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First, thank you to anyone taking time out of their day to read this and answer. Resources like this are incredible for amateurs like myself.

My question is based around power supplies, Arduinos (clone board), and LEDS. My device will use an Arduino to interface with a strip of 160 5VDC RGB LED's. Each color for each LED pulls 20 mA for a total of 60 mA at full bright, full white based on the datasheets that I can find. Total power consumption 9.6 A (this seems very high). The datasheet also makes reference to 3 to 9 W per 32 LED's so 45 W max. I'm going to consider the power consumption relatively negligible for the Arduino (20mA at most I believe, very small sketch running it).

I would like to power all of this from one supply so my question is: What do I need? The one supplier has an accompanying 5v/6A supply they say can power 200 LED's which is feasible if they are not all on simultaneous (which they rarely will, but I'd rather be safe).

The next question is what isolation do I need between the Arduino and the LED strips. I obviously won't hook the strip to the Arduino 5V pin, but could I share with one line directly to the Arduino, one line to the LED strip from the supply and a shared ground?

Finally, based on the previous two questions, could this be powered with a rechargeable battery? And no, not a car battery. Something like a NiCad or Li-Ion battery pack.

Thank you in advance for any insight you can provide.

Thank you again.

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    \$\begingroup\$ when you refer to 'isolation', I don't think you mean isolation. Isolation means arranging things so that there is no easy electrical path between the things being isolated. In this situation, you are in fact sharing a single supply between the two loads, which is fine in this case, but it's not isolation. \$\endgroup\$
    – JustJeff
    Jan 13, 2012 at 11:33

2 Answers 2

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Power seems to be an important aspect in your design, so you might consider using different LEDs. Low-current LEDs for instance take 2mA instead of 20mA.

Or maybe 5mA through your existing LEDs will produce enough light for your taste.

Another angle would be to design your LED drive circuit for as low a voltage as you can. If you can design it for 3V and you use a switched power supply to create this 3V from 5V (or maybe 12V), you have saved 40% energy. This is especially effective when you use a battry, which produces a lower voltage over time.

I guess that when you want to iluminate (nearly) all LEDs you can get by with illuminating them each a bit less. This logic could be incorporated in your software, so the worst case current would be reduced.

You must design your circuitry for the worst case, but for battery life it might be more realistic to calculate with averaged cases. So get some more info on what you want to show when you need to know how a given battery will last.

As often, your one good question results in an avelange of questions, and some questioning of your basic assumptions. That's system design :)

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  • \$\begingroup\$ The low current LEDs are an option, however tough to find. What Im looking at specifically is a flex strip of RGB LEDs that are driven by WS2801 IC's chained together which can then be individually addressed, make cool effects, dance to music, etc. The nice thing about that chip is that it can PWM the LEDs for a crazy amount of colors as opposed to the 7 colors of digital driven LEDs. That being said, I will review the datasheets of both the IC and the LEDs and see what I can do to get the consumption lower possibly or rethink the battery option all together. Thanks for the input \$\endgroup\$
    – Danger Johnson
    Jan 13, 2012 at 15:13
  • \$\begingroup\$ Nice chip! Keep in mind that there is bound to be a limit on how many of those strips you can chain, due to voltage drops due to the current consumption, so you might need to operate some of the chains in parallel. The chips have a constant current mode, so you can go for a supply voltage lower than 5 to save power. \$\endgroup\$
    – Wouter van Ooijen
    Jan 13, 2012 at 16:00
  • \$\begingroup\$ Are you sure that you can drive all the leds in the strip independently? \$\endgroup\$
    – clabacchio
    Jan 13, 2012 at 16:08
  • \$\begingroup\$ Check the datasheet sparkfun.com/datasheets/Components/LED/RGBSTRIP.pdf for some spectacular examples \$\endgroup\$
    – Wouter van Ooijen
    Jan 13, 2012 at 20:32
  • \$\begingroup\$ Yup, thats the correct datasheet. Pretty neat I think. Voltage drop is a concern. Data and clock pins will be always need to be on one circuit. But the 5V and GND can be disconnect from the chain and another power supply added there i.e. 5 strips with 5 power inputs with but all linked for serial input. Thanks for the link and feedback \$\endgroup\$
    – Danger Johnson
    Jan 14, 2012 at 15:20
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My suggestion is to create an external supply that feeds both the LED strip and the Arduino separately, and then decoupling the Arduino from the LEDs using power transistors or (better) integrated drivers.

But the use of a battery depends strongly by the use that you are going to do of the LED strip: if you are going to use the whole - let's say 9 A current (that is much) consider that a 9000 mAh battery (that is BIG) would last one hour.

Maybe a laptop battery or so could fit but still don't expect to use it for a long time.

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  • \$\begingroup\$ Good call on the laptop battery. 7.7A off the one I have beside me. And another good call on the power transistors. I am curious about the integrated driver usage as I am not familiar. Thanks again \$\endgroup\$
    – Danger Johnson
    Jan 13, 2012 at 15:06
  • \$\begingroup\$ I was thinking to something like this nxp.com/products/lighting_driver_and_controller_ics/…, but you can also use a simple MOS \$\endgroup\$
    – clabacchio
    Jan 13, 2012 at 15:25
  • \$\begingroup\$ Thanks for the reply. Very cool chip and I can definetly see some future uses for me. However, it may not apply to this project. Thanks for the link though \$\endgroup\$
    – Danger Johnson
    Jan 14, 2012 at 15:23

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