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I've been trying to adapt the design for power distribution layed out in this raspi cluster design.

their design.

While looking through the researcher's design, I couldn't find any use for jumpers 2 and 3, espcially since the photographs seem to show no connections on jumpers 2 and 3. I opted to remove those jumpers and use only a single LED and ended up with this design:

my design.

The design successfully powered two raspberry pis connected to a standard PSU, salvaged from an old PC (from around 2001~2002), that provides 5V at up to 42 A. However, when connecting three raspberry pis, the boards were powered momentarily (board LEDs flicked on for a second) then shutoff. When checking the fuses of the power board, 2 out of 3 of the fuses in the configuration blew out (all except for the fuse in the center board). I'm a newbie to the electronics configurations and I was wondering if I left something critical out of the design or if something else is going wrong here.

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  • Hello and welcome. I have edited your second link. If it does not fit, well I guesse with your increased rep you should be able to edit it again. – Ghanima Jan 9 '16 at 21:31
  • This question is off topic for the Pi. Your problem is the power supply. These are not designed to be used unloaded. – Milliways Jan 9 '16 at 22:26
  • What fuse did you fit? The indicated device is a "Littlefuse 1812L110/33MR" a 1.1A 33V Polyfuse which I think is similar to the ones used on the older RPis - however a PC type SMPS type power supply has usually, like @Milliways suggests a minimum load requirement as well - and it is quite likely if that is not presented the voltage regulation may go out the window (as can the magic-blue smoke that the RPis originally contained). It is possible that those polyfuses might have helped contain the damage, if the overload was not too much... – SlySven Jan 10 '16 at 1:32
  • ... and they may reset (allow a day for this) before you try and see if there is any life left in the poor wee Pis - with a "normal" PSU (the SD cards may have been corrupted anyhow so you may want to check/re-flash those separately). Let us know how the testing goes as, if you have become a mass RPi killer, your question may be in line to get an "rip" tag! 8-/ – SlySven Jan 10 '16 at 1:38
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    @SlySven the pis are ok actually, the fuses made sure of that. However, the fuses (I'm not sure of the bran, bought it from a local electronics store) were supposedly rated for 1.5 A. They've seemed to work in smaller configuration and situations where I connect 1 pi to another that's powered via USB. So I 99% agree this is probably an issue with min load. – OKUZA Jan 11 '16 at 0:30
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On the original schematic, the author use the term 'JPx' usually meaning Jumper, however, JP1 and JP2 serve the same purpose; JP3 is just a test point, maybe to skip the fuse.

Your design looks ok and should work.

The only issue here is the old power supply. Old power supply run steady only when the load is also steady. Voltage regulation is not good when the load is low and often, no voltage at all with small load.

PC's have 12vdc and 5vdc, again, cheap design call for both loaded and working; so I think that the problem is on the Power supply. Maybe if you add a dummy load on +12vdc, will accomplish better voltage regulation.

You are providing over 40 amps and you need merely 4 Amps to run your Pi

Power Supply.

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  • When you say that voltage regulation is good when the load is low, does that mean if Loaded more rasbpis on the 5V rail it would solve this? Or should I still add the dummy load to the 12V rail – OKUZA Jan 9 '16 at 22:58
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    (Some) old PS work better with 60%+ load. The load on the 12vdc side is needed. Use regular a car lamp and you will have light for your project. Note: voltage regulation is NOT good with low load. – fcm Jan 9 '16 at 23:18

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