LED number plate bulbs

[superchargedstu]

noticed a few lexus and mercs have led rear numberplate bulbs. i had a quick look on ebay and noticed a couple of places doing them. has anyone else fitted them on here and if so, do they upset the bulb warning lights on the dash??

stu

[Dragrad]

They might well do; due to the lower wattage drain they might show up as a bulb failure. But an addition of an appropriate in-line resistor to counter should prove ok. Maybe an "expert" will be along soon.... :lol:

[T-Cut]

Any LED you fit instead of an ordinary filament bulb will require a load resistor fitted in parallel with it. This will overcome the 'blown bulb' warning that will otherwise be displayed. Every LED requires its own resistor of an appropriate size.
You can get bare resistors and prewired kits from eBay, but they're usually more expensive than the LEDs themselves. It makes replacing all the little bulbs with LEDs a pretty expensive affair. You have to wonder whether it's really worth it?

TC

[lee_86]

i have led sidelights and led number plate bulbs,warning lights comes on and they also pulse but not too noticeable

[T-Cut]

The pulsing of LEDs is due to the blown bulb detection system running continuously in the background. The system checks the integrity of the lighting circuits by sending a pulsed voltage through them. If the circuit is sensed to be open (as in the case of an LED fitment) it will continue to pulse whenever the circuit is switched on. The result is the LED brightness varies many times per second and so twinkles. I'd have expected this to be an MOT fail item, but never heard of anyone finding out.

The incorporation of a load resistor is to stop the sensing pulse and thereby switch off the blown bulb warning.

TC

[mark_bonsai]

What value of resistor would you need?

They're only a few pence from Maplin and a simple job to solder in-line with some heat shrink over them.

[T-Cut]

Originally Posted by mark_bonsai

What value of resistor would you need?

In theory, this varies with the bulb you wish to 'mimic'. The application of Ohm's Law will give you the theoretical resistance to fit. First calculate the current flowing through the bulb at 12 volts as follows:

watts = volts x amps

Then insert the current into Ohm's Law:

volts = amps x ohms

That's how most of the eBay vendors seem to do it anyway, but I doubt it's really necessary.

a simple job to solder in-line with some heat shrink over them.

Putting them 'in-line' won't work. They must go in parallel with the LED or it won't glow properly. Also, remember that LEDs are polarised, so have to be installed the right way round positive/negative-wise.

TC

[mark_bonsai]

Originally Posted by T-Cut

In theory, this varies with the bulb you wish to 'mimic'. The application of Ohm's Law will give you the theoretical resistance to fit. First calculate the current flowing through the bulb at 12 volts as follows:

watts = volts x amps

Then insert the current into Ohm's Law:

volts = amps x ohms

That's how most of the eBay vendors seem to do it anyway, but I doubt it's really necessary.



Putting them 'in-line' won't work. They must go in parallel with the LED or it won't glow properly. Also, remember that LEDs are polarised, so have to be installed the right way round positive/negative-wise.

TC

Thanks for the explanation. Not hard to tell I don't know that much about electrics...

[mach1rob]

http://cgi.ebay.co.uk/Load-Resistor-...3A1|240%3A1318

hth

[black olive]

Ive used these and they are superb.

http://www.ultraleds.co.uk/42mm-leds...te-p-1461.html

and the load resistors are here

http://uk.rs-online.com/web/search/s...duct&R=6150410