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Thread: buck converter sizing

  1. #41
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    Default Re: buck converter sizing

    The converters get pretty hot at anything above 1 amp and need some sort of airflow to stay cool.


    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.
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  2. #42
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    Default Re: buck converter sizing

    Hopefully will have a chance to give it a test run this weekend. Regardless of how hot they get, I'll put some heatskinks on them but I am not sure about the airflow... will have to see.

    I will be using a mean well LRS-350-24 Power Supply (15amp / 350w / 24V) to power 6 buck converters and 6 x 5 volts 50 pixels props. I was thinking of using 18 gauge SPT2 or 18 gauge landscape cable from the PS to the buck converters. voltage drop and amps should not be a concerned or am I overlooking at something? Thanks!

  3. #43
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    Default Re: buck converter sizing

    18awg cannot do 15a on a single wire. If you have at least two runs from the psu to your lights then all should be good


    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

  4. #44
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    Default Re: buck converter sizing

    Quote Originally Posted by MartinMueller2003 View Post
    18awg cannot do 15a on a single wire. If you have at least two runs from the psu to your lights then all should be good
    Thanks Martin for the reply.

    iI guess I was (am) missing something and I'll go with bigger size cable (e.g. landscape 14 gauge) if needed but would it be incorrect to base the cabling on the draw on the circuit rather than on the power supply?

    Layout: 6 props with 50 pixels pulling 0.06 amps per pixel + 6 ESPixelSticks
    - Expected total current draw: 6 X 50 X 0.06 = 18 amps at 5 V (neglecting draw from the ESPsticks)
    - Equivalent current draw at 24 V: 3.75 amps
    - protect the cabling at the power supply with a 5 amp fuse
    While the power supply can handle 15 amps the circuit with the props on it will be calling for less than 4 amps on the 24V side, thus the thinking that 18 ga would be plenty. Is this wrong?
    pixel wreathes rev01.pdf

    Thanks!

  5. #45
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    Default Re: buck converter sizing

    Your calculations are correct. And yes you can base the wire gauge on the fuse your are using. 18AWG can handle 4A without an issue. In general the fuse needs to have lower (or about equal but never higher) current carrying capacity than the wire it is protecting. I am so used to loading my supplies at 80% I forget to consider lower power calculations.


    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

  6. #46
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    Default Re: buck converter sizing

    Thanks Martin for confirming the data.

    I finally put the buck converter in service for a test today. It does get warm but can't put a number on it, not having a way to measure temperature. Not too bad though, can still touch it! I still put a heatsink on the converter after the test.

    On a separate note, I was a little surprised by the current draw for the pixels I got:
    Full white: +/- 1.9 A
    Red, green or blue: +/- 0.9 A each
    I was expecting full white to be the sum of red, green and blue, so closer to 2.7 A but not even close. Maybe my meter is way off...

  7. #47
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    Default Re: buck converter sizing

    There is newer small buck converter based on the XL4005/4015 chip that is capable of delivering 5 amps with high efficiency. It too can be purchased from Chinese sellers for around $1-$2 dollars a pop. The basic circuit form taken from the datasheet is very similar to the LM2596, although the board size is slightly wider and longer. The XL4015 internal oscillator is fixed at 180KHz, whereas the LM2596 is fixed at 150KHz. The XL4005 oscillates at 300KHz, but I only have a XL4015 board to test.

    I purchased 2 of these boards from Solu on Amazon.com:

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    They were more expensive at $6 each, but the shipping was fulfilled by Amazon so I could get them in a 2 days. I don't think the quality of these boards from Solu are any better than the various cheaper Chinese resellers. The only testing I've had a chance to do is constant load testing. I was able to verify that the converters were able to deliver 5 amps at 5 volts without issue other than heat. The boards I got had heatsinks already attached, and at 5 amps they got very hot to the touch but remained stable. At 3 amps the heatsinks were very warm to the touch but much less so than the LM2596 board driven at 3 amps. At first blush the XL4015 seems to be a more efficient converter than the LM2596, but more testing is needed. I hope to do more sensitive testing soon...

  8. #48
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    Default Re: buck converter sizing

    Found them on ebay for $1.35. At 5A they look to be worth the bump in price.


    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

  9. #49
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    Default Re: buck converter sizing

    Quote Originally Posted by rhildinger View Post
    There is newer small buck converter based on the XL4005/4015 chip that is capable of delivering 5 amps with high efficiency. It too can be purchased from Chinese sellers for around $1-$2 dollars a pop. The basic circuit form taken from the datasheet is very similar to the LM2596, although the board size is slightly wider and longer. The XL4015 internal oscillator is fixed at 180KHz, whereas the LM2596 is fixed at 150KHz. The XL4005 oscillates at 300KHz, but I only have a XL4015 board to test.

    I purchased 2 of these boards from Solu on Amazon.com:

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    They were more expensive at $6 each, but the shipping was fulfilled by Amazon so I could get them in a 2 days. I don't think the quality of these boards from Solu are any better than the various cheaper Chinese resellers. The only testing I've had a chance to do is constant load testing. I was able to verify that the converters were able to deliver 5 amps at 5 volts without issue other than heat. The boards I got had heatsinks already attached, and at 5 amps they got very hot to the touch but remained stable. At 3 amps the heatsinks were very warm to the touch but much less so than the LM2596 board driven at 3 amps. At first blush the XL4015 seems to be a more efficient converter than the LM2596, but more testing is needed.I hope to do more sensitive testing soon...
    rhildinger,
    Looks interesting, thanks for sharing. I was wondering if you had a chance to check those more. happy with them?

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