Well...end of fun for today.Q4 damaged!I used a quite large heatsink for Q4(with mika insulators) but it became really hot during tests(i could barelly touch the heatsink which was 15x10cm).Q2 was all the time cool, it did not heat up(4x2cm heatsink). I didn't use thermal grease.I will do volt measurements tomorrow when i get some new 2n3055(i will buy a stock of them ;D )
audioguru2
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Hi Ta,
OOps, your output transistors melted!
Just think how hot the original project's single output transistor would get.
Your heatsink (only one?) is way too small for such a powerful project like this one. I would use your 15x10cm heatsink for about 15 to 20W. Since your faulty project was supplying 5A into a 2.7 ohm load, your output transistors were trying to dissipate a total of about 107W.
Thermal grease must be used to fill the microscopic valleys in the transistors and heatsink. Don't use a mica insulator, mount the transistors directly to the heatsink with thermal grease then insulate the heatsink from the chassis. Maybe it is best to use a separate big heatsink for each output transistor.
If you used a 30V transformer and calibrated the current regulator's pot at 3A, if you short the output with the voltage at 30V and the current at 3A then the output transistors will dissipate about 61W each.
I hope you use a much bigger heatsink with thermal grease but without mica insulators, and turn it on for short time periods until you fix the current jumping to 5A. ;D
OOps, your output transistors melted!
Just think how hot the original project's single output transistor would get.
Your heatsink (only one?) is way too small for such a powerful project like this one. I would use your 15x10cm heatsink for about 15 to 20W. Since your faulty project was supplying 5A into a 2.7 ohm load, your output transistors were trying to dissipate a total of about 107W.
Thermal grease must be used to fill the microscopic valleys in the transistors and heatsink. Don't use a mica insulator, mount the transistors directly to the heatsink with thermal grease then insulate the heatsink from the chassis. Maybe it is best to use a separate big heatsink for each output transistor.
If you used a 30V transformer and calibrated the current regulator's pot at 3A, if you short the output with the voltage at 30V and the current at 3A then the output transistors will dissipate about 61W each.
I hope you use a much bigger heatsink with thermal grease but without mica insulators, and turn it on for short time periods until you fix the current jumping to 5A. ;D
Using a fan blowing over the heatsink could be a solution, too, if you don't want to buy a new heat sink. You need a very big heat sink to get 123W away without active cooling and even than the thing will get hot as hell. That is not good for the caps and will spoil the accuracy of voltage and current regulation, because the heat will spread inside the case.
audioguru2
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Hi Ta,
He, he. ;D ;D
I knew you would ask what size. I could crunch some numbers, select a suitable one, then you'll say you can't get that one.
Use a fan with two of your existing heatsink (no mica, use grease) like Thomas says.
Make it variable speed like my pc and like some hi-end audio amps. Use a digital display or bar-graph to show the temp. ;D
He, he. ;D ;D
I knew you would ask what size. I could crunch some numbers, select a suitable one, then you'll say you can't get that one.
Use a fan with two of your existing heatsink (no mica, use grease) like Thomas says.
Make it variable speed like my pc and like some hi-end audio amps. Use a digital display or bar-graph to show the temp. ;D
audioguru2
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Hi Zeppelin,
Welcome to our forum. ;D
If you are going to use two 2N3055 transistors and a 30VAC, 4.3A, 130VA stepdown power transformer and high voltage opamps as recommended here, then each transistor will have about 38V across it when the output is at 3A and the voltage is low or shorted. Therefore each transistor must dissipate about 57W.
In the forum of the 5A version of this project
http://www.electronics-lab.com/forum/index.php?topic=196.msg23794#msg23794
a heatsink 234-2520 from RS Electronics Israel was asked about. RS might be the same company as the one in the UK. Wakefield in the USA have a similar heatsink.
The thermal resistance of a metal T03 cased 2N3055 transistor is 1.5 degrees C/W and the thermal resistance of this heatsink is 1.4. Therefore with 57W of dissipation in a transistor and an ambient temp of 30 degrees C, the junction of the transistor will be 187 degrees C.
The absolute max for the 2N3055 is 200, so this is very close to operating at the absolute max.
Notice that I haven't included the 0.7 degrees C/W thermal resistance of a transistor insulator in my calculation since it would make the transistor overheat. But a fan could be used to increase the efficiency of the heatsink.
