ESC32 with MAX_CURRENT set at 15A, but actual limit is more

[johandm_be]

[LPR]

Johan

I have not played with the ESC32 for many months but when I calibrated my motors and ESC32 with a 5s battery I found the motors took around the same amps as I had set the ESC32 to.
I played with lower settings and higher and found if you go too high the motors and ESC32 will lose sink and the ESC32 will disarm. Try higher setting and if you hear the motor make a strange noise while your calibrating them you are losing sink and you will not get all the calibration numbers.

I sounds to me like you might not be getting the PWM signal up to 1950 so you don't get full throttle.

I have 10 HK 17 x 5.5 and I find about a 25% difference between the amount of power the props take to run at 50% throttle while testing them on one motor and ESC32 setup. There is a big difference from one prop to the other in my set of props.

Larry

[johandm_be]

Hi Larry,

Thanks for your reply.
I was setting the throttle over UART (with the DUTY command) so I am certain I put it to 100%.
I found that at lower voltages (for example if I change to a 4S battery with the same parameters) then it will allow higher currents.

for example: for ESC#1 above:
if I tell it "duty 100" with a 5S battery (at 20.25V) then it limits the FET duty cycle at 76%, indicating a current of 6.50A (external power meter shows 7.22A)
if I tell it "duty 100" with a 4S battery (at 15.92V) then it limits the FET duty cycle at 97%, indicating a current of 8.00A (external power meter shows 9.44A)

The parameters I listed above were from the motor database and I think these were calibrated on a 4S battery. I wonder if that is the reason the current limiting is so far off.


Note that prior to this I have flown with different ESC parameters that I calibrated myself on a 5S battery. Those currents were much closer to the limit I set. Initially that had been working fine but at some point my craft crashed and from the logs we determined that one of the ESCs/motors failed. I repaired the craft and put 6 new ESCs + 6 new motors + 6 new props on it. After 2 flights it crashed again with a motor/ESC failing.

After the 2nd crash, I tested all 6 ESCs and motors from the craft and found that one showed a synchronisation problem when throttle went beyond 70%. That was surprising, because: I did test all 6 ESC+motor sets thoroughly with a bench setup prior to mounting them and then all 6 worked fine. And 2 flights later at least one shows synchronisation problems at 70% throttle.

When I put the parameters from the table above in that ESC it works fine again. That is why I am now leaning towards using the values from the motor table instead of my own calibrated numbers. But I am a bit uncomfortable by how much the current is limited with these settings.

Kind regards,
Johan.

[LPR]

Johan

I'm thinking you are running too high of voltage for the props you have. What is the KV of your motors kv 610 or kv 390?
Even a kv of 390 may be too high for the motor when using 5S battery. Looking at T-Motors charts I see that they don't use 17" prop with a 5S battery till the kv is down to 330.

I had the same problem when I tried to run a 5010 motor on 28 volts with a 15 x 5.5 prop. The motor and prop worked fine with 4S battery. I used 50 amp optos from RC Timer with SimonK firmware. The motors would lose power for less then a second but that was long enough to crash.
The amount of watts a motor can handle is a function of the RPM the motor is running. Too large of a prop can hold the RPM too low and then you can only use a portion of the maximum watts the motor is rated for. The higher the voltage the lower the amps you can use.
My solution for the 5010 was to shorten the props to 10.5" and that stopped the loss of sink.

Larry

[johandm_be]

[LPR]

Johan

I would get a RC Timer 50 amp opto ESC and see how many watts you use at full throttle. If it is higher than the motor rated watts you will likely have a problem with keeping the motor in sink with the ESC. The RC Timer 50 amp Opto is the cheapest 7S ESC I could find.

Larry

[johandm_be]

Hi Larry,

I know that if I'd use a regular ESC then (at full power) my current will be over 15A. With a 17" x 5.5 at 5S, the current will be about 18.5 Amps. And these motors only take 15A peak, 11A continuous.

But: I am not using a regular ESC. I am using the ESC32 and it is set to limit the current. I can see that it does that by limiting the duty cycle on the FETs when throttle is set high. And I can verify that with an external power meter.

The ESC current limiting is effectively limiting full throttle (100% duty cycle) to something like 75%; as if I'd never push the stick past 75%. (in fact I can see it is rescaling my range so that 100% is really only 75%)

Because of that the motor never exceeds 15 Amps. So, I am not running the motor over-current nor over-power. I am really only limiting the resolution I have on throttle.

Kind regards,
Johan.