Build a Smoke Stopper for Mini Quad and Drones

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.

The DIY smoke stopper was created by “mnemennth”, link to his thread on RCG at end of this tutorial.

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.

Too lazy to build your own? You might want to consider the “plug and play” PPTC smoke inhibitor.

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 :)

Steps

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.

Credit

5 thoughts on “Build a Smoke Stopper for Mini Quad and Drones

  1. Ricardo

    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.

    Reply
  2. Jon

    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

    Reply
  3. MisterWho

    …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.

    Reply
  4. Sebastian

    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…

    Reply
    1. voodoo

      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.

      Reply

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