I am building various trek model ships. I went to different electronic stores and bought different color led's 3mm and 5mm in size.
To start, I bought a roll of 360 ohm resistors to use with each led.
My cct are run in parallel to the power supply--9V battery or 9V plugin.
I have noticed, that when combining certain leds in parallel with other color leds, one will not work.
After some research I found out that every color led has its own unique forward voltage drop.
Some of my led's are just the clear bulb (but will illuminate different colors), other leds are just colored (red/green ect).
Has anyone come across this issue and what was your solution?
Using different value resistiors for each color/size led?
Multiple LED lighting and resistor values
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frollsshontay
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G'day, I learnt about this the hard way, and am still learning. However, long story short, I have learnt to do a circuit with each colour, for example, red or white, and running all of those circuits in parallel. The reason for this is that different LEDs have different requirements (amps, volts etc). An example of this is my galactica build, that has white interior lights, blue engines and red LEDs for other areas. It took me months of experimenting, swearing and whiskey, but I finally got it going. Of course, Once I got it working, I found a how-to guide on the web... Forgotten where though...
Ben
Ben
If anyone else needs to calculate resistor values for leds, you could do worse than try this site:
http://led.linear1.org/led.wiz
Generally red or green leds will have forward voltages around 2 - 2.2v and white or blue will be around 3.2 - 3.4v
Use a forward current of around 20mA as a maximum.
All values are best checked with the data sheet for each led but the values above will provide a start point
http://led.linear1.org/led.wiz
Generally red or green leds will have forward voltages around 2 - 2.2v and white or blue will be around 3.2 - 3.4v
Use a forward current of around 20mA as a maximum.
All values are best checked with the data sheet for each led but the values above will provide a start point
WiredFX
Small Lighting and Effects UK
Small Lighting and Effects UK
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Styrofoam_Guy
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If you wire your LEDs in parallel and not in series, then you absolutely can have LEDs that require a different forward voltage. Each LED should have its own resistor value as appropriate to its specs.
You said you have a 9V power supply, so here's an example. Let's say you have a red LED (3.5 volts) and a green LED (3.0 volts). For simplicity, let's say they both use 0.02 amps.
How much do we need to drop the voltage for each? For the red LED: 9V - 3.5V = 5.5V. For the green LED, 9V - 3V = 6V.
Let's plug these numbers into Ohm's law to find out the resistor values that drops the voltage by 5.5 and 6 volts. R is resistance (ohms), I is current (amps) and V is voltage.
R = V / I
R = 5.5 / 0.02 = 275, so the red requires a 275 ohm resistor.
R = 6 / 0.02 = 300, so the green requires a 300 ohm resistor.
As long as the LED and resistor pairs are wired in parallel and not end-to-end, you can have any combination of LED values. For my current project, I have a 12V power supply, LED strips, and a few different kinds of LEDs. They all get along quite nicely.
Hope that's helpful!
You said you have a 9V power supply, so here's an example. Let's say you have a red LED (3.5 volts) and a green LED (3.0 volts). For simplicity, let's say they both use 0.02 amps.
How much do we need to drop the voltage for each? For the red LED: 9V - 3.5V = 5.5V. For the green LED, 9V - 3V = 6V.
Let's plug these numbers into Ohm's law to find out the resistor values that drops the voltage by 5.5 and 6 volts. R is resistance (ohms), I is current (amps) and V is voltage.
R = V / I
R = 5.5 / 0.02 = 275, so the red requires a 275 ohm resistor.
R = 6 / 0.02 = 300, so the green requires a 300 ohm resistor.
As long as the LED and resistor pairs are wired in parallel and not end-to-end, you can have any combination of LED values. For my current project, I have a 12V power supply, LED strips, and a few different kinds of LEDs. They all get along quite nicely.
Hope that's helpful!
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Madman Lighting
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Everything you guys said is absolutely true but I think you're missing the crux of the matter.
LEDs are current mode devices, not voltage mode devices. For those that are not engineers, that basically means that the way to control LED power is to control the current flowing in them.
When you guys pick resistors for a given battery voltage, you are in fact doing that and it will work just fine. Just remember a couple things:
As the battery drains, dimmer with the LED become. (duh!)
There is something called a "tolerance stackup" issue here. Basically that means that the voltage on the LED has a range of values it will have, say plus or minus 10% of what you measure on any one LED. If you put a bunch of LEDs in series, that adds up and messes up your calculations. So only stack up 3 or 4 at most and calculate for the worst case.
My stuff uses constant current regulators so you dont have these issues but I understand that not everyone wants to buy it.
LEDs are current mode devices, not voltage mode devices. For those that are not engineers, that basically means that the way to control LED power is to control the current flowing in them.
When you guys pick resistors for a given battery voltage, you are in fact doing that and it will work just fine. Just remember a couple things:
As the battery drains, dimmer with the LED become. (duh!)
There is something called a "tolerance stackup" issue here. Basically that means that the voltage on the LED has a range of values it will have, say plus or minus 10% of what you measure on any one LED. If you put a bunch of LEDs in series, that adds up and messes up your calculations. So only stack up 3 or 4 at most and calculate for the worst case.
My stuff uses constant current regulators so you dont have these issues but I understand that not everyone wants to buy it.
That Madman Who Lit Up Deep Space Nine
I'm totally not an electronics expert, so I'm just going by what I've gleaned from LED teaching pages and people I've nagged for help. 
This sounds interesting. Can you describe the purpose of the current regulators? If it can improve my lighting, I'm all for it. Is there a diagram somewhere?Madman Lighting wrote:My stuff uses constant current regulators so you dont have these issues but I understand that not everyone wants to buy it.
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Madman Lighting
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Ah. OK.
There are two kinds of regulators for electricity. Voltage and current.
Everyone knows about wall wort power supplies that make 12 volts. These regulate the voltage to 12V and supply UP TO their rated current, usually a few hundred milliamps.
A current regulator controls how much current flows through it, and anything else in series with it, but not voltage. LEDs like to have a specified current in them to control brightness. More current makes them brighter, less makes them dimmer. My stuff controls the current in a series connected string of LEDs, and you can have as many LEDs as the available voltage will support, up to 18V in my case.
You'd have to know some electrical engineering to understand how a current regulator actually works but thats the basics.
There are two kinds of regulators for electricity. Voltage and current.
Everyone knows about wall wort power supplies that make 12 volts. These regulate the voltage to 12V and supply UP TO their rated current, usually a few hundred milliamps.
A current regulator controls how much current flows through it, and anything else in series with it, but not voltage. LEDs like to have a specified current in them to control brightness. More current makes them brighter, less makes them dimmer. My stuff controls the current in a series connected string of LEDs, and you can have as many LEDs as the available voltage will support, up to 18V in my case.
You'd have to know some electrical engineering to understand how a current regulator actually works but thats the basics.
That Madman Who Lit Up Deep Space Nine