General questions on salvaging parts from old PSUs

Discussion in 'General Electronics Chat' started by Bp_968, Jan 4, 2014.

  1. Bp_968

    Thread Starter New Member

    Dec 25, 2013
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    I have 6 older PSUs on my desk now. 2 are from ATX PCs and one of those I'll be converting to a lab/bench supply very soon I hope!

    The other 4 PSUs are all QD units from COMPAQ servers. Everything is mashed in on top of each other. I'm just curious what precautions need to be taken to avoid being electrocooked or destroying important parts :) Should I short the leads on the caps or something? I'm still in newb hobby mode so I try to avoid HV stuff for now (though I have a stack of nixies I want to build SOOON!

    Its a bit of an open ended question so its why I took some photos so maybe if I'm lucky some of the more skilled members will jump in on the conversation and point out interesting uses for the various bits. I especially couldn't help but notice the huge 450v cap on the PSUs as well.

    I realise I'm probably being extra paranoid but I'm new to anything over 12vish and new to Electronic at this level period. And those are the last of the old worthless servers I can strip for many years to go :)


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  2. Bp_968

    Thread Starter New Member

    Dec 25, 2013
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  3. wayneh

    Expert

    Sep 9, 2010
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    I can't help you but I wanted to commend you for noticing the high voltage caps and connecting that observation with a potential risk. That's a lot better than finding out the hard way. :eek:
     
  4. inwo

    Well-Known Member

    Nov 7, 2013
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    I'm not much help either, but I do want to warn of the bad habit of shorting caps.

    Test with a meter. Preferably a low impedance analogue meter. You can then watch them drain to safe levels.

    I was in this habit of shorting as a last test before coming in contact with leads.

    I'm probably the only one here who has shorted a buss capacitor on a de-energized 5kw vfd and lived to tell.:eek:
     
  5. debe

    Well-Known Member

    Sep 21, 2010
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    I strip a lot of old computer PSUs, good source of switching transistors & Mosfets, also Shottky diodes.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    20kv from a colour CRT - ON, not off. :eek:
    Max.
     
  7. inwo

    Well-Known Member

    Nov 7, 2013
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    I can come close.

    An old tv with wire wrap pins.
    2nd screen supply.

    Pin melted right thru my finger. Cauterized it nicely.

    Woke up on the floor.:eek:

    Did you see this?
     
  8. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Thinking of those that would read your posts, could you try to post smaller pictures? Usually 640 x 480 is enough here.
     
    inwo likes this.
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The HV caps will all be safe if power has not been connected for 24 hours or so. Depending on the circuit some discharge to "safe" within a few minutes.

    If you are worried you just put your voltmeter across the cap and if it is charged to a high voltage you can see it. :)
     
  10. Bp_968

    Thread Starter New Member

    Dec 25, 2013
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    Thanks for the info everyone! I'll make sure to test the caps and *not* to short them!

    Sorry, resized them. there are two reasons they were the size they were:

    1> I'm used to forums resizing them automatically now and if you include a larger size it gives people the ability to zoom in on the image for more detail (seeing part #s, etc). Apparently this software doesn't do that.

    2> I usually resize my images based on a percentage. I took these photos with our new 24 megapixel D600 instead of the usual D4 with its 16MP. That ended up making the images larger then I intended them to be :)

    640x480 is so awful terrible I couldn't bring myself to do it. their 790 at the horizontal so they should fit even the old monitors at 1024x768. 640x480 looks bad on a 24" monitor, its basically microscopic on a newer iPad ;)
     
  11. alfacliff

    Well-Known Member

    Dec 13, 2013
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    If your salvaging electrolytic caps, look under the cap for signs of leakage, or a distnct smell of used kitty litter when desoldering, that indicates bad caps. also, any bulged caps should be trashed.
    cliff
     
  12. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    If the PSUs are not working you risk to keep the failed components as well. Kinf of a roulette...
     
  13. wayneh

    Expert

    Sep 9, 2010
    12,139
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    That TV I was working on a while back had at least one cap showing over 200V after 2 weeks idle. I found it with the meter, not with a spark, and that has left a permanent memory. I had previously thought 30 minutes or so would have been enough to de-energize everything. Now I'm a a believer. Treat every cap as if it was loaded.
     
  14. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    I usually embed the smaller resolution pictures and attach the full resolution ones.
     
  15. Bp_968

    Thread Starter New Member

    Dec 25, 2013
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    All of them were previously working. The ones in the photos came out of some old P3 servers that are basically scrap at this point. The PSes look amazing and are stuffed full of goodies, but are proprietary so basically useless at this point.

    Each of the systems I stripped had dual units so I got 4 of them out of the two servers.
     
  16. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Yep, TV's can be a different beast for sure!

    Generally PC PSUs charge the main cap to mains AC volts * 1.4 which can be dangerous, but they usually have 400k to 800k resistance across that cap to ground, which supplies the start current for the SMPS brain circuit. For that reason they won't hold any significant voltage over time.

    However you are very right about the need to treat all HV caps like they are "loaded". :) I still probe 400v caps with a voltmeter before putting my fingers anywhere near.
     
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