Hooking up -48v DC power supply?

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DellAxim

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I have a power supply that was removed from some kind of rack mount telecom equipment, rated for -48v DC input. (-38 to -60) Otherwise it appears to be a normal ATX style power supply. I'm going to be using it with a computer running from a 48v battery.

How do I hook this up? The negative 48v confuses me. There are 3 large input wires: green/yellow which is tied to chassis ground, black, and white. Is the white wire positive? Should the chassis ground be tied to the negative on the battery?
 
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DellAxim said:
I have a power supply that was removed from some kind of rack mount telecom equipment, rated for -48v DC input. (-38 to -60) Otherwise it appears to be a normal ATX style power supply. I'm going to be using it with a computer running from a 48v battery.

How do I hook this up? The negative 48v confuses me. There are 3 large input wires: green/yellow which is tied to chassis ground, black, and white. Is the white wire positive? Should the chassis ground be tied to the negative on the battery?
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These types of supplies are intended for when you have a facility DC rectifier and are delivering straight DC power to racks. I won't give advice as to what the color scheme is because I don't want to be held responsible. You'll want to look at the schematics/instructions. It can vary highly per country.. White could be positive, it could be negative.. It could be ground.

All of that being said, I wouldn't advocate using this thing. It doesn't make sense outside of having a giant facility DC rectifier.
 
I am well aware of what they are for. They are used everywhere in the telecom industry where absolutely everything (even the air conditioning) runs on 48v DC which is provided by giant batteries any time there is a power interruption. It's a facility wide UPS. It makes perfect sense to use in an application where my power source is exactly the same voltage, I just don't use outdated backwards DC nomenclature. I'm not sure what this exact supply powered, but it clearly follows the ATX standard colors and connectors. There is basically no info available online for it.

The only concern I have is accidentally hooking it up backwards and smoking it - the input connector is proprietary and not labeled. It simply plugs onto some normal spade connectors on the board though.
 
Nobu said:
no label on the board either, back or front?
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Nope, totally blank, except for the label that says -48v. I checked the green/yellow with DMM, like I said that touches chassis ground, the black and white do not touch the ground or each other.
 
DellAxim said:
I am well aware of what they are for. They are used everywhere in the telecom industry where absolutely everything (even the air conditioning) runs on 48v DC which is provided by giant batteries any time there is a power interruption. It's a facility wide UPS. It makes perfect sense to use in an application where my power source is exactly the same voltage, I just don't use outdated backwards DC nomenclature. I'm not sure what this exact supply powered, but it clearly follows the ATX standard colors and connectors. There is basically no info available online for it.

The only concern I have is accidentally hooking it up backwards and smoking it - the input connector is proprietary and not labeled. It simply plugs onto some normal spade connectors on the board though.
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Great, good luck.
 
Would it be possible to upload a pic of the PCB? Tracing the traces often helps here.
 
Another clue - there is a 20A glass fuse on the input, tied to the white wire. Do they put the fuses on the positive side in -48v stuff?
 
DellAxim said:
When you have nothing of value to say, it's generally best to just hit the back button. This is a cheap surplus power supply, not a nuclear generator.
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You already had your answer before you posted, apparently. No one here can tell you which color to use safely. White is typically positive, but without posting the brand, what region the PSU is from, etc WTF did you expect? You apparently know it all anyways, so like I said, good luck.
 
Mchart said:
You already had your answer before you posted, apparently. No one here can tell you which color to use safely. White is typically positive, but without posting the brand, what region the PSU is from, etc WTF did you expect? You apparently know it all anyways, so like I said, good luck.
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I expected others who know about power supplies to help, and that's exactly what they are doing. This is not a major mystery. I suspect there are people here that work in the industry and may know exactly what I am talking about. There is a 50/50 chance it will work if I randomly pick wires. There's also a chance nothing bad will happen if they get mixed up. If I knew the specs and the region don't you think I would have posted that? If it goes into nuclear melt down I will just buy another, I am not poor. Jesus...it's not even dangerous like 120v could be.

