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Blinking Lights! What is a Flasher Unit?

flasher popple unit  Many modern-day indicators and hazard flasher units available today can trigger a flashing circuit by pulse switching; old-style flasher units (like the tin can type shown) work differently and contain a bimetallic strip. A bimetallic strip is made up of two different conductive metals riveted, welded or brazed together so that when a current is passed through it (indicator light on), the two metals expand and contract at a different rate. The lower plate that expands the most creates curling or a bend in the strip that breaks the connection and allows a circuit to switch off (indicator light off); these types of strips are reliably timed when the correct current flow through the indicator lights is available. When the expansion bending of the bimetallic strip breaks a circuit, the current passing through the curled metal plate dissipates, causing the metals to contract back into place, and the circuit switches back on. This is displayed by the lamp switching On/Off or blinking; the process is repeated until the switch that instigated the circuit is switched off.

bimetallic strip function
  Often the cause of slow or rapid flashing is the value of the current required to heat up and expand the metals. If you are a standard domestic motorist and your indicator flashing speed becomes erratic or slow, you should get your vehicle checked out by a Professional. Causes can range from bulb failure (visually obvious or connection), cable problems (continuity), earth or ground joints and, in the case of additional trailer lighting, changing the characteristics of the circuit. One of the most common faults occurs when LED light bulbs (requiring less current) are replaced in the flasher circuit.

Typical flasher set-ups can be understood using this format:
4 (lamps) x 21W (bulbs) + 5W (dashboard warning lamp)
2-4 (2 to a maximum of 4 lamps) x 21W (bulbs) + 5W (dashboard warning lamp)
Worth noting: When the load on a bi-metallic strip becomes too great, the strip can distort or disintegrate, and the flasher unit fails. 



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