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Old Aug 19, 2010, 03:39 PM
717
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How hot is too hot for my 85A ESC?

I've had several flights to date on my H9 Spitfire (electric conversion) using a Turnigy Brushless ESC 85A w/ 4A SBEC. The cowling of the Spitfire is tight and streamlined with no cooling ports. I like the way it looks and don't want to cut any cooling ports if I don't have too so I tried to buy higher rated components and not push them too hard. I've measured 55A draw at full power static thrust run-up and the since the ESC has an 85A rating I have been hopeful all would be well without much airflow.

Well today I pulled the cowling off and did a 2/3 throttle static run-up for five (5) minutes. I then touched the ESC cooling fins and they were pretty warm- uncomfortable to the touch but could leave my finger on it for the most part if I like a little pain. I also used an infared temp gun to measure 140 deg F but I'm not sure how accurate it is. BTW- motor and lipo are barely warm AND I'm not using the built-in SBEC, and yes I disconnected the red wire from the ESC to the RX.

So how hot is okay? And how hot is too hot?

I thought a 2/3 throttle 5 minute static run-up would be fair since the airplane is unloaded during flight and I don't spend a lot of time flying at full throttle. Obviously full throttle static will generate even more heat but I'm trying to determine what's going on in flight, not on the ground. And I don't have any fancy in-flight measuring devices.

I noticed in the ESC manual it states that the ESC will reduce output power when the temp exceeds 230 deg F. I measured 140 deg F on my run-up. I know this is a big spread but I'm just wondering what's normal for temp on most ESC's? I've never had any of my ESC's get this hot, hence the reason for my concern but this one doesn't get any air flow either.
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Old Aug 19, 2010, 04:40 PM
717
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Update- I used a professional laser aiming temp gun which also confirmed 140 deg F on the ESC. So that's two guns which read 140 deg F.
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Old Aug 19, 2010, 06:40 PM
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At 2/3rds throttle the ESC is going to run hotter than at full throttle, especially under a static test. a five minute static run is too long in my book.
One other question, what is the full throttle current that your setup is producing?
Pete
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Old Aug 20, 2010, 01:07 AM
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I aslo want to know it.
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Old Aug 20, 2010, 01:59 AM
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Thats much to long to static run an electric plane, from what I have always learned and practiced (and experienced first hand). The plane actually UNLOADS in the air and the amp draw goes DOWN. You holding the plane is making it work harder, if that makes sense. That is why some people prefer systems like Eagle Tree that give real time data that is stored then recalled on a computer. You shouldn't static test a model for more then 30 seconds...I just do it to make all the necessary measurements (volts, watts, etc). And your components aren't getting the airflow they need to properly cooled. These two together will overheat your setup, as you have begun to see.

Your setup certainly looks acceptable from the numbers you have posted as far as amps goes. If your drawing 55amps static at WOT then you ESC will come down room temp.
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Old Aug 20, 2010, 04:08 AM
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unloading may or may not happen, depending on what prop you have,

Electronics is safe to about 400F at the chip: generally 70C - (160F or so?) is fine.

Its always better to be cooler, but you can run electronics hotter than you can run neo magnets.
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Old Aug 20, 2010, 12:04 PM
717
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Hi everyone.

Thanks for the feedback. Yes the full-throttle current is 55amps. And yes I know five minutes is a long time and that the airplane "unloads" in the air. But my concern is that my electronics are not getting airflow in flight anyways because this airplane has no cooling ports, therefore whether it is flying or on the ground, the airflow is the same. I wanted to simulate what might be going on during flight at 2/3 throttle (which is my cruise power setting) to see if things are getting hot. 2/3 throttle on the ground is obviously a higher load but I figured if all went well on the ground then I'd know all is well in flight.

BTW- since there are no cooling ports I am not able to land the airplane and quickly examine components for temp. I'd have to remove the spinner, prop and cowling to do so and that takes several minutes, by which point everything is cool to the touch. So I performed my run-up test with the cowling off in order to measure temp along the way. However the ESC does not receive prop wash airflow as it is mounted behind the firewall.

Vintage1- my prop is a MAS 3-blade 16x10.

I used my friends laser temp gun to measure the can of the Turnigy outrunner motor at 100F and the 6S/5000 lipo at 70F. The ESC was the hottest component at 140F but this was the temp of the cooling fins. I don't know if this means the temp inside the ESC box is higher or lower?

PilotPete2- Why does the ESC run hotter at 2/3 throttle vs full throttle? I think I have heard about this before but had forgotten about it during my run-up test. Anyway if this is the case then I think my ESC will be fine under all conditions in flight despite the lack of airflow ports.
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Old Aug 20, 2010, 07:18 PM
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OK, Vintage can handle that one better, but the short version is that at partial throttle, there is more heat generated by switching losses in the FET's
It sounds like you have a good setup there with an 85A rated controller and only 55A at WOT.
Good luck,
Pete
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