Keep alive for constant LED lighting?

[randgust]

OK, I think I know what I'm doing but I've just been proven I don't.

I did the standard LED constant lighting with an electrolytic capacitor and it was a total fail.  That's with a bridge rectifier, the capacitor across the output, and supplying an LED with the stock recommended LED resistor.

Lights fine.   Still flickers.  No improvement.  Further research proved that the electrolytic capacitor I'm using was probably way undersized, I'm trying to fit it in an N passenger car, and what fits is only 10MF.   I'm seeing a minimum recommendation of 470MF, which is about an oversize load size on an N flatcar......

So, I'm looking at keep alives, which I 'think' would do the same thing as the capacitor, right?  Just using an ultracap instead of electrolytic.   There's several out there, this is the littlest one. https://www.tcsdcc.com/product-page/ka-n1
Would you wire these into the bridge rectifier just like the other capacitor?  It is too small?   Just trying to kill the flicker.

TCS website says "If you would like to attach a Keep Alive® unit to a non-TCS decoder, you need to connect the wires across the output of the bridge rectifier on the decoder. You will need to consult your decoder manufacturer for a schematic or wiring diagram."    I'm not doing a decoder, I'm doing a DC lighting circuit, and I think it should be the same thing, but as of this moment I'm questioning what I think I know.

[peteski]

Randy, addressing the elephant  in the room first, if the wheels and track are clean, the LEDs will be nice and steady - no flicker with no additional caps.

I'm assuming that the cars have all-wheel pickups (like Kato passenger cars).  I routinely run those passenger trains on friends layout with no flicker.  but the wheels need to be cleaned regularly (just like you do it on locomotives).

When we run the NTRAK layout at the shows, many club members complain about flickering passenger car lights, because they don't clean the wheels. I take one of their cars and clean the wheels for them and guess what?  No more flicker!

As for the size of caps, what was the voltage rating on that humongous 470µF capacitor?  You only need caps rated 20 or 25V, and those are fairly compact.  Also capacitors produced in the past were physically larger then the currently available caps.  Maybe you had one of those larger caps.  Also, the surface-mount (SMD) tantalum caps are much more compact than equivalent aluminum electrolytic caps.

If you still prefer adding keep-alive circuit, how about using one of those "power keepers" others use with their decoders? They use a pair of tantalum caps rated 900µF and are nice and small.  Basically similar to TCS KA-N1 circuit, but probably less expensive.  All those consist is a couple of caps, a diode or two, and a resistor.

And yes, you can utilize that type of a keep-alive the same as you would a discrete cap. Add them at the output of the bridge rectifier.

[randgust]

This is on my drumhead lighting for a Kato passenger car.   I'm getting tired of constantly cleaning wheels when there's no other pickup issues.   I'd put Rapido lighting easy-peasy strips in because the original kato lighting pickups were too much wheel maintenance.
The capacitors I got were 100V.
If those 'power keepers' are similar and cheaper and just go across the rectifier, great, but you'll find a lot of irrelevant stuff searching for 'power keeper' so what is it called?

I was even looking for small ultracaps and that was a dead end.

I've had Richmond Controls boards for my headlights and caboose lighting forever, this just didn't seem that complicated.  I know it doesn't have to be big because my caboose lights will stay on for about 5 minutes after they charge up.   There's some kind of magic capacitor in there.

[peteski]

LOL! If that 470µF cap was rated  for 100V no wonder it was HUGE!   If you had one rated for 20V, it would have been much, much smaller.

I seem to recall that Richmond uses  Super Caps which have very low voltage rating (usually 2.7V), and enormous capacitance (in hundreds of thousands of µF).  But that circuit (while small) it is much more complex than just some diodes and resistors).

The power keeper module has been mentioned recently in this section of the forum. It is from Iowa Scale Engieering.
https://www.iascaled.com/store/ModelRailroad/Run-N-Smooth/CKT-DCCSA
Someone else mentioned that TCS KA-N1 is slightly smaller physically.

[randgust]

Well, thanks!  I'll try one of those.

[GGNInNScale]

Take a look at Tayda Electronics for SuperCaps.  They are mostly 2.7 or 3V, but you can stack them (total capacitance is reduced by separation of charge, of course), but does not really matter for your application.

[randgust]

Hey Peteski, the Iowa Scale Engineering power keeper worked GREAT.   Tiny, does the job, completely satisfied.

Getting me to say that is like spotting a Sasquatch riding on a Unicorn....

[peteski]

LOL Randy, I'm glad that it exceeded your expectations, and it wasn't  anywhere as large as that 470µF 100V capacitor!