Make an electronic warning triangle

Sam Coles explains how to make a flashing warning triangle to help you stay safer in the event of a breakdown

Mandatory items when you are travelling in mainland Europe include hi-vis jackets and a red triangle which, in a breakdown, must be deployed at a distance from the rear of your caravan to warn oncoming traffic that there is a stationary vehicle ahead.

Most of the commercially available triangles are of the folding variety, which come packed inside plastic sleeving for storage. But in the main, they are small and can easily be missed when deployed.

This project covers the construction of a 450mm-high triangle that has a large reflective red and yellow surface area and alternately flashing red LED triangles (one inside the other), which draw attention to it, especially at night.

We would advise using this to supplement your original triangle, rather than replacing it.

The two LED triangles are driven by an electronic car flasher unit, which in turn powers the operating coil of a changeover relay, also commonly used in cars. Although heftier than needed, both have been chosen because they are cheap and readily available.

The power source is eight alkaline D cells in series (the battery holders will need to be connected accordingly), giving 12V. These D cells have a long storage life and the warning triangle will, it is to be hoped, spend long periods not being used. Should the need arise, they have plenty of capacity to run for extended periods.

The batteries should be replaced if the triangle is used for any length of time.

Most batteries are sealed and won’t leak if discharged, but finding the batteries are flat in an emergency is best avoided.

The skills needed for this project are an ability to solder and some basic carpentry.

Parts

Sheet of 3.6mm plywood (1220 x 600mm) Enough 12mm plywood for triangle sides and stand swivel (I used some scrap wood) One 5A rocker switch

5m of red LED strip, which must be IP65 grade with self-adhesive backing. Only cut this at a point showing a pair of shears 2m of 50mm-wide red self-adhesive reflective tape

0.5m of 100mm-wide yellow self-adhesive reflective tape

Four rubber feet

One M5 30mm bolt, one M5 self-locking nut and three M5 ‘ Penny’ washers

One 40A 12V changeover relay

One electronic indicator ‘Flasher’ unit (bimetallic types will not work) Connector strip (12-way,

5A ‘chocolate block’ variety)

Two D cell four-way battery holders

Eight alkaline D cells

Wire, crimp connectors, heat-shrink sleeving, wood glue, small wood screws

Tenon saw Soldering iron Protractor or angle gauge Crimp tool Drills

Heat-shrink gun

Time taken: around three hours

1 Use a protractor or gauge to mark up 60-degree sides of triangles on the 3.6mm plywood 2 The marked-up plywood. Each side of the triangles should be 50cm long. Now cut out the triangles using a tenon saw 3 Cut three lengths of 12mm ply, each 4.5cm wide. Cut an angle at each end 4 Mark a line 12mm in on one of the triangles and then apply a thin strip of wood glue all round, within the line 5 Stick the three strips of 12mm plywood onto the wood glue as shown (use panel pins to hold them while glue hardens) 6 Cut two pieces of 3.6mm plywood and stick one on top of the other in the triangle body. Paint outer surface of triangle 7 Cut three strips of red reflective tape and stick to the three sides of the triangle 8 Cut some yellow reflective tape for the centre. Cut three lengths of LED strip for the sides of the yellow triangle, and another three for the red triangle 9 Remove plastic from the ends of the LED strips with a sharp knife 10 Solder wires onto the LED copper pads, observing polarity. Place heat-shrink to protect the soldered joints 11 Drill holes at the triangle corners for LED wires, then remove protective backing and stick down the six strips 12 This is the inside of the triangle, showing LED wires ready to connect. Note swivel stand arrangements 13 Inside completed warning triangle. Flasher unit and relay are attached to the plywood using double-sided sticky pads 14, 15 Inner and outer triangles lit