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Convert
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Converting 12V (PCIE) power to 5V

Sat Dec 29, 2018 11:39 pm

I have a fairly proprietary system that is powered by switching PSU that only seems to output 12v. The mainboard has a 10pin header that outputs 12v so you can power PCIE video cards (obviously it's a unique connector, but the breakout cable is a dual 2x3 PCIE power cable). I have no intention on installing a graphics card, instead I'd like to add an SSD and therefore need 5v. I can easily figure out which pins supply 12v and which ones are ground, obviously, but what's not so obvious to me is how to safely step down the 12v to something the SSD can reliably use.

Would something like this work: https://www.amazon.com/NOYITO-Three-Ter ... 66874?th=1 I could of course DIY a similar solution but this is an easy way to convey the idea.
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Re: Converting 12V (PCIE) power to 5V

Sat Dec 29, 2018 11:54 pm

Yes, something like that should work.

FWIW the one you linked is an "old school" linear regulator (based on the LM7805, which dates back to the 1970s). Downside of this is they tend to generate a fair amount of heat; using one to step 12V down to 5V will result in a regulator efficiency of less than 50%... i.e. the regulator will actually use more power (and generate more heat) than the SSD you're powering from it. Upsides are that they are simple, put out very clean power, and are extremely reliable (provided you don't push them past their limits).

Something based on a modern switching regulator design would be more efficient (but may cost you a bit more).

Edit: And if you do go with that specific one, make 100% sure they send you the 5V version, as they list both a 5V and a 12V. The listing is a little muddled, and using the wrong one is a recipe for a fried SSD. I'd check the output with a multimeter and some sort of dummy load (e.g. a case fan) to verify that it is putting out 5V before hooking up the SSD to it.
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ludi
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 1:12 am

This is a switching version of the same thing:

https://www.amazon.com/Regulator-DROK-C ... +converter
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 2:16 am

OK, I'm guessing you have USB3 ports.
All USB ports provide 5V to the outside world-as long as you have a spare port-should be easy to modify a USB cable to
provide 5V to SSD.
If you have a multimeter, soldering iron, skill, and some balls, you could follow that 5V back to the MB, and take a line from there.
Most SSD's will also work off 3.3V.
good luck.
 
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 2:35 am

HERETIC wrote:
OK, I'm guessing you have USB3 ports.

Might not be a good assumption given that it's some sort of weird proprietary thing with a non-standard PSU, but yeah... if there are USB ports with sufficient wattage capability, that could be an easy source of 5V with no voltage converter required.
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 3:16 am

Be certain that you don't also need a 3V3 rail before you take the plunge.
 
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 9:28 am

Shobai wrote:
Be certain that you don't also need a 3V3 rail before you take the plunge.

In my experience most don't seem to require it. I've used passive Molex-to-SATA power adapters to power SSDs on multiple occasions, and have had no issues. There certainly could be some out there that need it though, since it is part of the SATA power connector spec.
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Convert
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 10:55 am

I was looking at the switching versions but the reviews made me worried given what I was powering. Since I don't know much about this stuff it makes it hard to distinguish between user error and crappy designs. That's one of the reasons I was interested in the LM7805 since it seemed like a slightly more "foolproof" option, though I'm guessing that's a bit of a logical fallacy.

Perhaps I should re-evaluate if there’s a way I can find 5v somewhere in the system as suggested.

I won’t be needing 3.3v, I believe that’s only common on 1.8 SSD’s.
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 11:44 am

Convert wrote:
I was looking at the switching versions but the reviews made me worried given what I was powering. Since I don't know much about this stuff it makes it hard to distinguish between user error and crappy designs. That's one of the reasons I was interested in the LM7805 since it seemed like a slightly more "foolproof" option, though I'm guessing that's a bit of a logical fallacy.

Perhaps I should re-evaluate if there’s a way I can find 5v somewhere in the system as suggested.

I won’t be needing 3.3v, I believe that’s only common on 1.8 SSD’s.

The LM7805 is indeed a solid and relatively foolproof piece of tech; that's why it is still available, even though it has literally been around since the 1970s. Its only major downsides are its horrible efficiency (which shouldn't be a show-stopper for a low power device like a SSD), and the fact that it needs an input voltage that is at least ~3V higher than the desired output voltage (not a problem in your case since you're going to be powering it from a 12V source).
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 1:18 pm

ludi wrote:
This is a switching version of the same thing:

https://www.amazon.com/Regulator-DROK-C ... +converter


Not quite. The circular pot on the top left corner means that you can change the voltage of the DROK converter. Its **almost** the same thing, but to use this one well, you need to have a voltmeter + screwdriver to set the voltage right.

-------------

I have a question though: why not use a standard 5V wall wart?

https://www.digikey.com/product-detail/ ... ND/5247140

The idea of a 120V AC -> 12V DC -> 5V DC converter just cringes my efficiency brain. If you don't have a 5V line, its probably more efficient to just buy a 120V Wall AC -> 5V DC direct converter. Its not even that expensive. The only downside is a potential ripple issue, but +/- 100mV pp and +/-5% load regulation probably is within the ATX specs. In any case, I'd personally prefer a new Wall Wart to a 12V->5V switching-converter.

