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Thread: Two power supplies question

  1. #1
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    Default Two power supplies question

    I am running two 350 watt power supplies for a 1600 pixel mega tree. Each one will power 1 side or 8 outputs of the board.

    My question is do you use two 16 gauge power cords or one power cord and just jump the tree wires to the next power supply.
    I saw where some do it both ways and like to do it the right and the safest way.
    Thank you for your input
    John

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    Default Re: Two power supplies question

    If itís just two power supplies you can just jumper across to the other one so you donít run two power cords into the box.

    One thing to consider when working with electricity on either side (AC/DC) of your power supplies is to measure and calculate for your self.

    There are a lot of variables when calculating current that we donít see or know about your show. These unknown things can change how/what suggestions and responses you get and the accuracy of the answer.

  3. #3
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    Default Re: Two power supplies question

    There are 2 things you do need to make sure of,

    1. That the Grounds (DC) between the 2 PSUs are connected, this can be done by the light strings, just making sure that GND is contiguous across the tree. Or you can run a jumper between PSUs

    2. That the +V is cut between the sections that each PSU feeds
    Matt

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    Default Re: Two power supplies question

    700W at 120v is about 7A. A single 16 gauge extension cord can handle that load. The same is not true for the low voltage side. You did not mention the PSU output voltage. Assuming 12v then each PSU is supplying ~30A, It will take at least three 16 AWG cables from each PSU to get that much current to the lights and you will have some pretty serious losses if you are going any significant distance. I try to keep my 16 AWG cables at less than 8A.

    FYI: @5v you are pushing over 60A per PSU. That takes a lot more wire to feed the lights.


    2019 - Just moved into a new home (yet another change of plans). Will be dim but not dark. Too much to do at the new place to leave time for a show.
    https://www.youtube.com/channel/UCyX...ttrsZNARkUce0Q

  5. #5
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    Default Re: Two power supplies question

    I'm not sure I understand all of what you guys are saying. The two power supplies are side by side and have 16 awg jumping all three terminals plus minus and ground. They will feed the 16 strings 8 to a side per power supply and will travel about 3 feet away from the power supply. I plan to use 1 feed from each side to power 200 pixels that are 20 feet away.

    What am I not doing right? What do I need to do?
    Thanks to all who are trying to help me
    John

  6. #6
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    Default Re: Two power supplies question

    Your 100 pixel legs use 100 * 0.06A = 6A. Well within the carrying capacity of a 16 AWG wire.
    200 pixels per string = 200 * 0.06A = 12A per string. The string itself is most likely at least 200" long (1" spacing) or 400" long (2" spacing). 16 AWG would be marginal at 12A and going over 400" to the end of the string just makes things worse. Also, you will need to power inject at least every 100 pixels (12v, 5v = every 50 pixels).

    What I am saying is that to use 16 AWG wire to drive 200 pixels 20' away you will need to have two wires from each of the 200 light strings going to the PSU to keep the wires from overheating. FYI: Many people decide to limit the intensity settings for the pixels. This allows you to use 16 AWG to drive more pixels. IMO this is a dangerous thing to do.


    2019 - Just moved into a new home (yet another change of plans). Will be dim but not dark. Too much to do at the new place to leave time for a show.
    https://www.youtube.com/channel/UCyX...ttrsZNARkUce0Q

  7. #7
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    Default Re: Two power supplies question

    I think I see your confusion. Split the two different parts. The AC side and the DC side.

    On the DC side you are being told to watch the size of your cabling because at low voltage DC, say 12 volts, you will need bigger wires to get from the power supply to the pixels, or pixel controller. On the AC side, since the voltage is higher, you don't need as big of a wire.

    Doing the math - In a pure environment (no calculations for equipment efficiencies, etc.), 120 watts at 12 volts is 10 amp. That same 120 watts at 120 volts is 1 amp. So when Martin says "700 watts at 120 volts is 7 amps", the combination of both of your power supplies, your power wire - on the AC side - can be the smaller size. 16 gauge is rated at 13 Amps according to my wire chart. At 120 volts, that 16 gauge wire would be able to carry 1,560 watts. No problem running both of the power supplies off of it.

    FYI - We do it all the time here. Up to three 300 watt power supplies off of the same feed cable. We opt to use 14 gauge (just as our standard and to be a bit safer) for two power supplies. We have never had a warm cable. Of course, your mileage may vary.
    Last edited by algerdes; 06-11-2019 at 12:33 PM.
    Live, Laugh, Love.

  8. #8
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    Default Re: Two power supplies question

    I did some more D&D I can and will run my controller at 70% power.
    One more question do I need to connect the ground from string 8 and string 9 on the pixels since they are both on different power supplies?

  9. #9
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    Default Re: Two power supplies question

    Maybe. You will need to run "data plus V-" from the end of one string to the start of the next string (if you are daisy chaining the strings). If you have a dedicated "data plus V-" going from a controller output to each leg of the tree and to the remote strings then the V- strap between PSUs is optional.


    2019 - Just moved into a new home (yet another change of plans). Will be dim but not dark. Too much to do at the new place to leave time for a show.
    https://www.youtube.com/channel/UCyX...ttrsZNARkUce0Q

  10. #10
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    Default Re: Two power supplies question

    Thank you Martin and others for all your input.
    I ran 16 awg for 110 input and ran 14 awg from each power supply to each side of the controller. I ran 18 awg for the three feet to each of the 16 individual strings. I ran 16 awg from each power supply to the 20 feet for the two differential receivers.
    I put 1 string of 100 pixels in each controller and ran three songs and all looked good.
    Thanks to all for your help.
    Come on Christmas.
    John

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