Options to supply power for ~120 NeoPixel wearable?

[tdemark]

I am working on a wearable project that uses an Arduino Uno and 4 NeoPixel rings (60, 24, 16, 16).

I have have calculated the power needs to drive the NeoPixels:

"Rainbow" Mode - All pixels running the rainbow function that is in the example libraries. It looks like it is the equivalent of one component led on at all times for each pixel. 156 pixels x 20 mA/pixel = 2320 mA

"Chase" Mode - A white arc spins around the 60 NeoPixel ring. The "arc" is a 3 pixel ramp up, 1 full on, 12 pixel fade. So I assume 15 pixels at 30 mA and 1 at 60 mA = 510 mA

"Combo" Mode - "Chase" mode with the three small rings in "Rainbow" mode. 510 mA + (20 mA * 56) = 1630 mA

I think the primary display modes will be "Rainbow" and "Combo" so an average of 2000 mA draw is probably right. The goal is to power the wearable for 8 - 10 hours.

I am going to build in a way to set brightness level via a push button so that I don't need to drive the pixels more than needed for the environment. That being said, I still need to plan on carrying roughly 20 amp-hours. This is a "one night only" event a thousand miles away so there won't be any ability to tweak things on-site.

With that in mind...

Does my math look right for consumption? I am assuming that the Arduino itself isn't adding much more to the total.
Any thoughts or suggestions for power options? I don't mind changing batteries every so often. Amazon lists some high amperage NiMH AAs (2600 mA) relatively cheaply.
A power supply of 4 of them would last for around 4 hrs, right?

Does this sound plausible or should I be looking in another direction?

Thanks,
- Tony

[Franklin97355]

The 2600 is an optimistic figure of the ma Hours of the battery. In an ideal world you would get 1.3 hours but in real life probably 30 minutes. I would look at LiPo batteries for their power to weight/size ratio.

[tdemark]

I finally was able to hunt down a voltage regulator so that I can test the project at higher loads (I've been running at about 10% brightness and using the power feed from the Arduino.

The rainbow effect will be plenty bright at 60% brightness. That brings the current down to 1360 mA.
The chase uses fewer pixels, so I can drive it a little higher at 80% for 400 mA.
For the combo, it is 400 mA (chase) + 656 mA (3 ring rainbow) and thus 1056 mA.

All-in-all, the load has been cut in half. I am also going to drive the arduino separately with a 9V battery. I would assume that isolating it as much as possible from the heavy draw (and diminishing voltage as the battery wears down) would be a good thing. Right?

From the Duracell data sheet on Coppertop AAs, a single AA will provide 0.9V after 1 hr at 1A draw.
If I put 6 of them in a power pack, is the power available roughly linear? That is, if I connect them in series would I have roughly 5.4V after 6h at 1A draw?

[Franklin97355]

If I put 6 of them in a power pack, is the power available roughly linear? That is, if I connect them in series would I have roughly 5.4V after 6h at 1A draw?

Series ups the voltage while parallel ups the current. So after 1 hour at 1A you will have 5.4V

[adafruit_support_bill]

Alkaline cells have a steady decline in voltage over the discharge cycle. If you want a flatter discharge curve, LiPo or NiMH cells (e.g. Eneloop) are a good choice. NiMH cells come in standard AA sizes, so they fit in standard battery packs. Their nominal voltage is 1.2v per cell - but they will hold very close to that output level up to the end of their useful discharge cycle.

[tdemark]

I am going to try out four power options:

1 x 9V Alkaline
6 x AA Alkaline
6 x AA NiMH
"50000" mAh LiPo battery pack

I am running 9V test right now with the highest current draw setting to see how long the display will last (not very long, I suspect).

[tdemark]

40 min run time for the 9V.

It was an off-brand 9V that had a "Good Till" date of Dec, 2012 so I don't have a data chart to reference like if it were from Duracell/Energizer, etc.

Looking forward to trying out the other options later this week.

This is only powering the LEDs now. I will have a separate power source for the Arduino. Speaking of which... I have a three N.O. switches that control display modes. Is there any difference from a current perspective from using internal pullup resistors and an external one? That is, if I use the internal pullups, will the fact that the pins will be HIGH all the time except for momentary clicks change the run time on a battery appreciably?

[adafruit_support_bill]

The pullups should not affect run-time appreciably. When in input mode a GPIO pin has a very high impedance, so the current consumption with an open switch is negligible.

[pettiross]

@tdemark, thanks for sharing your work and experience! I'm putting together a 100 NeoPixel wearable for my daughter's Halloween costume right now, and was just about to stumble down the same path you have so graciously shared. I'd love to hear how your battery tests go.

I'm making a cape with the hundred NeoPixels scattered over the back and a Flora driving them. I'm going to run two stainless steel ribbons: a power rail along the bottom edge and a ground rail horizontally across the top of the field of LEDs. I'll load up the batteries along the bottom edge, at least once that edge exists...

[tdemark]

The power tests are going well.

From Amazon, I picked up an 8-pack of 2800 mAh NiMH for ~$18. I installed them in a 6-battery holder (for 7.2V). I powered the LEDs only (the Arduino had a separate 9V battery). My initial test lasted 3.5 hours. From what the reviews are saying, I should be able to eek out a little more after a few charge cycles. One issue with this is that the voltage regulator gets burning hot.

Also from Amazon, I picked up a 50,000 mAh LiPo battery pack for ~$38. I ran a test yesterday running both the LEDs and the Arduino. The output is 5V so I split the power before the regulator into the Arduino. It ran for 10 hours and only lost around 25%. The VR barely got warm. Assuming I don't come across any quality issues with the pack over the next two weeks, this is what I will be using.

That being said, I will also carry the NiMH battery pack "just in case".

Let me know if you want the specific items I purchased.

[adafruit_support_bill]

One issue with this is that the voltage regulator gets burning hot.

What are you using for a voltage regulator? Linear regulators are not particularly efficient and burn off the excess voltage as heat. You can find switching "buck" regulators that will make much more efficient use of the battery capacity. We have these that will handle up to 3A: https://www.adafruit.com/products/1385

[tdemark]

It's just the 5V VR that came with a NerdKit that I purchased a few years ago.

Not sure of the exact part number, but it appears to be similar to:

http://www.parts-express.com/7805--5v-v ... -220--7805

As for replacing it, the USB LiPo pack produces 5V so I won't need it. For my "backup" NiMH pack, I'm stuck with the one that I have because the buck regulator is out of stock and I am on a tight deadline. Would love to have used a Pro Trinket, too, but that has the same issue. This stuff is too popular!

[adafruit_support_bill]

Yes, the 7805 is a linear regulator. They are easy to use, but not so efficient. You should probably have a heat-sink on it if you don't already.
Also note that 3xNiMH cells is 4.8v - which is close enough to 5v for powering most electronics.

[pettiross]

@tdemark, yes, I would like to know what model LiPo you got from Amazon. While my odds are probably good at getting one that works well, I'd hate to find I picked the one that has some random flaw. Thanks yet again for your generosity.

[michaelmeissner]

Another possibility is something like this 18650 battery pack: http://www.ebay.com/itm/161248883701?ss ... 1436.l2649

It can provide 2 separate USB outputs (5v), and one separate output for 3.7v (4a), 5v (2a), 9v (1.5a) and 12v (1a). If you put in 6 18650 batteries, it should last a long time. Note, the 18650 batteries aren't included, and it is best to pick them up from a supplier in your country.

I don't have that model, but I do have this one, which is smaller (it only takes 2 batteries, but it has a built-in plug for recharging): http://www.ebay.com/itm/White-5V-9V-12- ... 56699b6316