If I used heatsinks as small as this one, I would not use a transistor insulator but use thermal grease and a fan. The heatsink improvement by using a fan is discussed at www.wakefield.com . ;D
View attachment 37329
Welcome to our forum. ;D
If you are going to use two 2N3055 transistors and a 30VAC, 4.3A, 130VA stepdown power transformer and high voltage opamps as recommended here, then each transistor will have about 38V across it when the output is at 3A and the voltage is low or shorted. Therefore each transistor must dissipate about 57W.
In the forum of the 5A version of this project
http://www.electronics-lab.com/forum/index.php?topic=196.msg23794#msg23794
a heatsink 234-2520 from RS Electronics Israel was asked about. RS might be the same company as the one in the UK. Wakefield in the USA have a similar heatsink.
The thermal resistance of a metal T03 cased 2N3055 transistor is 1.5 degrees C/W and the thermal resistance of this heatsink is 1.4. Therefore with 57W of dissipation in a transistor and an ambient temp of 30 degrees C, the junction of the transistor will be 187 degrees C.
The absolute max for the 2N3055 is 200, so this is very close to operating at the absolute max.
Notice that I haven't included the 0.7 degrees C/W thermal resistance of a transistor insulator in my calculation since it would make the transistor overheat. But a fan could be used to increase the efficiency of the heatsink.
If I used heatsinks as small as this one, I would not use a transistor insulator but use thermal grease and a fan. The heatsink improvement by using a fan is discussed at www.wakefield.com . ;D
View attachment 37329
I changed the 2n3055's.Now everything is fine :I checked the voltages you mentioned and they are ok,I put the 2 transistors in the same heatsink(I forgot to buy another one :-\ ,tomorrow i will) using thermal grease and a 12V pc case fan..Everything seems fine and i am currently testing the psu with 2A output on 2.7ohm load.One thing i noticed is that one transistor get much hotter than the other one(so as the heatsink below the hotter,meaning that it does not heat because it doesn't come to good contact with the heatsink,I believe).Can someone (audiogugu ;D ) explain it?
audioguru2
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Hi Ta,
Good, you fixed your current jumping problem by replacing the 2N3055 transistors that were destroyed by over-temperature. ;D
Since one new one gets much hotter than the other, you can measure the voltage across each one's 0.1 ohm emitter resistor to see how well they match. The low value emitter resistors help a little to match the transistors without much loss. You could match transistors better yourself, or use emitter resistors up to 1 ohm/5W to force them to be more equal with a loss of up to 1.5V at full load.
The thermal grease provides poor electrical contact from the transistor's collector to the heatsink, so I hope you are connecting to each collector with a terminal fastened to its mounting bolt.
A burr on a hole on the heatsink will prevent a transistor from making good thermal contact.
Good, you fixed your current jumping problem by replacing the 2N3055 transistors that were destroyed by over-temperature. ;D
Since one new one gets much hotter than the other, you can measure the voltage across each one's 0.1 ohm emitter resistor to see how well they match. The low value emitter resistors help a little to match the transistors without much loss. You could match transistors better yourself, or use emitter resistors up to 1 ohm/5W to force them to be more equal with a loss of up to 1.5V at full load.
The thermal grease provides poor electrical contact from the transistor's collector to the heatsink, so I hope you are connecting to each collector with a terminal fastened to its mounting bolt.
A burr on a hole on the heatsink will prevent a transistor from making good thermal contact.
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
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
Or maybe this one?
I tried to show how I see this heatsink in the psu box as a back wall :
MaksarView attachment 37332
I tried to show how I see this heatsink in the psu box as a back wall :
MaksarView attachment 37332
audioguru2
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Hi Maksar,
Those heatsink extrusions are very long pieces that you must cut to length yourself.
It is difficult to mount them so that the fins are outside the case but the wiring is inside. I think they are mounted to the inside rear wall of the case with the top and bottom of the case having air slots.
The extrusions have their thermal resistance rated for 3 inches long pieces. For this 3A project where each output transistor must dissipate a max of 57W, a heatsink thermal resistance of 1.4 without a transistor insulator or a thermal resistance of 0.7 with a transistor insulator, for each output transistor, will heat them almost to their max.
Hi Ta,
Your 2N3055 transistors have a very poor match. Even with 1 ohm emitter resistors they won't match.
They are all different but usually match pretty well if they are from the same batch.
Maybe one of yours was made on a Friday afternoon by one manufacturer, and the other was made on a Monday morning by another manufacturer. ;D
Those heatsink extrusions are very long pieces that you must cut to length yourself.
It is difficult to mount them so that the fins are outside the case but the wiring is inside. I think they are mounted to the inside rear wall of the case with the top and bottom of the case having air slots.
