Hello, I am using a 3DR PM on my hexacopter, and I fear that my amp draw is nearing the 90A limit. So what would happen if the PM failed after too much amp draw? Would it just stop giving voltage and current information and stop its BEC output or would it completely cut power to the ESCs?
It won’t fail per se, but would apply a voltage to the ADC above Vcc. This can cause either autopilot damage or reset.
It wont cut power etc… It just electrical damage may happen.
You could just remove the one wire connecting the current sense and use the voltage only monitor. Voltage level is more critical than current monitoring.
The other option is to add a atto pilot sensor, and not use the PM (you can still use the regulator part just disconnect the voltage and sense wires)
I do not really wish to disagree with billbonney, as I am not sure about the IC used in recent power modules,
but what I can say for sure, is that ACS758x sensors, (up 50…200A ) are source limited to 3mA , in other words, they are completely unable to increase Vcc or a APM/Pixhawk above allowed levels even when over-saturated.
If you check out whatever module 3DR is using for the 90A sensor, - it’s most likely limited in the same way as a good practice for use with an A/D input.
(unfortunatly I failed to find the schematics/BOM for APM power module)
All eagle files etc… for each OSHW component sold by 3DR is linked to from the entry in the store.
It’s not a sensor but a INA169 OPAMP that amps the voltage across the current sense resistor (which is 0.001Ohm). The opamp is powered by the battery. Which is much greater that Vcc. This means when you exceed 90A the voltage from the OPAMP exceeds 5V.