers), and compare it against the fleet averages. When the engine went out of the averages, it was time for major inspection and/or overhaul.

One of the major types of life testing is "HALT" or Highly Accelerated Life Test:

https://en.wikipedia.org/wiki/Highly_accelerated_life_test

A major part of HALT was lots of thermal cycling (min/max temperatures, very fast ramp time, little time "soaking" at min or max temps).

It was amazing how fast a product could fail (for me, disk and tape drives for computers in the early to mid 1980's). Just 2x cycles per day (not that fast of ramp) between min/max rated temperature--And the "poorly designed/constructed" units would typically fail in less than 2 weeks of cycling. In general, any units that went over 2 weeks of cycling, never did fail in the ~4 weeks I had for evaluation.

-Bill

Dave Angelini

Bill, what happened after the 4 weeks you had it😏

I say that because the "old" guy I worked with in those years use to say it survived the thermals just long enough to get it to the military/aerospace sub.

BB.

They were returned to vendor (passed or failed). In theory for failure analysis (if needed).

Most just disappeared never to be heard from again, and most of the new companies disappeared too.

Bill