PTC is just a little reset-able fuse
Originally Posted by wildwilly1
I guess I must be a dumb*** I have no clue what you are talking about doing with all that the ptc rload. do you care to elaborate for me step by step thx
- You can search and find the cheap ones, I think radio shack may have them.
Every PTC has its own specs, when the current is over the designed specs, it will get hot and pop open. The good thing is when the voltage is not there, it's just a fuse = .5 to 3 ohms just like a resistant of a tungsten bulb.
In the circuit I'd drawn, 3 things are connected parallel, the PTC, Rload and the LED bulb.
Here is how a tungsten bulb resistance behaves, cold = 3ohms, hot = 30-60 ohm, so when no voltage applies, PTC sits as .5-3ohms (the sensor detects that and happy), then when the light switch turns on, PTC gets hot 12.5v/3ohms = 4A current over the design current of .1-.2A, and pops open (high resistance), at this time the Rload of 30-35ohm takes over maintain the 250mA to your LED, the sensor is happy and your LEDs are on without over current also.
As soon as the switch is off, the PTC reset and becomes a fuse again (.5-3ohms).
Parallel resistance of all three components is less than the lowest resistance which is the PTC//Rload//LED.
The sensor sees PTC resistance when cold, when it's open (hot), it sees the Rload//LED ~ Rload (30-35ohms) because the LED resistance is about 80 ohms. The reason it doesn't throw a code even if LED is burned out, because it always sees RLoad 30-35ohms.
For 5w parking bulb 2825 I used RLoad = 60 ohms 10W.
For 26w DRL bulb 1156 I used Rload = 35 ohms 50W.
For License plate LEDS, I don't use Rload, just PTC.
"Current and resistance
The actual resistance of the filament is temperature-dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohms when lit, but the cold resistance is much lower (about 9.5 ohms)"
I don't know if it makes sense, but that's how the circuit works.