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Power Diversification

Discussion in 'Power Supplies' started by Odd_Socks, Feb 5, 2016.

  1. Odd_Socks

    Odd_Socks New Elf

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    Hi,

    I am a newbe here and I was just wondering if people ever use any form of diversification when working out what power supplies or cabling to use.

    Oven here in the UK the house wiring for the ring main is rated at 32A but that only covers 3 sockets pulling full load, but we normally have many more sockets than that.

    I am sure most displays use a fraction of the full power possible at any one time and I am wondering if this is ever taken in to account.
     
  2. fasteddy

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

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    Most design their systems for full white which means maximum load because its safer to do so and it allows for more creative freedom when sequencing, so if you wanted to use full white over the whole display then you can. The other consideration is that we use switch mode power supplies which will shut down if overloaded as apposed to a circuit breaker or fuse which has thermal/time characteristics, so if you go over the rated current then normally it will take time to trip based on how much you have gone over the rated current.
    The other consideration is that with diversification in house wiring then normally you never have everything on, you wont have the oven, the toaster, the fry pan, all the TVs, all the lights and everything else that you have on at the same time and if you did then you trip the circuit breaker or blow the fuse, in most cases this is not too much of an issue as you just go and reset the circuit breaker or fuse and run a few less things at the same time and learn to manage with it. But if you are running a lights show and you have a part of your sequencing which overloads the power supplies then its going to be an ongoing issue until you change the way it is sequenced to ensure it keeps within the limits which takes away some creative freedom on how you want to sequence.

    The other issue is that many confuse the current of mains voltage with that of low voltage and think that 5 amps at 12v volts (60 watts) is 5 amps at 240v (1200 watts) when in fact that same 5 amps at 12v is actually only 0.25 amps, so some think that they will overload their house system when in fact a very large show can run from a couple of circuits. My show ran from 2 circuits and one of those circuits had the computer and other household items shared with it. Its only when you use incandescent lights that you will run into power issues but not many use those anymore and instead use efficient LEDs

    As far as using diversification for wiring size then again this is very different to mains voltage because of cable resistance which is the big enemy of low voltage applications, the thinner the cable the more resistance per metre which in turn means a higher % of voltage drop per metre and because low voltage applications use higher current for the same amount of power as if you were using mains voltage then this is not a good path to take with low voltage application

    So if you use diversification in your lighting design then realize it will behave differently to that of mains voltage and will cause you more issues then its worth
     
  3. David_AVD

    David_AVD Bite my shiny metal ass!

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    Some people with really large displays may need to use multiple circuits. Personally, mine is all on one dedicated 20A circuit.

    I prefer to calculate the consumption on a worst case scenario, not what I think the likely maximum would be.

    The other issue can arise when putting a lot of switchmode power supplies on one circuit. The inrush current (when they are first powered up) can trip the breaker.

    My display has 2 control boxes, each with 4 200W - 320W switchmode power supplies and I've never had an issue. As usual, individual results may vary and all that.
     
  4. OP
    OP
    Odd_Socks

    Odd_Socks New Elf

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    Thanks for the replies guys.

    The whole thing about the fact of the power supplies shut down, and needing to modify the sequence make a lot of sense.

    I do have a background in the electrical and electronic fields so I am aware of some peoples confusion with the current drawn rather than the power.

    I am looking to run 12v supplies to local 5v regulators, to reduce the problems of voltage drop, but I do understand what you are saying about the issues this can cause.

    I was under the impression that most Switch mode supplies nowadays have a special resistor to reduce the inrush current problem.

    I am hoping to install some remote current monitoring in my system so that I can keep an eye on the demand.
     
  5. fasteddy

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

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    Using Voltage regulators is a great way of increasing the distance and minimising the size of cable used. I sometimes use 12 - 48v regulators and then bring back using a 48 - 12v regulator, There are some losses doing it this way but you can get a very long run using the same cable compared to 12vdc

    You are correct that power supplies are designed to handle the in rush current and looking at the specs of a meanwell SP450-12 power supply you can go over the max rating but it says on the spec sheet that a 33% duty cycle maximum within every 30 minutes - Average output power should not exceed the rated power. The peak load for 10 minutes is rated at 516 watts.
    So if you really wanted to then you could overload the power supply for short periods, but then pushing a switch mode power supply to it s max and then a little further is not really good practice and wonder how that will effect the life of the power supply in the long term
     

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