sarumlight
Member Since: 07 Nov 2008
Location: Off the Plain
Posts: 1590
  
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Hi Kabous,
The formula is right but it doesn't quite work like that. When it's hot, a light bulb has a pretty constant resistance, so the power is proportional to the voltage. If the voltage is higher than 12V, the current and power drawn by the bulb increase, but as you say, this wouldn't cause the fuse to blow.
However, when the lamp is first switched on, the filament in the bulb is cold, and its resistance is much lower, so a higher current flows. It's only for a very short time until the filament heats up, but I think it's this current that causes the fuse to blow. Increasing the fuse rating makes this less likely to happen.
What you don't want to do is increase the fuse rating beyond the current the wiring (and relays and switches) are designed for. Someone who knows more than me about the D3's electrics should be able to tell you if 20A is safe.
David
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 21st Jul 2009 9:44 am |
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Kabous
Member Since: 11 Jul 2007
Location: Mokopane
Posts: 233
  
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Thanks, I sell fruit and vegetables so my knowledge on electrics aren't the best, thanks for the info. What i did is replace the 15 Amp fuse with a 20 A. I monitored the wires running to the spots for overheating and it didn't get hot, the fuse however felt quite hot on the top. BTW there is a relay fitted to the system. I had the spots on for about 10min with the vehicle stationary and nothing went wrong. The 15 Amp fuse lasted only about 2-3min. Next thing I want to do is get a tongue tester to messure the amps drawn by the spots and I will then report back. Thanks for all the inputs and comments, all is much appreciated.
Cobus Bekker White MY2011 SDV6 HSE
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| 22nd Jul 2009 3:58 pm |
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