Powering "dwarf" track lights


GGNInNScale said:
OK, time to chime in- DO NOT use such high currents in the LEDs. They may be a bit brighter but they are getting hot which will degrade the output. You only need about 3-5milliamps for really bright lights. So, R = Voltage/Current. Use about 1kOhm for 3V, 1.5kOhms for 5V, and 3.3kOhms for 10-12Volts. Not really critical. The resistors can be 1/8W or SMD versions, really does not matter, depending on space available. I would attach a picture of an 0201 with an SMD resistor, but my camera cannot see it.... Resistor substitution boxes can be found on the internet for under 10 bucks if you want to play around easily. Remember that LEDs are diodes, so they are polarized devices- just check your connections with the diode tester in a multimeter.
Click to expand...
Would something like this work do you think ?

4-40V in 1-35V out (DC to DC)

1716056750885.png
 
GGNInNScale said:
OK, time to chime in- DO NOT use such high currents in the LEDs. They may be a bit brighter but they are getting hot which will degrade the output. You only need about 3-5milliamps for really bright lights. So, R = Voltage/Current. Use about 1kOhm for 3V, 1.5kOhms for 5V, and 3.3kOhms for 10-12Volts. Not really critical. The resistors can be 1/8W or SMD versions, really does not matter, depending on space available. I would attach a picture of an 0201 with an SMD resistor, but my camera cannot see it.... Resistor substitution boxes can be found on the internet for under 10 bucks if you want to play around easily. Remember that LEDs are diodes, so they are polarized devices- just check your connections with the diode tester in a multimeter.
Click to expand...
Most of the lights I've looked at come in around 3v/20 milliamps, so if I use a 3vdc supply, does that mean I don't need a resistor?
 
Smudge617 said:
Would something like this work do you think ?

4-40V in 1-35V out (DC to DC)

View attachment 187784
Click to expand...
Hi Yes this will work just fine to supply the voltage. The 2596 is an adjustable voltage regulator chip. It is a step-down regulator, with a minimum output of ~3V or so. It needs at least 4.5V input to function stably. It was designed at National Semiconductor (now TI). The circuit is a bit of overkill for your needs, but easy to use and pretty cheap. I use a big 5V supply (actually 4 of them) that can supply up to 5Amps, with distribution busses around the layout. I tie into these with either resistors for LEDs or servos, or LAA108 solid state relays , or small step-up voltage sources when I need 9 or 10V (about a buck each).
 
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Toolbelt said:
Most of the lights I've looked at come in around 3v/20 milliamps, so if I use a 3vdc supply, does that mean I don't need a resistor?
Click to expand...
For me, this is "way too much current". I would use at least 470Ohms or maybe 680Ohms. Protects the LED and if it blows short (not likely, it would normally blow open), protects the power source. I have been building circuits since I was a youngster (like 8th grade).... I like to keep my amplifiers and other circuits running cool. Not great if you are trying to make a buck, but if you want them to last 40-50 years (my first 120W audio amps from 1972 are still running nicely...), then you back things off a bit. :)
 
Toolbelt said:
Running cooler might also mean less bright, yes? I assume there's a minimum "trigger" voltage and a top end limit as well? So trial and error to find the sweet spot?
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You really will not notice it... Yes, the LED will not light below a threshold voltage (varies by color- has to do with the physics of the materials used in the active part of the LED). The easy way to do this is with a power supply (say 5 to 12VDC), then a resistor substitution box and a couple wires. Connect the LED with the box set for high resistance, then switch to lower resistances until you get the brightness you like. Then V=IR, and you can calculate the size of resistor to work with whatever voltage you have in the engine, car or building or street light, etc.
The top end? Well, that is going to be determined by the internal construction of the LED device. Some LEDs are just diodes, some have internal resistors, and some have circuits (like blinkers). So, you have to check the manufacturers spec sheet. There is a limit above which all LEDs will "poof".
 
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