Resistors & 48V DC Question

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Altanore

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Hello everyone, I'm new to the forum!

I am planning a project with LED lighting with DMX. The controller I'm wishing to use has an output of 48 volts DC and 4 amps on each channel.

Now, I only have knowledge in building LED circuits for 12V DC.

On some of the channels, I will want to connect a single LED and of course I'll need a resistor. However, at 48V, I'm wondering if I need a special resistor that can handle such voltage? I used an LED resistor calculator and it said I would need a resistor that could handle 22 Watts... thats a little too much. Those things are too big for my project.

Any help is appreciated! Thanks!
 
Well, if you want to run more than one LED per output, then put the LEDs in series to save power. The other option to look at is running the "controller" at a lower voltage. Post a link to the "controller" so we can see if this is viable.
 
Series the LED's is your best option. 20 red LED's yields 34 Volts, and R to drop down from 48V.
15 white LED's ± 45Volts and R to drop down excess and set LED current at about 15 to 20 mA.

If single LED on 48 Volts say 20 mA will yield a resistor of 2400R and 1 Watt.

I would go for 2700R or use 2 in series of 1500R to split the heat over the resistors.

Then multiply it out by the amount of LED's required.
 
I take it that this is a high power LED?

Build a switching regulator.

I'll post the circuit (which is very simple) if you're interested.
 
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I still don't understand why you're using 48VDC; is this going to be powered from a UPS or wind/solar powered installation?
 
Hero999 said:
I still don't understand why you're using 48VDC; is this going to be powered from a UPS or wind/solar powered installation?
Click to expand...

I agree. It sounds like the outputs are programmable/adjustable, depending on the number of LEDs in use. See if you can step it down.
 
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I have been in contact with them about the board. I just sent an e-mail asking if the voltage is adjustable. They do have another board that runs at 12V but each channel can only support 20MA.

I've decided that I will have to connect LED's in a series. Save money and I wont have to get heavy duty resistors .

It's just the very high power LED's (1-3 watt) that I will have problems with. I know there are LED drivers for these type of LED's but the only ones I have found can only handle an input up to 32V.

This project is for a computer case modification. The controller board will either be connected to the computer power supply or wall outlet... I'll probably have to make an external box for all the hardware.
 
Altanore said:
Thanks!
The controller in question is:
http://www.celestialaudio.com/ca_dmx_32_nfet/index.html
Click to expand...
Just set the LED power supply to the level you need. The lower the better. ie: If the longest, and the the highest voltage drop LED string, needs 8V, then make the LED supply 12V and burn the remaining 4V in a resistor. No need to supply it with 48V at all. All they mean is that is good UP to 48V if you needed it.
 
Oh.. i didn't seem to clue into that! Well that saves me from all the trouble then.
Thanks for the help everyone.
 
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