LED Brake Light

[Tony C]

For those who were interested at the Beds, Bucks & Northants meeting tonight in the LED brake light I've just fitted, I got it from Maplin here

 

52mm Red LED Cluster

P/N BL0307-50-44

 

It needs a resistor in series so that the 14-ish volts from the alternator doesn't blow it up. I can't find the receipt for the resistor, but I expect Chris W could advise on a suitable one.

 

It is quite bright 😬

 

BRG SV 😬 It is only with the heart that one can see rightly; what is essential is invisible to the eye. (Antoine de Saint-Exupery)

[Chris W]

From the Maplin specification, I have extracted the relevant data needed for the calculation of the resistor value.

 

viz:

 

1. absolute max forward current 250mA

 

2. typical forward voltage drop 9.6v

 

If we take the maximum voltage that the battery/alternator will produce as say 14v, and the maximum current to be limited to say 200mA to keep under the absolute rating, then the calculation is as follows:

 

(14-9.6)/0.2 = 22 ohms

 

Power in the resistor = (0.2^2) * 22 = 0.88W (say 1 watt)

 

So we need a resistor of not less than 22 ohms and of at least 1W dissipation.

 

The best fit in the Maplin catalogue is part no. W22R which is a 22 ohm, 3 watt resistor priced at £0.29 each inc VAT. A higher value, within reason, is also OK - it will just mean the cluster is less bright but don't go lower in value or you,ll risk burning out the LEDs. The resistor size is 22x9x10mm

 

Chris

 

2003 1.8K SV 140hp see it here

[Chris W]

PS: forgot to mention the resistor can be fitted in either lead, positive or negative. It makes no difference.

 

Chris

 

2003 1.8K SV 140hp see it here

[Big Brother]

Tony,

 

Do you have any photos on how you fitted it to the car?

 

Steve

Se7en-Up!

Less is more!

Eagles may soar, but weasels don't get sucked into jet engines!

[Bob Ruddock]

Hi

I have been interested in fitting a high level brake light and have considered the motor cycle repeater type with a strip of battery driven LEDs with a sender replacing the normal brake light bulb. It has the advantage of no wiring and is a strip approx 20mm x 180mm.

How is it proposed to fit the cluster mentioned?

 

C7 RSR

The big blue one getting ready for the Grand Carrotland Tour of Scotland.

[Tony C]

Thanks Chris, I knew you could be relied upon for the detailed info. on the resistor.

 

Steve, here is a picture, though the flash didn't do my work any favours - the wiring is stuck to the bottom of the FIA bar diagonal with black silicone and is almost undetectable. The brake light wiring was tapped into at the LH rear light plug and the resistor is inside the bracket. Very simple - even I could do it 😬

 

I made-up the bracket from a strip of ally sheet and the diameter of the cut-outs is 38mm.

 

Hope this helps.

 

BRG SV 😬 It is only with the heart that one can see rightly; what is essential is invisible to the eye. (Antoine de Saint-Exupery)