Bi Colour LED for Loco

[WIMorrison]

I picked up a nice (but old) second hand OBB diesel for a few quid that had incandescent bulbs fitted that I intended to rreplace with 5mm bi-colour LEDs but I cant make them work.

 

I have connected the blue wire (Lenz Silver Mini+) to the common Anode and the white to one side and yellow to the other through a resistor but they will not work. I have tried removing the resistor but that doesn't work - I am at a loss as if I take a red/green signal and connect it the lights change correctly.

 

What am I doing wrong? 

 

Iain

[Simon G]

Have you tried putting a simple analogue 12V (or less) across the LED lights?  I would test them like this before trying any DCC testing.  I am no expert on LED lights, but if you have removed the resistor, you may have cooked them already.  If you have a decent multimeter, you may be able to test them if it has a diode test facility.

[WIMorrison]

Panic not, the LEDs still work correctly - just not when connected to the decoder

[66C]

I picked up a nice (but old) second hand OBB diesel for a few quid that had incandescent bulbs fitted that I intended to rreplace with 5mm bi-colour LEDs but I cant make them work.

 

I have connected the blue wire (Lenz Silver Mini+) to the common Anode and the white to one side and yellow to the other through a resistor but they will not work. I have tried removing the resistor but that doesn't work - I am at a loss as if I take a red/green signal and connect it the lights change correctly.

 

What am I doing wrong? 

 

Iain

 

Hi Ian

 

Are you using a separate resistor for each of the white and yellow wires?

 

Also - is it a common anode led?  Not all bi-colour leds are common anode.

 

Regards.

[WIMorrison]

It is a common anode and I am placing one resistor in the anode line which I connected to the blue led. When I connect the LED to the track it works correctly showing either white or red, and neither at full brilliance. The resistor is 1k. 

 

I have tried it on another loco that I happened to have the top off and it doesn't work on it either, therefore it would appear to be something rather fundemantal I am doing wrong

[SRman]

I would guess that the problem is the blue wire is for a positive return - you need a common anode LED for it to work but it appears you have a common cathode one.. You could prove this by connecting the white or yellow wire (but not both) to the common rail and the blue wire to one of the outer tags, then trying it with power. Don't forget to retain a resistor in the line.

 

Edited slightly to correct an error in my original wording.

Edited May 5, 2018 by SRman

[WIMorrison]

@SRMan - it would appear you are correct as I have reversed the LEDs as you suggest and it works - however I am now left completely confused.

 

the anode is the +ve terminal and the blue wire is the +ve common return therefore in my book that is what I could connect together, this is also how all the model press describes what is needed (including the Lenz booklet http://www.lenzusa.com/1newsite1/Manuals/silvermini.pdf - page 7, yet you suggest the opposite.

 

The LEDs were purchased as common anode (https://www.ebay.co.uk/itm/Ultra-Bright-LEDs-3mm-5mm-10mm-Bi-Colour-Tri-Colour-UK-Seller/231756471674?ssPageName=STRK%3AMEBIDX%3AIT&var=531066217513&_trksid=p2057872.m2749.l2649 - 5mm red/white) yet they appear to be the wrong way round.

 

There is also the challenge that none of the model railway shops sell common cathode bicolour LEDs, they are all common anode.

 

Thoughts please?

[Phil S]

 

You do not mention the make or gauge of the loco... This doesn't assist.

You do mention it being a mini ... Therefore 6 pin ... Decoder from lens.

Do you have an LED tester? .. A useful little device costing about 5gbp +/- 3gbp ( sometimes excludes the 9vbattery)

With which you can verify these LEDs and help determine what resistor value you may need to get the correct brightness.

Do youhave a multimeter ? These can be bought from 5gbp upwards .. And a simple measurement on the ohms/ resistance range will show whether theLEDs are still okay. On the voltagerange you could check when the forward or reverse lights (enabled by F0/ lights on button) are being switched on.

