Having 2 PWM controllers in 1 circuit?

[Charles O'Connor]

I currently drive a 2013 Toyota Avalon Limited and I've installed extra ambient lighting in the footwells and in between some dash pieces where the newer models have OEM LEDs. There is a button near the map lights that toggles the Mood Lighting circuit High/Low/Off. I am certain that this button is a PWM controller.

My issue is that the LED tube lighting I have hidden away out of direct view is still too bright when the switch is toggled to Low. I found a nice PWM dial setup online but I don't know if I can add that controller downstream of the stock PWM switch without any drawbacks. Would having 2 PWM controllers on the same.circuit even work?

My DMM can't measure frequency so I cannot find the duty cycle of the stock PWM switch modes.

 

[SparkyChick]

There's nothing stopping you having two modules in series, but I suspect the results may be a little unpredictable. Depending on the design, one may suffer resets due to what could effectively be a very poor quality power supply.

 

[Marvo]

I've never actually tried it but I don't think it will work to have 2x PWM controllers in series and it could cause damage to one or both of them. If the light tube is out of view I'd look at putting a thin paper sleeve over the tube to soften the light. There's also all kinds of weird and wonderful photographic light filter plastic sheets available.

 

[Charles O'Connor]

Thanks for the replies so far! I figured having 2 would be weird - the second one would probably malfunction when it gets an already pulsed input.

The LED strips I use are housed inside rubber-like tube material that softens the light wonderfully, but does nothing to dim it. I suppose some sort of flexible filter film could effectively block out some of the light.

Are there any options I have if I want to solve this problem with electrical hardware? Ideally, I would love to be able to dim the LEDs further during night time driving, but then adjust them back to full brightness afterwards - mainly because the circuit is tied in with the courtesy lights that illuminate when I unlock/open the door. It makes everything easy to see at night when I'm entering and exiting.

 

[Marvo]

The fundamantal problem is that the tube is a higher lumen output than the other LED lights so it would need to be on it's own separate PWM controller to allow it to be set relatively lower which would compensate for its higher brightness. Both PWM controllers would then need to operate in tandem.

The only way I've seen this done is in a commercial set up with two PWM controllers that are addressable and both controlled simultaneously from a common PLC. In your case you'd have to replace the original PWM unit and install a second one as well plus a main controller.

I've never seen a similar set up that's suitable for use in cars although that doesn't mean they don't exist.

 

[Marvo]

Given the complexity and expense of an electrical solution I'd strongly suggest you try the paper or plastic sleeve method to relatively attenuate the light output of the tube and continue to run it on the existing factory fitted PWM dimmer.

 

[Jim_e_Jib]

As Marvo suggested, you could try some neutral density gel:

0.3 ND NEUTRAL DENSITY LIGHTING FILTER GEL THEATRE DJ DISCO 24cm X 24cm PAR 64 | eBay - https://www.ebay.co.uk/itm/0-3-ND-NEUTRAL-DENSITY-LIGHTING-FILTER-GEL-THEATRE-DJ-DISCO-24cm-X-24cm-PAR-64-/160730137619

It comes in various strengths, 0.3 being the weakest - you might need to experiment a bit to see which works best.

 

[static zap]

If not much wattage is concerned , a simple series resistor
(and parallel capacitor at NEW Led end of circuit , will react more to pulses)
a dimer lower setting -- will lose some from bright !

but this type of solution needs designing safely with
possible fire risks considered if LEDs short !
( unless someone knows values I'm too far away to
measure currents present)
--Your PWM box is an Active part
--This is known as a Passive solution ...
They will live together ok so long as no overload is triggered.
(maybe add a Diode to prevent back feeding, in case LED strip had some capacitors _ reason it may be less pwm responsive)