Heatsinks

[I like Cheese]

Hi Guys

i recently watched a youtube vid by Growmau5 about calculating heat dissipation through heatsinks. My problem is that i have no idea how to calculate the surface area of a heatsink and i can not get onto the website where it shows how to. Is there any one on here that know about this ?

Thanks in advance.

 

[gbauto]

It's my understanding that most use ~60% of the power you are running through the led as thermal load. Ex-100w COB would theoretically need 60w of dissipation to keep temp under control. There are formulas for calculating the exact surface area needed based on material but I tend to base my picks on the wattage information the manufacturer provides.

 

[I like Cheese]

Thanks for the reply gbauto.

I think i have crack it, you must just work the are of all the surfaces. e.g. if a box had sides of 4x4 cm, then the total surface area will be 96 cm2. Really simple, I was just over complicating it.

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[Danielson999]

IF you're using cobs you can use this DIY Cob Calculator to find out what length of extruded heatsink from HeatsinkUSA you will need depending on what cob, how many cobs and what amperage you're running them at. You can find it HERE

If you're looking for something a bit newer and more efficient you can try the pin-fin heatsinks (which I use). There are some in stock at NGL seen HERE. There will be an explanation on the site as to how much heat each will dissipate. I use the SST120's and run my cobs at 50w each and these pin-fin sinks will cool them passively with no problem. Add a bit of ambient airflow in your grow space and they simply increase the efficiency of your cob a bit better.

 

[I like Cheese]

IF you're using cobs you can use this DIY Cob Calculator to find out what length of extruded heatsink from HeatsinkUSA you will need depending on what cob, how many cobs and what amperage you're running them at. You can find it HERE

If you're looking for something a bit newer and more efficient you can try the pin-fin heatsinks (which I use). There are some in stock at NGL seen HERE. There will be an explanation on the site as to how much heat each will dissipate. I use the SST120's and run my cobs at 50w each and these pin-fin sinks will cool them passively with no problem. Add a bit of ambient airflow in your grow space and they simply increase the efficiency of your cob a bit better.

Hi Danielson999

Thanks for the reply.

I am going with 3 bars 700mm x 146mm with a config of 3-2- 3 for a 1 square meter tent. 2 with active cooling and 1 passive.

The cobs will be cxb 3590 12000-13000 lm. 36v 2.4 A. The drivers are hlg 185 1400b. And from the research I have done the cobs will run between 50 and 56% efficiency. That being 44 to 50% heat to dissipate. All 8 cobs are in total 400w. So 2 of the bars a little too small for passive.

 

[Danielson999]

I have some similar heatsink material. I can tell you from experience that the fins are spaced quite closely together which are not optimal for dissipation. I can't tell how thick the base of those are but if it's thick enough you might get away with running 2 cobs passively. I would still put fans on all 3 heatsinks though, it will increase the efficiency of your cobs and maximize how much light your plants get.

So you're wiring this in parallel?

 

[I like Cheese]

I have done the math. The total surface area is 3000cm2 more than what I need with 2 cobs, l also plan on fixing the drivers on it for more surface area. I thought the amount of light you get depends on how much power you give the cobs. Yes, I am wiring it.

 

[Danielson999]

Typically you will need 100cm²/w for passive cooling and 30cm²/w for active cooling.
150w on one bar = 75 heat watts. 75x30=2250cm² needed to actively cool.
100w on one bar = 50 heat watts. 50x100=5000cm² needed to passively cool.

3000cm² of material is good for about 100w of heat dissipation if you're using fans. So 3 cobs on 1 of your bars with fans will work.
3000cm² of material is good for about 30w of heat dissipation if using no fans. So it could easily handle 1 cob but not 2, driven at 50w per cob. Adding one fan in the center will make it easily handle 2 cobs.

 

[Danielson999]

The more power you give a cob the hotter it gets and the less efficient it becomes. If you ran 1 cob on 2 separate bars, one using a fan and one not using a fan, the cob using the fan would be providing more light to the plant because less power is getting turned into heat and more is being turned into photons.

 

[I like Cheese]

I have done the math. The total surface area is 3000cm2 more than what I need with 2 cobs, l also plan on fixing the drivers on it for more surface area. I thought the amount of light you get depends on how much power you give the cobs. Yes, I am wiring it.

