Quote Originally Posted by DreadedHermie
I get it. I was about to suggest you call that setup a CFL-assisted-by-LED grow, though.

Yep, have thought along those lines but am obviously working my way through some other details first. (Like building a basic, working light!) Rectangular aluminum stock with forced air cooling through the center seemed more realistic for me to attempt; my plumbing seems to cause flooding.

Well, I think you just opened up some new possibilities. For some reason I was thinking the current regulators needed to be close to the load; I'd planned to mount 'em on the 'sink near the LED's. I prolly misinterpreted the data about filter caps needing to be close to the current regulator(s).


I had planned on keeping the power supply out of the grow area, but are you telling me I can keep the current regulators adjacent to the power supply?

Zackly!
The closer the better.
Eliminates the need for a tantalum cap on the input to the CCR. That in turn eliminates the need for a diode.
Same with the output of the CCR.
You do not need a capacitor because of the nature of the load.
With no output cap to reverse bias the regulator, no "protection diode" is needed. Keep it simple.
16 ga. wire would suffice, but I'd use 14 ga. stranded and a plug/socket right at the lamp.
I used a 4 pin hard drive connector with a seperate ground return for the Red and blue supplies.
The CCR will hold whatever current you wish when using thinner wire, but why waste watts in da wire?

I could mount them in a separate case and keep the light nice and neat. This would also let me use the 338's in a TO-3 package, which seem much more popular, and look like they'd dissipate heat much better.

You got it straight away!
Impressive.
It's gonna be fun working with you.

BTW, I don't see any "proper operation assumes adequate heatsinking" type disclaimers on any of the 338 family, unlike the LM317's.

Look harder, I'm sure it's there somewhere.
Might have to dissipate 16W. or more! So a heatsink is in order. And, in this case, bigger is better.

I also can't figure out what the voltage drop across the 338's is-- in one graph it looks like they'll want 1.5-2 volts at around 4 Amps. Help??
If you allow for a 3 volt drop across the regulator and the 1.25V. drop across the sense resistor in your design, you should have enough headroom to keep the 338s happy.

Now, I'm havin' fun.
Weezard