Some makes of loco . especially pre DCC days. May use a chassis return for the directional lighting .... And so, on any model, it is advisable to check with a Meter before installing anything new.

Edited May 5, 2018 by Phil S

[RAF96]

I have installed 3-legged common anode red/white leds using blue to the centre leg and white and yellow respectively to the outer legs and they work providing you have a resistor in the outer legs. In fact I use a resistor in every leg.

You say you have tried it reversed and it works, that tells me the leds are common cathode, despite the supplier notice. Keeping the resistor in line try it across a simple DC supply (AA battery) to confirm positives and negatives.

The other thing to watch is to have separate resistors at each end as when you cross connect the colours front to back the dominant led will swamp the other and it will appear that you have a wrong circuit. I use a central resistor board with three wires going to each end and the decoder/socket - see picture.

For DCC you normally need common anode, but there are some Hornby models with either logic on their main pcbs. The Bromsgrove Models installations site covers these in detail.

I have a breadboard where I can set up these lighting circuits to prove resistor values, etc then the parts can be soldered into the model knowing the circuit logic is good - see picture (note this diagram only shows resistor in blue wires.

Rob

 

Edit to correct orientation of picture...

 

 

Edited May 6, 2018 by RAFHAAA96

[DY444]

You say you have tried it reversed and it works, that tells me the leds are common cathode, despite the supplier notice. Keeping the resistor in line try it across a simple DC supply (AA battery) to confirm positives and negatives.

 

 

^This.  Beat me to it.  You do not appear to have confirmed the device is common anode.  Until you do that you'll never solve this.

Edited May 5, 2018 by DY444

[66C]

Hi Ian

 

It looks as though you have been supplied with common cathode leds.

For DCC purposes you do need common anode - I used those supplied by Express Models.

The correct wiring is blue wire from the decoder to the common anode - usually the middle connection to the led.  The leds should be accompanied with a note of which connection is which - each should be a different length.

Do not be tempted to use a single resistor in the common lead - this leads (ouch!) to problems when you wire in the lights at the other end of the loco - don't ask how I know that!

I always check the operation of leds before wiring them into a circuit - I have come across single colour leds that have a shorter connection to the anode instead of the usual short connection to the cathode - so always check.

 

Regards.

 

Edit - the other posts above beat me to it!

Edited May 5, 2018 by 66C

[WIMorrison]

All​ wise words from everyone - the mistake I seem to have made (not unreasonably) was to trust the packaging from the supplier (UK) which states that they are common anode.

 

​I will order some more that hopefully will be common anode ...

 

​(watch this space )

[Nigelcliffe]

If buying components from the UK from an electronics supplier (eg. Farnell, RS, Rapid, etc), then they usually come in properly labelled packages with reference to spec sheets. 

 

Three legged two colour 5mm LEDs are about 20p each, though you might have to order five or ten at a time

http://uk.farnell.com/kingbright/l-59egw/led-bi-col-5-mm-red-grn-3-pins/dp/2001770

 

 

- Nigel

[66C]

If buying components from the UK from an electronics supplier (eg. Farnell, RS, Rapid, etc), then they usually come in properly labelled packages with reference to spec sheets. 

 

Three legged two colour 5mm LEDs are about 20p each, though you might have to order five or ten at a time

http://uk.farnell.com/kingbright/l-59egw/led-bi-col-5-mm-red-grn-3-pins/dp/2001770

 

 

- Nigel

 

Caveat emptor!

 

The example quoted is a common cathode led - this is not mentioned on the web page but in the downloadable specification.

 

Common cathode multi-colour leds are relatively cheap but remember that for DCC lighting using the white and yellow wires from the decoder a common anode type is required and these are generally less common and more expensive.

 

Regards.

[newbryford]

 

There is also the challenge that none of the model railway shops sell common cathode bicolour LEDs, they are all common anode.

 

Thoughts please?

 

DCC Concepts do a range of positive common bi-colour LEDS specifically for use with decoders.