As for the output side of things, yes, I already know everything I need to know about it, I didn't ask any questions about that, or if I "should" use anything. It's standard ATX.

You are being entirely useless. I was trying to be nice, just get lost. Thread crapping is not welcome. People like you are an enormous problem on forums these days.
 
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White should be negative 48v. Ya should be able to ground the positive terminal on the battery and run the negative to the White. I would advise against leaving the ground floating and powering a computer off it.

If you want confirmation open it up. It's dc so it should make it apparent.
 
DellAxim said:
Did you bother to read any part of this thread?
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Just the op. The rest of the thread was abit to fucking hostile to parse ;)

Chassis ground should be positive on the battery and needs to be tied to earth if u plan on plugging in a monitor or any ac devices to this computer

Look for some diodes in the psu before the mosfet stages. Should give ya an idea of direction
 
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NattyKathy said:
Would it be possible to upload a pic of the PCB? Tracing the traces often helps here.
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I'm not very good with discrete electronics but this is as detailed as I can get. In the top left corner the two pins you see are the chassis ground. The 5 pins about 1" below that are the white wire on the outside and the black wire on the inside, with the fuse on the white side.
1.jpg


The input side with absolutely no polarity markings:
2.jpg


Full board:
3.jpg

The only markings. I cannot find anything about "Rackable 4004F" besides a bunch of surplus ones for sale. Seems to be another one just like it labeled "SGI" but I can't find any info about that either.
4.jpg


Does anybody know if these -48v systems (specifically in the US) typically have the fuse on the negative side? The chassis ground will be connected to real earth.

I know this isn't that big of a deal but the idea of black being positive makes my brain hurt.
 
DellAxim said:
Does anybody know if these -48v systems (specifically in the US) typically have the fuse on the negative side? The chassis ground will be connected to real earth.

I know this isn't that big of a deal but the idea of black being positive makes my brain hurt.
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Telecom is weird and uses positive grounds. I can think of a few reasons why positive grounds were used, but I'll spare the details that'd probably give you a headache.

https://www.poweringthenetwork.com/uncategorized/negative-48-volt-power-what-why-and-how/

In the case of this power supply, white is most likely + and black is - in regards to battery voltage, which would make sense where the fuse is located. What I can't say is if the green ground wire is floating or not. If you test continuity and don't have a connection from green to black or white, you most likely have a floating ground and green should be connected to literally the earth and not either terminal of the battery.
 
Thank you for the info. I won't be able to power it up for a couple days but I will post the results. The ground wire is indeed floating.
 
Alright, I finally had a chance to hook it up to the batteries. It works! White-positive black negative. Green wire plugged into building ground.

Anybody that needs a good DC power supply should consider trying these, they're cheap on ebay and better quality than a lot of those cheap chinese DC power supplies. You can even buy relatively cheap surplus 48v server batteries....

I appreciate the advice.
 
What are the output specs like? Rackable Systems and SGI (Silicon Graphics Incorporated) dates this back to the early 2000s. I'd imagine it would be heavy on 5V given the vintage.
 
NattyKathy said:
What are the output specs like? Rackable Systems and SGI (Silicon Graphics Incorporated) dates this back to the early 2000s. I'd imagine it would be heavy on 5V given the vintage.
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+12v - 38A
+5v - 30A
+3.3v - 10A
-12v - 0.5A
Combined total 456W MAX
Also says "Date code 0935" - anybody know what that means?

Probably not for the latest and greatest mining rig, but not bad.
 
DellAxim said:
+12v - 38A
+5v - 30A
+3.3v - 10A
-12v - 0.5A
Combined total 456W MAX
Also says "Date code 0935" - anybody know what that means?

Probably not for the latest and greatest mining rig, but not bad.
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Decent specs provided the capacitance has held up. "0935" would mean 2009, week 35 (Aug 24 - Aug 30) which lines up with the SGI / Rackable timeline (RIP)
 
Yeah, my biggest concern is the caps, though they seem high quality and mounted nicely with a bunch of silastic smeared all over. At $20 shipped I think I'll get a few more as spares, it came with a nice set of ATX cables also. I'm guessing somebody replaced these after a period of time for reliability, but probably not terribly long. These should also work great from a 12v source also if you used a cheap boost converter first.

