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Ground Loops using 2 power supplies

Discussion in 'Power Supplies' started by dariansdad, May 22, 2014.

  1. dariansdad

    dariansdad New Elf

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    I’ve been reading some stuff about using 2 power supplies for 1 controller. My question is regarding tying the 2 grounds together to NOT create a ground loop. I’m confused on the ground loop issue.
    1. Is it the grounds on the AC input side tied together or the DC output side? The AC side is already tied together at the main power panel, right?
    2. If it’s on the DC side, do I just use a jumper wire from one V- out on PS #1 to a V- out on the #2 PS?
    Any help would be appreciated.
    Ron
     
  2. davrus

    davrus Silent Elf

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    Negative for all the DC connections should be common. So, yes, the negative connections should be connected, with a wire thick enough to carry the full potential load. The issue here is about the return path of your DC circuit.


    This is a different issue than the earth contact on the AC side. (which is where ground loop plays a role).
     
  3. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Keep the AC and DC seperate as you are using a switched mode power supply and dont confuse a mains voltage ground/earth with a DC ground, these are 2 entirely different things and should not be connected together


    You dont really need to tie the grounds togther at the power supplies if you are using 2 power supplies (1 for each bank) on a controller with 2 power inputs as the outputs are seperate anyway, so something you really dont need to worry about with many controllers with 2 power supplies

    When you do need to connect the 2 grounds together between power supplies is when you are using power injection with different power supplies along the same length of string/strip. The reason this is needed is that no two power supplies are exactly the same and if we do not have the ground connected together in these situations then we can end up with a situation where one power supply draws a lot more current or the 2 will ocillate between eachother on current draw because the ground potential is not equal between the 2 power supplies, this will cause issues like flickering of the lights and may even damage the power supply after a period of time.
     
  4. DanJ

    DanJ Full Time Elf

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    Eddy--ignorance question here--I would have figured "ground" is "ground", assuming we are actually talking about earth ground (which should be the case in a house AC system, right?). Should the DC actually be hard-routed to a ground rod stuck in the ground? Thanks!!!
     
  5. ԆцряєсϮ

    ԆцряєсϮ Senior Elf

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    No dont get confused between the primary (Mains) side and secondary (DC) side.
    The Ground they are talking about is -ve on your Secondary or DC side of your supplies. This should not be connected to "Ground" literally.
     
  6. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    No The AC system and the DC system are completely different, People sometimes call Earth in a mains AC system ground as well. This can cause some confusion

    With an AC system we have something called an MEM which stands for main Earth and neutral, the earth and the neutral are connected (linked) togther, most times in your junction box and then connected to the earth stake

    But if we were to do the same thing with a DC circuit using a switch mode power supply and connect to a grounded earth then we will cause all sorts of issues.

    So Always keep the DC and the AC seperate and treat these as entirely different voltage systems regardless if some names seem similar.
     
  7. DanJ

    DanJ Full Time Elf

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    Thanks Eddy. Flange-head here (mech engr...) so I figured ground was ground. I will have to look at my PSU setup from last Christmas; I think I tied my V- into my AC ground/neutral.... So, should the DC system be tied to an earth ground rod then?? Sorry to bug you to death on this.... THANKS!!!!!!!
     
  8. ԆцряєсϮ

    ԆцряєсϮ Senior Elf

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    NO - Do not connect your V- on the DC side to Earth or an earth stake/ earth rod or anything else likely to be connected to the ground.
     
  9. DanJ

    DanJ Full Time Elf

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    Thanks Ruprect. So the V- is basically just a floating negative reference as opposed to a ground?? I appreciate the info. The reason I am asking all this is I have seen industrial (analog systems) systems setup as floating and non-floating grounds, so I am kind of picturing those systems when asking these questions....
     

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