You should receive more response in this Forum.

 

The PWM is there regardless if a head light is connected or not.

The add-on anti-flicker harnesses are a Resistor and a Capacitor wired in parallel with each other, which are wired in parallel to the LED head lamp. When the voltage pulses, are in the OFF voltage cycle, the capacitor will discharge through the resistor and cause the OFF cycle to smooth out.

For more information, look at the basics of how an "RC" circuit functions.
https://en.wikipedia.org/wiki/RC_circuit

 

thanks for the reply.
I understand why a capacitor would help with PWM, but my buddy used a harness that appears to be only a metal encased resistor. And it worked - until the resistor burned out. I suppose there could have been a capacitor in there somewhere, but it sure looked like simply a power resistor.

 

Are you sure it wasn't used for the rear tail lights? The rears don't have a PWM and the reason a resistor is needed for those is because the circuit is determining if the bulb is burned out or not. If it senses an open circuit, then it will go into hyper flash mode. Therefore, a resistor is needed to trick the circuit into thinking the stock bulb isn't burnt out in the rears.

 

Standard lights (Incandescent and halogen) do not use PWM.

The TIPM senses current draw on the lights and the current draw must be within a certain spec. If it isn't then it shuts the light circuit down, but with led there is a current but just not the correct one. The circuit gets shut down and then starts up again, current draw gets checked again, and then shuts down again. This happens over and over again effecting a 'flicker' or "hyper flash".

The resister simply increases the current draw to what it is supposed to be so the TIPM does not mistake it for a burnt out light. In most cases a capacitor is not required.

 

This is incorrect. All Incandescent headlights on our JK's use a PWM. The PWM was implemented to extend the life of the incandescent lamps. It also gives the designers a way to control the brightness of the lamps.

 

Interesting you state that standard light don't use PWM, it's really more like you don't notice it as much because the pulsing of a standard light bulb is largely overcome by the filament not shutting down as fast as a LED does.

I have a video clip I took while facing the windows of a business at night. You can even see the PWM in the standard parking light bulbs on my Jeep, and it's horrible watching the JW Speaker J2 halos flash, but the headlight output of the J2 is smooth because of how it was made - built in anti-flicker.

 

So that's why the OEM incandescent headlights are so crappy.

 

Yes, the H13 isn't a great design to begin with, but feed it the on off signal and the lamp output is reduced due to "average voltage" being lower than the "on voltage".

 

I reversed engineered our JK's PWM when I was changing my headlights to LEDs and was going to post a write-up to clear up any doubt/confussion but never got around to it.

This is what the inside of an Anti flicker harness looks like.

It's a 220 ohm resistor in parallel with a 2200uf cap.

This is what our JK's PWM headlight voltage looks like. Yes, I connected an O'Scope to it and looked at all possible scenarios. It's a 90Hz squarewave pulse with a 86% Duty cycle. The total cycle duration is 11mS with an off time of 2mS. 9mS on, 2mS off. The battery voltage, is 14 volts, and becomes a 12 Volt average voltage due to the PWM. This is when the JK is running. When the JK is not running, it becomes a constant 12V DC voltage. Thus, the result should be that there is less noticeable difference between the brightness of your headlights when the JK is running compared to when not running. If the PWM was removed when running, the brightness difference between running and not running would be much greater.

The 2mS off time is not long enough for your eyes to detect it when it is connected to an incandescent bulb, since there is a filament in the bulbs that needs to cool down after turned off, but it is long enough to be noticed by your eyes when using an LED since LEDs will turn off instantaneously. It's also noticeable with the incandescent when viewing it with a video camera as mentioned previously.

This is what the anti-flicker harness (adding the cap+resistor in parallel to the PWM) does to the PWM voltage. The Cap is discharging through the resistor, during the off cycle where the voltage never drops low enough to turn off the LED head lights.

 

That is great data rednroll, good stuff!