Decoder powered LED strip

[AdeRail]

Hi again, back again with another question.

 

Inspired by my recent fitting of a sound decoder and lights to my class 57, I am now moving on to kitting out my Hornby Class 156 DMU.

 

 

I am adding a Howes ESU sound chip to this one, and I have also got an express models front and tail light kit to fit.

 

 

I am also going to fit a cab light, and while I’m at it I thought I would fit coach lighting so I can see inside.

Now, I have a roll of led lighting on a strip with sticky backing that I’ve seen people use for coaches, the kind where you can cut it at 3 led intervals and use the offcuts too.

What I want to know is, can I power this strip from the decoder?

As it’s a DMU and only two units long i don’t want to power it from pickups, I’d much rather switch it on and off as and when I want, but would a decoder be powerful enough to power two car lengths of leds?

 

 

The ESU decoder has four aux Outputs I think so I could power each car from a different Output, hmmmmm

 

Any thoughts as I can’t find anything searching on this forum?

 

thanks

Ade

 

[96RAF]

In principle yes but...

You need to make sure what is hanging on each function output is drawing xurrent within the limits for that output.

Some ESU sound chip outputs are logic level not full current outputs so choose the correct one(s) for your lights..

Rob

[Chrissaf]

The multiple blocks of three LED sticky strips are designed for 12 volt operation and have integral built in resistors (so you don't need to fit any additional ones). Although designed for 12 volts they will operate down to about 9 volts (see why below). They are designed for low current consumption, but to be 'belt n braces', cut your strips into the lengths you want to install and measure the current drawn on a 12 volt supply. I would be very surprised indeed if the measured current came anywhere close to the 100mA max of a typical decoder output.

.

The reason for the strip cut lines being in blocks of three, is because the LEDs are configured such that each block of three are wired in parallel across the 12 volt supply, but the three individual LEDs in each block are wired in series. A white LED has a forward bias voltage of between 2.7v and 3.2v, thus three in series need a minimum of about 9 volts give or take a bit to light up (can be as low as 7.5 volts but dimmed at this voltage).

.

Note that this minimum voltage requirement does not make them 100% compatible with being fitted in a DC Analogue powered carriage as the track voltage can potentially dip below 9 volts. This is not quite so much of an issue for DC Analogue controllers that have a PWM output, as a Pulse Width Modulated output is created from pulses of 12 volts with different 'mark / space' ratios. LEDs being semi-conductors are fast enough to react to these very short pulses of voltage.

[Britannia Builder]

I fitted these LED strips to my 3-car Hornby class 101 DMU and they work very nicely. I wired them to the blue and green wires of the decoder (non-sound) and added an extra resistor to reduce the brightness. The resistor was probably 1K or 2K ohms from memory and so the maximum possible current at 12 volts is only 6 or 12mA. I ran fine flexible (multi-strand) wires between the carriages. It's worth adding a few dabs of PVA glue to secure the LED strips, in addition to the self-adhesive strip which I find can peel away.

 

Regards, John

 

[AdeRail]

Ok thanks everyone, and John you’ve convinced me to give this a try.

 

 

The lighting kit from express models for the front and rear headlights comes with a connector for between the carriages, so you can still seperate them, I would like to put one of these on my carriage lighting between cars, but I don’t know what they are called! Any ideas?

[Chrissaf]

As the light kits you are using are from Express Models, is it likely that they are using their own connector products that can be purchased separately - see below:

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[AdeRail]

Doh.........

Thanks for pointing that link out to me Chris, I can’t believe I missed it!

 

 

I’ve found these on amazon https://www.amazon.co.uk/gp/product/B073YD57LT/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

 

They would work out a lot cheaper if they are suitable.

[Chrissaf]

JST connectors are quite common connectors, the 2 pin variety will be a little larger than the Express Models 2 pin connector, but have the advantage that the JST connectors are keyed and will only connect one way round (preventing polarity reversals).

.

Note: Hornby use a 4 pin JST for the four wire link between the current range of Steam locos with decoder and speaker in the Tender (motor in loco).

[2e0dtoeric]

As you mentioned polarity reversal, if you put LED strips into a dc loco, they will only work going in one direction, but not the other, as LED's, as you well know, are polarity conscious! You would need to incorporate a bridge rectifier, as well.

[Chrissaf]

Ade wants to use a DCC decoder output from the loco end. He specifically said he didn't want the hassle of adding coach pickups and use track power. Therefore the bridge won't be needed.

[2e0dtoeric]

Agreed - but YOU wrote -

Note that this minimum voltage requirement does not make them 100% compatible with being fitted in a DC Analogue powered carriage as the track voltage can potentially dip below 9 volts. This is not quite so much of an issue for DC Analogue controllers that have a PWM output, as a Pulse Width Modulated output is created from pulses of 12 volts with different 'mark / space' ratios. LEDs being semi-conductors are fast enough to react to these very short pulses of voltage.

Which is what I was responding to!  😛