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Derating curves

Discussion in 'Power Supplies' started by AAH, Mar 21, 2014.

  1. AAH

    AAH I love blinky lights :) Community Project Designer

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    Whilst looking at the data sheet of a 600W Meanwell supply (http://www.meanwell.com/search/hrp-600/default.htm) I noticed the derating curve and that got me thinking about a number of posts and discussions in chat about putting multiple power supplies in 1 box, jamming power supplies in tight or non forced air ventillation.

    On a hot summer day in Aussieland it is quite likely that the power supply will have an ambient temperature of 40C if it is in the shade when it is powered up. If it is, or has recently been, in direct sunlight then the ambient temp inside the enclosure could easily be in the mid to high 50's. Once the power supply starts doing it's stuff things will get hotter. As the graph shows the allowable output power drops from 100% of full load at 50 degrees to 0% if the temp gets over 70C. This reinforces what I have said in chat and post that squishing power supplies into small enclosures and also not using forced ventilation can be scary dangerous. The only difference to my earlier posts is that I didn't realise the 70C was the cutoff for Meanwell supplies. With the 12 and 24V supplies being 88% efficient and the 5V being 82% efficient there is the potential for a very large amount of heat to be produced inside what is sometime enclosures only just large enough to squeeze 1 or 2 power supplies into.
     

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  2. logandc99

    logandc99 Dedicated Elf

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    Thanks for that. That's some very useful information to be aware of.
    As summer starts sometime in mid Feb in Auckland :( the air temp by the time the lights get switched on in Dec around 8:30pm is probably nothing higher than about 22 degrees if your lucky (sadly a hot summers day is around 26 to 27 degrees in Auckland) and then cooling to 18 degrees or below over the evening which is a far cry from the temps you experience in Oz. However, in light of your info, I am going to make sure the temps in my enclosures are not climbing to the levels you have mentioned in your posts as I am guessing the cheaper Chinese power supplies are less forgiving than the Meanwells when it comes to over heating. The last thing anyone wants is to have the twinkly lights of their display suddenly replaced by the flicker of yellow flames.
     
  3. multicast

    multicast Senior Elf Generous Elf

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    Very.. Very important.
     

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