ESC overheating.

[Mike Blandford]

The MOSFETs in ESCs do have a maximum voltage rating, so ESCs are rated by voltage as well as current.

The whole operation of a brushless ESC is very complex. The motor windings act as an inductor, so when the ESC switches the current off, the inductance creates a "back e.m.f." (separate from the e.m.f. generated due to rotation). With brushed motors, this caused current to continue to flow and needed a "catch diode" to prevent a very high voltage spike from occurring. Brushless ESCs also need catch diodes, but these are built into the MOSFETs. One disadvantage is the voltage drop across these diodes is around 0.6V, and with a significant current flowing there is a noticeable heating effect. Some ESCs may avoid this by switching the MOSFET on to short out the diode, but this has to be done very carefully or the battery is shorted out by having the "wrong" two MOSFETs on at the same time.

It is also important to have some cooling for the ESC. I recently started using a FrSky Neuron ESC. This includes full telemetry including the ESC temperature. While the installation should have provided some cooling flow, it clearly didn't work very well, the ESC temperature kept going up through a flight, and I've seen it as high as 77 degrees C. I added a small air scoop to direct air in to the ESC, now it doesn't go above 31 degrees C.

Mike

[Keith Miles 2]

Mike,

You are probably technically correct about ratings but the same could be applied to many other items.

Current however, in practice, in this application is the more important consideration, I would think.

[Nigel R]

"By the way, hardly any of my esc`s have any cooling airflow whatsoever due to restrictions imposed by the models"

You are asking for trouble, taking that approach.

[Nigel R]

"And current x voltage IS watts"

Not when dealing with AC inductive and/or capacitive loads.

[Martin McIntosh]

Very low currents and way overrated esc`s in the examples stated. They get hot but not alarmingly so. I would not care to try it with some of the higher end set ups.

[Dickw]

Posted by Keith Miles 2 on 08/01/2020 23:52:30:

DickW,

May I ask the purpose of your incendiary experiment?

Ha Ha

"Incendiary experiment" is probably a good description but it is actuall related to use in a particular electric glider competition (F5B) where we push things to the limit using very high power in short bursts. That incident was about 10 years ago and thankfully such fires are rare.

The first 200 seconds of an F5B flight is gliding as fast as possible round a measured course (150m long) using the motor as little as possible (video of that bit here), we then go into a 10 minute thermal duration and end with a spot landing.

I started flying in these comps in 1987 using 10 cell nicad packs at about 500 watts. We now use 10s Lipo and 5kW+ - which in a 2m glider is huge fun.

On board data logging, coupled with telemetry, keeps us informed and allows system development "at the edge".

Dick

Edited By Dickw on 09/01/2020 10:44:57

[Keith Miles 2]

Posted by Nigel R on 09/01/2020 09:32:37:

"And current x voltage IS watts"

Not when dealing with AC inductive and/or capacitive loads.

Now you’ll really confuse ‘em!

[Keith Miles 2]

Posted by Dickw on 09/01/2020 10:42:08:

Posted by Keith Miles 2 on 08/01/2020 23:52:30:

DickW,

May I ask the purpose of your incendiary experiment?

Ha Ha

"Incendiary experiment" is probably a good description but it is actuall related to use in a particular electric glider competition (F5B) where we push things to the limit using very high power in short bursts. That incident was about 10 years ago and thankfully such fires are rare.

The first 200 seconds of an F5B flight is gliding as fast as possible round a measured course (150m long) using the motor as little as possible (video of that bit here), we then go into a 10 minute thermal duration and end with a spot landing.

I started flying in these comps in 1987 using 10 cell nicad packs at about 500 watts. We now use 10s Lipo and 5kW+ - which in a 2m glider is huge fun.

On board data logging, coupled with telemetry, keeps us informed and allows system development "at the edge".

Dick

Edited By Dickw on 09/01/2020 10:44:57

Most interesting!

Always wondered what you guys got up to. I see it now!

Love the “where the hell did that go?” camera work. Hilarious!

Edited By Keith Miles 2 on 09/01/2020 13:22:59

[PatMc]

Posted by Keith Miles 2 on 08/01/2020 23:37:16:

Posted by PatMc on 08/01/2020 21:29:51:

Posted by Keith Miles 2 on 08/01/2020 20:36:37:

Posted by Denis Watkins on 08/01/2020 16:06:59:

This is why we go up with a higher W value ESC

Perhaps why Century props went down a gear

And why we should throttle up and down in flight, into turns and manoeuvres

Initial leccy model builds, in the olden days, had the ESC on the outside of the model

From Brushed and heavy packs of old, we have come a long way surely

Agree on points one and two.

Throttling up and down is, surely, a flying issue not an ESC overheating issue?

And, yes, we have come a long way which is why I don’t buy the argument that you need to fly in a particular way to avoid an ESC failure.

Do electric cars and full size aircraft use similar technology?

If, so, and we accept the “cautionary throttle operation” theory, I see a big problem there!

Edited By Keith Miles 2 on 08/01/2020 20:50:49

ESC's are not limited by Watts but by current & voltage discretely not by the combination.

To whom does that last line belong, it ain’t mine?

And yes, I am fully aware of how ESCs are rated.

By current. In Amps!

And current x voltage IS watts.

I’m an electrician!

Looks like a posting mix-up here!

Very confusing!

Edited By Keith Miles 2 on 08/01/2020 23:39:49

I was aiming the comment at the statement "This is why we go up with a higher W value ESC" with which point you agreed.

ESC's are not rated by Watts. They are rated by current and they are rated by the number of cells in the supply battery [effectively the voltage] but they are not rated by the combination of the two limits.

[Keith Miles 2]

PatMc,

Yes, totally agree!

I don’t think you and I, at least, have ever disagreed!

Maybe any misunderstanding resulted from tangled posts?

Edited By Keith Miles 2 on 09/01/2020 21:45:20

[Piers Bowlan]

Back to the OP. The late, great, Dave Burton wrote many informative articles demystifying electric flight for us mere mortals. 'ESCs work hardest at mid throttle settings' and I was happy to take that as read and leave the understanding as to why, to others. There is no reason why an ESC should fail if it is properly specified and fit for use. I have bought countless ESCs over the years and never had one fail or 'smoke', perhaps I have just been lucky (probably).

Many of my ESCs are Hobbyking Plush which I believe are re-branded HobbyWing ESCs - not the cheapest or lightest perhaps. As Simon said earlier, always ensure there is plenty of 'headroom' as he puts it between the Amp rating of the ESC and the maximum current drawn, I usually work on 20-30%. It will cost a little more but will last forever so will be cheaper in the long run and the weight penalty will be negligible. Finally, cooling... A hot ESC is an unhappy ESC and more likely to let you down .

Edited By Piers Bowlan on 10/01/2020 10:21:43