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Old 6th July 2012, 09:32 PM   #1
400kg is offline 400kg  Turkey
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Default 2kw pull-push offline smps

is stable and strong
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Old 7th July 2012, 02:19 AM   #2
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I give you an A for effort but i do not think you could really get 2KW out of this SMPS. First i belive the transformer should have primary winding’s closer to 30 turns each, not 15 turns (385vdc, 50khz, 1800Gauss at 80Deg C, Ae 3.68). Second, your homemade litz wire with 14 x .45mm wires would have a RAC around 5. My calculations show you are running about 3000 Gauss, the limit of N87 ferrite.

You say it is running stable and strong at 92% efficency? I find that hard to belive. Even if the transformer was not running saturated, the high RAC would make efficency very low.

I would like to hear how you tested this SMPS and to hear from others about their thoughts on this. Because the build is well documented with pictures and has an informative schematic it is easy to run calculations on this design. I think this could be a good learning experience for all of us.
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Old 7th July 2012, 09:50 AM   #3
marce is offline marce  United Kingdom
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From the pictures of the copper it you dont seem to have a clear divide between the input and output sections of your PSU. It usually should be obvious as a copper free divide underneath the transformer.
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Old 7th July 2012, 12:33 PM   #4
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I took another look at this SMPS today and looked at the secondary. It is 16 strands of .65mm and it looks like the transformer was wound as Pri, Pri Sec. This would give an RAC on the secondary of at least 18.

I would sure like to know how much power this SMPS could actually deliver for a length of time and what temperature the core reached.
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Old 8th July 2012, 06:23 AM   #5
luka is offline luka  Slovenia
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why on earth you used push-pull for offline? to prove a point?
what main transistors did you use?
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Old 8th July 2012, 12:53 PM   #6
400kg is offline 400kg  Turkey
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Quote:
Originally Posted by powerbob View Post
I took another look at this SMPS today and looked at the secondary. It is 16 strands of .65mm and it looks like the transformer was wound as Pri, Pri Sec. This would give an RAC on the secondary of at least 18.

I would sure like to know how much power this SMPS could actually deliver for a length of time and what temperature the core reached.

yes 300w load MOSFETs too hot, but warm transformer
I incorrectly calculate the primer
and also makes noise amplifier
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Old 8th July 2012, 12:55 PM   #7
400kg is offline 400kg  Turkey
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Quote:
Originally Posted by luka View Post
why on earth you used push-pull for offline? to prove a point?
what main transistors did you use?
hi luka main transistors is ihw20n120r3
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Old 8th July 2012, 02:04 PM   #8
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400KG, i think you did a good job choosing your switching transistor. For 240vac input you need at least an 800vdc rated transistor and yours is 1200vdc. You also have plenty of current for switching with a 20 amp rating.

The concern with push pull besides the high voltage rating needed for the transistor is that push pull topologies tend to have a flux walking problem. If the core becomes unbalanced from slightly different primary winding’s or uneven heating of the transistors the transformer flux will start to walk either to the positive side or negative side and the transformer will saturate. The only fix for this is a very high speed current sense circuit to give you a cycle by cycle current limit. This problem can be totally avoided by using a half bridge driver that has a capacitor in series with the primary winding to continually adjust transformer imbalance.

You might want to look at your output section also. You have many 470uF capacitors paralleled up but no high frequency high current capacitors. I belive those 470uF capacitors will have a short life in this application.
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Old 8th July 2012, 04:42 PM   #9
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400KG, when you rewind your transformer you must use less wires. Your RAC is to high.

Proximity effect (electromagnetism) - Wikipedia, the free encyclopedia

You will be much better off using 4 strands of .45mm for the primary and 3 strands of .65mm for the secondary. You will not have enough wire diameter for continuous 2kw output but it will be OK for a 2kw music system.
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Old 27th August 2012, 01:08 PM   #10
ISTPYRO is offline ISTPYRO  Portugal
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Hello powerbob,

I'd like to know how did you managed to know that RAC 400kg design has an RAC around 5?

Regards.
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