LED Lights in Loco

[Claire1707821735]

Hello,

I'm trying to wire up 2 flickering LEDs to work forwards and in reverse so that it will look like fire in the firebox. I thought I had it worked out, using led drivers, diodes and a capacitor, but one of the lights seems to blow each time.

I'm assuming it's to do with the motor and back EMFs, but how can I stop this happening; does anyone have a wiring diagram that they can point me towards, as I'm getting through LEDs trying various things!

Thanks all!

[Chrissaf]

Draw a schematic of the circuit you have tried that blows the LED and post it as an image. Then more targeted advice can be given as to where you might be going wrong.

You need to use a 'bridge rectifier' on a DC Analogue loco to run LEDs.

The motor back EMF will nearly always affect LEDs on a DC Analogue loco when using an unsophisticated circuit. Special control boards for LEDs are typically seen in factory equipped models that have LEDs. You just need the circuit to include a bridge rectifier to handle the voltage polarity reversals of going backwards and forwards. Using a bridge means that you then only need one LED not two.

[ColinB]

It could be the inductive load of motor putting nasty high voltage spikes across the LED. What value resistor are you using? I agree with Chrissaf a bridge rectifier is a better idea, which means you only need one led, you can then also put a 10uf capacitor across the resistor led chain which will smooth the voltage.

[Buz]

Hi Clarie

I don't see any resistors in your parts list.

A LED works on about 1.5 V your loco works on 12v this could well be why it blows all the time.

Check with the driver instructions to see if any resistors need to be supplied by you.

However that said Crissaf is our resident expert in these matters.

regards John

[Claire1707821735]

Let me draw up a diagram with where I am currently at. I've tried with various things adding a resistor before seemed to completely stop any lights! I'll try and do that this evening!

[Chrissaf]

Just be aware that images are held for approval by a moderator. Most images are now getting approved within a 30 minute time frame, subject to time of day posted.

[Chrissaf]

Since your promised circuit schematic hasn't yet materialised. I shall try a different tack. Rather than debug your existing circuit(s). I have offered a couple of suggestions for new circuits below. The second one includes a voltage regulator. This will help to stabilise the LED brightness as the speed goes from sedate to racing. The capacitors should not be left off the circuit as they stabilise the voltage regulator operation. Right click and save image, then you can open it in an image viewer of your choice and see it in a larger size.

The component parts for the above circuits can be purchased from Rapid online component mail order. Note that the resistors are in packs of 100 and there are some 'minimum 5' order numbers to be taken account of for the other components. But even then, the total component cost is still relatively low.

Component links from Rapid On-line [all links below are clickable]

ST LM317LZ Adj Voltage Regulator 100mA TO92

DC Components W005M 1.5A 50V Bridge Rectifier

TS1900 1uf 35V 5.08mm Tantalum Bead Capacitor

TS170R 0.1uF 20% 50V Y5V P:2.54mm Radial Ceramic Capacitor

TruOhm CR-012 1K 0.125W Cf Resistor - Pack of 100

TruOhm CR-012 220R 0.125W Cf Resistor - Pack of 100

TruOhm CR-012 330R 0.125W Cf Resistor - Pack of 100

TruOhm CR-012 100R 0.125W Cf Resistor - Pack of 100

[Claire1707821735]

Apologies for not replying sooner I used the schematic here - if you scroll to the bottom.

http://trainelectronics.com/LED_Articles_2007/LED_104/index.htm

Moderator edit to make link clickable LEDs_104 - Constant Brightness Circuits

I got these drivers from CPC https://uk.farnell.com/microchip/cl2n3-g/led-driver-temperature-compensated/dp/2448491 and used the orange LEDs below. (3mm).

These are the diodes:

Thanks @Chrissaf - I'll take a look at your schematic as well :)

[Chrissaf]

I've looked at the circuit diagram using your CL2N3 current limiting semi-conductors. In theory it should have worked. Since yours didn't, I can only assume you made an error wiring it up. All the key components are polarity sensitive and all have to be wired the correct way round. Another possibility is the DC Analogue controller you are using. Not all DC controllers output DC. Some output voltage spikes in a saw tooth waveform up to 20 volts plus. What controller brand / model are you using?

Adding resistors to your circuit will not work at all. Any resistance you try to add will be countered by the constant current aspect of the CL2N3 operation.

I would also suggest, that rather than using a standard orange LED, that you get a 'flickering' orange LED - see link below. The flickering will give a more realistic display for a firebox.

3mm | Bright Components

My second schematic with the voltage regulator has previously been built by me and it works.

PS - You posted your image post above FIVE times. Four of the duplicates have now been removed. I have also reduced the size of the second image as the original image over-powered the post.

[Claire1707821735]

Apologies - my phone was being weird - I think it may have just hung up on the posting and I clicked it again. Noted for future reference though - thanks for sorting it out for me!

Just to add - the LEDs are a flickering type - and I definitely checked the direction, as it works ok without the loco in the mix.

The type of loco wouldn't make a difference would it? I'm using a 1970s princess motor /chassis.

It works fine when you test my schematic without the engine on the circuit, but when you add it one of the lights dims, stops flickering and then slowly blows after reversing the direction a few times - presumably when it spikes?

Moderator note - please don't use the blue button to reply. Just write your reply in the 'reply Text Box' at the bottom of the page.

[Chrissaf]

Subject to the motor type and its condition in your loco it may have weak magnets and/or producing very high back EMFs. The author of your circuit states it worked for him in a high current loco configuration. Without using a scope to see what exactly is going on it is not practicable for me to theorise on the cause of your issue. The bridge rectifier in my suggested circuit should be better able to handle back EMFs produced by the motor windings. The voltage regulator in my second circuit works on managing the voltage rather than the current, thus in theory any large back EMF voltages should be shunted by the regulator.

Another minor point, your CL2N3 is fixed at 20mA. Although this is within the spec of LEDs, LED's will perform just as well at 10mA and last longer as a result. My second circuit as drawn, is designed on a current of 10mA.

[Claire1707821735]

Sorry forgot to add - the controller is an old one from a set I had in the 90s! I got it out to test the loco etc, as I was using a chassis I got off eBay to adapt it to a Battle of Britain class.

It's a basic Hornby r.921

I'll give your suggestions a go first - thanks for your help!

[Chrissaf]

Is this your R921 controller?

The style of this controller is almost identical to the slightly later R965. The China made R965 uses a SCR [silicon Controlled Rectifier] output stage. Thus the output is not proper DC. Now if your earlier R921 controller uses similar technology to the Chinese R965, then this could feasibly be the cause of your issue in the way the non DC controller output interacts with your 1970's designed loco motor.

R965 Controller for comparison.

[Claire1707821735]

Hi - yes it's that one I think- see attached photo. Hopefully it isn't too big!

I wouldn't normally use that controller as it lives in the box with my old night mail express set, but it's one that was to hand.

Do you think that your circuit diagram would handle any problems with this controller? Just trying to cover all bases!

[Chrissaf]

Without looking at your controller output on a scope I wouldn't like to say. I suggest that a more modern capable controller would be the better all round solution, not just for your LEDs, but your locos as well.