Powering a router off a PC power supply

Discussion in 'General Discussion' started by Jsjolly, Jul 9, 2008.

  1. Jsjolly

    Jsjolly Addicted to LI Member

    HELP!!!!! Powering a router off a PC power supply


    I want to know if it is possible to power my wrt54g v1.0 which uses 5V 2A, directly off the 5v rail of my PC power supply. The router PSU has broken so I was thinking of cutting the cable at the broken PSU end and connecting it to a 5V molex connector of my PC PSU.

    Blue brick or working unit?

  2. mstombs

    mstombs Network Guru Member

    You are not the first to do this - but as I've warned before a PC PSU can put out 30A + on the 5V rail, so think about an inline fuse and think about your house insurance!
  3. Jsjolly

    Jsjolly Addicted to LI Member

    Doesnt it just give the amount of amps requested by the router?. There are other peripherals in their also, cdrom, floppy drive, hard drive (I know they run off different voltages), they dont blow up. There are a few projects out there that change a PC Power supply into a bench PSU and run these routers, without using an inline fuse, what is the difference between them and the way a PC power supply works then?. I was in the process of converting an old PSU to do this as well, so any more advise or info, links would be greatly appreciated.
  4. HennieM

    HennieM Network Guru Member

    Jsjolly, you are quite right: the router will draw only the Amps (I guess it's not more than 1.5A or 2A) that it requires.

    What mstombs is warning you about is this:
    If something goes wrong with your router - say a chip blows - your router would be fried anyway, no matter what power supply you used.
    However, as there now is a short circuit inside the router, and because the power supply will not blow (soon) because it CAN deliver like 30A or more on the 5V, you can have a fire or other damage to the things NEAR the router. Like if there's a curtain closeby, it can catch fire.

    If you have a fuse in the 5V supply that blows at say 3A, the above scenario would be prevented.

    If you had the normal power supply, the power supply itself would blow when the short-circuited router draws maybe more than 3A or 4A (because the power supply CANNOT deliver more than that), and prevent damage to the stuff around/near the router.
  5. mstombs

    mstombs Network Guru Member

    Absolutely, it will work just have to link a couple of pins on the motherboard connector to turn a PC PSU into a high power 5 and 10V source, but its if something goes wrong - the thin cable is particularly vulnerable as it will not be protected. Consumer goods have to pass lots of basic tests and should 'fail safe' by design as far as possible.
  6. Jsjolly

    Jsjolly Addicted to LI Member

    Thanks for your input guys.

    I have made a bench power supply from an old Pc one and tried it with the router, it doesnt power up, no pop,or bang or anything. Power is going into the router ok. The fuse and thing on the right are both getting a 5V supply, but the one on the left has no voltage and i`m guessing its faulty so want to replace it.

    Does anybody know what they are in this picture and where I could find a replacement?

  7. Stavr0

    Stavr0 Addicted to LI Member

    +5V sb

    If high amps is a concern, you could run the router from the Standby voltage, it's usually limited to 1.5A to 2A, more than enough for the router.

    As for short-circuits, yes, lots of things will melt. But the good PSUs will shut down on overload. I know, I was using a PSU to test a car adapter when I shorted the voltage while connecting the cigarette adapter using alligator clips. A nice spark, then the PSU cut out right away. I'd still add a 2A fuse there just in case.

    You can get a lot of voltages out of a PSU by using combinations of 3.3,5,12,-5,-12:
    * low amp only, uses negative rails which are usually 0.5A
  8. mstombs

    mstombs Network Guru Member

    They look like ceramic inductor 'chokes'. They will be on both sides of the incoming power supply, so one will be at 0V. Their job is to filter out high frequency EMC to/from the router.
    Only a straight piece of wire round round ferromagnetic material - not much to go wrong!

    I'm sure there will be a 3.3V regulator somewhere - can you find and measure the 3.3V rail - usually available on the serial interface at least.
  9. mstombs

    mstombs Network Guru Member

    I would be more concerned about sustained overload than short circuit for the fire risk. A 30A rated PSU will not shutdown if a fault pulls 20A, the designers will have assumed 2A rated PSU which would shutdown via fuse or thermal overload.

    Not a likely scenario - but there are reasons commercial products have to comply with basic safety design requirements.
  10. Jsjolly

    Jsjolly Addicted to LI Member

    Thanks for your information all. It is very helpful :thumbup:. I am unable to find the 3.3v as I cant seem to find any voltage past the (red lines) points on the picture. The cap looks healthy and the inductor doesnt look burnt or anything.
    The light blue lines say 5 volts, the yellow line says 5 volts and the two red lines say 0 volts. Do you think one of these has burnt out.
  11. mstombs

    mstombs Network Guru Member

  12. Jsjolly

    Jsjolly Addicted to LI Member


    I have tested this component and am getting 5v going in, but only 1.2V coming out. I think this might be the problem and the 3.3v regulator you mentioned. I gently pushed down onto the chip and the power light and diagnostic light (briefly) came on. Possibly the problem?. I am going to see if its dry jointed by running the soldering iron over it, but I think it is actually faulty. Where do I find a replacement?.

    EDIT: The lights only came on because I was shorting two pins.
  13. DrTibbs

    DrTibbs Addicted to LI Member

    No reason why it shouldnt work. You might also look into PPOE
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