Capacitor and rectifier question on lighting

[grenadier1943]

Did a search about this but still confused.  I have wired up a couple of cabooses with lights.  Not LED lights but regular bulbs from some old Athearn BB locos.  My problem is that the light flickers when running on the track.  My understanding is that a capacitor will eliminate the flicker.  Would I run a wire from the left track to the bulb and then a wire from the right track to a capacitor and then from the capacitor to the bulb? If this is the case what size capacitor would I need?  Do I also need a rectifier?  BTW im using DCC.  Please keep the answer simple.  I served 25 years in the Army as a grunt so I need a KISS (Keep It Simple Stupid) answer. LOL.  Thanks in advance.

Mike Kingsbury

Chessie WM

[gregc]

a capcitor can help.  It would be wired in parallel with the bulb.   But since track polarity changes, you need a non-polaized capacitor, the larger the better.

most larger size capacitors are polarized.   They will pop if wired with the wrong polarity

[gmpullman]

Hi, Mike

A lot of your answers may be found here...

http://cs.trains.com/mrr/f/744/t/221225.aspx

 {{SORRY, yesterday I could make links clickable—TODAY, no dice}}

Scroll down to Geared Steam's post and click on that link for some useful info on "flicker free lighting" for a start.

Hope this helps, Ed

[fwright]

You do not want to put a capacitor - especially a large one - directly across DCC-powered rails.  It will act as a short circuit to the higher frequency components of the DCC signal.  At the very least, the DCC signal will be distorted, perhaps enough to cause operational problems.  At worst, your DCC booster will see the capacitor as a short circuit, and shut down the unit.

The simplest way to address the issue is to use a function-only DCC decoder.  Many decoders have the capability to add a "keep-alive" capacitor downstream of the diode bridge - you would want this capability.

Another simple solution is to install a battery and magnetic reed switch to power the lights, with a battery charging circuit optional.

In the case of both the battery or capacitor, changing from bulbs to LEDs will significantly lengthen the time by which the lights can be powered by battery or capacitor.

my thoughts, your choices

Fred W

[gregc]

sorry, Fred is right.  Didn't read that you were DCC.

but then why not use a bridge rectifier and put the bulb and cap in parallel across the rectified output.

[MisterBeasley]

gregc

...but then why not use a bridge rectifier and put the bulb and cap in parallel across the rectified output.

Yes, that's the answer.  Most likely, the big capacitors that you find will be electrolytic, so they have a + and - on them.  The rectifier, too, will have positive and negative, so it's important to connect them correctly.  LEDs are also polarized, but standard incandescent bulbs and resistors are not.  Since you're using DCC, it does not matter which rail connects to which input of the rectifier.

[Texas Zepher]

grenadier1943

Not LED lights but regular bulbs from some old Athearn BB locos.

Those bulbs pull a lot of power.  A large capacitor will be needed to keep them from flickering. I mean any amount will help reduce the flicker but a good solid "on" condition will be a large capacitor.  I have not priced capacitors recently but it might be cheaper to buy lower current lamps and smaller capacitors than the large cappys. 

[grenadier1943]

Guys thanks for the input.  I was hoping to do an easy cheap fix.  I did find some videos on YouTube so I will watch and see what can be done.

Have a Merry Christmas