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Friday, 28 December 2012

Making A Current Blasting Power Supply With Old ATX Power Supplies


what is Current Blasting? I hear you ask..
Well sometimes when you have a fault with a piece of equipment it's not always easy to track down the issue - it usually comes down to a failed component that has shorted internally - a single failed component of possibly thousands so one method of tracking it down is blasting it with high current (at a low voltage)
It is quite a fun method of trouble shooting because most of the time the failed component explodes off the board, starts smoking or gets very hot.
so what's the best method of doing this? well get a high amp power supply which costs loads of money OR make one out of an old computer power supply.
You have probably seen people make power supplies out of these before for powering their projects which I don't personally think is that great of an idea because of the high current involved but you can use it for that if you wish.

The reason why these things are great for current blasting purposes is because the junked one I have (which is from a very cheap case that had a power supply on it) has a 5volt rail of 27 amps, a 12 volt rail of 13 amps and a 3.3volt rail of 25 amps. which as you can imagine is more than enough.

now for the usual "danger" crap...
I'm sure by now you're used to reading disclaimers and warnings to the point of being desensitized by it and it is easy to ignore these things.
but these things can be very dangerous so you need to take a lot of care when building/hacking these things. They have a lot of capacitors which may retain high energy even when the unit is unplugged. you NEED to make sure they are discharged before you start handling it - that goes for the filter capacitor on the IEC mains input - sometimes they don't have a bleed resistor and can discharge 240 volts (or whatever your local voltage is) into you which I can assure you bloody hurts.

2 Things you must be aware of to use these things

1. in order to switch it on you need to solder the Green wire to Ground (black wire) I suggest
doing this by means of a switch. The green wire will be labelled "PS" or "PSON" on the main PCB

2. some ATX power supplies need a minimum load to function which is around 200mA
to achieve this you must bridge the 5 volt and Ground terminal with a 22Ω resistor.

if you're interested in how this was worked out you can use ohms law
R(resistance)=V(voltage)/I(current) so you type into your Calculator
5 / .200 = 25 so you have the answer 25Ω and you round down to your nearest value which was 22Ω in my case


Anyway here are some pictures, if you have any questions don't hesitate to ask. 



Bare ATX PCB
very cheap supply I found in my shed


I found this on the net some time ago, I'm not sure who it belongs to so if it's yours let me know and I will credit you and your site

9 comments:

  1. If you need more current, try to obtain an old server power supply. I have one from an old server i got for free, It supplies

    12v At 25 Amps
    5V At 34 Amps
    3.3 V at 40 Amps

    They're a really handy thing to have in the lab.

    Stephen

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  2. It seems, at least according to my google searches, that you are the only one on the web who has anything to say about this repair technique. What can you tel me, or where can you send me to get me on my way to building or acquiring this tool?

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    1. really? it's quite an old and famous technique - in fact I saw it used on a dave jones video not so long ago....quite right google says nothing - i'll find you the video where it is explained
      it's about 30 minutes in https://www.youtube.com/watch?v=F-VnbzXjH9I

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    3. What kind of power supply is that Dave's using in the video? Protech ...something.

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    4. Would this work well for the mod? http://www.amazon.com/dp/B004GLBIB4?psc=1

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    6. Daves is a rebadged one of these..

      http://www.ebay.co.uk/itm/Maas-SPS-9250-25-Amp-Regulated-Power-Supply-Unit-/180643124213?pt=UK_Mobile_Phones_Communication_Radio_Parts_Accessories&hash=item2a0f2b53f5

      and yes that would work but it's strongly advised that you don't do what most people do and use it as a normal bench power supply because you may build something and accidentally current blast something you don't want to blast. however there are actual kits to make these types of power supplies.
      and of course there are a few power supply projects on this site.

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