when is an ESC being overworked?

[trillian]

What I trying to find out is some kind of range in which an ESC generally needs to operate, or below which it might be over-stressed.

I have a Hirobo SDX converted to electric. The gear ratio is not changeable due to having to work within the design of the frames, so I'm stuck with 8.7 to 1.

Soooo, if I use a simple calculation of KV (510) x nominal voltage (44.4 for 12s) x 90% efficiency factor divided by the gearing of 8.7 to 1 I get a theoretical max headspeed of 2340.

My question is this; If I run at 2082 headspeed that is 80% of the max (not counting any efficiency factor). Or put another way, it is 89% of the max adjusted for 90% efficiency.

What I'm trying to get at here is, I know ideally you want your top headspeed to just start to touch 100% throttle as output by the ESC so it is working at it's best. My question is, if the top headspeed is always something like 89% of that max throttle is this generally OK or will that be working the ESC too hard? (I am using governor mode on the ESC so keeping in mind it needs some headroom)

Basically I don't need 2300, I don't even need 2200. If it was nitro I'd aim for 2000 in idle-up.

My other options would be to go less than 12s (11s is actually the sweet spot). Or if I could find a lower KV motor that is no larger in diameter than the 600mx that would be an option. --- the problem with going 11 or 10s is that it seems Gens Ace does not make a 5s or a 4s 25c 2600 pack So it looks like to go with any lower cell count would require completely different LiPos and right now I have two Pairs of the 6s 2600s, which arguably I could sell, it's just a hassle (plus, on 10s it would prob need slightly bigger packs as well).

----- minor correction---- apparently Gens Ace do make a 5s/ 25c/ 2600mah pack as I just bought two from Giantshark but that size is nowhere to be found on the Gens Ace website So I'll try 11s as well and see where that puts the throttle %.

I will add that it flies very well at a headspeed of 2170, has plenty of torque and everything is staying very cool (but then you'd expect it to be cool when the outside temp is freezing).

specs are;
Align 600mx
Hobbywing 70HV
12s via two 25C 2600mah Gens Ace
tested using TT 600mm blades

[electricsceadu]

i was always led to beleave that an esc works best between 80 and 100% of its max
anything below 80% and the esc builds up heat

if the sdx is all running cool i'd run it for now and keep an eye out on the temps when the weather warms up

but having said that about an esc my converted morley bell 47 on 6 cell was running at 60% throttle with the align 75amp esc without any heat build up in the motor,esc or batteries

[Made2Fade]

when is an ESC being overworked?

For me 80% would be borderline. You could also consider a larger ESC. Or find a way of improving the cooling on your current one. A fan wired in or a larger heatsink etc
I have a personal rule of a border 85%.
Best find out how cool it runs in warmer temps first then go from there id imagine. 80% is acceptable if its running cool.

[cjcj1949]

I think there's been a bit of oversimplification. If you use an esc at less than 100% it should run cooler as the fets will spend less time on. However the esc doesn't control the current. The load on the motor and the ir of the battery does that (for a given % switching ratio). If you load an esc so much that it can't get above 80% then it will get hot, but that isn't down to the esc but the limitations of the motor and lipo combination in providing the power demanded by the system. I would monitor the current through the esc and its temperature.

[steve_b]

I think it also depends on which ESC you use, if you go down the Kontronik route then they recommend that you run it at 80% - 85% max to allow the governor enough headroom to work.
From what I understand of the Castle ESC's, never used them so I could be wrong, then you need to run them nearer to 100% because they don't have the same capability of the Kontroniks to run at lower throttle settings and tend to get hot.

[steve_b]

I think there's been a bit of oversimplification. If you use an esc at less than 100% it should run cooler as the fets will spend less time on.

When a FET is turned on fully or off then there's little power dissipation, so less heat, the power being dissipated in the FET is at its greatest when it's between off and on. So when you're running at less than 100% then you end up dissipating a lot of power in the FET and as a result generating a lot of heat.

[cupracing]

You also need to see how many amps your motor is capable of drawing vs the amp rating of your esc. Closer to 100% might make it run cololer but will draw more amps

[Jamin_00]

Kontroniks are different.

Helijive is 65%-70% and the Jives and Kosmik are around 80%

This is if your using the gov. To high rpm and you max out the PWM and the gov cant increase the throttle to compensate under load because your PWM is already maxed out so this results in decaying headspeed.

[trillian]

Kontroniks are different.

Helijive is 65%-70% and the Jives and Kosmik are around 80%

This is if your using the gov. To high rpm and you max out the PWM and the gov cant increase the throttle to compensate under load because your PWM is already maxed out so this results in decaying headspeed.

I know with the Castle Ices when you choose governor mode they seem to want a really large amount of headroom to give a desired speed and the throttle percentages it requests don't have any direct relationship to the actual percentage of ESC output. With the Hobbywing you don't have logs or setup software like that.

