Over Volting

Discussion in 'Power Supplies' started by bigstott, Jul 10, 2014.

  1. bigstott

    bigstott New Elf

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    I was wondering if anyone has used say a 16.6 v power supply on their 12v pixels before. Will over volting hurt?? Especially for log runs where the is v drop anyways?
     
  2. AAH

    AAH I love blinky lights :) Community Project Designer

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    Powering the pixels with that much extra volts is likely to cause issues especially if they happen to be 1 pixel/led nodes rather than 1 pixel/3 led pixel strip. As it is only when all the pixels are on white that the power supply and cabling is under full load and the most voltage drop is experienced. Winding the supply up to maybe 13V if you were having very slight voltage problems might be acceptable but the 1st pixels closest to the power supply are reasonably likely to be damaged by the extra heat that they have to get rid of with those extra volts. Heavier cable and a better power injection layout is a better option than trying to wind up the volts. If it is very difficult to get from the power supply to the pixels then the use of dc-dc converters and running 24V or 30V supplies may be an option. There's been a few topics lately on the use of dc-dc converters and info is starting to get into the wiki.
     
  3. BundyRoy

    BundyRoy Senior Elf

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    Is there a specified tolerance on what the pixels can take. With the PSU the output voltage is generally slightly adjustable. My PSU is currently on 12.5V and I have some 12V pixels hooked up to it with 10m of 2.5mm2 cable between the PSU and the pixels. So I figure (have not measured) that the voltage will be closer to 12v by the time it gets to the pixels.

    My concern is that it is highly likely that I will hook up other pixels effectively straight to the PSU at some stage as well. This is when the 12.5V will become more important. Is there an acceptable tolerance on the 12V or should I wind it back to 12V to be sure.
     
  4. David_AVD

    David_AVD Good news, everyone!

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    As Alan said, the big issue is when there is a low load (no lights lit) on the power supply. The voltage at the pixels is then whatever the power supply is set to as there's very little voltage drop in the cables at low loads.

    Much better to beef up the cabling. Using thinner cabling (and adjusting the voltage up as a "crutch") can also lead to instability in the system. This results in the pixels flashing and sometimes "locking up" when pushed to high brightness levels.
     
  5. BundyRoy

    BundyRoy Senior Elf

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    Thanks David. I guess I'm asking it the wrong way. If I have 12V pixels what voltage can I have at the first pixel before it will cause damage in the long term. Is there a stated tolerance (like 5%) that they can handle or can you never exceed 12V without shortening the life of the pixel.

    Whilst on that note, can under voltage cause shortening of the lifespan as well.
     
  6. David_AVD

    David_AVD Good news, everyone!

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    12V pixels will likely have a greater tolerance to higher voltage in an absolute sense. So a 12V pixel should be ok with 12.5V, but I'd only push a 5V pixel to 5.25V max.

    The 12V pixels I've seen have a 5.1V zener diode (a type of regulation) in them and that protects the actual pixel chip's power input. The main issue with overpowering 12V pixels is the extra voltage across the internal resistors and the output stage of the pixel chip. This causes failure by overheating.

    With 5V pixels there is no zener diode, so excessive voltage can kill the pixel chip in short time. Various pixels have different maximum voltage specs. Also a 0.5V (for example) increase in voltage can cause a significant increase in power dissipation in the pixel chip.
     
  7. BundyRoy

    BundyRoy Senior Elf

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    Thanks David. So do 12V pixels emit much heat in normal operation. Just trying to see if feeling heat is a safety check. Should I panic if I feel any heat or is some heat normal. I guess you probably don't feel much through the silicon cover anyway.
     
  8. AAH

    AAH I love blinky lights :) Community Project Designer

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    12V nodes waste about 0.5W when on fully white which is probably just enough to eventually feel a temperature rise through the silicon. 12V strip has 3 leds in series and there is a much lower power loss. If you put higher than 5.5V into some 5V pixels then you will feel some heat and if you give it long enough there's a chance that the lights could start emitting heat even after you remove power [​IMG]
     
  9. fasteddy

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

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    16.6 volt is way to high, I have used 12.8 volts for longer runs as this is about 5% above which should be OK.

    The issue you have is that the amount of voltage drop will vary depending on the load and so when the lights are off but still powered up you will have minimal voltage drop and this is what will cause you issues.
     
  10. multicast

    multicast Senior Elf Generous Elf

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    VOLTAGE DROP IS PROPORTIONAL TO the current flowing in the cable. ( ohms law ).


    If you have no current flowing, there is no voltage drop...
     

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