# DIY Redundant ATX PS?



## taz420nj (Jan 6, 2016)

Well the power supply on the Plywood Server just crapped out on me, and I got to thinking maybe I should invest in a redundant supply so next time it fails I'm not without a file server until I get a replacement.  However I found that redundant supplies in ATX are brutally expensive and I was wondering if it was possible to buddy up a pair of off the shelf ATX supplies.  In my PowerEdges, I know the supplies run in parallel all the time, which halves the load on either supply, they don't do any sort of switchover  - a lesson learned when I had my first power outage with them and they overloaded the UPS because the draw doubled (the UPS is only on one circuit and I tested the load with both supplies plugged in so I thought it would handle it lol).

I'm sure I can do it by making Y connectors and diode-isolating them, but I don't know how the PWR_ON and PG signals would need to be handled.

Anyone have any insight?


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## Brusfantomet (Jan 13, 2016)

people have been using 2 supplies previously.

Since you are talking about using diode isolating i assume you have some idea about electronics, and know that normal diodes can have 0.6 to 1 V drop (best io could find in quick search was STTH3002 with Vfw = 0.7 V), putting that previously good 12V into 11.4 V and out of ATX spec, the 5V is eaven worse and 3.3 will realy suffer. there is probably diodes with lower V drop but you want max 0.15 v drop over the diodes.

Other than that it shuld not be that much of a problem, just send the PWR_ON and PG signal to both PSUs, with the diode protection it will work (given LDO diodes)


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## taz420nj (Jan 14, 2016)

Yeah I did think about that, and my main concern is that if one supply fails in a way that leaves a rail shorted, that it'll take the other one out with it.  That's why I want to isolate them.  I was thinking about using Schottky diodes since they're lower drop, but the ones with the lowest forward drop are only available with low forward current ratings..  So has anyone ever measured the draw on a single wire (not rail ratings)? I can get them with 0.25v forward drop (would be a hair out of spec on the 3.3, but most supplies test with 3.4 anyway so I don't see it being a problem) but they are only rated up to 6A..  I know they are all paralleled to each rail in the supply, and I cant see a single 20ga wire ever having that much current but I don't know if they are paralleled back together on the motherboard or if they each go to specific places.


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## Brusfantomet (Jan 14, 2016)

for 3.3v 6A should be more than enough.
If you have a clamp A meter you could measure the ca draw of each wire.

Its also a question of what hardware the server has.

but i think 6A should be good for most wires, 6A at 12 V is 72W, a standard P4 cpu coenctor has two 12V cables, a 8 PCI power cable has 5 12V cables making the load per cable  (150W / 5) / 12v = 2.5 A.
Most of the cables are paralleled, but some might no be, either way 6A should do. You will need a lot of diodes tho, 24 for the 24 pin contact (12 of the pins are power pins), 4 for the cpu power, 6 for the s-ata power. this might help with what cables to modify.

If you like to tinker with stuff you could also get PSUs that have adjustable feedback for the voltage regulation, and adjust it up a bit. But opening a PSU does put you at risk of getting a high voltage shock that could kill you.


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## silentbogo (Jan 14, 2016)

What's the spec? if you have a low-power system, you may get away with a PicoPSU with UPS function and a pair of laptop PSUs.
Aftermarket redundant PSUs are expensive. I could only find this Athenapower unit for $299:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817338047

It is possible to make a DIY PSU out of a pair of smaller units, but it will be a project for more than one weekend. A simple splitter for running 2 PSUs in tandem most likely won't cut it.


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## silentbogo (Jan 14, 2016)

And there is also this:
http://www.ebay.com/itm/I-Star-TC-5...658192?hash=item280f50fed0:g:VOsAAOSwGotWkCPF

Almost identical unit, older model, quarter of the price.


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## taz420nj (Jan 14, 2016)

Brusfantomet said:


> for 3.3v 6A should be more than enough.
> If you have a clamp A meter you could measure the ca draw of each wire.
> 
> Its also a question of what hardware the server has.
> ...



Yeah I know it's a lot of diodes but theyre less than a buck apiece, so it still comes out less than buying an actual redundant supply.  And I've opened power supplies before and have been whacked by high voltage before lol.




silentbogo said:


> What's the spec? if you have a low-power system, you may get away with a PicoPSU with UPS function and a pair of laptop PSUs.
> Aftermarket redundant PSUs are expensive. I could only find this Athenapower unit for $299:
> http://www.newegg.com/Product/Product.aspx?Item=N82E16817338047
> 
> It is possible to make a DIY PSU out of a pair of smaller units, but it will be a project for more than one weekend. A simple splitter for running 2 PSUs in tandem most likely won't cut it.



Oh it would smoke a PicoPSU lol.  It's a Supermicro server board with dual Xeon E5430s, 16GB RAM, and 6 hard drives.  It's my media server/ripper/transcoder.


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## taz420nj (Jan 14, 2016)

silentbogo said:


> And there is also this:
> http://www.ebay.com/itm/I-Star-TC-5...658192?hash=item280f50fed0:g:VOsAAOSwGotWkCPF
> 
> Almost identical unit, older model, quarter of the price.



Thats actually not bad..  I'm considering buying it.  Thanks


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## Kursah (Jan 14, 2016)

+1 to that ebay unit, that's how I'd do it. 

That's one of the cleanest board-mounted PC/server builds I've ever seen, nice work taz!


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## taz420nj (Jan 14, 2016)

Kursah said:


> +1 to that ebay unit, that's how I'd do it.
> 
> That's one of the cleanest board-mounted PC/server builds I've ever seen, nice work taz!


Thanks!  It was a cheap solution to otherwise having to buy an expensive extended-ATX case


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