Portable power Halloween's a-coming', me hearties,

Portable power
Halloween’s a-coming’, me hearties, and some of ye may be thinking about donning some garb festooned with hundreds of LEDs that glint and sparkle like a chest full o’ treasure! (Today IS International Talk Like A Pirate Day, after all. But I’ll stop now.)

How do you power your portable LED projects? Please share your tips! (Has anyone actually run LED strips off 3.7v LiPo battery directly without stepping it up to 5v?)

Here are some of basic ideas:

If your whole project can run from 5 volts, there are a lot of easy and nicely packaged portable power packs. Often they are sold as “emergency phone chargers” or similar; they often have a USB port for power and an on/off switch – both very useful. Capacities run from 2000mAh (about the size of one AA cell) to monsters like this 13,500 mAh lithium polymer pack (which is a bargain on sale for $35)

If your project runs from 12 volts, you can either get an 8-cell battery holder (8 x 1.5v = 12v), or potentially even use a sealed 12 volt lead acid batter. But note well: lead is heavy. (This is the kind of insightful revelation you’ve come to expect from us, I know.)

In general, there are two ways to go: (1) carefully calculated power, experimentally verified power requirements and (2) you just wing it, hook up more power than you could possibly need, and don’t worry about it. The second method works fine, but you tend to wind up carrying around heavier batteries than you actually need. A little testing and experimentation to find the lightest / smallest batteries that will work for you is probably worth the time.

So: how so you power your mobile LED projects?

I am able to run my WS2811 60/m strip straight off my lithium ion batteries, and it works pretty well. Got ~20 hours out of 2x18650 at 25% setBrightness()

Thanks, Matt. How many pixels were you running total, and what was the ‘typical’ LED light level like? A pure hue?

42 LEDs total: https://plus.google.com/u/0/communities/109127054924227823508/stream/f932cd25-77bc-4f5d-ba7a-1917d4b9f9ac. I didn’t realize it until I saw something about the Teensy not being good for 16MHz when not on 5V, but it seems to work fine with the lithium battery powering VCC directly.

edit: answer ALL the questions. on the 20 hour demo the breakdown was probably 50% black/white only images and 50% rainbows/fades/strobes. Within those patterns/images but pixel duty cycle (nonblack vs black pixels) was ~75-80%.

I took it with me to a music festival called Rootwire here in ohio and had a ton of hooperchix all up in my business. I also cracked the casing on the #2 prototype, but learned something from it, so all good.

Great topic and timely for me! I am building a a wearable tshirt with a 16x16 neopixel matrix. The problem is the power. Not that I would ever run it at full power, but at full power it would draw almost 16 amps. I think it is likely that I will run it with brightnesses that could draw 4 - 6 amps.

It seems that a LiPoly battery is the way to go. I have a couple questions though.

  1. The lowest voltage that could supply that many amps is 7.4v. What is the right way to step down the voltage with the high current?

  2. I am worried about the safety of wearing something with such high current. I’ve seen others that have made wearable a with hundreds of LEDs. What are the safety concerns and precautions?

I don’t think you need to run in series for that kind of current, but doing so allows you to use a buck DC-DC converter (step-down) instead of a boost (step-up). Search DC-DC step-down module and you’ll find a ton of stuff.

I also took this route once with a large project (420 WS2811 pixels in 7 circles - seed of life) and have blown up more DC-DC modules that are under rated than I care to remember. It’s doable, but one wrong guess in your algorithm or FULL-WHITE on all pixels and POOF there goes the converter.

Running direct off 4-6x 18650 cells in parallel (make sure they’re balanced!) will give you some headroom. My WS2811 pixels worked down to 3.3V, yours may not… testing required.

