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February 8, 2015

Block Wiring and Stopping LED’s from Burning Out

Shaun asks readers:

“Hi there, I’m wiring for twin cab control and would like led indication. If I wire across the switches how do I stop the leds from burning out?

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9 Responses to Block Wiring and Stopping LED’s from Burning Out

Kevin says:

February 10, 2015 at 7:27 am

Hi Shaun you will need to add a current limiting resister to the anode lead of the L E D this will need to be calculated to the voltage that you will be having on the switch.

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- Newman Atkinson says:
  
  February 10, 2015 at 4:47 pm
  
  Yep Kevin is absolutely right, Don’t forget the resisters. Your lights will last a very long time.Newman
  
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Geoffrey Logan says:

February 10, 2015 at 5:20 pm

If you are using a 12volts DC supply then most common LEDs that operate on 1.3 volts need a1000ohm resistor

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gio says:

February 11, 2015 at 8:08 pm

evans desings leds come ready to go in many sizes y may power w track power 9volt or 3 volt batterywatch type ,aa ,or aaa they come in a variety of colors ,including flashing leds as well it has endless posibilities with out the hassle of soldering &calculating resistors

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shaun says:

February 12, 2015 at 1:01 am

Thanks for your replies, diodes will receive full track voltage with one leg tied and resistored, so they won’t carry track current.
I also have thousands of infared diodes ( sender and receiver in a little combined head ) if anyone has a use for them.

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curtis says:

February 12, 2015 at 9:05 am

if you got access to a junk yard or some late model junkers the dash assys have small resisters for each dash light because the 12 volt leds cant take the alt surges volts. i have a truck dash that gave me 12 tiny led lights that plugin and the 12 resistors that go with them.i use these and have had no problems on board or in any home made signals.

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shaun says:

February 13, 2015 at 12:08 am

Thanks people for your ideas.
My leds have come from scrap electronics – so at the right price.
I’ll be using miniature on/off/on switches with a led wired across the output terminals, with the cabs wired in opposite polarity.
Will try a 1k resistor and see what happens.

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Frank Bushnell says:

February 18, 2015 at 9:55 pm

Because of track polarity reversal on a DC layout, put two LEDs in inverse parallel (opposite ways round) with one resistor (1kOhm) in series with the pair. If the LEDs are different colours, they will also form a voltage polarity indicator.

Alternatively, a diode bridge can be used to supply the single LED & resistor. (Nice tiny IC bridge chips are cheaply available.)

If your purpose is to show which way the switch is set (regardless of track polarity), grain-of-wheat (or grain-of-rice) bulbs across the rails will also do the job.

There are also accessory (electrical) switches that fit under the (track) switch to indicate the direction it is set.

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Shaun says:

February 27, 2015 at 1:08 am

Thanks Frank – I found a wiring system that will do my cab indications – but I was also trying to work out a switch indication system. The one big problem was how to show switch position independent of block cab indication.
My switches are wired with jumpers across the diverging tracks beyond the frog – so will always indicate the same regardless of direction – could this be “fixed” with leds?

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