using 1/8" aluminum plate for grow light. how many sq. in per watt (cob led)
@dbrn32 - thought I’d give you some extra work to do. Hehe.
Can i borrow your thread a second? While the light jedi is coming anyway?
What is the diff in the 4 digits describing the aluminum plates… the 6061 T6 or the 3003 H14 for examples… which is preferable?
probably a mix of aluminum and magnesium…different grades of alum.
I have used 6061 and 5052 without issue. I’m sure there are others that would do great too. But I’m gonna need a little more info before I can just say throw some leds on plate of any sort.
@graf which cobs are you looking at? I think you’re gonna struggle trying to cool cobs on a plate alone. The heat transfer point is just really condensed. Also, we’ll need to consider some ambient temps and performance data.
I’m almost positive if I put 4 50 watts cobs on a reasonably sized piece of .125 plate they would burn up. But I literally just got done watching 200 watts of led strips do it.
The numbers denote different alloys: silicon content, magnesium, copper, etc and has bearing for heat treating and welding. The thermal mass and thermal conductivity will vary depending on alloy as well but for our purposes in these temperature ranges there is very little difference.
Thanks. Answerded my other question
i know the guys at chill led advised against using .125 plate with their pucks…lol
figured i would just throw that in as well…
Yup. They sent you some data right? If I remember looked like below 40 watts per puck to be reasonable?
That being said, the pucks are a lot bigger and way more dispersed thermal load than any of the cobs I’ve seen.
no data,just a bigNO
OK, I cannot use an aluminum plate. Next question, how to choose a heat sink? I’m trying to decypher the technese in data sheets. Thermal resistance = degrees C / Watts. I assume the degees refers to the difference between ambient and the desired temp of the COB. So, with a 30 degree room and trying to keep the COB at 85 degrees, the temp figure would be 85 - 30 = 55. We’re trying to cool a 28 watt LED, so we need a thermal resistance of less than 1.96. Am I anywhere close?
Ya you’re on the right track kinda. There’s a lot to consider though.
For example, 85c is maximum allowable case temperature for most cobs. Your ambient temp will play into that, but that temperature can’t be referenced from air temp. And you really don’t want to size your heatsink to run the leds anywhere near the maximum allowable case temp.
Bridgelux data sheets and application notes have some really good info explaining most of the stuff you’re asking. But I hesitate to point you there without a little more info on what you’re looking to do.
Taking a step back and looking at the big picture. Ballpark figures are around 4 square inches of surface area per heat watt on an actively cooled heatsink. And like 18-20 square inches of surface area per heat watt on a passively cooled system. There certainly are a few exceptions. That’s why I asked which leds you were looking at. If we can get an idea of performance and projected current will be a lot easier to see what kind of thermal load we’re talking about. I’d be happy to make a few recommendations. @1BigFella seems to have quite a bit of experience here too, I’m sure he’d be happy to provide some input.
Are you hung up on using COB’s? If you can get the same performance out of some other configuration like strips or QB’s you can use that 1/8" aluminum.
Just a thought.
Exactly where I was going. Just too little info I guess. I can certainly find pin sinks for up to 100 watts, or extrusion to run active. Those damn qb 120 and 132 will run without anything.
Rapid LED has some nice 140 mm pin heat sinks that they say are good for 80 watts. $19 each. They are predrilled and tapped for several different COBs, but nothing stops you from drilling your own holes. Also, that is for 80 watts of heat, so with a decent COB getting 100 watts of power it would only generate about 50 watts of heat.
Other than that, I agree with dbrn32’s numbers. Keep in mind that hot air rises, so passive heat sinks mounted so the hot air around the fins can’t rise, don’t work well. Fortunately, with lights we usually mount the LED, COB, or strip on the bottom with fins or pins on top. I see a lot of smaller heat sinks on ebay, and there is no reason you could not use several of them mounted on some 1/2" aluminum plate to give you enough square inches of surface area.
If you are really ambitious, we’ve talked about soldering or gluing aluminum roofing nails on 1/2" aluminum plate with thermal epoxy, to make a DIY pin heat sink in any shape you want. Nobody here has actually done it, though.
Thanks for the info, you’ve been a big help. I am an old retired guy with a lot of time and not much money. Cheap, DIY interests me. I have an 18" x 24" plate that I was going to use to light a 3’ x 3’ tent. But I am back to square one now.
Look into @dbrn32 diy qb lights forums. You could fill that plate up with led stribs (bridgelux or arrow) and have relatively cheap very powerful lights for $200-250 if u dont mind a bit of work
Like @PurpNGold74 said, I just did a bridgelux eb strip build on piece of aluminum similar to that.
Guessing 580 mms? How many whats that thing pulling?
You could load that plate with EB strips and run that handily. You won’t give anything up in performance over a QB.
The 560’s are 24 watts each.