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westend's avatar
westend
Explorer
Nov 04, 2014

DIY PC power supply charger

I had stumbled across this instructable article about converting a PC power supply to a multivolt power supply/charger. Since I had a few lying around, I thought I'd give it a go.

I pretty much followed the Instructable project but added a few twists, mainly the binding post panel outside the PC supply. Here's some pictures:

The Antec supply I used has two fans so I removed the top cover fan, first-


Next step is to break out all the wire lead packages and cut all the connectors off-


Circuit board is protected with a plastic bag while I do some dremeling and drilling-


I used a .125 aluminum panel for the binding posts where all of those cut wires are then connected-


In the original article the wires are connected to the binding posts which are mounted in the original case. It was difficult to do that with a fan attached to the top cover, not much room. Here, the wires are led out of the case and attached to the binding posts-


The power supply trying mightily to charge a very old SLA battery. All the voltages are spot on. If I wish to use this as a 12 volt charger or maintainer, I will either mess with the original circuits or add a DC-DC converter. In this Wiki-how article, the author reports the 12V rail capable of 23 amps. There is also the possibility to combine the -12V rail and the +5V rail to get 17V.



Like all projects like this, I was a couple of pieces short, a 330 ohm resistor to make an indicator LED, and a mini-toggle to interrupt the DC output. I swear I had those before I started, lol. Anyhow, maybe some of you have an old PC supply laying around and can put it to some use. I could have added USB slots for charging phones or may add a battery holder to charge two AA batteries. Those always seem to be in demand.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Nov 04, 2014
    Saludos Amigo! Love your well thought-out presentation. IMO you covered all the bases!
  • westend's avatar
    westend
    Explorer
    Nov 04, 2014
    Thanks, guys. I could have made it a lot sexier with red posts but I have a container of 200 black ones and only a few reds left. I'm saving those for audio projects where phase is important. As it is, the bits and pieces all came out of bins. Like I mentioned, I was short a resistor, a toggle, and I need to update my shrink wrap inventory.

    Next project is a few of those cheap wall wart battery maintainers. I think I have diodes...hmmm, better pick some up when I get the other pieces. :B
  • BFL13's avatar
    BFL13
    Explorer II
    Nov 05, 2014
    I like this! I have two of those things from obsolete PC towers so why not?

    Would the booster Mex was playing with be right for that? If the power supply can do 12v and 23a, then what would the amps be at 16v?

    http://www.ebay.com/itm/DC-DC-600W-12-60V-To-12-80V-Booster-Step-Up-Power-Supply-Module-/251667269211?pt=LH_DefaultDomain_0&hash=item3a9889c65b

    My buck converter test didn't come out "right" perhaps due to a poor match in the set-up I tested it with, so I would not want the same thing to happen with a boost type :(
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    Nov 05, 2014
    Old news but nice looking adaptation.

    However do be aware that on PC power supplies the 12V line is not "monitored" for voltage regulation.

    The +5V line is used by the power supply to regulate the voltage.

    So what that means is putting a load on the 12V line it most likely will drop or sag more under load since the 5V line is not loaded.

    So to keep the +12V from sagging you also need to load the 5V line.
  • BFL13's avatar
    BFL13
    Explorer II
    Nov 05, 2014
    If you put the 5s in with the 12s to make 17 (not sure how you would actually do that) would that satisfy the requirement so it wouldn't sag? Maybe then I could use my buck converter instead of needing a boost one.

    Nope, mine is a 15a so that 23a is a problem--would need to ensure "demand" stays below 15a somehow. It does have a 15a fuse on the input side though.
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    Nov 05, 2014
    BFL13 wrote:
    If you put the 5s in with the 12s to make 17 (not sure how you would actually do that) would that satisfy the requirement so it wouldn't sag? Maybe then I could use my buck converter instead of needing a boost one.

    Nope, mine is a 15a so that 23a is a problem--would need to ensure "demand" stays below 15a somehow. It does have a 15a fuse on the input side though.


    PC power supplies all use a "common" ground point so +5V and +12V lines can not be "tied" together in series to make 17V.

    It would take a lot of serious circuit board rework and engineering to "split" the +12V ground from the +5V ground. Basically all the output voltages are coming from ONE high frequency transformer. 12V, 5V, 3.3V come from "taps" on the transformer.

    You could use the -12V and the +5V to make 17V, however ALL the negative voltage outputs in PC power supplies are extremely "weak". The -12V is typically .8A (yep that is 800 ma) to perhaps 1.5A.

    The negative voltages use the same "taps" as the positive output but the diodes polarity is reversed. They use lower current diodes for the negative voltages and most likely smaller cap values along with smaller circuit traces. In short it will cost you more time and money attempting to rework the supply than if you simply just bought a supply of the desired voltage and current output.

    Since ALL the voltages are developed from the same transformer they simply monitor the 5V line for voltage regulation and all the other voltages will stay within the proper voltage ranges for the given ratings.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Nov 06, 2014
    The boosters REGULATE output voltage, there is no sag at the output even if there is at the power supply. Output wattage is the limiting factor. The BOOSTER must be set (pot) to not exceed it's amperage limitation. Read the specs carefully and observe them to enjoy a decent service life. Because of adjustable current limiting these things SHOULD be able to be paralleled for more current output if needed.
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    Nov 06, 2014
    MEXICOWANDERER wrote:
    The boosters REGULATE output voltage, there is no sag at the output even if there is at the power supply. Output wattage is the limiting factor. The BOOSTER must be set (pot) to not exceed it's amperage limitation. Read the specs carefully and observe them to enjoy a decent service life. Because of adjustable current limiting these things SHOULD be able to be paralleled for more current output if needed.


    Yes, your booster will "regulate" the output, however having a "stable" INPUT voltage makes for LESS "work" that the booster needs to do.

    This translates into LESS wasted energy (IE HEAT) and much higher efficiency :) , after all getting THE MOST efficiency is the end goal..

    Uneven loading of one of these power supplies can create an unstable power supply. They ARE designed to have a certain percentage of loads on all the outputs.

    You can run them in this fashion but it may or may not "work" in ALL cases. They are really designed to have a much larger load on the +5V than on the +12V and many newer supplies have a pretty hefty output on the 3.3V line as well.

    I did have a thought however.. It just might be possible to take two PC power supplies and take the +12V of one and the +5V of the other and connect them in series to get 17V..

    The only "catch" to this that I can think of is making sure that the safety ground is not tied to the common DC ground on the supplies which could setup a nasty ground loop..

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