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I need to put an LED strip (ws2812) which uses 18watt per meters at 5V.
I intend to use 1 meter but the power supply is 10 meters away.
I can't use bigger wire than awg20 which I know will cause big voltage drop.
I thought about mounting multiple leds in parallel but it would need a tone of wires which is quite expensive.
Could I use something like a supercapacitor to help with the voltage drop?
Ok so you need a stable voltage without an overly thick wire. You also don't want to put bulky components near the load.
So what are our options.
I wouldn't nessacerally rule out a regulator chip near the load. There are some impressively tiny switched mode converters available nowadays though heatsinking can be an issue.
Another option is "remote sensing". A pair of thin wires is brough back from the load to the power supply. This lets the power supply measure the voltage at the load and compensate.
If we know the resitance of the wires we can just build a power supply that compensates based on he known cable resistance but that risks overvolting the load if the cable is shortened.
Linear techonlogy has a clever soloution to this which they call virtual remote sensing. They use the decoupling capacitors in the load to measure the cable resistance and compensate for it without the need for physical sense wires or known cable lengths. The downside seems to be that it's measurements will cause some output voltage ripple.
Use a PSU with a higher voltage and then use one or more buck regulators near the strip to bring the voltage down to the strip's requirement.
Since you don't want to add cables or components on the LED side, it seems to me that your only option left is to compensate for the voltage drop in the source. Fortunately, your cable will have a relatively constant and fixed resistance that you can measure or calculate, and with this information and ohms law you know how much the loss will be. Remember that you will get the loss in both wires.
Fortunately, there are some ICs that does just this. I know because Linear Technology sometimes brag about them in the dead-tree journals they send me. The technique is simply called cable drop compensation. I'm sure there are other solutions from other suppliers.
Hacking together your own would be an option, and probably a fun exercise.
You can power it from your desktop 12V supply HDD port or laptop charger with a 5V step down regulator at the LEDstrip. ~$8.36 +shipping on Amazon
It's also waterproof.
- if you used 10 pairs of AWG20 this would work with only 10% loss in brightness (neglible)
- if you raised the supply voltage by V=IR=3.6A*1.28Ω=4.8V above3V =7.8V you would get exactly 18W at full brightness but then if the PWM's are not all synchronous at 10% dim, now the tiny SMT series R's that drop each sub-string may have twice the voltage drop from 5V now at 7.8V and burn up. or possibly never go as dim as originally.
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But this costs more than the LEDstrip, so Plan B is feed a 10m AC extension cable with remote DC power and try to figure out your next question of send PWM signal 10m long with good signal integrity.
The solution is not using a voltage regulator but a current regulator.
Nearly all LEDs intended for lighting are rated 350mA (but check the datasheet if you find it) and there are power supplies in the market which do exactly that. When you use such a power supply, the cable cross section doesn't matter any more as the regulator measures the current and adjusts the voltage accordingly. Automatically.
