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Old Jun 11, 2011, 06:39 PM
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Maximum safe ESC temperature?

I can't believe I couldn't find a definitive answer to this, but how hot is too hot for an ESC? I've got a pair of 30 amp Hobbywing Pentiums in a model that I just switched from 2s to 3s. The 2s pack static current was 16 amps, the 3s is about 25 amps. An external BEC is being used. I've flown the plane a couple of times with the new pack, and, after 11 minutes, the temperatures of the ESCs had risen about 60 degrees F, as opposed to 30 degrees with the 2s. It was a fairly cool morning--the temps after the second flight were about 120 degrees--but later in the day during the summer, the 3s pack could heat the ESCs up to 150 degrees or so. My questions are: 1) Is 150 degrees too hot? 2) Would longer flights (16-17 minutes) heat them up even more? I am prepared to replace them with bigger units, but it'd be nice to know it was necessary.

Thanks,
Jeff
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Old Jun 11, 2011, 06:47 PM
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i wouldn't recommend an esc above 85C and the microcontroller may be happier below 70C

though there are ratings like room temperature, industrial and military, military parts can take 125C to -55C
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Old Jun 11, 2011, 07:04 PM
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Quote:
Originally Posted by z-matrix View Post
i wouldn't recommend an esc above 85C and the microcontroller may be happier below 70C

though there are ratings like room temperature, industrial and military, military parts can take 125C to -55C
I personally wouldn't let any of my ESC's get to 85 degrees Celsius (185 degrees Fahrenheit). That seems awfully hot.
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Old Jun 11, 2011, 08:53 PM
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The answer is routing some air directly to the escs, then an exit, and yes the longer you fly the hotter they'll get!! move the escs if you have to into direct airflow, make sure the cooling plate or fins are exposed to air, exit air should be at least as big as entrance. FWIW DOug B
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Old Jun 11, 2011, 09:16 PM
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Okay, considering that 150 degrees F = 65 degrees C, so far it's sounding like I shouldn't be all that concerned. Doug, I hear you about ventilating the electronics. Normally I would make more of an effort along those lines, but it's a white airplane, and though there's a convenient exit hole, an entrance hole for air would be pretty conspicuous...

Jeff
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Old Jun 12, 2011, 09:13 AM
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The average person cannot keep their fingers on a surface that is over 130F/54C, it is just too hot. So I use that as the cutoff temp in static testing, when I cannot hold the ESC I back off the throttle.

I have mostly Castle Creations ESCs and they tell me that they can handle a sustained 160-180F in use (temp leveled off, not still rising). So if I want to push the ESC harder than where I can hold it I put a temp sensor on it (an eLogger V3), hold the ESC in the prop blast as I static test it, and find the throttle setting that will keep it at 160F or so. Then I mount the ESC externally and test it again in flight.

The prop will normally unload a little in flight and that and the better cooling keeps things under control.

If I want to mount an ESC internally I static test it in that location with the eLogger and assume that the cooling air flow will not be any better in flight.

I am not a chronic full throttle flyer, I generally am flying backed from full throttle but I like to know that I can survive sustained full throttle runs.

Jack
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Old Jun 17, 2015, 02:55 PM
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im hitting 150 F as my esc is in a sealed box not receiving any cooling... hoping that I can use this box to be fully waterproof airplane... too hot?
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Old Jun 17, 2015, 03:42 PM
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65C is high, but OK. Depending on how it's being measured.

Commercial grade electronics are typically spec'd for operation from 0-70C as measured at some location on the component itself. Industrial and Military parts are rated higher, but these are all the same parts. Manufacturers "bin" based on parametric performance of the components. The parts that show higher operating margin become the more expensive higher rated parts. Thing is, they tend to yield a lot more parts with higher margin than they need. So generally, the lower-graded Commercial parts will work every bit as well as the Mil-spec part when it comes to temperature, they're just not guaranteed to work at the higher temps.

What you actually care about is the "Junction Temperature" of the FET. This is probably spec'd for a maximum of 125C. Your 65C is well below that, but it's probably not a measure of the junction temperature of the FETs but a location on the PCBA nearby the FETs. So your FETs are actually running hotter. But even assuming a 40C gradient, you're still comfortably below the maximum junction temperature. Which is why I think you're OK.

But keep in mind you're operating near the thermal maximum and the reliability of the ESC will be impacted, probably severely.

Also, in an enclosed space, heat is going to tend to build up. Particularly if your enclosure is plastic (good electrical insulators are usually good heat insulators, too). Is the 150F you measured at the ESC after a full battery under flight loads, or only a short initial test run? As the run progresses, the ambient temperature in the enclosure is going to increase and the ESC will get hotter as a result. You have operating margin at 65C but not a lot if the enclosure's going to get 10-20C hotter over the duration of an entire flight.

Might be harder to waterproof than plastic, but you might consider an aluminum enclosure. You could mount the heat-sink side of the ESC to the inside of the enclosure and get fairly effective cooling while still maintaining water tight integrity.
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