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Thread: Two power supplys

  1. #1
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    Default Two power supplys

    Please see attached to see if I have this wired right. I don't want to take a chance and mess up.
    Thank you
    JohnIMG_1081.jpg

  2. #2
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    Default Re: Two power supplys

    Quote Originally Posted by oldandslow View Post
    Please see attached to see if I have this wired right. I don't want to take a chance and mess up.
    Thank you
    JohnIMG_1081.jpg
    From your drawing all appears to be right.

  3. #3
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    Default Re: Two power supplys

    As BobBee says, OK. The key is don't EVER connect the positives from two different power supplies together. Each will be trying to control to a set voltage that is slightly different from the other. Each will try to adjust its output, they will fight each other until something gives, usually one or both power supplies may die in the process. This is easy to do when you are power injecting and forget that a different power supply is powering the other end of the string.
    Ed
    Happily retired

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    Default Re: Two power supplys

    Quote Originally Posted by ezellner View Post
    As BobBee says, OK. The key is don't EVER connect the positives from two different power supplies together. Each will be trying to control to a set voltage that is slightly different from the other. Each will try to adjust its output, they will fight each other until something gives, usually one or both power supplies may die in the process. This is easy to do when you are power injecting and forget that a different power supply is powering the other end of the string.
    Hey Bob,

    I don't power inject, but I've seen this brought up before, so I'm not sure what's correct. I remember reading that injecting from a separate PSU is okay as long as they share a common ground. Assuming this means input grounds on the PSU or is what I remember bad advice?

  5. #5
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    Default Re: Two power supplys

    Just make sure you tie the commons together and it will be good. (-) side.

  6. #6
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    Default Re: Two power supplys

    Common ground may be a bad term in this context. Many of our PSUs have an earth ground and that should be connected to the grounding pin on your power plug.

    Some people use the term ground to represent the voltage reference coming out of the PSUs. For those without electronic exposure, the interchangeable use of the term ground and V- and earth ground can be confusing. Hence, I use the term V- (since that is how most of our PSUs tend to be labeled) to represent the reference output of our PSUs. If you are using a PC or Server supply then they are labeled ground.

    At any rate, it is a bad idea to have both V+ and V- connected between two supplies at the same time. Either one alone is NOT an issue. We tend to connect the V- lines from our PSUs to each other to provide a common reference with respect to the data lines. This means that you need to take great care that the V+ lines from the PSUs do not get connected to each other. Doing so makes "bad things" happen.

    Summary:
    • PSU Input
      • Line - Typically known as the "Hot" wire in a home wiring system.
      • Neutral - This is the reference line in a home wiring system.
      • Ground - Third wire in a home electrical system that is connected to a wire that goes to a piece of metal that is in contact with dirt somewhere near your home. This is usually connected to the metal case of your PSU.

    • DC PSU Output
      • V- (aka ground // common) - reference voltage coming out of your PSU. Often connected to the V- coming out of other PSUs.
      • V+ (AKA hot / power) - Positive voltage (with respect to the reference output). Typically is never connected to another PSU.


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  7. #7
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    Default Re: Two power supplys

    but usually the bigger controllers are made to connect 2 diferent psupplys. they have seperate psupply connections and the circuitry inside them keep the v+ from each supply seperate

  8. #8
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    Default Re: Two power supplys

    Quote Originally Posted by ezellner View Post
    As BobBee says, OK. The key is don't EVER connect the positives from two different power supplies together. Each will be trying to control to a set voltage that is slightly different from the other. Each will try to adjust its output, they will fight each other until something gives, usually one or both power supplies may die in the process. This is easy to do when you are power injecting and forget that a different power supply is powering the other end of the string.
    I always tell people, power supplies are not batteries, they can not be put in series

  9. #9
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    Default Re: Two power supplys

    Quote Originally Posted by drew999999 View Post
    Hey Bob,

    I don't power inject, but I've seen this brought up before, so I'm not sure what's correct. I remember reading that injecting from a separate PSU is okay as long as they share a common ground. Assuming this means input grounds on the PSU or is what I remember bad advice?
    You want to tie the DC -V of the two PSUs together, which since the -V (GND) wire for the string of pixels needs to run the entire length of the sting - they are automatically tied together. You never want to cut -V in a string because the Data is in reference to GND (-V)
    Matt

  10. #10
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    Default Re: Two power supplys

    Quote Originally Posted by MrDudeMan View Post
    but usually the bigger controllers are made to connect 2 diferent psupplys. they have seperate psupply connections and the circuitry inside them keep the v+ from each supply seperate

    Make sure they explicitly say this. Power supplies intended for "multi-power supply" use, or "stacking", can be good - but make sure they are intended for this. The power supplies commonly used in this hobby are not. Our common supplies will fight with each other till one wins and the other one (or both) dies an awful death. "Magic Smoke" may or may not be included.
    Live, Laugh, Love.

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