I have been digging around the internet trying to learn about wiring LEDs and would like to make sure I am understanding correctly.
I am wireing bicolor LEDs for a control panel and I discovered the hard way the resistors that came with the LEDs get very hot. I am using a 12 volt power supply I had sitting around for my DC bus and the resistors that came with the LEDs are 1/4W 470 ohms for the green, and 1/4W 430 ohms for the red. From what I have found the resistors are getting hot because they are for 6 volt not 12 volt; is that correct? To have the resistors not get hot I need 1k ohm resistor. From what I think I found, I can connect the existing resistors in series and make a higher ohm resistor to see what could happen. Because I do not have a electronics store near I would like to have an idea what I need so I don’t have to order a bunch of resistors I don’t need.
Thank you in advance for any help I can get. I have so much to learn!
at 12V and an LED voltage of ~1.4V, a 430 Ohm resistor results in 25 ma of current and the resistor disspating 0.26 W of power, just exceeding its rating. an LED has a typical max of 20 ma
putting two 430 resistors in series results in a more common 12 ma and the resistor handling on 0.07 W
on the other hand, using a 5V supply results in 8 ma and the resistor handling 0.03 W.
If you are looking for a three color search light head LEDs I couldn’t find a bi-color LED that didn’t have hot spots and when attempting to come up with yellow everyone I tried looked terrible, 1/3rd red, 1/3rd green and 1/3rd yellow with very obvious hot spots. I tried several batches of both common anode and common cathode all looked terrible.
The perfect fix is the Bivar SMTL4-RGY LED. It doesn’t have a lens but you can cut off the lens from any 3mm LED and attach it to the SMTL4-RGY LED. I used solid 3mm Acrylic rod, stuck the rod in my cordless drill and rounded it off with 120 grit sandpaper. To me the frosted lens looks better than clear.
I bought my Bivar LEDs from Mouser Electronics, 25 for $24. The price like everything else is going up, I just ordered 20 more at $1.08 each.
I would say that just because I use 5 volts to power my LEDs you don’t have to do it that way. I would say that most if not all the members on the Forum use 12 volts with 1000Ω resistors. I use 5 volts because I have a lot of Arduino micro processors controlling my lighting and animation that operate on 5 volts.
I use 4 volts to power the lighting in my passenger cars, coaches and cabooses, I’m probably the only one on this Forum that uses 4 volts.
I would suggest staying with 12 volts and just buy a slug of 1000Ω ¼ watt resistors. If the LEDs appear too bright use a pair or three 1000Ω resistors in series for dimming the LEDs. If you want to make them brighter parallel the 1000Ω resistors. Make sure the LEDs don’t exceed the 20ma max current.
If you don’t have a multimeter get a cheapo from Harbor Freight or off ebay and learn how to use it. You will need it constantly to build your layout.
Now this is probably my ignoranc, but my thinking was that since I am planning to have several control panels with different colors of LEDs so it would be to handy to use lower ohm resistors. I’m going to do more reading and digging before changing anything. I’m starting to think about just add a 5v bus and pick up a regulator to drop my 12v power supply.
I stock the standard resistor assortment values. You could start out with a ¼ watt assortment off eBay and when you get the hang of using them buy the sizes you use the most in bulk.
Don’t go with a regulator, too inefficient. Get DC to DC Buck Converters. They come in several sizes, 2 to 8 Amp. I use all sizes, mostly the 8 Amp continuous 12 Amp intermittent.
Keep in mind that one reason for prevalence of a “5V” standard is that this is the nominal voltage for earlier versions of power in Universal Serial Bus (USB) connections. As such you could use any of the enormous volume of USB chargers, cables, ‘wall warts’ or other adapters for power – for example, a car adapter with USB port is already a “12V” to 5V converter…
That is very true – but that was at high current (and often high logic-related heat dissipation!) usually from dedicated rails. The 5V stuff he was talking about is the current range of things like Arduinos, and I think that voltage was intentionally chosen to allow OTS USB connectors and power – you saw the idea explicitly in the ‘push’ to use one of the USB micro connectors as a European standard for cell phones years ago. I think it is a sensible thing even if the nominal cores and other components are using a lower voltage at extremely low currents.
That all is good to know, I wondered why I one site I found for buck converters said they had USB ports. I did find a wall wort stashed away that has 5v output, but I like to over do things and decided to get a Buck converter and run a 5v bus.
Chicken or the egg? USB is 5V because all the logic was already 5V. And no need for +/- 12V for old style serial ports since they have all but disappeared. ANd what started out as low current has now grown to many amps, the latest iterations now about to fully power and charge a full laptop, not just a smartphone level device.
Unles LEDs are the only thing you plan to drive on an accessory power bus, I’d consider running a higher voltage bus and using smaller buck converters like these:
to drop the voltage when necessary. Each one is good for an amp or two (which is a lot of LEDs) and they are adjustable, so you can set one for 5V out for the LEDs, another for 9V out to drive some accessory that needs 9V, etc.
On a small layout you cna probably get away fine with just running a 5V bus, but if you later install some accessory that needs 12V, then you will be runnign a second bus. On a larger layout like mine, I’m starting witht he higher voltage so that I have a wide range of voltages available, but also so that even a long way from the power supply, if the 12V has dropped to 11V because of loss in the wire, the output of the buck converter will still be 5V to power the circuit I have attached to it. With these particular converters, if you want 5V out, the inoput needs to be 6.5V or greater - but if the output is set for 5V, it doesn’t matter if the input is 8V, 12V, 16V, all the way up to the maximum limit of 35V - the output is always 5V. Very handy little gadgets.
For now I building a small layout and running an extra bus is easy, I ran it last night. If I’m ever allowed, er, can build a large layout I will remember this. Thanks everyone!
