I want to dim a commercial LED strobe module and can't seem to figure out what wattage the resistor needs to be. Most posts are about single or multiple LEDs with their known forward Voltage etc. like e.g. this post here demonstrates.
My module however is a self contained unit with, as it seems, Voltage regulation and micro controller integrated.
The LED strobe module is an emergency vehicle strobe mini light bar type:
Voltage: 12-24 / 10-30 VDC, 3 x 3 watt LED elements, Average current draw: 500mA@12.8 VDC, Max current draw: 700mA@12.8 VDC, Self-contained 22 flash patterns
I will run it on approx. 13.9V on a motorcycle (both battery and running engine) and found that a 400 to 500 Ohm resistor gives me the desired brightness.
I arrived at 400 to 500Ohm by trial and error using 3W rated resistors, which I believe are overkill for the final circuit.
My test rig is an 18V Li Rechargeable for a power drill, actually giving 19.2V and using the 500ohm the voltage drops to about 9.35V for the light module.
I tried to get the Wattage using this power source thinking it'll be save enough on the lower Voltage on the Moto:
W = 0.7A * (19V-9V) = 7W ?
It's huge for a LED light plus the 3W resistor barely gets warm. I suspected something in the range of about 1 to 2 W hence testing with 3W resistors.
Can somebody shove me into the right direction? What have I missed here?