Hi everyone,

I'm encountering a some troubles with LED passenger car lighting, and can use some expert help.

I am installing a few of the Schonwitz lighting strips: https://modellbau-schoen...beleuchtung-gelb-h0-n-tt

I am putting on a buffer capacitor to avoid flickering. (with 100ohm resistor to limit inrush) I used a 470uF capacitor (25v) and was surprised to find that the light strip almost immediately dims to zero upon a power cut. This is on the test bench. While it doesn't "flicker" - it also doesn't do a good job of keeping the lights on for a second, nevermind two. It just rapidly fades instead of flickers.

After much confusion, I tried out a 2200uF, 35v capacitor - just because I had it on hand as a comparison. Similar results! (maybe a touch slower, but still not what I would expect)

I thought I would turn to the experts: any ideas what might be wrong? I have tried 2x light strips and 2x capacitors of each size, and the same results across all cases.

Or am I overthinking this, and once installed they will be fine? Or maybe the strips draw some massive amount of power? (it says 100mA at the midpoint, which isn't crazy?) Attached are images of the strip with large capacitor for reference.

Thanks in advance!

Dear All -

I am no wizard circuit designer (so this might be wrong), but if I remember my physics correctly, then the capacitance F required to run an average current I for s seconds at voltage V would be:

F = (I * s) / V ,

so for your values and a guess of about 10 V, I'd get

F = (0.1 A * 1 s) / 10 V = 0.01 Farad.

Your capacitor is 0.0022 Farads, so it is a bit small to carry the required charge. Using a lower current LED strip (10 mA perhaps, but dimmer lights) would make your solution work.

Osoraku

That sounds an awful lot of current for a strip of LEDs like that. It must be like the sun shining in the coach with that much current.

Hi

I am using similar Viesman strips (but with the rectifier and pot meter cut off) or the LED strips "on the roll" in my coaches.
I feed them via a separate rectifier, have a 10K resistor in line and a 470 uf , 25V in the DC section.
Light stays on and dims out after 2 ~ 3 seconds.... so 470 uf works!

Try with a higher value resistor and see what that does...

Jean-Pierre

This is indeed correct. (but a good guess) And to eliminate a variable I've tested without diode/resistor and got the same results.

Connect two 470 µF in parallel if one is not enough.