Which capacitor for one led?

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dan8400
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Which capacitor for one led?

Postby dan8400 » Thu Dec 29, 2016 12:27 pm

Hi

I am running a single red led (with resistor) in the back of a class 43 hst. It works but sometimes flickers due to poor pick up. I would rather add a capacitor than faff around adding more wheel pickups. It gets power enough of the time for a capacitor to take up the slack

Any ideas anyone?

Thanks
Dan

ETA: I'm using DCC
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Flashbang
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Re: Which capacitor for one led?

Postby Flashbang » Thu Dec 29, 2016 1:17 pm

Think I would trail, by connecting a 100uF or 220uF 16v or 25volt electrolytic capacitor, directly across the LED feed before the LEDs series resistor ensuring correct polarity. Decoders Blue wire is Positive. This should charge to the decoders function output voltage and allow a small charge into the LED to prevent flicker upon power loss.
But really its best to improve pick up contact to stop the flicker in the first place. Keep wheel rims spotlessly clean and rail tops too.
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Re: Which capacitor for one led?

Postby dan8400 » Thu Dec 29, 2016 1:23 pm

Thanks flashbang,

I am running the led directly from the rails into the resistor and led. No decoder in the trailing HST car

Thanks
Dan
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Re: Which capacitor for one led?

Postby dan8400 » Thu Dec 29, 2016 1:24 pm

It is an old style Lima Dummy Powercar. One bogie picks up one rail and vice versa.

Thanks
Dan
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Flashbang
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Re: Which capacitor for one led?

Postby Flashbang » Thu Dec 29, 2016 1:28 pm

Ah that is vastly different
You will need a bridge rectifier and a larger capacitor possibly? 470uF plus a series resistor for the bridge rectifier to remove the instantaneous loading as the capacitor charges.

Use this example but with just the one LED ...
http://www.brian-lambert.co.uk/DCC%20Lighting-20.png
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End2end
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Re: Which capacitor for one led?

Postby End2end » Thu Dec 29, 2016 3:38 pm

Could this method be used to light the 3 LED's (all with 1K resistors attached) in my 4 wheel coaches using rail pick up?
viewtopic.php?f=1&t=50754
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End2end
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Re: Which capacitor for one led?

Postby dan8400 » Thu Dec 29, 2016 4:42 pm

Flashbang, a question.

I have the led already in the trailing power car. It works in either direction. Is this bad for the NCE powercab? I also run some bufferstop LED's (the same ones as the one in the hst power car) from track power.

Did I ought to run these (buffers) from a separate power supply? And do I need to rewire the hst powercar led?

I don't mind doing the work, just need an expert opinion to guide me

Thanks
Dan
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Flashbang
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Re: Which capacitor for one led?

Postby Flashbang » Fri Dec 30, 2016 11:21 am

dan8400 wrote:Flashbang, a question.

I have the led already in the trailing power car. It works in either direction. Is this bad for the NCE powercab? I also run some bufferstop LED's (the same ones as the one in the hst power car) from track power.

Did I ought to run these (buffers) from a separate power supply? And do I need to rewire the hst powercar led?

I don't mind doing the work, just need an expert opinion to guide me

Thanks
Dan

Hi Dan

You wont do any harm to the PowerCab. The LED wont overly like it to much having DCC directly fed to it though with suitable series resistor it wont hurt it too much. If you wish to remain with this configuration I personally would add a series diode into one lead of the LED. A 1N4001 diode or the smaller 1N4148 would be fine for one LED.

What will look strange is the white headlight being on when rear car is being towed. The rear light then should be a red! Hence initially I thought you had a decoder fitted which would turn On/Off the white headlight depending on direction of travel. This has to be the best option IMO.

You only need to consider using a separate power supply for the buffer LEDs if you have lots of them lit - say 20 or more. Assuming each LED draws approx. 20milliamp then 20 will take 400ma or nearly 1/2 Amp from the PowerCabs DCC output, which is reducing the available power for the trains.
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Re: Which capacitor for one led?

Postby Flashbang » Fri Dec 30, 2016 11:26 am

End2end wrote:Could this method be used to light the 3 LED's (all with 1K resistors attached) in my 4 wheel coaches using rail pick up?
viewtopic.php?f=1&t=50754
Thanks
End2end

In deed it can. You wont then get the flicker. But the lights will always be on when the carriage is on DCC powered rails. This could be over come by fitting a decoder and using the function output to control the lights. Function only decoders are available or just use a cheap motor and function decoder
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Re: Which capacitor for one led?

