| Electronics > Projects, Designs, and Technical Stuff |
| My constant current load - 90W , 3A 30V |
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| Spikee:
So i ordered a few parts: Artic cooling freezer 7 pro rev. 2 : Artic silver thermal adhesive : http://www.arcticsilver.com/arctic_silver_thermal_adhesive.htm 50k 10 turn pot 12bit dac MCP4728 (samples) 2 new 100W resistor 1ohm 10 0.1 ohm 3w resistors im gonna test how much power i can get out of one IRFP064N using a computer heatsink which has heat pipes. I want to see how close i can get to the 200W (@25deg c. ) value using 2 normal speed fans on the heatsink. This will be an interesting experiment . gr. spikee |
| blackdog:
Hi Spikee, I have here almost the same material as on your picture for a test :-DD One tip, do not use a mica washer, mount the 2 Fets direct on the bottum of the heatsink. Check the bottum of the heatsink if it's realy flat!!! Chack the specs of the IRFP064 Junction to Case 0.75C/Watt, Case to Heatsink 0.24C/Watt, total 1C/Watt Linear Derating factor, 1.3W/C Respect the datasheet/Fets :D Checkout EEVBLOG #105 so that you NOT blow up your fets... Kind regarts, Blackdog |
| LEECH666:
Wouldn't that potentially short the drains of the two FETs? I reckon that's a bad thing. How do you ensure insulation if you mount your FETs like that. Thermal grease? Cheers, Florian //EDIT HERP DERP, confused drain with source. The metal part of the TO-247AC is internally connected to the drain but those are connected together anyway. Pleaase forget that I asked this question. |
| Spikee:
--- Quote from: LEECH666 on December 07, 2012, 02:14:49 am ---Wouldn't that potentially short the drains of the two FETs? I reckon that's a bad thing. How do you ensure insulation if you mount your FETs like that. Thermal grease? Cheers, Florian //EDIT HERP DERP, confused drain with source. The metal part of the TO-247AC is connected to the drain but those are connected anyway. Forget I asked this question. --- End quote --- If you dont want electrical connection you need to make sure that the past of fet #1 does not hit the metal or paste of fet #2 . This is discribed in the artic silver guide / manual for this product. I did some thermal calculations and you can put around 115W in the mosfet and get a junction temp of 170 deg c. (175 max) so one fet would be enough for one cpu cooler. example: 90W from psu (30V , 3A ) The 1 ohm resistor will drop 3V ( 1 ohm *3 A ) So the mosfet gets 27V and 3A (81W) Rt j-c = 0.75 max Rt c-h = 0.24 min Rt h-a = 0.3 typ. - fan on high Freezer 7 pro (calculated from some results on the internet , seems to give around the same number) so Rth (j-a) is ~1.3 deg. C / W Temp ambient = 21 deg. C/W This all results in a junction temp of 126.3 deg. C. (175 max) It all depends on how fast the heat pipes can transfer the heat but i'm guessing its kinda instant. If my calculations are correct in real life you would only use one mosfet per cpu heatsink because it can utilize it fully. gr.spikee |
| T4P:
Careful about using it at 175C, 125 is so hot the mosfet can unsolder themselves and seriously running them at the edge is no good for reliability and i suspect even wire insulation melting/board lamination peeling off or a track peeling off and be careful of the heatsink itself, that heatsink is about 0.21 at OPTIMUM settings with the fan hard on |
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