I recently saw the specs for the typical 3DR power module, which stated the following on the max current: “About 30-60 amps continuous and 90A for a few seconds burst should be fine”.
Now, I’m using mine in a quadplane which can draw nearly 50 or even 60A at times, when climbing with the vertical motors.
My question is: Assuming the module failed, would that actually cut power to my motors altogether? Or would I just lose power/current sensing and power supply for the Pixhawk itself? I can live with the latter as Pixhawk could use backup power from the servo rail. But the former will be catastrophic on a valuable model! Thanks!
It depends on whether or not the shunt burns out. Since the shunt is a resistor the more current that passes thru it creates heat and temp rise with the square of the current. Maximum temp for any shunt is 145C. Beyond that, the alloy it is made from, called manganin, will be permanently damaged and it can simply burn out and not pass power any longer.
The power modules with their tiny shunts for the Pixhawk system were designed back in the day for little DIY quad rotors et al. They have not scaled well to the modern 12 and 14S power systems in use today. Therefore I don’t use them anymore. There is no way I will trust an expensive helicopter to a tiny shunt the size of a pencil eraser.
One alternative option (which I use in helicopters) is ESC telemetry/logging, which is available in most high-end ESC’s these days.
Christian Mauch makes a great alternate power module: http://www.mauch-electronic.com/
They even come with calibration data, so setup is easy. Hall effect, not shunt resistor.
The Mauch module looks like a good alternative for your application. The hall effect sensor, which is what is used inside the ESC’s with power logging/telemetry, doesn’t have the heating problems of a shunt at high current flow.
Eventually I would like add support for ESC logging/telemety in ArduPilot for 12 and 14S single and twin-engine vehicles. I use the ESC telemetry at present only to my RC radio with a SPI interface on the receiver. There was another thread recently where I mentioned this, and apparently it could be done for multi’s as well according to the comments of one of the developers that commented on it. As the operating voltages of large aircraft have continued to rise it becomes less and less practical to try to step down 50V power to 5V with a switching regulator, making dedicated 2S flight systems power battery a necessity to power electronics and servos. And a different method will have to be used to measure current or power.