Adding capacitance to Kato passenger car lighting kits

[carlso]

Thanks Pete for your time and great effort. I now understand how the car I showed was wired.

Carl

[peteski]

Thanks Pete for your time and great effort. I now understand how the car I showed was wired.

Carl

Sure,  I can't guarantee that the circuit you saw was identical to what I presented, but it is likely similar.

[carlso]

That may be true Pete,but now I know how to wire it properly, so I am not afraid of dissecting this job "to learn".

Carl

[peteski]

I'm glad to be of service Carl.  I only did some bench testing of these circuits.  When you guys build and install them in your cars let me know how well they work.   You could even try them with lower value capacitance (like 100 µF) and see if that is sufficient to reduce the flicker.

[milw156]

Pete, how would using a 470 ohm resistor instead of 100 affect this circuit? Increase the time to charge???

[peteski]

Yes, the 100 ohm resistor limits the capacitor's charging current (which lengthens the charging time).  Higher resistance will lengthen the charging time, and since the LED is also constantly draining up some current (as it glows), there will be less voltage available to the LED.  However since white LEDs are very efficient, the reduced brightness might not be apparent. Resistors are cheap - feel free to experiment as it will not cause any damage.

Is there a reason you want to make that change?

[milw156]

It was the lowest ohm resistor I had in 1/4 watt, the only 100 ohm resistors I have are 1/8 watt

[peteski]

It was the lowest ohm resistor I had in 1/4 watt, the only 100 ohm resistors I have are 1/8 watt

If you connect 4 470 ohm in parallel you end up with a 117.5 ohm resistor, but it also takes up a lot more space than a single resistor.  You could also connect  2 pairs of 100 1/8W resistors in series (so each pair is 200 ohms), then connect both pairs together in parallel to become a new 100 ohm resistor rated at 1/2 W. Like magic! 

But then again, using 470 ohm resistor might give you acceptable results.  As I mentioned, try it and see if it works for you.

To be honest, resistors are so inexpensive that I would instead recommend purchasing a kit of resistor on eBay or amazon.  They are usually sold in a range of values (resistance wattage and type of package like leaded or SMD) and for probably less than $20 you can have plenty of resistors. Very handy if you are planning on doing some electronic work on your model trains (like this project).

[milw156]

I had actually thought about 2 100's x 1/4w in
parallel but wasn't sure enough about the math.

[peteski]

I had actually thought about 2 100's x 1/4w in
parallel but wasn't sure enough about the math.

Well, that would have resulted in a 50 ohm resistor. That is why I mentioned that you would need 4 resistors.

[milw156]

yeah, I can never keep straight what is additive, and what isn't. I understand JUST enough not to have killed myself, yet....