Using DCC chip for LED(s) in DC loco

[Harry Mantheakis]

Is it possible to use a DCC chip to power/control one or more LEDs in a DC loco with constant brightness when the loco is running?

The objective would be to have constant brightness only whilst the DC loco is moving, and the loco itself is powered using DC via the tracks.

I have used different types of integrated circuits to do this, but they are bulky, especially when you start adding resistors.

Just wondering if I have been missing a trick! I suspect the answer is "no".

[gallopingalice]

The answer is no. I'm pretty sure.
However the 'Minitrains' headlamps are almost constant brightness when using their PWM controller, which supplies 12volt pulses. A diode, resistor and LED, all of which are available as surface mount, would suffice.

[Harry Mantheakis]

Funny you mentioned a PWM controller - I have just ordered one!

[B.Meldon]

Egger-bahn managed to do this in their blue electric loco back in the 1960

[Harry Mantheakis]

Hello Brian.

DCC chips (which I have never used, and have no knowledge of) amaze me because of their ability to control the power supply to LEDs (let alone the motor, of course) with such incredibly small components.

Even a small bridge-rectifier (to enable LEDs to light up when the train is running in either direction) is bigger than a DCC chip. Bridge-rectifiers drop precious voltage too, and you still have to use some kind of (relatively huge) IC component to regulate the power-supply to the LEDs.

Hence my question: I was just wondering if there is some way to take advantage of (hack, in computer-speak) the miniaturised components on a DCC chip, whilst running everything off DC.

[jimowers]

I do get a constant LED light in either direction in a Chris Ward railcar using the Digitrax DZ125 decoder on DC. It also pulls away very smoothly at low speed.
I put all the instructions for installing these decoders in a OO9 News article last year.

[Harry Mantheakis]

Jim, this sounds very promising. Thank you for posting.

How do I get hold of this article?

[jimowers]

Time just seems to fly by! It was actually OO9 News August 2012. If you look in the letters in the next Railway Modeller there may be a smaller mention of fitting a decoder to a Kato 11-103 following on from my Dean Hill articles, failing that the edition after.

[petersmith1942]

I assume Jim achieves this because Digitrax decoders are dual mode, ie they can be run on DC or DCC . A lot of decoder fitted locos have this dual mode facility but some decoders these days do not have this capability so check before you buy. Most,if not all dual mode decoders can be programmed to be DCC only and some claim this improves DCC performance. So many second-hand locos with DCC have DC disabled and will need reprogramming by a buyer wanting to use them DC. I always ensure dual mode is enabled if I sell a DCC fitted loco
Most DCC systems these days do not offer a DC option but Digitrax systems allow one DC loco to run on a DCC layout
Peter Smith

[jimowers]

There are many confusions around DCC. My work has always been based on new chassis, such the Kato ones. Yes, the DZ125 is a dual mode decoder and out of the box you should not need to change anything.
I think mentioning DCC systems may confuse things here if you only want to work directional lights in DC.

[petersmith1942]

Yes I agree Jim, just wanted to avoid possibly misleading someone once dual mode mentioned. It seems though an expensive way to get constant lighting!
Peter Smith

[jimowers]

Being a bear of little brain, if it works then I am happy. Nobody to my knowledge has published anything in OO9 News that has worked as well for me. I also like to have the option of running on DCC if the opportunity arises.

[Harry Mantheakis]

Jim, thank you again for the feedback. I will keep a lookout for the Railway Modeller letters.

And Peter, thank you for highlighting the programming pitfalls.

There are some dots that I need to join-up on this topic, but from what I gather...

(a) A new Digitrax DZ125 decoder may be fitted (without modification) to a loco, and made to run the loco on a DC layout using a DC controller.

(b) I need to ensure 1KO resisters are fitted onto the negative pins of each LED.

Please correct me if I am wrong!

This Digitrax forum posting says that 'pulse power' controllers are NOT compatible with their decoders - something to bear in mind:

http://www.digitrax.com/tsd/KB176/analog-operation-of-digitrax-decoders/

As it happens, I have Kato chassis, waiting to be fitted to a Kerr Stuart kit sitting on my shelf - so this might be my next project :)

[jimowers]

That looks about right.
I can confirm that fitting a DZ125Z to a Kato 11-103 is written in a letter on p1010 of the December 2014 Railway Modeller.
Good luck with your modelling.

[Harry Mantheakis]

Thank you Jim - much obliged!