Speaking of POOF…
I keep thinking it might be cool to be able to tell the library a maximum total current draw and if you try to draw more than that it’d just auto-dim the whole strip down to the limit value for the (transient?) duration. It’d have to take ‘dark energy’ etc into account, etc…
I think we’d want this to be strictly optional, as it would use up some CPU cycles and many people would rather just ‘be careful’ than incur a CPU overhead. On the other hand, I’ve lost track of how many times I’ve screwed things up (hi @Daniel_Garcia ) due to inadvertently mismatched current draws. Even though “I’m careful”, I might use it anyway, at least during development.
Putting it on the future dev todo list.

Holy crap, HELL YES! I would love that feature, “Safety”. Tell it a per-pixel max draw current, dark current, and maybe even R-G-B max currents if you felt like measuring them.

Every strip project I’ve done so far has been portable power:

Led Fur Gauntlet was 1 square lipo pack (Like this: http://www.adafruit.com/products/328) which is plugged directly into a flora with the JST-PH connector. From the flora I have power going out of the VIN/GND to a 5v boost regulator (http://www.pololu.com/catalog/product/2564). This powers 66 WS2811 Leds with at least 6 hours of life at 100% brightness (though I’d say half of the modes on there only have some pixels lit up each frame). I’ve never seen it run out of power, but the lowest the battery was when I had to recharge it was 3.4v.

Led Tie uses 6 AA alkalines (Here is a good set of benchmark tests of common Alkaline brands under high load: http://www.batteryshowdown.com/results-hi.html). I’m using a 6 battery holder behind the tie, wired into an Osepp Nano, with VIN and GND going into a 5v step down regulator (Also from Pololu). This powers 114 WS2811 LEDS for more then 6 hours (I’ve also not seen the power run out on this wearable yet).

Led Hat uses 2 26650 LI Ion batteries ( These http://www.amazon.com/gp/product/B008YAPRUQ/ref=cm_cr_ryp_prd_ttl_sol_0) wired in series, and regulated by a 5v step down regulator from pololu. This is running 120 LEDS forever basically… as an example I wore this almost non-stop at burning man when the sun went down, so at least 20+ hours and still going strong.

Led Vest is a bit more complicated of a power system. I rushed this to completion before Burning man and fried my Teensy with not enough time to get a replacement. I ended up dividing the vest into 2 halves with their own separate but shared power systems and Osepp Nanos that talked to each other. basically 2 units of 6 AA battery holders with an adjustable/higher current regulator (http://www.aliexpress.com/item/Ultra-small-LM2596-power-supply-module-DC-DC-BUCK-3A-adjustable-buck-module-regulator-ultra-LM2576/739489407.html). This was running 358 LEDS but I think I only got about 3 hours out of it… Though I think I blame the weird power system, and the possibly “not quite exactly in sync” voltage setting of the 2 regulators.

My LED Staff used 2 18650 Li Ion Rechargeables in series and a 5v Step down regulator for 120 LEDS for about 3 hours as well (full brightness)

Another LED vest I helped my girlfriend make was only a 4AA battery pack to a flora (With diode) to 144 LEDS though at 75% brightness which would last about 4 hours on Ikea batteries before starting to get dimmer.

Also an LED Tutu we made with WS2801 12mm LED strand (Only using 21 leds) was also a 4AA battery pack that ran about 6 hours so far… still no battery change out.

Overall I’ve found pololu’s tiny buck/boost regulators to be awesome up to about 2A when it gets too hot and starts causing issues with lights… so anything about 120 LEDS or less it is ideal for. But if running more then that on a single power source it might be good to go with the bulkier/higher current regulators (if regulating is key).

I’ve also used some of the “charging packs” in a pinch. I think I got 2 hours on my LED Tie at a festival with one of these plugged into the Nano Usb port: (http://compare.ebay.ca/like/251210390689?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y&cbt=y&lpid=33&item_id=251210390689).

My next project is to build an electric scooter which will already have a regulated 5v 3A power source pulling from the main 44v drive batteries(12s3p LIPO packs), so I will likely LED all over that thing easier then usual.

