Ac to Dc electrical question

[J.J.]

Ok electrical and/or computer gurus i need everyone's expert advice/help.  I need a power supply to converts ac to -48v DC.  

This week I scored some servers that one of our customers decided they didn't want after the rack failed.

So I have a few rackable brand half depth servers sitting at home.  The only problem is that they run off Dc power. (The company was experimenting with this style vs the standard ac servers)  I have one of the converters from the rack too..I just won't use that many at once to make it worthwhile hooking up. Well the wife wouldn't appreciate the power bill that is.

So any idea where I can find such a beast.  I am gonna start off with just having one sever going. If I decide to go for more than 1 I can just hook up the rack adapter.

[Brad Johnson]

How many thousands is one of the purpose built power supplies?

Brad

[J.J.]

Yeah the server rack that has been retrofitted directly from the mfg is pretty pricey.

They don't seem to want to encourage anyone to convert them to the normal standard of using an Ac plug...so thus I need a external converter..hopefully cheap

[Brad Johnson]

Building or converting a supply that's got clean enough output may be more than buying he power supply. Is the supply directly integrated into the rack or is it independently replacable?  What about picking up a used rack somewhere?

Brad

[J.J.]

I have one of the power supplies..it just uses 2700 watts of power... That's what I need to run all 5 at once...for just one server going it seems overkill...

[Brad Johnson]

It uses that much all the time, or it's capable of up to that much if required?

Brad

[Hawkmoon]

Computers don't run off 120-volt a/c -- the power supply converts it to DC and reduces it to 12 volts and 5 volts. I suspect your servers have an internal transformer that does a similar reduction, to the voltage the motherboard and drives actually need.

Why not just buy a couple of conventional power supplies and be done with it?

[J.J.]

Hate to find out. I would have to change some house wiring up for it before installing thus I am trying to find an alternative.

[Brad Johnson]

What brand/model server?

Brad

[mtnbkr]

8 deep cycle batteries: 2x 4 in series. [/there, I fixed it]

Chris

[J.J.]

Rackable brand server...no model number listed.... When rackable and sgi merged all the old rackable pages are gone..so I can't even research specs of the old rackable server to narrow it down.

I will have to boot it up to get more info...

[J.J.]

Yeah i can just hear the wife now if she saw that array sitting in the closet...

[zxcvbob]

How many amps?  (almost sounds like it was designed to run off the DC bias on a telephone line)

[Nick1911]

Firstly, be aware that modern switched-mode power supplies like are used in computers are actually very efficient.  Even if it's capable of 2700 watt, if you only draw, say 150 watts out of it, you might find losses of only, say, another 20 watts.

For a dedicated supply, depends on how much current you need to deliver at 48VDC.  If 2700 watts, that's a big power supply, 56Amps output.  So, something like this: http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2106722_-1

But you probably won't pull nearly that amount of power.  If you only wanted to shift, say, 500 watts: http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2105164_-1

In your case, I would connect up the actual power supply you have, hook up measuring equipment to the input and output, turn everything on, determine how many watts you actually need, and how inefficient your power supply is at producing it.  If it's efficient enough, you're done.  If not, you now know how many watts of power you need to be shopping for.  Without actually measuring it, we're just speculating.

[zahc]

8 deep cycle batteries: 2x 4 in series. [/there, I fixed it]

Chris

You may be more right than you know. As already mentioned, high-wattage DC power that is CLEAN does not come cheap. Audiophiles sometimes use battery supplies...the power supply is possibly the most important part of a traditional stereo amp.

48 volts is a common voltage because it's just under the "dangerous voltage" threshold which is 50V. Power-over-ethernet is 48V, for example.

[J.J.]

http://www.craftec.info/productPDF/MiniPlantOrderingGuidefor1U_2054136R2.pdf

Finally found the power supply that I have

As you see way to much

[Nick1911]

As you see way to much

Too much capacity is only a problem if the power supply is inefficient.

This is a little 1U deal, correct?  Is it exceptionally heavy for it's size, implying a ferroresonant 60hz transformer?

I fully expect that it's swithed-mode.  It honestly might not actually eat much power when lightly loaded.  The Kill-a-watt would be an easy way to determine what it's actually pulling with your gear running.   Barring that, you can use a simple true-RMS multimeter to record voltage and amperage consumed, multiply together and get watts.  [And before calls me out on it, residential customers aren't billed on power factor, so even if that's not the true power consumed, it doesn't matter.]

[RoadKingLarry]

How many amps?  (almost sounds like it was designed to run off the DC bias on a telephone line)

Telco runs 48VDC all over the central offices to supply rack mounted equipment. Hold over from olden days since the DC plant already exists.

[J.J.]

Yeah it's a heavy one unit.

A theory is floating around about the efficiency of dc powered servers and how less heat means easier to cool and etc...

I need to go raid the rack for the correct plugs or install a different plug in the house to try and get one of the mods working...I just wanted an easier simpler power supply but looks like that won't be cheap.. Or easy.

[Tallpine]

8 deep cycle batteries: 2x 4 in series. [/there, I fixed it]

Chris

Yeah, I was going to suggest 4 12v batteries in series, each with a 12v charger attached 

The way that we jump an M35 is to hook up jumper cables from two pickups 

[Doggy Daddy]

try and get one of the mods working...

Yeah.  Good luck with THAT!  Why do you think they have all that time to spend on the web?   

[Scout26]

What is this "work" of which you speak?

[GigaBuist]

I'd grab a Kill-a-watt like Nick suggested and see what the power supply actually draws with one system on it.  My Sun x86 boxes have 1500 watt power supplies on them but usually only suck down 300-330 watts while in operation.

What kind of AC input does the power supply take? You mentioned needing to drop a different outlet into your house to use it.  I'm not aware of a 110V 50 amp outlet, but I am also not very knowledgeable about such things.  I do know that because my rack runs everything through a UPS that requires a 30 amp 125V circuit I had to use one of these until I got a proper dedicated 30amp 125V plug: http://www.amazon.com/gp/product/B002YB108Y/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1

Didn't feel bad about using the adapter for a year because I knew my draw was below 15 amps thanks to the Kill-A-Watt already mentioned.

[J.J.]

That's the guy. But it takes a nema 20 to that. Just gonna make a nema 20 to standard adapter for now and only run one of the r rectifiers in the 1u unit