The extrusions have their thermal resistance rated for 3 inches long pieces. For this 3A project where each output transistor must dissipate a max of 57W, a heatsink thermal resistance of 1.4 without a transistor insulator or a thermal resistance of 0.7 with a transistor insulator, for each output transistor, will heat them almost to their max.
Hi Ta,
Your 2N3055 transistors have a very poor match. Even with 1 ohm emitter resistors they won't match.
They are all different but usually match pretty well if they are from the same batch.
Maybe one of yours was made on a Friday afternoon by one manufacturer, and the other was made on a Monday morning by another manufacturer. ;D
audioguru2
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Hi Zeppelin,
Most panel meters can't measure their own supply. They need a supply that is completely isolated from what they are measuring. Some people wind a new winding on their transformer (torroid is easy) to power their panel meters. ;D
Most panel meters can't measure their own supply. They need a supply that is completely isolated from what they are measuring. Some people wind a new winding on their transformer (torroid is easy) to power their panel meters. ;D
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,
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,
audioguru2
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Hi Maksar,
That heatsink extrusion mentioned a length of 87 inches so I thought it is sold that long.
I don't know the calculation for a different length than 3 inches, when you double it then the thermal resistance certainly doesn't become half.
A thermal resistance of 0.2 would be great with a fan and you can add 0.7 for a transistor insulator. Then at 57W in a transistor and a 30 degrees C ambient its junction temp would be 167 degrees C.
Without a transistor insulator and without a fan, the junction temp would be 144 degrees C.
You'll have to calculate the 5A version separately but the temp will be only a little higher.
There isn't a requirement to limit the metal transistor's junction temp to only 100 degrees C because its max rating is 200 degrees C.
2 heatsinks are required for the 3A project, and 3 for the 5A project.
I think the fins on the heatsink must be vertical to allow for convection cooling.
That heatsink extrusion mentioned a length of 87 inches so I thought it is sold that long.
I don't know the calculation for a different length than 3 inches, when you double it then the thermal resistance certainly doesn't become half.
A thermal resistance of 0.2 would be great with a fan and you can add 0.7 for a transistor insulator. Then at 57W in a transistor and a 30 degrees C ambient its junction temp would be 167 degrees C.
Without a transistor insulator and without a fan, the junction temp would be 144 degrees C.
You'll have to calculate the 5A version separately but the temp will be only a little higher.
There isn't a requirement to limit the metal transistor's junction temp to only 100 degrees C because its max rating is 200 degrees C.
2 heatsinks are required for the 3A project, and 3 for the 5A project.
I think the fins on the heatsink must be vertical to allow for convection cooling.
audioguru2
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Hi Zeppelin,
Common opamps are designed for a 30V supply, 36V absolute max. I posted some with 44V absolute max.
If you want this project to produce a well-regulated 30V at full load then its positive supply will be more than 38V at full load and about 44V without a load and when the transformer's voltage increases without a load. Add some more voltage when your AC or refrigerator shuts off. Then add the 5.6V negative supply and look for another opamp with a 54V supply rating. The OPA445AP is the only one I could find. It is $9.50US today at Newarkinone and Digikey if you buy only a few, less cost if you buy 25 or more. ;D
Common opamps are designed for a 30V supply, 36V absolute max. I posted some with 44V absolute max.
If you want this project to produce a well-regulated 30V at full load then its positive supply will be more than 38V at full load and about 44V without a load and when the transformer's voltage increases without a load. Add some more voltage when your AC or refrigerator shuts off. Then add the 5.6V negative supply and look for another opamp with a 54V supply rating. The OPA445AP is the only one I could find. It is $9.50US today at Newarkinone and Digikey if you buy only a few, less cost if you buy 25 or more. ;D
audioguru2
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Hi Zeppelin,
The original circuit supplies up to 41V (with no load) to its opamps that have an absolute max supply voltage of 36V. If you use cheap opamps with a 44V supply rating like the MC34071 or TLE2141 then they will be happy.
Then the project might be able to supply 2.5A at up to about 25V, if its little Q2 and its single Q4 don't melt.
Replace the original 2N2219 for Q2 with a cheap but powerful TIP31A and the project will be a bargain. ;D
The original circuit supplies up to 41V (with no load) to its opamps that have an absolute max supply voltage of 36V. If you use cheap opamps with a 44V supply rating like the MC34071 or TLE2141 then they will be happy.
Then the project might be able to supply 2.5A at up to about 25V, if its little Q2 and its single Q4 don't melt.
Replace the original 2N2219 for Q2 with a cheap but powerful TIP31A and the project will be a bargain. ;D
