12v to 5v converter board for PSU

[rephaima]

Hello all,

This is all just hypothetical and may not work, but here goes. If I had an atx power supply, say 860 to 1000 watts with 60 amps on the 12v rail and say 30 on the 5v rail is there a way I could go about making a converter that would convert the 12v@60amps to 5v@ 60 amps leaving me with 30amps on the 12v and 60 on the 5v? It may not be possible but I thought I'd ask. It's for a special server I'm working on and a converter board that I could prototype would be much cheaper than having a custom power supply designed. Unless of course any of you know of an ATX form factor supply that offers 60A on the 5v rail. I haven't found one. Thanks in advance for any assistance.

Jason

 

[(*steve*)]

It would be easier to create a switch mode supply to give you 90 amps at 5V from the 12V rail (it would almost certainly draw well under 60A).

At these currents "easy" is relative. It may not be a simple project.

 

[OLIVE2222]

I agree, it will not be a simple project. One solution can be to start from a ATX supply and to:
- rewind the transformer to have lower voltage
- modify the feedback divider

Doing someting in the 90 amp range from scratch must only be done, to my eyes, by highly skilled engineers.

Olivier

 

[rephaima]

Thanks for the responses guys. I was just looking into it. I'll trust your advice as you're all much more knowledgeable in this area than I am. If anyone comes up with possible working solution, I'm open to suggestions. I was kind of thinking of a daughter-board style setup, external to the PSU that would do the splitting and converting for me as opposed to ripping the PSU open, but again, I'm out of my league. I'd still like to hear any suggestions you all may have. May spark off an idea I can run with.

Thanks all

Jason

 

[rephaima]

One more question since this seems to be a no go. Anyone know of any power supplies out there, atx form factor or possibly server style that would offer 60 amps on the 5v rail and 50 - 60 on the 12v rail. It's a long shot but then I'd just need to fab up a custom harness. While I prefer atx, something with larger dimensions could possibly be worked with. I figure something in the 860 - 1200 watt range. I'm not lazy I've been looking. It's just uncommon to find a supply with 60A available on the 5v rail. Thanks all.

Jason

 

[OLIVE2222]

Hi, this is the more powerfull ATX power I have found (1500Watts):

http://www.enermax.com/home.php?fn=eng/product_a1_1_2&lv0=1&lv1=43&no=159

this is 25Amp in the 5V branch and 30 amp in the six 12V branches.

By the way which is the configuration of your server to explain such needs?

Olivier

note, it's not being lazy to look at the most straightforward solution, it's just being pragmatic

 

[rephaima]

Thanks for the reply. The project is a network attached storage device. The reason I need the high amps on the 5v is because it holds 50 hard disks. Currently I'm using multiple custom PSU's in the unit and am looking to change over to a single redundant supply. Easier said than done apparently.

Jason

 

[OLIVE2222]

OK, it's more clear now. You don't need 60 Amp but, let say, 60 times 1 amps.
This is different, and it's the reason why I have asked details.

So combined with 2 or 3 1500w power supply, you can divide your problem by converting the 12Volts locally. You can go for a super easy down converter on each disk or something (still not to hard to do) like one converter for 5 disk.

I use Traco DC/DC converters very often, but other "high brand" should be as good.
For discrete design simple switcher IC serie (National or ON semi) are OK too. The super cheap and easy solution is the following:

http://www.murata-ps.com/data/power/oki-78sr.pdf

5$each

here no even needs for bulky electrolytic caps

Olivier

 

[rephaima]

Thanks for the help. The solution sounds great coming from you, but you'll have to excuse my ignorance. How many of these would I need to work with a 50 drive system and just to clarify this for myself, these will do what I was looking for which is basically steal a few amps from the 12v rail. I know, my ignorance is showing. I design and build and am into hobby electronics, but this is obviously out of my league and I don't mind admitting it.
Thanks,

Jason

 

[OLIVE2222]

First don't worry about your "ignorance" or being "out of your league" or any think alike!
I am glad to help !

To ease the maths we go for 1 Amp on 5V and 1 Amp on 12v for each disk
and one 1500watt PSU.

Basically:
- we keep the 5V 25amp as it
- we keep 3 X 12V 30 amps as it
- we convert 3 X 12V 30 amps to 3X 5V 30 Amps (this is theoretical)

so we have:
115 amps in 5V and
90 amps in 12V

according to the assumption here above the maximum become 90 disks

You maximum needs can be so from 3 X 12V/5V 30 Amp down converters to
90 X 12V/5V 1 Amp down converters

Up to you to decide how many local down converters you want according to practical implementation, easiness, cost.....

Deeper look is still needed but if you feel that it can be your solution i can go further with you.

Olivier

 

[rephaima]

The three converter option sounds like it would work best in my situation. I'm glad for your help. If you could point me to a data-sheet or product that fits the bill I'd be glad to read up.
As for implementation and plumbing these inline with the PSU any thoughts you have on that would be great as well. If it's to much to ask, say the word. You've already been a great help.

Jason

 

[OLIVE2222]

OK Jason, here under a suggestion for 30 Amps down converter

http://www2.mouser.com/ProductDetai.../LSN2-T-30-D12-C/?qs=b13bmSh8y6yQ2VTwFyspVg==

It's not fully of the shelf as you need a PCB to star connecting the disk but this is just plumbing.

I don't know were you are located so I go for a worldwide dealer, if you can find other thinks locally especially in surplus go ahead.

Soon I will do a cabling diagram for you.

Olivier