Where's the ground??

Discussion in 'General Electronics Chat' started by dengel, Sep 26, 2007.

  1. dengel

    Thread Starter New Member

    Sep 17, 2007
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    I have a power supply that outputs 12V and 5V. It has a mini-din plug with 4 pins, 2@12V, and 2@5V. I want to connect this to a fan controller which has a four pin molex connector 12V/grd/grd/5V.

    Can anyone tell me where I find or what I use for a ground for this type of a connection.

    The spec on the power unit are:
    Input: 100-240 VAC 50/60Hz
    Output #1: +5V @ 1.5A #2: +12V @ 1.5A
    Specifications/Features: Removed from New Equipment Desktop switching supply. Over current protection. Std. IEC 3 wire input connector. 4ft. output cable with 4Pin Mini DIN connector.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    The ground is the metal shell that surrounds the pins. You could scrounge a mini-DIN socket from a dead motherboard or something. Your local PC repair shop should have a bin full of dead MB's.
     
  3. mrmeval

    Distinguished Member

    Jun 30, 2006
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  4. dengel

    Thread Starter New Member

    Sep 17, 2007
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    thank you for the response, I have a 4 pin mini-din socket to plug the power supply into. However the socket only has 4 pins out the back (2@12V & 2@5V). There is a metal shroud on the socket that the metal shroud of the power supply socket goes over. However I'm not sure if they actually contact each other when plugged in.

    I guess I could solder a wire to the shroud, but this seems so messy and not the RIGHT way to do this.

    Any thoughts.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Doesn't the shroud of your socket have a connection? Like, via hold-down screws or solder tabs?

    Try using a meter on it.

    I don't know what your mini-DIN socket looks like - do you have a photo, or part number?

    I did receive your E-mail on this - but it's best to just post your Q's in the forum; you'll receive responses more quickly that way - besides, E-mail can get "lost" and people might not check E-mail for days.
     
  6. dengel

    Thread Starter New Member

    Sep 17, 2007
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  7. SgtWookie

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    Jul 17, 2007
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    OK, wait a minute. ;)

    Why don't you plug the power supply into your mini-DIN jack, and then simply measure between the four pins by themselves?

    I have a feeling that you'll find that two are ground (or return, if you will), one is +5v, and the remaining is +12v.

    The two grounds/returns might not be connected to each other inside the power supply in an attempt to avoid a "ground loop". But you could start off (with the supply UNPLUGGED and the leads all shorted together for a few seconds) by taking resistance measurements between each of the four pins to see if two of them are shorted together. If so, you've probably found your grounds.

    Put your negative meter lead on one of those two, set your meter for +20v range, and plug in the power supply. See which pins result in +5v and +12v measurements - or thereabouts.
     
  8. dengel

    Thread Starter New Member

    Sep 17, 2007
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    You know that is exactly what I thought it should be, but was thrown off by the diagram from the power supply company.
    www.powersupplydepot.com/productview.asp?product=16246+PS

    I don't have a meter, but maybe I can head over to Radio Shack for some help.

    I appreciate your time and hopefully I won't bother you again!!
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Yeah, it's hard to get much done without a meter - pretty basic tool.

    Harbor Freight Tools sells DMM's pretty cheap on sale - $3-$4. I picked up a few of them, and found they're pretty accurate.

    It's always good to have an analog meter, too - even a "cheapie". Makes it easy to spot-check caps and the like.
     
  10. dengel

    Thread Starter New Member

    Sep 17, 2007
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    Well, the shield is the ground. I just drilled a hole thru the connector and soldered the ground wire to the outside of the shield.

    thanks again
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    OK, there you go and now we all know ;)

    That'll work - make sure your ground wire is heavy enough to take the combined max power; 1.5A @ 5V + 1.5A @ 12V. What gauge your ground wire needs to be depends upon that combined power and how long your run is. I always go for overkill - why use a 2x4 when a 4x6 will work just fine? ;)
     
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