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Thread: Modding ATX PSU to Continuous PS

  1. #1
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    Default Modding ATX PSU to Continuous PS

    I have recently become very interested in the Raspberry Pi and I have seen some super-computer mods that gang 4, 8, 16...even 128 Raspberry Pi's together into a clustered supercomputer...really impressive. I am interested in distributed computing which could take advantage of dedicated clustered (parallel) cpu's. The current power requirement for a Raspberry Pi 3 Version B board is 5 volts and 2.5 amps. I have seen some demonstrated mods on YouTube, but the power supplies are hoaky...I did see one 8 clustered supercomputer mod with two moded power supplies in the background...but the person who did the youtube was more interested in a stupid light show with LED's than explaining how he had moded obvious ATX power supplies in the background. I said, "AH HA!)...so I have been studying ATX mods all over the internet and getting some excellent information, but before I jump in and actually attempt to build a continuous power supply/supplies for a clustered computer, I want to have some good advice...and I read that this is the place to come and get it...

    Now I understand that the red wires in the PSU are +5 volts. But for each Pi cpu in the cluster I need 2.5 amps. If the PSU says +5 volt/20 Amps, does that mean that each of the red wires carries 5 amps if I have four +5 Volt wires in the PSU? I saw one comment that said ATX specs say 6 Amps. I also need to add a 10 Ohm 10 or 20 Watt Sandstone type resistor as a load to stabilize +12 volts outputs on the +5 Volt side...(yes, I will build each supply with other voltage outputs even though +5 is what I need right now for the Pi's). I would like a little help on this, as I am not sure what I am going to get on each 5Volt output current wise. I have read some modders saying all the red wires (save for the load resistor wire) should be ganged together for a total AMP output...but that would mean I would have to use a single output terminal with multiple 5 volt wires coming out off a single 5 volt banana connector...not exactly appealing! Should I bunch two red wires together and have two output terminals of +5 Volts and 10 Amps each? I have a feeling, that due to resistance in the circuit, the current will not be exactly what I am thinking theoretically...so what is the Amp min and max? If possible, I want to power at least 4 Raspberry Pi's per power supply to build an 8 clustered super computer which would need two PSU's to do the trick.

    Also, I read that multi-rail is better, I need to assure voltage stability, 20+4 pin is better than a 24 pin connector, and guarantee continuous output and be certified as 80+ on efficiency. Not sure which PSU meets these that you have reviewed.

    What is the advantage of a larger Wattage PSU? Let's say, an 850 over a 500 Watt? Is it more available +5 volt connectors and higher output Amps? Cn I do what I need to do with a smaller PSU or do I have to have a larger PSU? What do you recommend to do the job I am proposing?

    Lastly for now...On the output signal of the +5 volt side, should I build a voltage regulator circuit to clean up the +5 volt signal coming out of the PSU? Is this necessary to get a cleaner +5 volt signal input into the Raspberry?

    By the way, power is connected from the +5V DC source through a microUSB 2.0 connector to each Pi board.

    Thanks for answering my questions.

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    Default

    You don't need to put load on the 12V if you have a PSU with DC-DC, because then the 5V already comes from the 12V.

    Two 5V wires should be able to carry 10A, three wires is better of course and should be possible, a PSU should have enough wires for that.

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    How many pi 3's do you want to connect? When I have more time I'll give you a real detailed answer.

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    A PSU like the Corsair CX450M costs 30 dollar after rebate on Newegg and is able to deliver 20A on the 12V. The CX450M has DC-DC so you don't need to load the 12V, because the 5V already comes from the 12V. The 24 pins ATX connectors has five 5V wires and the molex and sata cable could give you two extra 5V wires, but they're not necessary.

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    If his running it at as a cluster, it should be fine giving them 2a each. Main reason they stated 2.5 was for peripherals.

    Cx450m would do well.

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