LED lighting on a budget!

[Jandrews]

thanks

 

[swearint]

Curious whether anyone has built this yet? I am planning on building some 'actinic' supplemental strips and I am considering this approach rather than using Meanwells.

Todd

 

[wisewendell]

Is it possible to individually dim each string?

 

[wisewendell]

Could you use a PWM circuit on each string?

 

[kcress]

Yes you could. It would step up the complexity.

If that was your interest you might be better served using a driver off the DIY driver - sticky thread.

 

[MosMike]

That's an interesting design, but my calculation show that with 8 XP-G there's no need of an efficiency-eating resistor.
24V for 8 LEDs will give around 400mA per LED.

 

[der_wille_zur_macht]

That's an interesting design, but my calculation show that with 8 XP-G there's no need of an efficiency-eating resistor.
24V for 8 LEDs will give around 400mA per LED.

If you're suggesting someone hook HP LEDs to a typical DC power supply with NO current limit resistor (or other method of controlling the current) then it's a disaster waiting to happen.

Firstly, LEDs essentially look like dead shorts to a power supply. Hook up an LED without any current limiting device and you'll either kill the LED or trip the protection features in the power supply.

Secondly, even if you somehow managed to get it to work (i.e. used a power source that had a high enough built-in impedance that it was essentially self-limiting), you'd be playing a huge guessing game. The V/I curves published in the datasheets are essentially rough suggestions - in real life, this relationship can vary SIGNIFICANTLY from LED to LED - hence kcress's design uses an adjustable power resistor, because simply "doing the math" will sometimes not even get you in the right ballpark, much less give you the exact result you're hoping for.

 

[kcress]

For one string having more LEDs equaling more Vf than the supply voltage it could work. But your 400mA value is a total crap-shoot. It might be 50mA or if could be 800mA.

You won't have any control of it and no way to measure it.

The power being rejected by the resistors is pretty small in comparison to the power delivered to the LEDs.

 

[wisewendell]

Yes you could. It would step up the complexity.

If that was your interest you might be better served using a driver off the DIY driver - sticky thread.

Even if you used a already built 24v pwm module? Found em on ebay for $9 shipped.

 

[kcress]

If I'm not mistaken the DIY ones cost about $6. But whatever floats your fishies!

 

[wisewendell]

If I'm not mistaken the DIY ones cost about $6. But whatever floats your fishies!

Ehh for $15 dollars extra I could get the 5 premade in a project box, would take me forever to make them.

 

[goldenfamaliy]

kcress, thanks, using your write up, I was able to make a fairly decent led setup for my 40 gallon. I am using 12 10 watt leds (Royal blue and warm white). All being controlled from my arduino.

 

[kcress]

Hey! That's great!

Do tell.

What specific LEDs?

Any chance of a picture?

 

[jpccusa]

Question about heat sinks: since LED's don't generate much heat, and since I am trying to save as much money as possible, would it be okay to use a flat sheet of aluminum to stick the LED's to? One or two 120mm fan(s) would be added to the setup.

 

[kcress]

Sure that would work fine for a typical build. As long as you aren't cramming the LEDs tightly together or running them at extra high currents. Add fans and you can use just about anything as a heatsink.

 

[wisewendell]

I have finished my LED build! Took a little over a month but here it is! http://www.youtube.com/watch?v=hTAdWjHG29g

 

[kcress]

Nice. But why did you post that in here?

 

[Daniel G]

Question about heat sinks: since LED's don't generate much heat, and since I am trying to save as much money as possible, would it be okay to use a flat sheet of aluminum to stick the LED's to? One or two 120mm fan(s) would be added to the setup.

I am working on something very similar. I'm using two 12" x 24" x .25" sheets though. Also I will be adding heatsinks on top side with fans mounted. Haven't really started because I'm still waiting on some supplies.

 

[jpccusa]

I am working on something very similar. I'm using two 12" x 24" x .25" sheets though. Also I will be adding heatsinks on top side with fans mounted. Haven't really started because I'm still waiting on some supplies.

I actually found CHEAP U-channels at Home Depot that I will be using instead of the flat aluminum sheets.

Take a look here.

 

[Daniel G]

I actually found CHEAP U-channels at Home Depot that I will be using instead of the flat aluminum sheets.

Take a look here.

That is pretty neat. I've been hearing good things about U-channels like that. Earlier last week I think i saw a heat sink made up of aluminum angles which is neat too. Well I almost finished my fixture and the sheets are great. I didn't add the heat sinks so I just went with drilling holes on the sheets. Keeps it real cool.