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Everything You Always Wanted To Know About LEDs But Were Afraid To Ask
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 Posted: Mon Jul 1st, 2019 03:23 pm
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corv8
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2foot6 wrote:
I think the issue is the LED is reversed.

It will make no difference whatsoever where the resistor is placed in the circuit.


Peter,

Makes sense.

Seems I thought too complicated.

Gerold




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 Posted: Mon Jul 1st, 2019 03:42 pm
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tebee
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If you are using normal layout power for your LEDs,
remember that most transformers for model railroad use supply unsmoothed DC,
you may see a flicker in the LED lights with this.


Either use a smoothing capacitor,
or one of the power supplies specifically made for LED lights.


Tom




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 Posted: Mon Jul 1st, 2019 09:14 pm
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Helmut
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Curent going from 0 to 100% 50 or 60 times per second,
results in a flicker no human eye is able to follow.

Only when other light sources driven by AC are present,
a sort of stroboscopic effect may occur.




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 Posted: Mon Jul 1st, 2019 09:27 pm
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corv8
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Unfortunately DCC decoders generate a similar effect when dimming lights.

When using a value below 80 or so (out of 255) you will see a distinctive flickering.

(no idea with which frequency this flickering will occur)

A plain bulb wouldn't show this effect.

One of the pitfalls of DCC.




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 Posted: Tue Jul 2nd, 2019 09:35 pm
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Helmut
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The dimming frequency is dependent of the decoder's make,
and sometimes is considerably less than 50Hz.

Continuous dimming is a relic from the times when bulbs were used,
and due to the filament's inertia, can be done at a rather low rate.

Today dimming mainly only makes sense for high/low beam headlight control.

So when output-dimming is off, no LED will flicker whatsoever.

It may be seen, however, when you have more than one protocol active at the same time,
e.g. DCC and Märklin-Motorola, and the lights are connected single-ended to one pickup.

This is an effect generated by the CU's timing when sending the telegrams out.




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 Posted: Wed Jul 3rd, 2019 08:24 am
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corv8
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Helmut,

My experience mainly relates to Lenz decoders,
which I use for all non sound locomotives....
Other decoders may act differently.

However, I use the dimming feature on some locomotives,
where I feel the light emitted by the usual LEDs is too bright....
Like on an old logging loco. 

A problem with Lenz is that you can only dim once....
you enter a value less than 255 for constant dimming,
but then no longer have the option to dim the headlight once more,
when stopping the train.
 
In this case, I connect the function leads C + D to the front + back lights,
and enter a lower value for them.

So I may operate the loco with F0 at value "150" when underway,
and switch to F2, value "80" when I stop her.




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 Posted: Sun Jun 6th, 2021 06:10 pm
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corv8
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Eric T wrote:
Also, can I simplify the installation process,
by installing a single resistor on the blue wire,
instead of putting resistors on both the white and yellow wires?


Only now have read this thread / question.


Yes, you may use one resistor in the blue wire,
for both front and rear headlamp. 

However, if you turn on both simultaneously (like in switching),
both will be dimmed somewhat.

So I do this only with locomotives,
where it's unlikely they use both lamps at the same time,
like single directional trolleys.




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