Ringfield upgrade to CD motor fitting LED lights

[Frankie2]

Hi guys, I've swapped my ringfield motor for a 12v CD motor. I've now fitted LED headlights from Black Cat but there seems to be feedback from as when I turn power on just enough to for the lights to come on they work, white/ forwrd, Red/ reverse but when I turn the power up to get the train moving ( HST 125 ) the lights come on, forward lights on but also red lights flickering, in reverse Red lights on but white flickering. Had anybody else had these issues. Regards Paul

[508006]

Hi Frankie2

I'm not much of an expert on electronics especially for lights but it sounds like there could also be a connection for the red lights which could be touching a connection for the white lights.

I'm not sure if you've seen them but I think there are videos on youtube which show how to fit lights for the HST, in fact if you checkout chadwick model railways channel there should be a couple of videos there where charlie upgrades the HST.

In the first he upgraded the drive and in the 2nd he fits the lights, he tells you everything you need in terms of the components he uses and gives a fully detailed description of the process.

I must ask if you are working in dc or dcc because the 2nd video of the upgrade is done based on a dcc layout.

Hope this helps

[96RAF]

It is all to do with the forward voltage and current draw required for each colour LED compounded by the load the motor applies at start.

With DCC its no problem as full voltage is always there, but with DC it depends upon the smoothness and quality of output by your controller.

That is also why decoders do not run well on DC circuits.

From memory you have to make current path breaks in the Black Kat modules to achieve the configuration you want.

[P-Henny]

As someone with some experience of designing electronic circuits. I believe my explanation more accurately diagnoses the cause of your issue observations.

The clue in your post that makes my diagnosis more likely to be correct is because the flicker does not appear until after the motor starts to spin generating 'back EMF'.

This reply assumes that the 'Black Cat' modules do not include specific anti EMF-flicker circuitry as part of their installation.

A fairly common issue when using DIY lighting that connects directly to the pickups that also power the motor. The motor generates 'back EMF'. This creates a reverse voltage potential that forward biases the LEDs that you don't want to illuminate in each direction of travel. Hence the white & red LED dim flicker you describe, whilst the correct direction white & red LEDs illuminate correctly.

Not an issue when the DIY lights are fed from the function outputs of a DCC Decoder.

There is no easy fix for this with DC Analogue locos as factory fitted LED Lighting on DC Analogue locos typically have a circuit board that provides additional circuitry to resolve the issue.

Significantly increasing the value of the LED current protection resistors can help reduce (but not completely eliminate) this unwanted effect. But increasing the resistor values too far can result with some dimming of LED brightness.

[Frankie2]

Thanks for the replies guys, most helpful and appreciated. P- Henny has got the diagnosis spot on and I was considering using a resistor. The wiring is correct on the circuit board but as stated the lights are wired to the pickups and the motor. I'll test the lights by swapping back to a ringfield motor to check if I still get EMF.

Regards Frankie2

[Frankie2]

P.S. it is a DC layout.

[96RAF]

Presumably you used these instructions to install your module . . .

https://blackcattechnologyblog.files.wordpress.com/2017/10/hst-lights-instructions-single-page-v5.pdf

. . . and took note of the general DC installation notes, but more importantly noticed your exact fault is spoken to in the last paragraph. . . .

On DC installations you may experience flickering of the LEDs and the 'opposite' colour may flicker also. This is due to dirty wheels, track or pickups, or worn motor brushes causing momentary breaks in the power supply to the motor. I recommend a good clean and service which will reduce this considerably.

Any problems, please email me on sales@blackcattech.co.uk

[What About The Bee]

It should be fairly easy to determine root cause.

Clip power leads directly to the motor leads, cutting out the track, wheels, pickups and etc. Apply power as before, forward & reverse.

If the root cause is dirty wheels & etc, then the opposite to direction flicker will no longer be present, as that has been removed by experimental setup.

If the root cause is back EMF, then the opposite to direction flicker will remain.

Bee

[Frankie2]

96RAF, yes I did follow the black cat instructions, still had the problem.

Currently doing track cleaning + wheel cleaning suggested by the bee. Putting power directly to power leads on the CD motor and the lights work as they should.

Cheers guys for the info...

[Simmo009]

I have done this conversion. Well worth the effort. I have included DCC chips in mine, and all is well. However, I have a power car at each end, and one reversed relative to the other. So, on DC, it goes nowhere. On DCC, it's like something nasty off a shiny shovel. Almost full scale speed in fact, and that's with 8 carriages between the power units.

[P-Henny]

Putting power directly to power leads on the CD motor and the lights work as they should.

 

 

This is because the voltage applied directly to the motor provides a clean unbroken robust voltage that swamps the reverse voltage generated through EMF. The opposite direction LEDs can only light if there is an appropriate voltage polarity across them. Only the motor EMF can generate the correct voltage polarity for the opposite reverse LEDs.

Any breaks in power created by dirty track/wheels and/or poorly adjusted pickups provides the opportunity for the reversed EMF voltage to become the prominent voltage present and therefore generate the observed flicker.

[What About The Bee]

Paul,

That is a wonderful explanation.

The back EMF will only be generated whilst the motor is in motion. When the forward commanded voltage stops, the motor and gears will gradually come to a halt due to friction and motor cogging.

The back EMF voltage will be a function of motor velocity and when that motor velocity drops sufficiently, the voltage generated will be insufficient for the LED to light. Obviously, a stopped motor will generate 0 volts of back EMF.

Hence the alternate direction LED flicks on then off, when the dirt momentarily interrupts the forward voltage

Bravo! Perfect sense!

Go Paul!

Bee

[Smudge617]

I have done exactly the same using Black Cat's lighting unit with my 125, but I don't have that problem at all, so not sure what's causing it with your's.

[Frankie2]

Hi Smudge,

That's interesting but also confusing. I'll have to try and clean everything again ( wheels & track ) and see if that works. Very strange.,