Postby End2end » Fri Dec 30, 2016 11:43 am

Unfortunatly Flashbang that would send my project costs spiralling as I'd need 5 deocders for the 5 coaches but looking at the link you posted I'm intrigued as to what ratings I'd need for the capacitor and what rectifier to buy as I am using 1K resistors on all the LED's.
I don't have any of these kind of items in stock and the maths escape me. :?
It does not matter if they are lit all the time or somehow a tiny switch was incorporated into the circuit.
Thanks
End2end
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Re: Which capacitor for one led?

Postby dan8400 » Fri Dec 30, 2016 11:52 am

Thank you very much for the info flashbang.

I will feed the buffer LED's from another source. (There will be around 15-16).

I only run this hst in one direction (planning another set when funds allow). So the rear car has only the red led to light the plastic diffuser which feed both external lights (original white bulb removed) No white at all.

The front car is a modern hst power car which I have bought in bits and am rebuilding. So I'll have the pulling power up front and a dummy which just needs lights. So your solution with a diode is easiest for me (I have some already).

Sorry if I haven't been clear in my descriptions of my hst set. As usual your answers are crystal clear and enable me to get my wiring jobs correct

Will I need a diode if I continue to add the capacitor?

Thank you
Dan
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Re: Which capacitor for one led?

Postby dynax » Fri Dec 30, 2016 11:52 am

Hi end2end, if you're handy with soldering electronic components, i have done a youtube how to for some automatic coach lighting using ldr's( light dependant resistors) and a transistor, which only come on when the ambient light levels are low or when going through tunnels etc,

https://www.youtube.com/channel/UCAtPj-BLBIqJLuvejfvB9Jg

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Flashbang
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Re: Which capacitor for one led?

Postby Flashbang » Sat Dec 31, 2016 2:35 pm

dan8400 wrote:Thank you very much for the info flashbang.

I will feed the buffer LED's from another source. (There will be around 15-16).

I only run this hst in one direction (planning another set when funds allow). So the rear car has only the red led to light the plastic diffuser which feed both external lights (original white bulb removed) No white at all.

The front car is a modern hst power car which I have bought in bits and am rebuilding. So I'll have the pulling power up front and a dummy which just needs lights. So your solution with a diode is easiest for me (I have some already).

Sorry if I haven't been clear in my descriptions of my hst set. As usual your answers are crystal clear and enable me to get my wiring jobs correct

Will I need a diode if I continue to add the capacitor?

Thank you
Dan

No problem Dan.

If you want to use just DCC from the wheels then I personally would add a 1N4001 or 1N4148 diode in series with one LED feed wires after the wheel pick up and before the LEDs series resistor.
If you fit the resistor into the LEDs Anode lead which is the positive longer LED lead then ensure the band on the diode faces the resistor.
If you have wired the resistor into the LEDs Cathode lead (shorter LED lead) then still fit the diode between wheel pick up and resistor but then the diodes banded end faces the wheels.
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Flashbang
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Re: Which capacitor for one led?

Postby Flashbang » Sat Dec 31, 2016 2:41 pm

End2end wrote:Unfortunatly Flashbang that would send my project costs spiralling as I'd need 5 deocders for the 5 coaches but looking at the link you posted I'm intrigued as to what ratings I'd need for the capacitor and what rectifier to buy as I am using 1K resistors on all the LED's.
I don't have any of these kind of items in stock and the maths escape me. :?
It does not matter if they are lit all the time or somehow a tiny switch was incorporated into the circuit.
Thanks
End2end

A 1K0 (1000 Ohm) resistor will be fine for the LEDs series resistor. If the LEDs are too bright swap it for a 5K (or 5 x 1K in series!) and retry, and so on testing with 10K - 15K until you reach the required level of brightness. The other alternative is to keep the 1K0 in circuit and add to this in series with the 1K0 a 10K liner sub min style variable pot (Middle pin to end of 1K0 and one of the two outer pins to the LEDs. Other pin is not used). Then by adjusting the pot you will have a minimum of 1K0 to a maximum of 11K in circuit! link to example pot
The other components used in the bridge rectifier circuit are --- Bridge Rectifier (Smallest possible) BR example Small round one in picture. 470R resistor Resistor 470R 470uF electrolytic capacitor... 470uF electro capacitor I have use Maplin as the examples, but there other much cheaper suppliers!

This Australian video shows the basic idea (with plenty of er ums too!) https://www.youtube.com/watch?v=WYkG37jI01w
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Re: Which capacitor for one led?

Postby TimberSurf » Sat Dec 31, 2016 4:30 pm

An even smaller bridge rectifier is the surface mount type
here's a similar video but with a deeper voice and with the 'er ums' omitted

https://www.youtube.com/watch?v=JiZ6Jj3OoK8
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