Help! Need easy, simple and reliable way to power serial & parallel LED circuits

M

Mark Janzen

G Scale Layout
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I have an outdoor G scale layout with about 65 structures that I want to install with LED lighting. The lighting requirements include building lighting on different floors, flood lights, porch lights, flashing tower lights, sign spot lights, etc. I currently have transformer providing 13.8V DC available at each structure. Each structure may have one or many LED lights in parallel and/or serial circuits. I have tried to install resisters at each LED to limit current and found it frustrating to vary the resistance to obtain the desired "brightness" needed. Reliability became a big issue. I use different types of LEDs (e.g. SMD, 5mm LED floods/spotlights/etc.) to obtain the desired type of lighting. The expense of the LED controller boards is also an issue.

Researching the WEB illustrates many electronic components are required to provide reliable voltage and current to commercial LED circuits. The use of MOV, PTC and NTC Thermistors, TVS diodes, etc. requires considerable knowledge and may be overkill for my needs.

Is there a simple and inexpensive way to provide reliable power to LEDs from a 13.8v DC power source? Buck converter to 3v DC plus PTC to control amps? Any advice would be appreciated! Specific components suggestions would be great!
Mark
 
LEDs are essentially current driven, subject to the voltage being within range.

I'm afraid it is a case of using resistors or another form of current limiting to set the desired brightness. They do not require individual resistors, providing all LEDs in that particular circuit have the same characteristics. SMD strips generally have the LEDs built in, and just require a voltage feed.

A more technical solution would be to use programmable LEDs. These have a small chip attached to each led, and are available in a variety of styles. You just then send a series of commands from a small microcontroller - I use Arduino, and the message is passed on from LED to LED via a single data connection. You can therefore vary the brightness and colour of each LED, and change it dynamically for a range of effects. This would of course require you to rewire and replace your current LEDs, but it could be a worthwhile upgrade!
 
If you go down the Arduino route I would suggest a kit for one. These kits can be had for between $20-30 from Amazon and include all the parts you could ever need to do a test setup before fitting to your buildings. I have a set bought from Amazon and it is a superb addition to the workshop. Simple easy to learn how to’s for the Arduino and different named derivatives can be found on You Tube.
 
As 3 minutes of fame 3 minutes of fame has said use resistors, appreciating that each circumstance is different, then use an LED calculate (link below to one, but there are many) and you can determine exactly what you need.

LED Resistor Calculator

Calculate resistor values for LEDs using this simple calculator. Enter any three known values and press Calculate to solve for the others.
ohmslawcalculator.com ohmslawcalculator.com
 
As Jimmy says, it's quite easy to calculate the value of the resistor needed. If, as you suggest) you have LEDs in series or parallel, then this site is useful

No need for a buck converter, just put in your supply voltage.

Alternatively, if you really want to use buck converters then get adustable ones like these (around a dollar each if you buy in bulk)
www.ebay.co.uk

2/5/10x Mini-360 DC DC Buck Converter Step Down Module 4.75V-23V to 1V-17V Set | eBay

1-5 - 10pcs Mini-360DCDC Buck Converter StepDown Module 4.75V-23V to1V-17V. < Compact and lightweight: It is compact and portable, high efficiency. Load regulation: ±0.5%. Mini size,compact and high efficiency.
www.ebay.co.uk

You could then put a random resistor (eg 1k) on the output side in series with your LED array and turn up the voltage using the potentiometer on the buck converter until you get the required light output from the LEDs. Make sure you start with the minimum voltage output on the buck converter and slowly turn it up to avoid blowing the LEDs. If they aren't bright enough at the highest setting then reduce the value of the resistor and try again.

Rik
 
I do not use resistors, I use the CL2-N3 which limits current to 20ma. I place 20ma leds in series, or pairs of 10ma leds in series. This unit is good for 5 to 90 volts, so it is a great way for managing current in large scale, but you loose on being able to vary the brightness.
 
Dan said:
I do not use resistors, I use the CL2-N3 which limits current to 20ma. I place 20ma leds in series, or pairs of 10ma leds in series. This unit is good for 5 to 90 volts, so it is a great way for managing current in large scale, but you loose on being able to vary the brightness.
Click to expand...
?
You would need your 10mA LEDs in parallel. - Else they would be fed with 20mA.

PhilP
 
Dan said:
I do not use resistors, I use the CL2-N3 which limits current to 20ma. I place 20ma leds in series, or pairs of 10ma leds in series. This unit is good for 5 to 90 volts, so it is a great way for managing current in large scale, but you loose on being able to vary the brightness.
Click to expand...
This is what I’ve been looking for!!!! Simple when using same amp/volt LEDs and inexpensive!
- Also found a way to very brightness by adding 1 or 2 more cl2-n3 in parallel. - Also found a cl25n3-G that will provide 25mA instead of 20mA.
- Also I can have multiple LEDs in series if I add a cl2-n3 in parallel and add 2v to power supply for each additional LED.

However, I’m struggling with how to use cl2-n3(s) with multiple LEDs wired in parallel. Any idea?
 
Dan said:
I do not use resistors, I use the CL2-N3 which limits current to 20ma. I place 20ma leds in series, or pairs of 10ma leds in series. This unit is good for 5 to 90 volts, so it is a great way for managing current in large scale, but you loose on being able to vary the brightness.
Click to expand...
What a fascinating device with such a wide input range.
 
You could also use a 7805 with a resistor, 7803 with (out) a resistor. (depends on how bright you want to have them.)
Those ones can handle up to 1A if you want more leds connected.
For experimenting the easy way i think a powerline to your experimenting board with a pot meter and a old fashion ic socket.
With your multimeter it would be very easy to determine the needed resistor, if needed.

There are also smaller voltage (in mah) regulators, i can not remember their name right now.

I buy them per 10 from ali, really cheap.
 
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