Build a Smoke Stopper for Mini Quad and Drones

by Oscar

A smoke stopper can help avoid damage when you power on a mini quad for the first time. Sometimes you might have a defective part or a short somewhere, the smoke stopper can limit the current flow and prevent “magic smoke”. In this tutorial I will show you how I build a DIY smoke stopper.

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Apart from testing RC models for the first time, a smoke stopper is also great for flashing ESC’s. When error occurs during the flashing process, there is a chance all the FET’s on the ESC might turn on at the same time, creating a dead short.

Don’t want to DIY? You can buy one.

How does a Smoke Stopper Work?

A carefully chosen light bulb can turn into a great over-current protection device. Connect it between your battery and quadcopter, so only a small amount of current is allowed to pass through, enough to illuminate the bulb but no more.

It saves your electronic components from current surges, and gives you a chance to troubleshoot the failure without having to replace the burnt-out parts.

What’s the Current Limit of a Bulb?

The light bulb turns on when there are enough amps going through the filament, but it restricts the current flow at its rated power. The current limit of a light bulb can be estimated as:

Current Limit (A) = Bulb's Wattage / Voltage of Battery

For example for a 27W bulb and a fully charged 3S LiPo (12.6V), the current limit would be about 2.1A.

Note that if there is a short in your quad, the current surge might be large enough to blow your bulb, it’s a fuse essentially.

Parts to Build the DIY SmokeStopper

Here are the parts I used to build my smokestopper:

Do you see that the 3157 bulb has two power rating? That’s because it has two filaments inside, one for higher current and the other for lower current. That’s why we are using a switch to select which filaments we want to use for different testing.

Wire gauge doesn’t matter since the device is designed for up to only 3A of current. Use any spare wires you have, preferably 20AWG or larger.

You can consider adding XT30 connectors if you want to use it for micro builds :)


Here is the connection diagram provided by mnemennth.

Note that there are 4 legs on the bulb, 2 legs on each side. The two legs on the outside controls the high current filament.

Lift and bend one of the legs to the opposite side.

The leg spacing on the switch is just wide enough to be mounted on the bulb directly, that’s super handy for soldering :) Of course, if you don’t want to do this, you can also use wires between switch and the bulb.

Now solder the switch and wires on the bulb according to the wiring diagram.

The other side.

To secure the wires and switch, it’s best to apply some hot glue.

Finally put the heatshrink on.

It was pretty easy to build the smoke stopper, took me about only 20 mins to complete :)

How to use Smoke Stopper?

Because these light bulbs are rated for 12V, it’s recommended to use 3S LiPo for testing. The creator said it’s okay to use up to 15V, so an empty 4S pack might also work.

When plugging in battery for the first time to your newly built quadcopter, always start with the “Low Current” mode to test all your accessories. It’s a 7W filament and only allows about 500mA of current to pass,  about enough to power up the FC, and initialize the ESC’s.

This is great for testing micro and nano quads, but it might not be enough to test larger quads especially when you have power hungry VTX or bright LED’s. If the bulb lights up and your FC and ESC’s keep restarting, you might want to disconnect the LED’s and VTX.

Once you’ve confirmed the quad is working under “Low Current” mode, you can now switch to the “High Current” mode (27W), with everything connected on the quad. You can check if the arm switch works, if the motors spin, and if the quad responds correctly to the sticks on the bench and so on.

If there is an electrical short, the bulb will light up brightly.

Note that the SmokeStopper is NOT “Bulletproof”. The bulb only limits the current and doesn’t stop it. If you wired the parts incorrectly in your mini quad, the small but continuous current flow can still damage them.


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Eder Nucci 29th March 2021 - 6:52 pm

I usually use a 2.1A power bank with an XT60 plug. It already has protection against short-circuit and cuts off the supply if the motors have a high consumption. Essentially it does the same thing. Nice article, congratulations.

Antonis Chaziris 5th January 2020 - 3:58 pm

Isn’t it possible that the bulb is lit and no short circuit exists? I.e. the drone is fine, just the current drawn from the FC and esc’s is enough to turn on the bulb..(?)

Oscar 13th January 2020 - 3:43 pm

It’s possible if you have power hungry devices connected, like a high power VTX and LED strips.
It’s best to disconnect these when testing, just leave the most important parts connected, like FC, ESC, motors, RX etc…

Rick 5th October 2019 - 7:36 pm

The bulb provides immediate current limiting, the fuse does not. Fuses take time to blow. The point of this device is not to blow the bulb, it’s to limit current that can destroy things. I agree with above ideas such as measuring for shorts with a multimeter, using a current limiting bench supply etc. but this is a pretty solid device that *could* save components.

Gary 4th December 2018 - 7:19 am

If you are using a bulb as a smake stopper as per the article it will not blow unless you are using more voltage than the bulb is rated for. It is not a replacement for a fuse, the bulb limits current but will never blow unless the voltage is too high for it. In most cases it will save what you are working on but not always. As the bulb heats up resistance increases, until this happens it does draw more current.

You should never power up even with the smoke stopper without measuring the resistance at the battery socket for your quad with multimeter. If you are getting close to 0 ohms then you have a short, fix it before powering up.

Ricardo 2nd June 2018 - 11:26 pm

Hello guys,

Just to clarify some ideas. If you use 12V supply or a battery with no more than 12V, on a 12V lamp it will not blow from overcurrent. If you have a short on the quad the bulb will shine at the maximum power rating but it will not blow. The bulb acts as a current limit component because the maximum current on the circuit will be the maximum current rating of the bulb. I’ve made my smoke stopper from a 5w/21w dual filament bulb. That means that a short circuit @12V will pass around 420mA with the 5w filament and 1,75A on the 21w filament.

Bob 30th September 2018 - 10:45 pm

Ricardo is correct, for example if you put a 12v bulb of any wattage directly across the terminals of a 12v battery then this does not blow the bulb. The wattage of the bulb divided by the voltage of the battery will determine the current flow in amps in the circuit. A bulb cannot blow because of a short, that is what the fuse will do.
I used to use a 60 watt bulb across the fuse contacts instead of a fuse when an intermittent short was blowing fuses in auto electrical diagnostics back in the seventies so that when the circuit short occurred the lamp would glow to max, it was easy then to move the wiring loom about to find where the short was happening rather than keep popping fuses in.

Fahmi Alias 3rd March 2019 - 6:25 pm

I planned on using 5/21w bulb too since its easier to find. Does it work as good?

Jon 16th May 2018 - 9:59 am

I think it is incorrect to claim a fuse or light bulb protects components against current surges. They don’t, they will allow way more than the rated current and take 10 or hundreds of milliseconds to blow. More than enough time to fry attached components. It will stop the battery exploding or catching fire in the case of a direct short so it is definitely worth using.
You have more chance of protecting attached components with a mosfet current limiter it was $7 for the bits You can use circuit breakers but they are more expensive

MisterWho 15th May 2018 - 6:18 pm

…or: Get a small bench power supply :-)
You can limit the current according to your needs and you see very fast if something is wrong. You also can check the volts which your fc shows in the configurator or on your OSD.

Sebastian 15th May 2018 - 6:11 pm

Why not use a fuse?
Replacing a blown fuse should be much cheaper than a automotive bulb. Choosing a suitable current limit is also easier.
Just a Suggestion…

voodoo 15th May 2018 - 11:49 pm

A bulb gives you some warning before it blows. A better idea would be to use a resetable fuse. I stick with a bulb because of the warning.