Hi,
I'm working on my first project.
I would like to control independently 5 led filaments using relays and my arduino.
Each led filament uses 3 Volts and 0.3 Amps
I'm going to use one relay per led filament but I'd like to use only one power supply for all filaments.
I'd like to make sure each led filament only receives a maximum of 3 volts, also I would like to calculate how much power my power supply should be able to provide, would it be 5 x 3 volts = 15 Volts?
Thanks
Normally you would wire them in parralell, so the required voltage is 3V for the PSU. The current adds up though, so you need a power supply capable of 5 * 0.3A = 1.5A minimum. I suggest a power supply capable of at least 2A.
What is going to limit the current to the LEDs?
Thanks Perry.
Looking at this calculator
I don't know either, but my starting assumption would be that they do. My first thought on seeing your question was "don't be silly LEDs don't have filaments", then I realised what you are talking about. I've never used one so I am not familiar with their characteristics.
The calculation you show says the LEDs have a Vf of 3V, so I think you can assume they behave like any other LED. You cannot power an LED with a fixed voltage like you are proposing, you have to use a current source of some kind. A slightly higher fixed voltage and a resistor will do for this. In the example you show 12V is ridiculously high as 9V is 'wasted', more to the point 75% of the input power (9/12) goes to heating the resistors. Maybe use a 4V (or 5V as these are common) PSU and a suitably calculated resistor, which I am leaving you to calculate.
If it is practical in your circuit you could consider putting them in series so the voltages add, but as I don't know what you are doing I don't know if that's a useful suggestion.
[Edit]
300mA constant current power supplies for driving LED lamps are common and cheap, they are the best thing to use I think.
If you were switching mains AC (120/240VAC) I would agree relays are a good solution. But for 3V, 0.3A, they are overkill. Just use some ordinary npn transistors like bc337. Use a 1K resistor between the Arduino digital pin and the transistor base pin.
No, you don't.
Power is not measured in Volts, voltage is measured in Volts. Power is measured in Watts. I believe you don't understand the most basic aspects of electricity, the difference between current, voltage and power, and how current flows in a circuit where components are connected in series versus in parallel. You need to go back to school. Take some basic tutorials on electricity. Otherwise you will just burn your led filaments.
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