LED resistors

Basic electrical and electronics, such as DC/Analog control.
brober
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Re: LED resistors

Postby brober » Tue Apr 06, 2021 12:34 pm

Looks like I'll be buying on eBay!

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End2end
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Re: LED resistors

Postby End2end » Wed Apr 07, 2021 12:45 pm

Not sure if it's any help but these are warm white LED's each with a 1K resistor lighting the building.
viewtopic.php?f=22&t=48176&start=990#p692971
Thanks
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centenary
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Re: LED resistors

Postby centenary » Fri Apr 09, 2021 8:51 pm

Here's a bit of an explanation and simply way to work out resistors for LEDs.

https://www.componentshop.co.uk/led-exp/

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Re: LED resistors

Postby Flashbang » Fri Apr 09, 2021 9:18 pm

brober wrote:Thanks for that guys. I am using Guagemaster WM1 as the PSU. It is rated at 1.25 amps. I may be approaching its limit with these extra 26 LEDs as it is also powering station platform lighting and goods yard standards. We shall see when I fire it all up. If necessary I will separate into different circuits with separate PSUs.

So, lets assume each lit LED draws 0.01A (10 Milliamps). 26 lit LEDs will be 26 x 0.01 = 260 milliamp, so still around 0.99 (990 miilliamp) spare capacity on the PSU which can provide a maximum, of 1250milliamps! That is almost 1.0Amp spare! But always allow a little bit of free headroom of say 100ma on the maximum rating.
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brober
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Re: LED resistors

Postby brober » Sun Apr 11, 2021 5:27 pm

As I have indicated before I am not electrically savvy!

I am looking at Brian's exceedingly helpful website and considering the wiring of the LEDs and the installation of the resistors. Brian's diagram (Electrical Page 3... Panel Indications and Seep PM1s) wiring shows the resistor set into the -ve return wire (black on the diagram). Now if I consider the power source is sending out power from the +ve terminal (red) then if the resistor is positioned after the LED then a full 12v will be hitting the LED. Have I got this wrong?

Using the link that Centenary quoted the resistor is shown to be "in front" of the LED in the +ve (red) wire. Hence my confusion!

Can someone please clarify where I should be placing the resistors... many thanks.

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Flashbang
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Re: LED resistors

Postby Flashbang » Sun Apr 11, 2021 5:31 pm

Resistors are limiting the current to the LED, That is their most important job. By default they also drop the volts too. It doesn't matter if they are all in the supply wires or the return wires. But where for example a panel pair of LEDs indicate Normal or Reverse point position, then can share one resistor in the Cathode (Negative) LED leads, as only one LED is lit at any one time. :D

Don't get hung up on volts arriving at a LED or which lead to wire the resistor in. So long as they have a series resistor of the minimum Ohm value required then they will work happily.. Increasing the Ohm value reduces the current the LED has available and eventually reduces that LEDs brightness until eventually it has insufficient current to illuminate. :o
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brober
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Re: LED resistors

Postby brober » Sun Apr 11, 2021 6:03 pm

Thanks Brian, clarification much appreciated. Hopefully I'll have no further queries. (I was going to say stupid questions but to me they are not stupid questions! ).
BTW all 26 turnouts are :now wired and switching perfectly.

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Peterm
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Re: LED resistors

Postby Peterm » Mon Apr 12, 2021 12:31 am

We all had to start somewhere mate. It's as the old saying, "you live and learn."
Pete.

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Flashbang
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Re: LED resistors

Postby Flashbang » Mon Apr 12, 2021 9:05 am

Hi
No problem and pleased to read you have your indications working.

The only stupid question is the one not asked :o Always ask and be sure :D
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BrodVictor
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Re: LED resistors

Postby BrodVictor » Fri Apr 23, 2021 9:08 am

Hi....Picking the right resistor esteem is basic to guarantee your LED gets appropriate voltage and current. To guarantee you have the right resistor you should know three qualities from your circuit.

Versus - Supply Voltage - This is the force supply that you are utilizing to control your circuit.

Vf - Forward voltage for your LED. This is the voltage needed to turn on your LED.

In the event that - Forward Current for your LED. This is the current needed by your LED for activity.

With these numbers you can compute the obstruction ® needed with the accompanying condition.

R = (Vs - Vf)/If

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Flashbang
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Re: LED resistors

Postby Flashbang » Fri Apr 23, 2021 9:50 am

You are correct. But doing this gives the MINIMUM resistor value in Ohms required. Increasing the resistance a little lowers the current consumption but does not reduce the LEDs illumination level and it also allows more LEDs to be add to the power source!
Of course, if the Ohm value is increased sharply then the LED will become dimmer in its light output until eventually it fails to illuminate at all when the Ohm value is excessive.
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Bufferstop
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Re: LED resistors

Postby Bufferstop » Fri Apr 23, 2021 10:40 am

You've just uncovered one of physic's dirty little secrets.
The voltage at a point needs to be with reference to something, usually earth, neutral, chassis or the like. The voltage across any part of a circuit is the potential difference.
12V on both rails, 0V potential difference = short circuit
+ 12v one side +3V on the other = 9V potential difference. (PD)
but we happily mix up the two terms and expect those not in on the secret to understand.
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