Im building a quadrocopter, so that's why im going to be using such a big power supply (for the tests, autonomic power supply will be a LiPo 3S - my 4 motors draw up to 20A current each). What kind of countermeasure should I include on my PCB to protect it, in case i make a short while soldering, or there will be a design flaw. The uC+step down regulator+gyro+esp wifi module shouldnt require more than 1 A (probably even less than 500mA).

Varistors and transils wont work because its not voltage thats going to be too big. Fuse/circuit breaker will probably be too slow.

So what should I use in this case.


Build your controller.

Check for shorts with an Ohmmeter before you connect to a power supply.

Test with lower powered supply (same voltage, less current) and fuse protected.

When all tests show the controller is OK, install it on the copter. Treat the controller as a sealed unit. Any change means you take it out of the copter, and repeat the low power tests.

This should catch any assembly errors.

If you can strap the copter down, you can run full power tests on the ground with fuses in appropriate places. When the full power tests run through with out shorting out, you can let the copter take to the air.

You really don't want to catch assembly errors with your expensive toy 50 feet up in the air. Find them on the ground, fix them, then take to the air.

  • \$\begingroup\$ The problem is this 106A 12V supply (from an old server or pc, i dont know) is all I have. I dont have any adjustable current power supply. Should I just use some small power supply, like from a router or something? \$\endgroup\$ – Lugi Aug 14 '16 at 14:08
  • \$\begingroup\$ Yes, a 12V wall wart like you would use to power a small router would be better than giving a potential short 100A to play with. Test with an ohmmeter first, then low power supply. \$\endgroup\$ – JRE Aug 14 '16 at 14:19

Typically they don't have much in the way of circuit protection.

One big reason is say with a main fuse, an isolated fault could blow it and drop the multicopter out of the sky even if it was only a short or intermittent fault condition.

It is also hard to judge a value to use as they can draw massive amounts of current in bursts.

I have thought of a polyswitch but I believe recovery time would not be quick enough before it crashes.

I see where you are going, I like to be cautious with design. There are some potential solutions on the board side, however again there are risks, allow for an isolated fault that will damage the board but may still be flyable or have it trip a protection device and lose all control ?

Maybe some others will have some ideas...

Reverse polarity protection is probably still worthwhile doing to prevent accidental damage when wiring/terminating.

  • \$\begingroup\$ I have bought 4 motor drivers, so even if my pcb got completely unconnected midair they would take care of making sure that it doesnt just drop dead (they will just reduce power, and its going to land). Reverse polarity protection is taken care of by the connector itself (only one way to connect). \$\endgroup\$ – Lugi Aug 14 '16 at 14:10
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    \$\begingroup\$ @Lugi - no, they won't. Motor drives should probably cut out if the signal from the main board stops, but even if they don't, without an active computer control the platform will quickly show its instability and fly in an unpredictable direction, quite likely into the ground under power, but possibly into you or someone else. You show a dangerous lack of understanding of how quadcopters work, to be contemplating building such a powerful and hence dangerous aircraft. \$\endgroup\$ – Chris Stratton Aug 14 '16 at 14:57
  • \$\begingroup\$ These motor drivers are connected straight to the power supply, not through the main board, theyre just taking a pwm signal from uC to adjust speed. And you are right, without uC running the PID controllers, its going to get unstable really really fast, but for the sake of tests it is going to be restricted to moving only up and down by a rope running through the middle of the frame. \$\endgroup\$ – Lugi Aug 14 '16 at 15:04

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