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Discussion in 'Algae Scrubber DIY' started by Kentth, Nov 13, 2017.

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  1. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Solid, 20 gauge. I use the hookup wire from a company called Vetco (tinned copper) but you can use the Radio Shack stuff, or doorbell wire from Lowes.

    If you break down this diagram to where the voltage drops occur, the only LEDs that would light are 6, 1 and 5 actually.

    LEDs won't conduct current until a voltage differential is present. But if you fix the voltage and vary the current, you get into trouble because the actual voltage drop will vary in a very tight window because of heating affecting the characteristics of the chip. So you could fix the voltage (using a constant voltage power supply) but then you're trying to match the required voltage drop (to get a certain level of output) and that is a moving target.

    So the answer is to fix the current and let the voltage do what it needs to do (i.e. constant current power supply that applies whatever voltage is needed to maintain a given current). You can't (easily) control LEDs by using a fixed voltage, which is why no one does it. Which is also why using resistors to try and manipulate the voltage is a bad idea in general. Resistors are useful in the other example where you have parallel strings that are splitting current from a source like in the DT fixture example (with the fuses and 3000mA source current) but in that case, you would be measuring the voltage drop across an individual string at various points of operation (cool, warm, hot) and then seeing what string has a lower Vdrop and adding in a resistor to bring that string up to match the other ones so that there is balance when you put the 3 strings together. Most people then under-drive the strings to make sure that they're OK if one string gets more current due to heating effects (i.e. using LEDs rated for 1500mA and pushing 1000mA current)

    So can you tell that I've had my fair share of EE classes? Not that I ever used them after college until I started building LED fixtures! (I have a BS in EE)
  2. Kentth

    Kentth New Member

    yep I can tell, kind of like talking to my friend, except you dumb it down closer to my level, I just give him more beer. that's why I can't wait to run this all past him. It all makes sense, I just have to read and get my head around it, which I normally do. I used to build radio transmitters and receiver, and stuff like that, back in the old days (early 70's). Still have a few boxes of vacuum tubes setting around. The fun one was the long wave transmitters, 135 kHz range, we built. We built four of them, (tired of CB's couldn't afford Ham, in high school) bought Navy surplus receivers. Got them to work.

    I will let you know how things turn out.

    Turbo likes this.
  3. Kentth

    Kentth New Member

    So I have everything up and running. The only thing I did differently was to spread the leds out more vertically. It seems to be giving me good coverage, will know after I let it run a week or so. Now on to the next project, DT lighting. Taking what you taught me on this project and applying it on a larger scale.

    Again thank for all the help.

    Turbo likes this.

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