During flight log reviews I note that the battery current being reported is fine up until a certain amperage. This could be due to a hardware issue (heat?), but wondered if there could be an issue with saturating the ADC?
It does not appear to happen at the same current level - so I am guessing it is more due to heat causing an issue with the current sense resistor, but the spec rates the current sensing of the FC at 90A. Has anyone else noticed this issue with this FC?
The trace below shows a test - only one of two ESCs are plotted, so BAT.Curr should be ~double the ESC shown. It appears about right up to ~12A - but never gets above 14A. I had a clamp meter on the battery during this test and it reported a “correct” value of ~50A max.
How is your esc current reported so you can plot it? Is it from esc telemetry? How is it so much higher than battery current so that it pretty much continues to go up when your battery current drops back toward zero?
Regardless, that’s not really the point. I think you just need to tune/calibrate the board current sensor settings, the Amp/volt value in the code, because what I think is happening is that at low current the discrepancy is not that much, so it seems “correct”, but since it’s a multiplier, at higher current, the difference is much more noticeable. It’s just really a slope on a linear graph, so your slope is just wrong/off, so toward lower x-values (voltage drop over the resistor), your y-value (current) is not that far off the actual current, but as the x-value increases, the amount the current is off, becomes a lot higher.
Also, measure the current in the line with an inline current meter (between fc board and esc), just so you can be 100% sure you are getting the correct value from the clamp meter. Sometimes a direct inline current value can be more accurate than a clamp meter current value, which uses hall effect to measure current. It can’t hurt to use a second meter (inline) to be absolutely sure.
How is your esc current reported so you can plot it? Is it from esc telemetry?
Yes, ESC telemetry.
How is it so much higher than battery current so that it pretty much continues to go up when your battery current drops back toward zero?
that is my question. Of course it doesn’t actually, it is a reporting error.
Regardless, that’s not really the point.
No, that is exactly the point!
I think you just need to tune/calibrate the board current sensor settings
Both the BATT_VOLT_MULT and BATT_AMP_PERVLT are single values - so the calculated output is linear. Any error is also therefore linear - but yes, at low current the delta is lower. However, the error %ge remains the same. In this case the error is close to zero until 12Amps then has an inverse response - not possible to be a calculation issue with a single multiplier.
Also, measure the current in the line with an inline current meter (between fc board and esc), just so you can be 100% sure you are getting the correct value from the clamp meter.
A properly calibrated hall-effect sensor is far more accurate for taking current measurements at this amperage than a shunt resistor.
I suspect that the use of a shunt resistor on the FC is the precise reason for this error, but was wondering if anyone else saw the same issue with the same FC. It could be caused (purely an example) by voltage drop in the board traces at higher amps.
that is my question. Of course it doesn’t actually, it is a reporting error.