Each bar is 8000cm2 total surface area. I have to dissipate 44 heat watts, and at 38cm2 per watt, it is all good. And the bars with 3 cobs on I have 66 heat watts, into 110 cm2. So I am missing about 3 cm in length hence the fan.

 

[Danielson999]

And about your potentiometer. Simply divide 100k ohm by the number of drivers you are using to determine what pot you should use. 1 driver = 100k ohm, 2 drivers = 50k ohm, 3 drivers = 33k ohm etc. If you use 2 drivers you use a 50k ohm pot. By adding a resistor valued at 10% of your 50k, means you use a 5k resistor which will allow you to safely adjust your power from between 10% and 100% without the flickering issues created when not using a resistor. Meanwell drivers are not supposed to be dimmed under 10% which is why you need the resistor.

 

[Danielson999]

Oh I see, I thought you were saying your total surface area was 3000cm2. So yes, 2 cobs on one bar will need a fan. 3 cobs on one bar will need at least 2 fans just to be safe anyway.

 

[I like Cheese]

2 cobs on 1 bar does not need a fan. I need 4840 cm2 to passive cool and I have 8000 cm2.

 

[Danielson999]

2 cobs on 1 bar does not need a fan. I need 4840 cm2 to passive cool and I have 8000 cm2.

If you're running them at 50w each then yes, you will need a fan with 8000cm2 of material. Obviously if you under-drive them the entire time you could get away with no fan but if you ever want to run them at max you will run a risk of burning your cob up. So how are you wiring them? I asked once before but you didn't answer. Parallel or in series?

 

[Danielson999]

Like I was saying, the fins on that material are not good for dissipating heat. They need to be spread out much further apart to let air vent out properly. A fan will be a very smart addition to that type of extruded heatsink. And whatever you do, don't use a 10k pot on your lights as suggested in the other thread you made. They won't run worth shit if you do.

 

[I like Cheese]

OK. Let's end this. I have all my data from Growmau5. Watch their videos and tell them they are wrong.

 

[Danielson999]

OK. Let's end this. I have all my data from Growmau5. Watch their videos and tell them they are wrong.

I've seen them a hundred times. Have fun running your cobs passively at 2.4a on a heatsink that doesn't work well at dissipating heat. I'm just trying to save you some time but hey, don't put a fan on them. And use a 10k ohm potentiometer too, I'm sure your setup will be running real sweet. Good luck and thanks for the help.

 

[I like Cheese]

Hi Danielson999

Thanks for the reply.

I am going with 3 bars 700mm x 146mm with a config of 3-2- 3 for a 1 square meter tent. 2 with active cooling and 1 passive.

The cobs will be cxb 3590 12000-13000 lm. 36v 2.4 A. The drivers are hlg 185 1400b. And from the research I have done the cobs will run between 50 and 56% efficiency. That being 44 to 50% heat to dissipate. All 8 cobs are in total 400w. So 2 of the bars a little too small for passive.

Try and read this again. Take your time and read it carefully.

 

[Danielson999]

Try and read this again. Take your time and read it carefully.

Yes, after reading it a second time you still state 2.4a for your cob. There is no such thing as a 2.4a cob, it's merely a measurement of the amperage it's being run at. I think the real problem is you don't know what you're saying

Anyway, if you go back and read carefully, you'll find multiple examples of where I asked you if you're wiring it in parallel or in series but you have never mentioned it. I understand if you don't get it, or don't even know how you'll be wiring it. It makes a difference in how much power your cobs will be getting, from any driver. I'm done trying to help. It seems like you don't speak english as a first language and there's nothing wrong with that...it just becomes difficult understanding each other. Good luck with your build and I hope you use the proper potentiometer for the job also, something else you've failed to mention even though I asked about it several times. Take care.

 

[gbauto]

OK- let me see if I get this. Cheese wants build a couple of arrays using 4- 36v cob's and needs to find out how much thermal dissipation he needs to be safe. The driver he spec'd will run each cob @1400mA when wired in series and that driver will be able to provide enough forward voltage(it does) for 4 led's in series. Each cob will run at approx. 50W at the driver rating-gives you a total of 200W/array. Most info I've seen for passive cooling suggests using 50% efficiency of the cob so 100W/array needs to get dissipated. You should be able to calculate the total area a sink design based on W/in2 the manufacturer provides. I do agree with Dan about using a 10k resistor to give the driver a base setting.