The 7805 solution is horribly inefficient, but it'd work damn it. You'll have no switching noise (+/- 0mV pp), and probably good load regulation. Its just horribly inefficient. Its basically a resistor that can sense its output... so it self-regulates down to 5V. It just wastes all the power between 12V and 5V and shoots it off as heat. Its the dumbest design possible, but that's why it works in so many situations.
 
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 2:00 pm

My understanding was that you could just cut the trace and solder the 5v pads and forget the pot, but perhaps it still plays a roll. Several reviewers state it didn't work as intended (their fault or the design) so I guess it could still be needed.

Wall warts have tended to be on the noisier side from what I've seen, though I suppose I could always add a capacitor. Finding a quality one has always been hit or miss for me (the wall wart).

I agree the 7805 is inefficient, but with the little knowledge I have about the probabilities of something more efficient killing the SSD or worse the host system, I was trying to be cautious.

Not set on any one solution, and I'm very thankful for all the insight you guys always provide on my off the wall electronic questions. Love you guys!

I have verified the PSU only outputs 12v, but I'm pretty sure there is 5v going to a backplane after doing some reading so I'm going to poke around with a multimeter and see what I can find. Hopefully I won't end up needing anything special.
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Shobai
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 6:05 pm

Another consideration for the wall wart option is how GND will be referenced.
 
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Re: Converting 12V (PCIE) power to 5V

Sun Dec 30, 2018 8:53 pm

just brew it! wrote:
HERETIC wrote:
OK, I'm guessing you have USB3 ports.

Might not be a good assumption given that it's some sort of weird proprietary thing with a non-standard PSU, but yeah... if there are USB ports with sufficient wattage capability, that could be an easy source of 5V with no voltage converter required.


"weird proprietary thing" is a huge understatement-system that gives up to 150 watts for PCIE and nothing for storage is really strange.
Perhaps Convert might be willing to give us more information on system, we might then be able to give better advice. I know a lot of
atom based systems used 12 volts-even some Intel ones.................

Be VERY choosy if using a wall-wart, some can have terrible voltage regulation....................
 
Convert
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Re: Converting 12V (PCIE) power to 5V

Mon Dec 31, 2018 8:22 pm

It's an image reconstruction server for medical 3d imaging. Honestly it smells like some kind of rebranded HP or something commissioned from them, I wasn't aware that HP did custom stuff without branding though? It's using a common slot PSU that only outputs 12v and slots directly to the motherboard. From the motherboard there are headers placed around (2 10pin and 1 24) that then feed OUT 12v and from my sleuthing it looks like it does in fact feed 1 5v line to a backplane. If HP didn't build it, whoever did it wholesale copied some of their stuff.

So good news that I do have a single 5v line to tap into! With the abundant extra 12v available I was still hoping to make use of it but I guess it's not worth the hassle without knowing enough to build my own robust switching step down.
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Re: Converting 12V (PCIE) power to 5V

Fri Jan 04, 2019 10:48 pm

Convert wrote:
So good news that I do have a single 5v line to tap into! With the abundant extra 12v available I was still hoping to make use of it but I guess it's not worth the hassle without knowing enough to build my own robust switching step down.


Just reading a mailer, and came across a car-USB charger. You know the type-plugs into cig lighter 12 volts (13.8.) in 5 volts out----$4.
Thought of this thread. Could be worth a play.
Don't know the quality of the output on those things, but if people are happy plugging $1000 phones into them?????????????
good luck.....................
 
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Re: Converting 12V (PCIE) power to 5V

Fri Jan 04, 2019 11:18 pm

HERETIC wrote:
Convert wrote:
So good news that I do have a single 5v line to tap into! With the abundant extra 12v available I was still hoping to make use of it but I guess it's not worth the hassle without knowing enough to build my own robust switching step down.

Just reading a mailer, and came across a car-USB charger. You know the type-plugs into cig lighter 12 volts (13.8.) in 5 volts out----$4.
Thought of this thread. Could be worth a play.
Don't know the quality of the output on those things, but if people are happy plugging $1000 phones into them?????????????
good luck.....................

It's possible that phones have more power conditioning circuitry built in, precisely because people tend to use dodgy chargers.
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Re: Converting 12V (PCIE) power to 5V

Sat Jan 05, 2019 10:05 am

just brew it! wrote:
HERETIC wrote:
Convert wrote:
So good news that I do have a single 5v line to tap into! With the abundant extra 12v available I was still hoping to make use of it but I guess it's not worth the hassle without knowing enough to build my own robust switching step down.

Just reading a mailer, and came across a car-USB charger. You know the type-plugs into cig lighter 12 volts (13.8.) in 5 volts out----$4.
Thought of this thread. Could be worth a play.
Don't know the quality of the output on those things, but if people are happy plugging $1000 phones into them?????????????
good luck.....................

It's possible that phones have more power conditioning circuitry built in, precisely because people tend to use dodgy chargers.


Cheep ones are a 7805 variant with a heat sink -- anything rated up 500mA, maybe even 1A. More expensive ones are a buck converter like the one ludi linked to.

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