Power supply for Raspberry Pi Cluster

[ziggyfish]

I want to build a 40+ node cluster of Raspberry Pi 3's (or the ODROID-C2) , and I am researching the best method to power these boards. As I won't be using the USB interface (only Ethernet), each Pi will draw Max 1.3A on full load (see https://www.raspberrypi.org/help/faqs/ , WHAT ARE THE POWER REQUIREMENTS? for details ).

So at max load the cluster will draw 40*1.3A = 52A. The input Voltage for each Pi is 5V. So total input required is 5*1.3A = 260W.

As building a switch mode power supply capable of handling that much current sounds complicated. I am thinking of using a PC power supply to power the Pi's ( http://www.antec.com/product.php?id=704514&fid=343&lan=us , 1000W in case I want to increase the size of the cluster at a later stage ).

The issue is, the power supply can only support 25A at 5V. However it has +12V rails which can handle the load I am after, so I am thinking I need a DC-DC buck converter.

So doing some research into buck converters, I see the TPS54292 will do what I need( http://au.element14.com/Search?catalogId=15001&langId=43&storeId=10184&categoryName=All%20Categories&selectedCategoryId=&gs=true&st=TPS54292 ).

My idea is to connect 20 of TPS54292's in parallel on a PCB ( using a modified a version of the circuit found on page, 21 of the above datasheet ). Is this the good idea?

Also how wide should the PCB traces be to handle such load (10 Pi's on each power rail = 13A each connector)?

[danadak]

If reliability is a concern, fault tolerance, might want to drop the single
centralized power system in favor of some form of a distributed system.

This might help with PCB trace sizing - http://www.4pcb.com/trace-width-calculator.html

Regards, Dana.

[michaeliv]

Multiple PC Power supply would be my recommendation.
Ex 2x http://www.newegg.com/Product/Product.aspx?Item=N82E16817153023 delivering 60A @ 5V.
You don't need to hook them up in parallel, just connect 20 PI's to each.

[ziggyfish]

If reliability is a concern, fault tolerance, might want to drop the single
centralized power system in favor of some form of a distributed system.

This might help with PCB trace sizing - http://www.4pcb.com/trace-width-calculator.html

Regards, Dana.

Dana,

Thanks for that link. The TPS54292 has current limiting capabilities, and also should act as a voltage regulator. So if a single Pi fails it shouldn't effect the others.

I was thinking at a later stage of adding a redundant PSU in the case one PSU fails.

My main reason of building this cluster is to test how an application I am running will run on a large cluster. The secondary reason is to learn a bit of electronics in the process.

Also considering at the end the cluster will have 40*4 = 120 cores, I want to test some distributed algorithms.

Thanks

Brendan

[ziggyfish]

Multiple PC Power supply would be my recommendation.
Ex 2x http://www.newegg.com/Product/Product.aspx?Item=N82E16817153023 delivering 60A @ 5V.
You don't need to hook them up in parallel, just connect 20 PI's to each.

I'll looking into using multiple PSUs. That one only produces 18A so would require 3 of them (see images for proof, the specifications are different to what it says on the side of the device) with only 2A available if I decide to add more nodes. Also it would be rather inefficient as each PSU would only use 33% of its capability.

Thanks

Brendan

[michaeliv]

Yes you would have to spend some time finding appropriate PSU with high current on 5V.
Inefficient from what perspective ? I guess space would be the only one.
I'm thinking it would be more expensive & it would consume more power to add buck converters on the 12v rail since they have only about 80% efficiency.

[MK14]

http://uk.farnell.com/tdk-lambda/ls200-5/psu-enclosed-5v-40a-200w/dp/1995938

About £44

5V

40 amps max output

There are others you can buy, with more or less output current. Or use multiple ones, and separate RPI3 supply banks.

Cheap ebay PSUs, are liable to go faulty after say 3 months, potentially with widely excessive output voltages, which could almost instantly blow up your thousand pound computer.

[bseishen]

Iv'e been pretty happy with MeanWell supplies. I would condider the quality between a eBay fire hazard and a TDK supply. If it was me i would split the rack into two banks and use two supplies. http://www.mouser.com/ProductDetail/Mean-Well/LRS-200-5/

[ziggyfish]

Inefficient from what perspective ?

Most cheap PC power supplies have an efficiency rating of somewhere between 50-70% at average load and is less efficient the less Watts are drawn. Also the age of the PSU also plays a part in the efficiency as as well.

Also because I am only using 1 of the 6 rails, the power supply is not going to last as long, where taking advantage of the 12V rails, I can take advantage of 5/6 (2x 12V, 1 -12V, 1 5V, and 1 5V for power good signals).

MK14, bselshen, I didn't know about these things, so will investigate further. Thanks for you help.

[ziggyfish]

http://uk.farnell.com/tdk-lambda/ls200-5/psu-enclosed-5v-40a-200w/dp/1995938

About £44

5V

40 amps max output

There are others you can buy, with more or less output current. Or use multiple ones, and separate RPI3 supply banks.

Cheap ebay PSUs, are liable to go faulty after say 3 months, potentially with widely excessive output voltages, which could almost instantly blow up your thousand pound computer.

I think this is the way to go. Thanks so much for your help.

Thanks

Brendan

[grifftech]

http://uk.farnell.com/tdk-lambda/ls200-5/psu-enclosed-5v-40a-200w/dp/1995938

About £44

5V

40 amps max output

There are others you can buy, with more or less output current. Or use multiple ones, and separate RPI3 supply banks.

Cheap ebay PSUs, are liable to go faulty after say 3 months, potentially with widely excessive output voltages, which could almost instantly blow up your thousand pound computer.

1 thousand pounds? That is a heavy computer

[MK14]

If the computer just sits there (no exercise), eating (Raspberry) PIs all day, I'm NOT surprised.

[3db]

You might want to take a look at what Bitscope are doing.
You'll find info here  http://www.bitscope.com/product/blade/

[LukeW]

Based on DigiKey pricing for 20x TPS54292, that's AUD$162.9 for those chips alone.

Each chip has two independent regulators, so you can use one for every two RP nodes.
Use one regulator per RP node; don't try and "connect them in parallel".

Plus you're gonna need the 40x power inductors, a pile of caps and other components for your design, plus the fab of the 20 regulator boards.

Compared to a couple of PC power supplies, it's an expensive solution and high-risk. You might say that the cost is justified as a learning exercise, and you're free to spend that much money if you want to, but what are you really going to learn other than designing the components of a single regulator around the TPS54292?

If we assume, say, 80% efficiency, 5V out, 12V in, 1.5A load, the 12V input is going to need about 780mA current capability per regulator node, or say about 32A total.

[matseng]

Get 2 cheap crappy eBay power supplies. They do not usually fail short, so your can safely parallel 2 of them to get a very reliable yet cheap solution.

Can any run-of-the-mill cheap PSU be connected in parallel without any special care?

[AustinTxBob]

One thing about Pis, they cannot tolerate much below 5v.  Start momentarily dropping down to 4.75 and you will start corrupting SD cards.  I'd aim for 5.1 or 5.2.

[pbgben]

In my design for a similar system i've gone with 5v PSU as suggested. The issue I'm facing currently is networking.




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