What is the right way to build and use a "smoke stopper" device to prevent a short or other improper wiring from damaging your electronics?
Is it different depending on what voltage you are using?
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There are different ways, but a common one is to put a light bulb in series with the positive battery lead.
This works because it will allow low currents through to power the flight controller, but if there is a surge in current from a short the bulb will light up and sap away the energy.
You need to make sure you have a light bulb rated for the voltage you intend to put through it - for example if you have a 3V light bulb and use it as a 6S smoke stopper, the filament will melt.
This guide by Joshua Bardwell is great to build a switchable smile stopper: https://youtu.be/I5a0TAmEwLE
There are two problems to mitigate here - incorrect polarity and overcurrent - which have different solutions but can be used together.
To protect against a battery being connected backwards you need to add a diode in series with the battery. This will cause a voltage drop - from 0.7V to 1.4V depending on the diode - and will need to be rated to handle the peak expected current.
To protect against overcurrent you will need a fuse, again rated to be above the maximum expected current. Fuses can come in quick blow or slow blow, depending on how quickly you want the fuse to react to overcurrent.
A small scale power supply with over-current protection also works well.
The type to get are little cheap build yourself units, with a display that allows you to adjust output voltage and display output current.
They can be powered from a lipo.
They are useful for a whole bunch of things, but in the smoke stopper situation they go to max current and that's it. The one I have is limited at about 3A which is similar in protection to a 36W 12V light globe. Obviously, smaller light globes give more protection by blowing up.