Building the SBT PSU

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#61
That is around 14V DC on the filter cap I guess ? Knowing what current flows would help to determine a good solution. You have some excess voltage that probably causes more heat than absolutely necessary. Point is that 8V transformers are rare and 7V might be too low. I think you can get away (note: this is not really correct engineering) with a 7V 2A transformer but it would strongly depend on model and make. As long if you have 9.5 V DC at the filter cap as the absolute minimum (lower limit of ripple voltage) and an added margin of let's say 1V it will work OK but it is thinking outside the box and quite custom made in that case. Using an 8V transformer would be more in the right line of thinking 😉

I see this company has 8V transformers:

http://www.tme.eu/html/EN/toroidal-mains-transformers/ramka_774_EN_pelny.html
 
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#63
Ryssen said:
In this post it says 560mA:

But I´m going to drill a couple of 20mm holes in the top (at the end where it´s safe from the mains)and some smaller holes in the bottom.
I would guess the heatsink is about 35-40 degrees C.
Click to expand...

Ooohhhhhh....only 560 mA....just 35 to 40 degrees (measuring that would not be unwise)... Don't worry too much although less excess heat would be nice. You do need some ventilation holes with a (guesstimated) 3W dissipation. 20 mm holes seem a little large, you don't want anyone to put their fingers in them do you ? Aligning them will be difficult and also having exactly round holes will be nearly impossible in a plastic case. If you succeed we want pictures 🙂

Using a transformer with somewhat less output voltage would be best.
 
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#66
How could I forget our own Amplimo ? With 7,5V it should be possible but one would have to try it out. Since the PSU has a 10.000 µF filter cap ripple will be low at 0.6A. Maybe someone of you knows the internals of the Duet ? If it can live with less than 9V it would even be better. I guess it has 5V regs inside. If those are LDO regs too maybe 8V DC output is more than enough. This would depend on the specifications of the LDO's that are used. Since it is all out of my design values one would have to try this out. I never owned a Duet.
 
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#70
You should measure the voltage on the large filter cap. You can use the Ampere meter connector for a normal 5A diode with 0.7V Uforward (or even 2 in series). Best would be to adjust the transformer voltage to a somewhat lower value. Less excess voltage means less heat....but all should be within the margins of the regulator to function properly. Like keeping balance on a cord 😉

Please measure the voltage, that is decisive in finding an adequate solution.
 
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#72
Two 5A diodes in series at the Ampere meter connector would make a difference. I would choose a different transformer like the 7,5V Amplimo (and keep the output at 8.8V) but that's me. The 2 diode solution will help though (but it is cheating) 🙂
 
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#77
I had to use 2 diods,and at the elyt the voltage is 13,4v and after the 2 diods 11,7v.
And the temp on the diods is....51 degrees C ....
And the regulaors heatsink is now ..35degrees C during playback.So it seems that whe are only moving the heat to the diods instead.
 
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