Testing Power Supplies... Idea

Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
edited November 2003 in Hardware
Ok, so I just bought a "550w" $30 PS from SVC to use as a bench PS. It's branded as a Real PC Power (www.realpcpower.com) PS, but it's got RAIDMAX fans, so it may be a leadman unit or something.

Regardless, I was thinking about how I could put the thing under a load and test it, without risking one of my high power draw systems (either the dual 2500s or the 2.4GHz 1800).

So, after pondering this for several hours (I'm too cheap to cough up $20/resistor for high-power heatsinkable resistors), I had a lighbulb go off in my head- INCANDESCENT BULBS!

They're dirt cheap; a bulb + socket = ~$3.00, if that; A 60w bulb will draw 5a @ 12v...

There's nothing I'm missing here, is there? All I'd have to do is pick up a bunch of bulbs that add up to the right amperage at each voltage, and wire it all up, right? It just seems waaay too easy...

Comments

  • Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
    edited November 2003
    So, this will work, correct?
  • primesuspectprimesuspect Beepin n' Boopin Detroit, MI Icrontian
    edited November 2003
    I'll point the resident electronics expert, Microman, to this thread.....

    /me goes to point
  • madmatmadmat
    edited November 2003
    When I was into rc-cars back in the early 90's we used to make what we called "dumpsters" for dumping our nicads at the same rate our motors drew which was 30a.
    A dumpster consisted of 15-12v dual element tail light bulbs with the cases soldered together with the glass parts opposing each other (i!i!i!i!i!i!) and the contacts were set up vertically when the thing was seen from the side laying horazontally.
    A wire was attached to the casing of one bulb thereby giving all the bulbs a ground and a wire was run from all the contacts in a chain so that all the bulbs ended up being on in a big parallel circuit with both filaments lit.
    Each bulb draws 2a with both elements burning so you can set it up for anything from a 2a draw to however high you want to go by just adding bulbs.
    To be tricky you can take and make 2 of them with 6 bulbs and run them alone or as a pair for a 12a draw or 24a draw.
  • botheredbothered Manchester UK
    edited November 2003
    How do you know what power the lamp will draw?
    It may draw 60w when connected to an ac supply but will be much higher connected to a dc supply. You'd have to measure the dc resitance and do a bit of ohms law.
    voltage over resistance gives you the current.
    voltage multiplied by the current gives you watts.
    But you already knew that, right?
  • jj Sterling Heights, MI Icrontian
    edited November 2003
    if you talking about a normal buld, like the kind that goes in a light fixture in your house...then yes your missing something. If your talking about a bulb that is rated at 12v ie. a small bulb from radioshack or a hobby store...then again I think you missing something. here is the low down

    House bulb---110v 60w. The current draw will be 60w/110v=.55a
    Now you need the resistence of the filiment of the bulb (this is what your missing. you get this by: 110v/.55a=200 ohms.

    Now use that resistance to find out the power draw from a 12v source. First get the current draw : 12v/200 ohms= .06a. Nexted get the power 12v*.06a=.720w

    If you have a clear bulb you will barely see the filiment glow. To test a 530w supply to 530w you will need 736 light bulbs. 736 light bulbs and sockets at $3.00 a pop = $2208.00 EEEKK!

    I would spend the $20 bucks for the high power resistor. Besides even on your calculations. 60w 12v @5 you would need 8 bulbs/sockest at $3.00 that = $24.
  • Mt_GoatMt_Goat Head Cheezy Knob Pflugerville (north of Austin) Icrontian
    edited November 2003
    Good one Microman! :thumbsup:

    Then consider the part I think about a lot these days is the amount of time and pissing around to do it! :rolleyes2
  • edcentricedcentric near Milwaukee, Wisconsin Icrontian
    edited November 2003
    Auto lights are the way to go.
    Go to the Flea market or junk yard and get a selection of fog lights or driving lights. Then wire them up for various drains. Big bulbs for these will draw 20A each so make sure that you check the bulbs carefully.
    Don't rely on measuring the cold resistance, work from the power rating.
  • botheredbothered Manchester UK
    edited November 2003
    Because of the way the filament is coiled the ac resistance is not the same as the dc resistance. You can't go off the wattage of the lamp if you're connecting dc to it. Measure the resistance. Do ohms law. The dc resistance will be lower than the ac resistance!
  • madmatmadmat
    edited November 2003
    I don't see why I took the time to make the above post. (reply 3 although I can tell no-one read it)
  • Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
    edited November 2003
    Madmat... ;D

    I read it. Sounds like a good idea to me, especially since I have an extra car sitting around... (parts car) :D

    Yeah, I probably missed something... I know basically nothing about electronics, except that if you feed 12v+ into a LED designed for <4v, it'll glow really brightly, make a fizzling sound, then go "bang!" and explode- literally. ;D
  • DanGDanG I AM CANADIAN Icrontian
    edited November 2003
    17-103-905-04.JPG

    $12.99 for the antec power supply tester @ newegg. I've used them before and they are great little tools. They have exposed pins that allow you to check the 3.3, 5 and 12v lines with a volt meter while the tester itself creates a load.

    http://www.newegg.com/app/ViewProduct.asp?submit=manufactory&manufactory=1516&catalog=350&DEPA=1&sortby=14&order=1
  • QCHQCH Ancient Guru Chicago Area - USA Icrontian
    edited November 2003
    I also have one and It works great. Plug it into a power supply and the tester is jumpered to force the power supply to turn on and a LED lights up to signify the the tester has power. Then you can use a multimeter to test the different leads. I'm not sure what type of load it put on the power supply...
  • Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
    edited November 2003
    qch- anywhere between 5w and 25w; mine has 2 5w resistors... but that doesn't stress the PS to any significant degree. It's fine for seeing if the thing will power on, but it doesn't really do much in the way of telling you what the actual maximum power output is.
  • Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
    edited November 2003
    Dan, the antec one has a single 25w resistor, I believe. It has the same problem I mentioned in my above post; I hooked up a bunch of crap I have sitting around to this PS (2 10,000RPM SCSI drives, 2 7200rpm drives, 2 24vdc/1a fans, a 92mm tornado, 2 60mm deltas, a 90cfm/120mm, etc., and the +12v line dropped to 11.8v; it tested @ 12.34 with nothing but the atx power supply tester... THAT'S why I want to put it under a good amount of load.
  • QCHQCH Ancient Guru Chicago Area - USA Icrontian
    edited November 2003
    Good call Geeky.... I will be talking with my Electronic Engineers to help me beef up a version of the Antec Tester.... hmmmm
  • muddocktormuddocktor
    edited November 2003
    The idea of using the 12v auto bulbs is a great idea, but you have to remember that when you first turn them on, the inrush current will be much higher for a second or so, until the filaments heat up. That is the reason why most incandescent bulbs burn out when you first turn them on. As the filament heats up, the resistance also increases, decreasing the amount of current flow. It would definitely be a good indicator on how your psu will handle sudden shock loads put on it, if your meter can respond fast enough to watch the voltage drop when you hook the load up.
  • Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
    edited November 2003
    The PS is DEAD. :D Rated 20a @ 12v... couldn't take 14a... ;D
  • muddocktormuddocktor
    edited November 2003
    Yeah, I know you smoked it's ass, Geeky:eek2:;D , but it still doesn't change the fact of using light bulbs for load testing for someone else.;)
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