Battery Powered Air Horn

A battery powered air horn is a fun little project. I had a set of car air horns from Harbor Freight laying around and wanted to do something with them. I came up with this.

The project can be made in a few hours with limited tools. Total cost is about $35 if you buy everything new. If you have an old electric tool that you don't mind modifying, it can be even less.

Project Materials -

• Warrior 12v Electric Drill (or Other Battery Operated Tool)
• Car Air Horn (Harbor Freight)
• 2 3"- 4" Hose Clamps
• Quick Disconnect Female Terminals
• Wire
• Heat Shrink Tubing

Tools -

• Phillips Screw Driver
• Files
• Wire Strippers
• Drill with 1/2" Drill Bit
• Soldering Iron
• Heat Gun

In order to modify the drill, you will need to take it apart.

The drill will have multiple phillips screws on the right side. There are then 4 screws on the front of the drill near the chuck (silver trim). After removing those four screws, there will be 2 more screws under the silver trim. Once all the screws are removed, the plastic body will split in two.

Snip the red and black wire leading to the motor. We will be extending the wires in a future step.

I played around with different ideas in mounting the horn and compressor to the drill body. I was originally going to use both horns, but found that it ended up being cleaner to use one of them.

I decided the best look would be to use the shorter horn inside the body of the drill and then mounting the compressor to the top of the drill. In order to do this, I had to modify the drill body for both the compressor and horn.

Clearance For Horn

I connected both halves of the body to together and then used a 1/2" drill bit to make a hole in the back of the drill body. I then used a file to clearance the hole until the back of the horn fit.

Clearance For Compressor

The Compressor will be mounted to the top of the drill body. It has a mounting lug that almost fits into a cavity on top of the drill. I started filing this opening in order to fit the compressor lug, but found that it was taking some time. I decided it was better to remove quite a bit of material from the compressor lug using a flap wheel on an angle grinder. Clearance both parts until the drill halves close easily.

Holes For Hose Clamps

The hose clamps will hold the compressor to the top of the drill. We can use the direction selector switch opening as one of the mounting points. It will not need modification. The second hose clamp mounting location will need clearance. I decided to use the bottom vent hole for the original motor as the mounting location since it avoids the horn inside the drill body. Use a file to clearance the bottom vent hole until the clamp can fit through the hole.

Before assembling the project together, you will need to extend the wires that were connected to the motor. Use a soldering iron and some wire to extend them. Then cover the connections using heat shrink tubing so that they are protected from shorts.

The Female Quick Connectors will be added to the end of these wires once assembled so that you can connect them to the compressor.

Start assembling the air horn.

• Start by placing the battery terminals, LED, and trigger into one of the halves.
• Fish the wires you extended through one of the vent holes.
• Thread the hose clamps through the selector switch opening and the vent hole you clearanced.
• Place the selector switch in a position where you can pull the trigger. You will need to figure out if it is in the correct direction later.
• Place the Horn into the body half and then add the other body half.
• Screw the body halves back together
• Attach the Compressor to the top using the hose clamps.
• Attach the terminals to the end of the wires and connect them to the compressor. Red to Positive, Black to Negative.
• Connect the tubing that came with the horns from the compressor to the horn.

Troubleshooting

• No Sound Compressor Running
• Check if there's an air leak from compressor to horn
• Check if the compressor is actually blowing air. If the connections are reversed, it will create a vacuum instead. Flip the selector switch using a screwdriver to reverse the polarity.
• Check horn if it is blown.
• Compressor Not Running
• Check if 12v is reaching the connectors. If there is 12v, then you can slightly loosen the bolts that hold the compressor together since there is an issue with the windings binding in the housing.
• If no 12v, then check if battery is connected and soldered connections.

Use

Try to use this air horn in short blasts because the wiring can get hot with prolong use due to the amperage being drawn by the compressor. If you wanted to do more wiring, you could add a relay to protect the wiring to the switch.