question

Duncan avatar image
Duncan asked

Does the MPPT 75/15 need extra cooling in hot conditions?

Hi

I just reinstalled my 75/15 with standoffs to improve passive cooling. I had noticed the unit getting very hot when outputting 12-15A in bulk mode when installed flat against a wall. Ambient temperature was 33 Celsius in a closed room.

I was going to add a heatsink to the metal back panel but just watched a video showing the back of the charger filled with sand (maybe this was a hoax) so I am not sure how effective that would be.

Would I be best reducing the max charge current to ensure longevity of the device? Or is the unit fully capable of operating at max output in warm environments? I can’t find any derating curves for the charger. The charger has been running faultlessly for a couple of years so no issues.

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2 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Dunk O,

Nice to hear you are wanting to take the best care of your equipment.

Some of the units do indeed have a thermal silica sand inside them to help with heat dissipation. No hoax!

Make sure your unit is running the latest firmware version, there have been improvements in the temperature derating for longevity.

The best thing you can do is maintain cool airflow over the unit, either passive room ventilation, or an active fan.

The unit itself will temperature derate to maintain a maximum operating temperature of 60 degrees, that is EXTREMELY hot to the touch, it would burn you if you held your fingers to the heat sink.

The MPPT's job is to charge batteries, so yes, reducing the maximum charge current would reduce the amount of heat generated, but that is a false economy if you aren't charging your batteries fully each day as a consequence.

The unit is capable of operating at maximum output, even in warm conditions, and it will protect itself automatically by derating if necessary.

I would not attempt to drill or otherwise attach anything to MPPT itself. Ironically that could cause you MORE problems, if you did need to go for a warranty return for some reason.

These units are backed by Victron for 5 years, and for an additional 10%, you can increase the warranty period to 10 years. On top of a little extra airflow, that would be safest and best plan for peace of mind long term.

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n-dee avatar image n-dee commented ·

Tech specs show that maximum operating temperature at 100% is 40 degrees.
Beyond that, I assumed that derating starts. Is this a typo in the specs?

regards,
Andreas

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Duncan avatar image Duncan commented ·

Thanks. It is rare that a response addresses every part of the question so succinctly!

I would have only attached a heatsink with thermal adhesive, certainly no screwing.

I think the addition of a gap between the metal back and mounting surface will help. But I guess the engineers determined it was not necessary.

I doubt the temperature exceeded 50 C.

The unit may have self down-regulated today as I did not see 15A only 12A in the bulk stage. I will study it more closely.


Thanks for confirming that the charger is designed to operate at max output when operating temperatures allow..

If needed I could use a small computer van controlled by the MPPT Load controller.


thanks again

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ Duncan commented ·

The dream of this community is if each question is answered properly and completely then the answer will serve another 1000 people who are also looking for the same information.

You can see the main visible difference between the 75/15, 100/15 and 100/20 is the size of the heat sink.

The small computer fan would be a great idea, if run during the day in a hot room.

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kevp avatar image
kevp answered ·

Apologies for posting a follow on question, rather than an answer, but it could be useful to you too.

Guy, (Victron Community Manager)

If I were to attach a small DC fan (say <1W) to my 75/15, could I connect it directly to the PV terminals? It seems that DC fans are pretty tolerant of the input voltage and more solar power (+heat) would cause the fan speed to increase. (Mine is an RV setup - I am already using the load output terminals to trickle charge the vehicle battery when the house battery is full and the vehicle batt <13v).

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dan avatar image dan commented ·

20221226-181444.jpgI have a 75/15 and i noticed it was really hot, i couldnt touch the back plate without burning my fingers, totally shocked it was that hot, i have some old cpu heat sinks and chose one that suited, using some proper heat paste i sat the mppt on it and instantly the temp dropped, i could hold my fingers on the plate without it burning and the mppt peaked at just under 15 amps, so it must of been saving itself, after reading your question i then got an old computer fan and connected it to the pv side of the mppt and let it run, it stopped at dark, hopefully it will start up in the morning. I have decided to permanatly run a heatsink and fan on the 75/15 from now on.

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