Why would you use a different number of chips to make an active unit vs a passive unit? His example was 3070 chips at 1a. There are a number of choices for passive sink at that level. So why would you change the number of chips?
We are on different pages...but I see what page your on...
Let me explain it this way...
700w light is the end goal...
Assuming same # of cobs and we will use the heatsinkUSA profiles for ease to relate to for most...
700w passively: means ~85inches of 10.8" profile...
84.15lbs...costing $557.6
700w actively: means ~81inches of 5.8 profile...
20.25lbs($140.94)...plus the 3
[email protected] and 3$ power supply...
costing $170.94
Now factor in the ability to drive harder and add cooling to decrease the cobs necessary
Passively: could take 18(~1.05a) cobs costing $720(@40ea)...totaling
$1277.6 for the cobs and heatsink(s)
Actively: could take 13 cobs costing $520(@40ea)...
totaling $690.94 for the cobs and cooling systems(heatsink(s), fans, power)
If you drive the passive design actually soft(<1a) and you get even more upfront cost.
Also...if you guys think that wiring fans is hard to do or any kind of real work...you guys are lazy. Look what we are talking about and doing in our gardens...don't give me that fans are complicated stuff.
If we go even farther into this DIY heatsinks...not just cobs...
Red monos have a shitty temp droop problem and will be effected by higher operating temps worse. With reds I would do the best I could to have a lowest Tj/Tc to keep them up to par with the cobs or blues.
Now, if I was a person just building one light for my one little flowering spot...then ya I could justify that kind of cost per light and tell myself the gain in efficiency is worth it...
But what about that fact I need 2, maybe 3 of these 700w lights...or what about the guy who needs 25+ of them. Cost becomes an issue to remaining practical and saving in the long run.
I run apache's too...I know about trying to get back expensive price tags...no reason for diy to fall into that too.