Electrical "Odds-n-Ends" for Model Railroading Enthusiasts                         

LED-CLD Current Limiting Device

What's a Current Limiting Device and what is it used for?  The Current Limiting Device, LED-CLD, is basically the Universal LED w/o the LED.  This allows you to utilize our current limiting technology for our standard A/C Ready LEDs as well as and standard LEDs rated at 12v or an accumulation of LEDs totalling around 12v.

You can apply a resister and a diode to an LED so you can use it in an A/C circuit, but once you're using variable power, how do you know what resister to select?  The pc board technology of our CLD accepts variable or fixed voltage up to 25volts AC (or DC) or more and regulates the milliamp output so that it is "just right" for the LED.  The circuit was designed around a 12 volt led so a load needs to be applied to the CLD equivalent to 12V.

Key Benefits

• Accepts variable AC or DC input
• Up to 20 - 25 volts (or more!) i.e. command control systems                                 
• Regulated output perfect for LEDs
• Use with our A/C Ready LEDs for a multitude of applications
  •  i.e. spike protection for a searchlight car, &
  • Passenger cars

Below I have some pictures showing what the LED-CLD can do for you:

1. A/C Ready LED w/o CLD
2. A/C Ready LED w/CLD
3. Using CLD with standard LEDs

What happens to a LED, like our standard A/C Ready LEDs in a circuit?

Our A/C Ready LEDs are rated for 12-14VAC, maybe up to 16VAC.  You can apply less voltage but too much voltage and you're applying too much amperage to the LED and it will drastically shorten it's life.  Look what happens:

Here we are applying 11.9 volts (pretty close to 12!) to a green A/C Ready LED.  Ours have a built-in resister and diode already so they can be used easily in A/C model railroading applications.   Note the meter on the right shows 14.77 mA.

In this case we've increased the voltage to 16v and notice that we're up to 21+ mA which is getting close to the edge of what most LEDs like.

Here we increase the voltage to 20, i.e. a command control application.  The milliamp output is way beyond where we want to be for that LED to last any time at all. 

Here's a blow-up of the CLD with A/C Ready LED (LED-SF-G) for your reference:

For hook-up, the CLD is wired in series, the A/C Ready LEDs in parallel.

Now, let's add a current limiting device, namely our LED-CLD to the circuit:

We are just connecting the CLD in series on the input side of the device. 

Here at 16 volts the milliamps are just 16, also.  And the CLD circuitry also help protect the LEDs from voltage spikes (i.e. when used in a searchlight car with single pickup.)

Now were at 20 volts, and still the amperage applied to the LED is within range.

Here we are at 30 volts - which is beyond most any application we're going to see. 

Using a CLD with standard LEDs - a more cost effective way to illuminate passenger cars!:

And here's a different spin. We take a CLD, this time on the OUTPUT side and use it to properly regulate power to standard LEDs.  This is a more cost effective way to illuminate passenger cars, but you'll need a little better soldering skills.  The circuitry is designed for nominal 12 volts, so you'll need to choose your LEDs or combination of LEDs to total about 9 volts to 12 or 14 volts.  (Colored LEDs are typically around 2 volts each, white ones are more.

Here's 3 red LEDs with 14 volats applied to them.  mA output is about 23. 

At 18v the milli amps have hardly changed.

And at 25 volts we're at about 25 milliamps.

Standard LED hook up example:

Here's the CLD, notice we cut the jumper wire to access the D/C side of the device.  The LEDs are connected in series.   The CLD is designed for 12v of load, but you can have about 6 - 14 w/o issue.

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Last modified: November 08, 2008