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I'm bit stuck and at the end of my knowledge. I'm building a light stick that is controlled by a teensy micro controller and using programable rgb led's. (ws2812) the led's run at 5volt and need quite a few amps. I'm looking at approx 8 amps if all 288 are on at full brightness and white. testing g was done with it plugged into USB on laptop and a few led's selected and low brightness and all was good. I planned to use a ubec to convert 7.2 - 11.1 input from lipo's to 5v. Issue was the led's started acting odd. I moved the data cable away from the power to the leds and it was a lot better so there is some interference in the power upsetting the data signal but only when using the ubec. I tried a different one I had and same issue but different effects. Iknow the ubec is basically a switching psu but how do I clean it. I'm using the ubec as it's the only device I can find that can give high current output. Found loads of buck converters on eBay but 2-3 amp is the max. Im open to other ideas if anyone has them. Did think.of a linear psu but current was again the issue and now also heat. Thanks in advance Lee

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    \$\begingroup\$ Do you have access to a scope? I think it is important to know the nature of the noise before attempting to clean anything. \$\endgroup\$
    – Wesley Lee
    Commented Oct 21, 2017 at 23:17
  • \$\begingroup\$ Hi Wesley. Apologies I did mean to say I don't have a scope or access to one sadly \$\endgroup\$
    – Lee Todd
    Commented Oct 21, 2017 at 23:19
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    \$\begingroup\$ Troubleshooting an undocumented power supply isn't really on topic here - to be able to apply engineering methods, questions need to be about things for which engineering documentation is available. Do note that you could use multiple lower capacity switching regulators each running a smaller number of LEDs. If your power needs to be fed a long distance, you might even do that with the step down conversion close to the point of load. \$\endgroup\$
    – Chris Stratton
    Commented Oct 21, 2017 at 23:25
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    \$\begingroup\$ How many mAh is the battery pack and what is the C-Rate? 40 Watts @ 8 Amp is a lot to ask of a Li-ion battery pack. This is more of a deep discharge lead acid project. Li-ion cost would be $100-$200 for 30-60 minutes. Be weary buying no name batteries. A 7200mAh battery for $20 is a scam. You need high energy and high power (e.g. Lithium Nickel Manganese Cobalt Oxide LiNiMnCoO2 or NMC) batteryuniversity.com/learn/article/types_of_lithium_ion \$\endgroup\$
    – Misunderstood
    Commented Oct 23, 2017 at 14:38
  • \$\begingroup\$ It's a light tool used in lightpainting. I've got a 7.2v lipo. The max power of multi amps is for very sorts periods and the lights flash. The big issue is what I think is noise/interference. The cable connecting the controller to the leds has the power and data in it. If i disconnect the data and use a separate wire moved well away it's works 95% better but can't do that in real world use. Since it works perfect when powered by USB (with less led's on) I'm assuming it's the ubec as it's the only difference. Hope that makes sense \$\endgroup\$
    – Lee Todd
    Commented Oct 23, 2017 at 15:24

1 Answer 1

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Use shielded twisted pair wire for serial data.

5 volts is not enough.

The WS2812 VDD and VCC power requirements are 6V-7V.

enter image description here

All 3 LEDs drawing 20mA x 3 x 288 = 27.28 Amps.

That's the Amps. The minimum Voltage is 6V x 27.28 = 103.68 Watts.

The LEDs alone could dissipate up to 50 Watts, With an avaerage of 2.933 Vf (R=2.2v,G=3.2v,B=3.4v) x 3 x 288 = 50.688 Watts

But efficiency is less than 50%.

6v x 0.02A x 3 x 288 = 103.69 Watts @ 6V = 17.28A

Give your UBEC an 80% efficiency and we have 129.6 Watts

Add a 10% margin and the battery requirement is now 142.56 Watts

You could use a electric bicycle battery. You will need an NMC Li-ion (high capacity and high current). The LI-ion for my Segway is $1,400.

enter image description here

If you use the WS2812B with 5V VDD then you would need 86 Watts @ 14.4 Amp.

If you calculated the power requirements for the LEDs without taking efficiency into consideration the draw would be about 8 amp. 58% efficiency (not including UBEC).

enter image description here

You may want to consider using Cree RGB CLMVB-FKA controlled with a TI TLC5973 3-Channel, 12-Bit, PWM Constant-Current LED Driver with a single resistor to set the maximum current. Or a TLC59731 3-Channel, 8-Bit, PWM LED Driver which uses a resistor inline with each LED.

enter image description here

The Cree RGB have an average Vf of 3.6 vs 2.9 (less power) The Luminosity of the RG and B are better matched. The TLC5973 can be powered with 3v up to 6v so it could be powered by a single cell 3.6v Li-ion eliminating the UBEC, Over all the power requirements would be much less and reliability much higher.

Uses a single wire interface. The datasheet shows how to properly wire power and data signal.

There is an on-board shunt regulator that allows you to power multiple LEDs with one chip.

enter image description here

The TI parts are superior to the NeoPixel. And MUCH better documentation.

  • Data Transfer Maximum Rate: 3 Mbps vs. 800Kbps
  • Internal GS Clock Oscillator: 12 MHz
  • Display Repeat Rate: 2,900 (typ) vs 30fps,
  • 4096 steps grayscale control vs 256
  • Output Delay Switching to Prevent Inrush Current
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  • \$\begingroup\$ Thanks for that info. I'm going to have to dig the data sheet as I'm sure they were 5v. Either I know it's a lot of power but as it flashes a pattern the chance of all being on at once and set to full brightness white is slim but could happen I give you. Best way to describe this is a home made version of the pixelstick. my main question still remains mind. Somthing upsetting the signal. I through about a linear regulator but the amps needed at peek and the heat I will need to remove may be too much, and that's not even looking at the unefficient they are. \$\endgroup\$
    – Lee Todd
    Commented Oct 23, 2017 at 15:53
  • \$\begingroup\$ I updated my post. the WS2812B is 5V. \$\endgroup\$
    – Misunderstood
    Commented Oct 23, 2017 at 16:03
  • \$\begingroup\$ That looks more like what I worked out. but what about filtering the power or is it simple enough to build one that's clean have found circuits bit they are all for lower currents like 1 amp. It's the noise/ interference that's killing me \$\endgroup\$
    – Lee Todd
    Commented Oct 23, 2017 at 16:07
  • \$\begingroup\$ My guess was that you have insufficient power and are dropping below 5V. You need to understand the discharge rate of the Li-po power pack. And your UBEC must be able to handle 15 Amps and 90 Watts. \$\endgroup\$
    – Misunderstood
    Commented Oct 23, 2017 at 16:09
  • \$\begingroup\$ Hi. Thanks for your help it's appreciated. I don't think it's power as it does light up just the colours etc don't show/flash what is expected. When it starts it does a rbg flash then.random colours. If i turn the brightness right down it still has this odd behaviour. At this low setting I can use the USB power from the laptop into the controller and it works hence why my head says interference of some kind. I've seen these dc-dc buck converters on eBay/amazon. Not sure if they are worth a go. They look like the case is a heat sink but might still be a switching circuit and I get the same \$\endgroup\$
    – Lee Todd
    Commented Oct 23, 2017 at 17:25

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