 

https://www.dccconcepts.com/product-category/dccconcepts-led-selection/

 

I fitted some nano red/white which are great for combined red/white marker lights on diesels (and electrics)

 

Cheers,

Mick

[WIMorrison]

Ignore this post - I was talking squirrocks

 

Edited May 5, 2018 by WIMorrison

[BoD]

Dagworth once posted details of an arrangement of resistors that worked with a common cathode bicolour. Blowed if I can find it though.

[WIMorrison]

I​ think I could make them work with a bunch of diodes but a reason for using bicolour is the lack of space to put in all the components which therefore prevents m sticking in a pile of diodes in addition to the resistors that are required, I will sort during the week when the correct LEDs arrive  

[WIMorrison]

Supplier has come back and told me that they have now found out that they have a whole inventory of LEDs that are CC when they thought they were CA - they are confused that no-one has reported this to them before!

 

They weren’t questioning that the polarity is wrong, simply confused that in 3 months no-one has ever sent any back - makes me wonder also

[WIMorrison]

Just to close this off I fitted common anode bi-colour LEDs today into the loco (replaced 'grain of wheat' bulbs) and the loco now has white and front a red at rear which change when your charge direction - just what you want on a bi-directional OBB Diesel

 

Just need to do the Bemo v51 now, and possibly some others

 

 

Iain

[Dagworth]

Dagworth once posted details of an arrangement of resistors that worked with a common cathode bicolour. Blowed if I can find it though.

The circuit that I once posted was for inverse wired two-lead bicolour LEDs rather than for common cathode.

 

 

Adding a pair of diodes around the tri-leg LED can convert it to effectively a two leg device. 

 

 

 

Andi

[Salmotrutta]

Supplier has come back and told me that they have now found out that they have a whole inventory of LEDs that are CC when they thought they were CA - they are confused that no-one has reported this to them before!

 

They weren’t questioning that the polarity is wrong, simply confused that in 3 months no-one has ever sent any back - makes me wonder also

That's because they are sitting in a box "waiting for that job that I never get around to". 

[LaScala]

Another tale of polarity confusion and no doubt it's all mine.

 

I recently bought a Dapol GWR O gauge autocoach with light bar and (I presume) two function decoder, likely a rebranded LAIS.

 

All worked well until I decided to add a directional lamp to the driver's end.

 

I duly wired up a DCC Concepts bicolour red/white Nano LED .

 

This also worked well on DC power.  Also easy to fit to the iron below the driver's window and wiring invisible.

 

Excellent.

 

Then I thought why not use the decoder to power the lamps?

 

I was able to identify white, yellow and blue pins, so confidently wired it all up.

 

Place on the track and disaster.  The tell-tale smell of decoder is all you need to know.

 

Turns out that the light bar is the opposite polarity to the Nano lamp LED.

 

I have checked the DCC Concepts manuals and cannot find anything that indicates a polarity, but it seems I'm boxed in, needing either new lamps for the light bar, a second decoder, or opposite polarity NANO's.

 

Of course, I already need a new decoder.

 

Are there any tips for how best to resolve this?

[Nigelcliffe]

1 - exactly how did you wire this ?     As I understand them, DCC-Concepts Nano LEDs come with series resistors.  I assume those were also fitted in series with the LEDs.   As such, they would either "light" or "not light" depending whether the supply from the decoder was the right way round.   The resistors would ensure that the current flow was minimal in any wiring combination.   To cause a decoder failure implies a short circuit, which to my mind, means a mistake in wiring.   
Leaving out the resistors could result in an effective short circuit through the LED, which could be toast for a DCC Decoder.  
Accidentally connecting one side of the decoder directly to pickups could result in toasting a DCC Decoder - lighting circuits may use track for one side of their power *if done correctly*.  

 

2 -  three-wire two colour LEDs come as either common anode or common cathode.    DCC-Concepts website says "common positive", so reasonable to assume that is correct.   

 

 

Resolution  -  needs understanding of the wiring changes being made.