ebay led light strips

I recently bought four of these led strip light to use as a tail/ brake light on my 06 gsxr 1000. The seller says that resistors are not needed for typical hookup(accent lighting). Beings that I need them to be dual purpose I know that I need to use resistors to dull them from full power when the brake is not applied. I just do not know how to figure out what size resistors I need or how many. I also am not quite sure on how to wire them up. I guess Im in a little over my head but its to late to turn back. Any help is appreciated, thanks.     

     

     

Emitting Color       Red
Operating Voltage       12v DC
Operating Current       160mA
Power       2w
Viewing Angle       35°-40°
Wave Length       630nm
Light Source       24 LEDs
Strip Length       9.5" (24cm)
LED Spacing       0.4" (1cm)
Wire Length       52" (131cm)
Strip Material         Soft PVC
Dimensions       9.5" x 0.25" x 0.5" (24cm x 0.6cm x 1.2cm)

If replacing the original bulbs etc - be careful! (Regulatory as well as practicals like too intense or sun-washout.)

You may have to experiment - LED illumination verses current is a tricky thing...


Treating them as a black box....
12V @ 160mA = 12 x .16 = 1.92W (~2W as claimed).

From V=IR, its effective resistance R = V/I = 12/.16 = 75 Ohms.   

Shall we assume 1/5th the current for tail lights?
Hence add 4x the resistance = 4 x 75 = 300 Ohms; hence a 270 or 330 Ohm resistor.
Resistor wattage? Assume 12V across the resistor, P = 12 x 12 /270 = 0.533 Watts. So a 1/2W resistor should be fine.
(It won't see 12V unless there is a short circuit, but it was just a sample "worst case" calc and 1/2Watt resistors are a common size.)

So try a 270 or 330 Ohm 1/2 Watt resistor.


Not that LEDs are resistive loads, but max current through the resistor alone is (say) 12V/270R = 44mA which is 1/4 of the original 160mA.

You might find that that is too high (because the LEDs turn off), or it's not enough (because even a few mA through a 20mA LED can still be quite bright.

Strictly speaking, it's not the proper way to do it. Normally I'd expect stop LEDs to be additional to tail LEDs.
But those LEDs will be wired in parallel strings, and if one string fails (goes open circuit), that means the other "tail" LEDs will be brighter.

I assume the LEDs are modern hi intensity which are ~3.4V (not the older 1.7V).

So is the 24 LED 12V@160A array 8 strings of 3 series-connected 20mA LEDs (hence 8 x 20mA = 160mA), or 6 strings of 4 series 26.7mA LEDs (hence 6 x 26.7 = 160mA), etc?
I suspect the former 8 strings of (3x) 20mA LEDs...
So if one string fails (open circuit), the rest will have nearly 15% more current....
Ideally the resistor would be in each string, but that makes bypassing the resistor more complicated.


The LEDs would be wired so that the resistor is in series with the string for the tail lights. (ie: tail +12V to resistor plus LEDs)

When stopping, the resistor is bypassed - ie, stop +12V to the LEDs.
This could be done with direct wiring depending on what other park/meter lights are used etc (the stop +12V will feed through the resistor to power the other "tail" lamps and vice-versa - this may have little impact on other bulbs, but then I'd chose the 330 Ohm resistor, else up the 270 Ohm resistor to a 1 Watt rating - assume a voltage of about 15V for such power calculations).

But start with a dimness test to see what resistor is suitable. For both day and night.