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  1. Hi! lol ;D I think in this case one heatsink will cost me >600$ ;) Did you try to request samples through Internet? Maksar
  2. Hi! Did anyone got heatsinks as free samples from AavidTermaloy, Wakefield or other company? Maksar
  3. Hi! Thanks audioguru. I think this point is clear now :) Here are the main components I have for the project (5A). By the way, I made PCB by myself. If some one is interested in it, I can post the Ultiboard files. Maksar
  4. Hi audioguru! I think you didn't understand me. :P If the transistors won't fit the heatsink in ambient temperature, I'll cut a little one of it's sides. The cutouts near the "shoulders" of the heatsink are only for providing the room for the transistor and heatsink to enlarge on high temperatures. First of all, I don't understand why we have to refer to 200 degrees temperature? This is the max temp. for 0W dissipation. According to the datasheet of 2n3055 there is the max temp. for each value up to 115W. So for ~60W we have to keep transistor only at ~100 degrees, and not at 147C. Am I right? If so, 3 transistors for 5A project, for example, is not enough. For 4 transistors: Dissipation for each 2n3055 is 190W/4=47.5W. If total resistance is 2C/W (I am complitely agree with your calculations) the temperature is 125C, while the max for 47.5W according to the datasheet is a little above 125C. For 5 transistors we will get much better situation. So I think that the best option for 5A project is 5 2n3055 transistors. :D :-\ I want to have only one but long piece of this heatsink on back wall, so that it's lengh will be the weidth of the case. What is it "natural convection"? And what do you mean by "max convection airflow"? Do you think it is critical if the fins won't be vertical (in the case of back wall of the case)? I think the hot air will go up by itself... ??? Maksar
  5. Hi audioguru! Interesting point, I didn't think about this! :D But I don't think that this is a big problem. You can make the "shoulders" the shape you want them to be with a dremel. Also you can enlarge the space near the bottom surface of the heatsink, so that 2n3055 will match. Or you can use dremel to match the transistors to the heatsink :) By the way there is other heatsink with mach more space: http://www.semikron.com/internet/ds.jsp?file=649.html But due to it's dimensions, I think, it should be the top wall of the psu box. Maksar P.S. Paint rulez ;D
  6. Hi! Why not to say simply, that we need 4 transistors for 3A project and 5 for 5A project? But still a large heatsink is needed (I probably will buy this one: http://www.semikron.com/internet/ds.jsp?file=648.html) with fan. Or it is posible to use more powerfull transistors with thermal resistence ~0.5 C/W (maybe there are even better transistors) and not 1.5 C/W as 2n3055 has. It will be enough to use 2-3 of better transistors). Also the best solution may be to do teramal control based on termal sensor (sample from Maxim semi, for example) and opamp. So the fan won't work all the time, but only when it is needed (rarely). Maksar
  7. Hi audioguru! As you can see the standard lengths are 15cm(5.8") and 29cm(11.5"). So it isn't so long and can be easily matched to the case dimensions (case's height and width are fixed and length may be variable for individual needs). Also I don't see problems to mount it as a rear wall, there are several options how to do this. The heatsink has 0.8 C/W/3", so it is ~0.5 C/W/5.8". With fans (200LFM): ~0.2 C/W/5.8". Am I right? The question is: Is this heatsink in length 15cm suitable for 3A project without fans and for a 5A project with 1 or 2 fans on the side wall of the case (and holes on the other side wall)? I think we need to require for 3A project as well as for 5A, that the temperature won't rise above 100C. And of course we sould use termal grease with insulator pads. Am I right? WBR,
  8. Or maybe this one? I tried to show how I see this heatsink in the psu box as a back wall ::) Maksar
  9. Hi! What about this heatsink? http://www.wakefield.com/extrusions/index1.cfm?index3=yes&ext_id=578&c_row=5&ext_ref_num=&ext_type=0&ext_width=7&ext_height= Does this one need fan too? (for 5A project?) I think the upside of the heatsink in the picture should be outside of the case. Maksar
  10. Hi! And one more question. :) According to the datasheet of 2n3055, after rising of the temperature above 100C the power dissipation falls under ~65W. So in this project 100C for 2n3055s is the max? Maksar
  11. Hi AUDIOGURU! Thanks for this explanation. I didn't think that it is so simple to calculate and determine the needed heatsink :o (After your post I got some reading on this topic). It seems like I'll have to use fan. But does an airflow has big influence on the effective heatsink resistance? What will be the temperature of 2n3055 if I will put the 80mm computer fan on the 1.4 C/W heatsink? Maybe I'll do termal control of this fan (or fans..) by using Maxim's temperature sensor. By the way, should I make aluminium case for psu? It has low termal resistance and is easy to work with, but it won't too soft? Maksar
  12. Hi! Do you think the heatsink 234-2520 on www.rsisrael.com (use search) for each 2n3055 is suitable or it is too big? ??? Maksar
  13. Hi! Ok, thanks audioguru. The problem is that I don't have these diodes and my local electronics store don't have them too. So I tried ;) ;D ;D ;D But it seems that I'll need to search BZX79C5V6 in the other stores :-\ By the way, I understand nothing in planes, however, your model doesn't look ugly at all. Pretty, small plane... But I believe to expert's word :P ;D ;D Maksar
  14. Hi! Can I use zener diode 1N4735A instead of BZX79C5V6? If the answer is yes, which resistances I need? Thanks for the answer. Maksar
  15. Hi Kain! Good job, your psu looks very good. And you know - ugly planes don't fly. ;D ;D ;D Can you make some more pictures of your psu? Especially I interested in the bottom side of the board and the case. :) I begin to build the same psu as well. 8) Maksar
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