Probably other types of surplus DC supplies available too, since the whole telecom world still runs on 48v. I remember seeing a larger 48v Dell supply somewhere.
 
DellAxim said:
Yeah, my biggest concern is the caps, though they seem high quality and mounted nicely with a bunch of silastic smeared all over.
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I would replace all of them if you plan on using the units for anything important. One in the pic has a date code of week 22 of 2008, making the capacitor 14 years old. That was still right in the middle of the capacitor plague and fake Nichicon and Rubycon capacitors were widespread and made it into everything. But even if they were genuine capacitors, you have no idea what kind of conditions the power supply operated in. It could have been in a smokin' hot network closet for years for all you know and be worn out.

DellAxim said:
These should also work great from a 12v source also if you used a cheap boost converter first.
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You'd need a ridiculously beefy 12v supply to do that, about 42 amps. You'd also need equally ridiculously thick wire. It's cheaper and more efficient to just have a 48v supply, and you don't need super thick wire for it.

https://www.ebay.com/itm/363699688565
 
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GiGaBiTe said:
You'd need a ridiculously beefy 12v supply to do that, about 42 amps. You'd also need equally ridiculously thick wire. It's cheaper and more efficient to just have a 48v supply, and you don't need super thick wire for it.

https://www.ebay.com/itm/363699688565
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You mean like...a BATTERY?! *GASP* Perhaps in a car?!!!?? Where might somebody find such exotic things?! Everybody knows small computers idle at 450 watts right? Shit my lawnmower puts out more amps than that...

Keep your geek pants on, I was just making a suggestion. Clearly I was not suggesting you connect another power supply, that would not make any sense. If you're starting with AC power, use an AC power supply. No, I'm not going to replace the caps just 'cause. And no, they don't have a 12 year end of life. This is not life support equipment. And yes, I understand the relationship between amps and volts quite well, better than most.

Somebody could very easily build their own custom UPS with something like this, and they could use many different types and voltages of battery. And it would be super cheap. I'm quite surprised nobody really knows what this is, I thought computer geeks were...smarter. This is just typical e-surplus. Very very common. Much better for DC projects than those worthless chinese "pico" power supplies.

I tend to forget how nit picky the bored nerds get, I remember why I don't post here anymore. I tend to find new building materials and think "hey, what can I make with this?" Other people see them and have a panic attack, screaming "IT DOESN'T HAVE A UL STICKER!! BURN IT!!". Feel free to do as you like in your own home.

Edit: if any power supply is likely to explode it's that cheap chinese ebay trash you posted. Those are garbage, even new. I'll take a 12 year old quality PS over that any day. More importantly and dangerously that chinese shit often leads to high voltage in places it should never, ever be.
 
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if we are talking about 120v supplies I would highly recommend https://www.ebay.com/itm/154877283544?hash=item240f67ccd8:g:wtoAAOSwgXxiHo96 ive used them thoroughly for mining at 80-110% continuous load.

48v psus are abit simpler although that pcb design looks ancient compared to every psu ive opened up. Should be fine and reliable within its limits. Building a local dc power structure from batteries can be benifitial however you are still dealing with voltage regulation on the battery charging side.
 
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DellAxim said:
Alright, I finally had a chance to hook it up to the batteries. It works! White-positive black negative. Green wire plugged into building ground.

Anybody that needs a good DC power supply should consider trying these, they're cheap on ebay and better quality than a lot of those cheap chinese DC power supplies. You can even buy relatively cheap surplus 48v server batteries....

I appreciate the advice.
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I know it's a necro bump, but this is like... the only place online I can find anything on someone using this. Did it "just work", did it have 5Vsb? were you able to use a standard ATX connector? I have one and I can power it up (followed your polarity) but it doesn't seem to DO anything, no 5VSB and if there is idle draw it is very low. I tried bridging ground to what "should" be the PS on, and nothing. I think I might have a dead unit :(
 
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