How to limit power consumption to a certain value?

Question

For the SAE Aerodesign competition, there is a requirement to create an electric RC airplane that does not exceed 750 W of power consumption at any time. The electrical circuit consists of a 22.2 V (nominal voltage) Li-ion battery connected to an ESC (DC motor speed controller) to power and control the brushless motor and also connected to a device called a BEC (Battery Eliminator Circuit) which is basically a step-down regulator to 5 V to power the receiver and servos.

I would like to know how I can create a circuit that does not allow consuming more than 750 W at any time during the flight

step one would be to find out how the power consumption will be measured — Jasen Слава Україні, Feb 25 '23 at 22:47
I forgot to mention but there is also a wattmeter connected that record and store Wp (highest value of power during each flight) — Jesus Vargas, Feb 25 '23 at 23:22
You could make a current limit circuit with a shunt, an op amp and a mosfet. Set the limit to 33A. This method is not very accurate but it’s easy to make — Panthera, Feb 26 '23 at 00:08
If you have a fancy enough ESC it will have this option built in. — user253751, Feb 26 '23 at 03:48
You can enhance the solution from @Panthera by increasing the current limit reference as the battery voltage decreases over time. — RussellH, Feb 26 '23 at 03:50

score 2 · Answer 1 · answered Feb 25 '23 at 23:27

It's not straight forward. You will need to measure the battery voltage and the battery current, multiply the two to get the power, compare that to 750 W, feed that into a servo loop, whose output overrides the speed control input to the Electronic Speed Control (ESC). You can to all that with the a microcontroller with A/D inputs and a PWM output.

score 0 · Answer 2 · answered Feb 26 '23 at 23:04

It's not enough to do it. You also need to prove it.

So you shouldn't be asking us how to do it.

You should be asking your sanctioning agency what their criteria are so that your airplane is "inspectable" to affirm it meets the requirements. That will generally inform (or force) your design.

How to limit power consumption to a certain value?

2 Answers2