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RazMan



Member Since: 18 Nov 2011
Location: Essexshire
Posts: 336

United Kingdom 2012 Freelander 2 SD4 XS Auto Fuji White
That old LED load resistor question again

I am a big fan of LEDs and I am determined to replace all of my car's filament bulbs to LEDs.

So far I have converted:

Headlamps (still experimenting with these)
Parking lights
Fog lights (Osram DRL / fog)
License plate lights
Internal lights (roof, footwells, boot, glovebox
Puddle lights
Hi-level brake light
Reversing lights

Now when it came to the stop / tail lights I encountered the dreaded canbus flicker on the tail lights (the brake 'filament' is fine) so I thought I would simply add a load resistor as so many websites will tell you. The general standard seems to be 6 Ohms so I connected a 6 ohm 50W resistor between the power and earth of the tail light and .... Voila! ..... everything worked fine. In the process of pondering where I should mount the resistor I had left the lights on for a few minutes and when I touched the load resistor it was so hot my skin sizzled and I got quite a nasty burn!!

Ohms law I states that a 6 Ohm resistor will pull 2 amps from a 12V supply and consume 24 Watts. I am trying to emulate (as far as canbus is concerned) a 5 watt bulb so does this mean I should increase the resistor value to something like 25 ohms to reduce the current and therefore also the heat? I am quite shocked at how much heat was being produced and if there are other people who have blindly connected these resistors to their new LED retrofits, I would not be surprised if someone's pride & joy has a fire! Cheers,
Raz
FL1 TD4 GS Auto 2001 Silver
FL2 TD4 Auto 2007 Black
FL2 XS SD4 Auto 2012 Fuji White

Post #347952 21st Apr 2018 2:42 pm
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dorsetfreelander



Member Since: 20 Jul 2013
Location: Dorset
Posts: 4336

United Kingdom 2014 Freelander 2 SD4 XS Auto Loire Blue

You obviously need to fool the system into thinking that a filament lamp is in place. The question is "what minimum current load is it expecting?" The 5W bulb will present a resistance of V^2/W ohms ie 144/5 or 28.8 ohms. The only way to find out the minimum is experiment with different resistor values (or borrow a variable resistance box) and see for yourself. Don't forget that the LED will be drawing some current too so perhaps 35 ohms will do. 3 x FL1 2 manual + 1 auto
5 x FL2 4 manual + 1 auto
Now Discovery Sport P250 MHEV SE

Post #347967 21st Apr 2018 9:40 pm
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RazMan



Member Since: 18 Nov 2011
Location: Essexshire
Posts: 336

United Kingdom 2012 Freelander 2 SD4 XS Auto Fuji White

Thanks for the excellent response Dorset - I have found some 33 ohm resistors on Fleabay so I will give them a try. Meanwhile I have connected 2 X 6 ohm resistors in series and these appear to run much cooler so I am definitely on the right track. It appears that anything over the LED equivalent of 5W does not upset the canbus because I have not found a need for load resistors anywhere else. Cheers,
Raz
FL1 TD4 GS Auto 2001 Silver
FL2 TD4 Auto 2007 Black
FL2 XS SD4 Auto 2012 Fuji White

Post #347973 22nd Apr 2018 7:49 am
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robbyvrs



Member Since: 14 Oct 2012
Location: Yorkshire
Posts: 430

England 2014 Freelander 2 TD4 Dynamic Manual Fuji White

I'm not sure why if my 14my has canbus it doesn't show a bulb out warning on the display when the 1st headlight bulb blew followed by the 2nd - still not replaced (not arrived in post yet?) so no headlights working and no warnings?

Post #347982 22nd Apr 2018 1:29 pm
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