On the throttle curves, when I first tached it I had an 80% flat throttle in idle-up and this was giving a headspeed very near the theoretical max (was showing about 2300). I then backed it down in the TX to 75% which came out at 2170 on the tach and I flew that for a few minutes and it seemed to work very well. 73% in normal mode resulted in 1900 headspeed. But as I say, these percentages are not really meaningful becuase the ESC just sees pulses and then turns that into a governed output.

(if it makes any difference, I think the frequency is 8khz and low timing but I'll have another look at that when I get a moment)

[Mike Sanders]

I can't get to grips with the theory that an ESC gets hot if it working at less than 100%. Isn't that exactly what an ESC is designed to do? If we wanted 100% all the time we might just as well have an on/off switch.
I may be wrong but I believe that it is current draw that creates heat. If an ESC is asked to put through more current than it designed to handle then it will overheat?
Am I also right in thinking that the field effect transistors in the ESC turn the current on and off many times per second and it is the frequency of this switching which provides a variable supply of (average) current to the motor? Either the current is on or it is off. What is there in between?
By way of an example that working on a low throttle does not produce heat let's take my 600e. The 12s. pack is capable of producing about 60 amps (for a short time). I only hover so don't use more than 50% throttle most of the time. The ESC doesn't even get warm in the summer.
I am not an electrical engineer so I may be completely wrong. If so I am sure I will be corrected. If I am right then the OP will have no trouble running at 80% throttle provided that the ESC is designed to handle the current which is thereby generated.

[pgkevet]

..everso technical innit? If'n it ain't smoking it must be OK <lol>

[trillian]

I can't get to grips with the theory that an ESC gets hot if it working at less than 100%. Isn't that exactly what an ESC is designed to do? If we wanted 100% all the time we might just as well have an on/off switch.
I may be wrong but I believe that it is current draw that creates heat. If an ESC is asked to put through more current than it designed to handle then it will overheat?
Am I also right in thinking that the field effect transistors in the ESC turn the current on and off many times per second and it is the frequency of this switching which provides a variable supply of (average) current to the motor? Either the current is on or it is off. What is there in between?
By way of an example that working on a low throttle does not produce heat let's take my 600e. The 12s. pack is capable of producing about 60 amps (for a short time). I only hover so don't use more than 50% throttle most of the time. The ESC doesn't even get warm in the summer.
I am not an electrical engineer so I may be completely wrong. If so I am sure I will be corrected. If I am right then the OP will have no trouble running at 80% throttle provided that the ESC is designed to handle the current which is thereby generated.

I think you're right in that it's not simply the ESC running at less than 100%, it's how much current your asking of it at that lower percentage. In theory I think if it's at 100% it is pretty much just allowing through the output of the Lipos directly to the motor.

So I guess it's not a completely straightforward question.

[cjcj1949]

When a FET is turned on fully or off then there's little power dissipation, so less heat, the power being dissipated in the FET is at its greatest when it's between off and on. So when you're running at less than 100% then you end up dissipating a lot of power in the FET and as a result generating a lot of heat.

Yes. I was responsible for a stepper motor driver many years ago. With escs though they are being switched at 8 to 16 khz all the time.

[cjcj1949]

..everso technical innit? If'n it ain't smoking it must be OK <lol>

There are lots of ways of destroying an esc. They can be made to be reliable but that comes at a cost. Prayer is probably best, all heli pilots have faith, often despite experience. The ritual of touch the heatsink after the flight often appeases the gods. If you don't the gods tend to sacrifice the esc.

[scallybert]

A problem with ESCs is due to the freewheeling current.

The motor windings have significant inductance, so when the FETs turn off, the current can't just stop flowing.

What ESCs do is to remove the battery voltage, but still provide a path for the current to freewheel down to zero. By default, this is through a sizable diode in the FET.

This works - however, the diode forward biases at ~ 0.7V. 0.7V * 50A is 35W and there may be two diodes doing this (one in each FET). Hence, heat & inefficiency.

Now, this freewheeling happens each time the current is turned off; and this kind of equates to more at lower throttle settings. [There was some hand-waving there...] . Hence some ESCs can get hot at low throttle settings (possibly also at higher PWM frequencies).

There are various techniques to deal with this. One is to only turn one FET off, so the other doesn't drop 0.7V. I believe later CC ESCs do this, and alternate between the two FETs as to which is off (spreading the heat - and upsetting RPM sensors...).

I believe Kontronik have the option of Active Freewheeling. Rather than have current flow through a diode; the FET is carefully controlled to act like a diode. When the current wants to flow in the direction that a diode would allow, the FET is switched on; when it starts to reverse, the FET is switched off. ie the FET is like an active diode: more complicated, but doesn't drop 0.7V while passing big currents.

Is this any help..? Er, maybe...

I reckon that provided your throttle settings aren't silly, and your ESC is well specced (ie it's well capable of supplying the current you want); you may well be ok. Keep an eye on how hot it gets. [Maybe do some test runs in the garden, -ve CP on the floor ?]

And if you blow it up, you have an excuse to buy a Talon 90, which seems to be well-priced...