As with all electrical devices in your vehicle the wiring is of utmost importance. Because this is so important with driving lights
, lets calculate the power required to correctly power a pair of 100W driving lights
Power Requirement Calculation
Assume the battery delivers 12V even though a car with the engine running will deliver about 13 -13.8V (dependant on battery condition).
2 x 100W gives us a total power requirement of 200W at 12V
Remember your physics and electronics - P = VI (Power = Volts * Current) or to calculate current I = P/V
The current required to power the globes is 200/12 = 16.66Amps or 8.33Amps per globe.
Add a some losses for the cable, relays and connectors and you will easily need 20Amps
- Lights must be wired using at least 20Amp cable or a high quality wiring kit. Have a look at any cable you buy and note how thick the cable is and whether it is multi strand or single conductor. Always use a multi strand cable in your vehicle wiring.
- You must use a relay when wiring your driving lights. You do not want to be running a 20Amps feed through the firewall. Also you should wire the relay to come on via the use of the vehicle's high beam.
- The relay should be rated at better than the required current i.e. greater than 20 Amps. It is not that uncommon to install a 70Amp relay. The better the relay the less current and voltage drop through it. Remember voltage drop is your worst enemy.
- You should install a fuse on the main feed from the battery before the relay. See diagram below.