Oh! One more portable power related thing. For the “Dumb” (so not FastSPI Related)12v strips, like 12v UV Led Strip (http://www.aliexpress.com/item/Free-shipping-New-arrival-UV-Purple-non-waterproof-5m-DC12V-5050-LED-strips-300-LEDs/864508660.html) or 12v RGB Non Digital strip(http://www.aliexpress.com/item/DC12V-5m-one-roll-5050-SMD-60LEDs-m-led-strip-waterproof-by-silicon-tube-IP68/654720379.html) which you can throw a few modes on with this controller (http://www.aliexpress.com/item/12V-Mini-3-Keys-RGB-LED-Controller-Brightness-Control-light-Dimmer-Dimming-used-for-led-3528/616167748.html) These can be overvolted with no catastrophic failure to at least 24v, but you can power with 2 9v batteries in series to 18v if only lighting like 50 or so.

I have not tried this with the 12v WS2811 strips, though I’ve also not had much success getting those strips to work at all yet… I had a project with these I gave up on a few months ago where it all Should have worked yet it would only work when probing the circuit voltage with my Multimeter…gave up trying to figure out the “Effect” the multimeter added to the circuit :stuck_out_tongue:

Some of the lion usb power supplies also put out 9v and 12v, which makes it really easy to have nicely packaged power supplies.

I like this one, as it has a hard on/off switch and charges from 12V, makes it easier to charge from a dusty solar panel.
“15,000” mAh @ 5v, or “6,500” mAh @ 12v
$37, shipped from China (i.e. order now if you want it for Halloween)

The external batteries would be a good option if you don’t have a large number of LEDs. The ones I see have a max of 2A output.

I like those external USB packs (can re-use them to charge my phone throughout the year!) and have gotten about 30 hours of light time on 45 feet of HL1606 from a 5000mAh. I didn’t strictly measure this year’s project (WS2801, 30 feet) but it felt like about 12 hours from a 5000mAh. I bought an extra "15000"mAh and used it for 3 nights in a row without it running out. With wearables I write patterns with battery life in mind: bursts of color that move across the surface but leave most LEDs off, dim to 50%, never use white, etc. As a result the 2A limit is never a problem (they do tend to allow a little overdraw but then shut down and you have to hard-reset them.)

I guess the HL1606 has a fairly low dark (0,0,0) current value?

Right - although I only learned about the WS2801’s power cost when I found this FastSPI group, so I’ve never tested my older HL1606 for it. It hadn’t even occurred to me that there’d be a constant draw but I guess it makes sense. Maybe moreso for the WS2811 everyone is using now… Seems like it’s constantly “working” (even for black) vs the WS2801 and especially the earlier strips like HL1606 which require more smarts on the controller side but might save power because you control the rate at which it’s doin’ it’s thing?

via eBay: “30,000 mAh” battery w/USB 2.1A outlet for $20. (“20,000 mAh” for $18) Free shipping from HK. http://www.ebay.com/itm/141006177628

You’re putting mah in quotes so you definitely understand - but for others: what is advertised as a 30k mah battery is often much smaller than that. First because of inefficient transmission: they rate it at a theoretical limit but in practice you get ~85% of that at best. And second because sellers in China lie about the capacity.

Check amazon reviews, there are a few people who for some reason (free samples?) religiously test the major battery brands with real products (phone/tablet) and measure the true output.

My pessimistic guess for Mark’s 30k example is that it’ll actually do less than 10k - just because price is a better indicator than what the box says. But I still highly recommend using these things as your batteries, since they put out a clean 5v AND are really useful in “real life”.

Uhh, wow those are crazy cheap. I think I’ll get a few to resell at festivals… maybe with some fancy sacred geometry laser engraved on them.


I got one of the ones from NewEgg (link above) and tested it overnight; seems like the real deal. I also like the digital display of remaining power (0…100).

No idea if the eBay ones are awesome or merely OK; let us know if you find out!