How to power 1m addressable RGB strip from one LiPo cell? - Page 1
Forum section: electronics / projects

author: miceuz
author_rank: Frequent Contributor
timestamp: January 10, 2014, 09:43:59 pm
content: I'd like to power 1m of this strip:http://www.ebay.com/itm/144-LEDs-M-WS2812B-Chip-Black-PCB-WS2811-IC-Digital-5050-RGB-LED-Strip-Light-5V-/310775026322?pt=LH_DefaultDomain_0&hash=item485ba29292For charging simplicity reasons I'd like to power it from one LiPo cell. I need 5V for a strip and for a controller. The strip draws 38W of power. Any advice on a cheapo ebay module? What could I use to roll my own solution? Any ready made designs for similar specs?

author: poorchava
author_rank: Super Contributor
timestamp: January 10, 2014, 11:12:58 pm
content: 8a boost converter from 3...4.2V range to 5V should be doable. Dig through websites of TI, LT, ST, NXP and the like of and your will find shit load of options. Prepare for a large inductor though, as at lower ranges of input voltage the current through the inductor may go up to 15A or something like that.I think a ready made module will be rather expensive...

author: peter.mitchell
author_rank: Super Contributor
timestamp: January 11, 2014, 09:29:15 am
content: I really wouldn't suggest that, 38W/meter, 5v is around about 8A. For a low voltage step-up/boost, thats pretty massive.That and you would need massive single cells if you planned on using it for any extended period of time, with the boost converter, at best you'd be pulling 9.5A for your cells, at worst, probably around 18-20A.If you want is simple, I suggest doing the following; put high current connectors on the cells, then make up a parallel lead and a series lead. Use the cells in series with a buck converter, use the cells in parallel to charge.

author: Psi
author_rank: Super Contributor
timestamp: January 11, 2014, 09:51:32 am
content: yep, as said above. Realistically you can't boost convert 5V @ ~7.6A from 3.8V @ ~10AIt is possible, but you wont find any ready-made modules that even come close.With voltages that low and 10's of amps of current things like power cable losses and switching vdrop make the efficiency absolutely awful.

author: miceuz
author_rank: Frequent Contributor
timestamp: January 11, 2014, 10:04:54 pm
content: It the buck topology better for cases like this?I have very limited experience with switching DC-DC converters - just hooked up a datasheet reference design of LM2596 once.

author: Corporate666
author_rank: Unknown
timestamp: January 11, 2014, 10:52:14 pm
content: Quote from: miceuz on January 11, 2014, 10:04:54 pmIMO...Power is power... 38 watts is 38 watts... if the volts go down, the amps have to go up. A single LiPo cell will run down to, say 3 volts or so. At 5V, 38 watts means about 7.5 amps. At 3 volts, 38 watts is more like 12.75. Even if you are 90% efficient, that's still around 15 amps. That is just a real lot for a switching power supply.Bucking it down from 6v instead of boosting it up from 3V is going to drop your current by half... the supply still needs to output 7.5 amps which is a lot, but doable.Look at something like the Richtek RT7258. They are super simple to use and the datasheets guide you through the design pretty well. Or, if this is a one-off I would just buy a DC-DC converter. GE Critical Power makes some nice units - 60 watts with 4-14Vin and 1-6V out at 10 amps. They are $8.50 in singles and drop to more like $6 in 1000pcs quantities, and just a 5-pin SIP module that you include in your design.Unless you really want to design the PSU yourself, I don't think you will come close to that price unless you are doing big volume and have the resources to spare on the design.http://www.digikey.com/product-detail/en/NQR010A0X4Z/555-1161-ND/2270975

author: miceuz
author_rank: Frequent Contributor
timestamp: January 12, 2014, 12:19:37 am
content: Thanks a lot!It's a one off, so I didn't want to invest too much time into power supply when there still are lots of things to do on MCU side.

author: Niklas
author_rank: Frequent Contributor
timestamp: January 12, 2014, 12:40:54 am
content: From the LiPo's perspective things are quite rough unless you use cells that are made for higher currents. "Cheap Ebay" cells will most probably have a very short life expectancy at 5+ Amps and deliver just a few minutes of light per charge.

author: miceuz
author_rank: Frequent Contributor
timestamp: January 12, 2014, 12:58:59 am
content: I'm not going to skimp on batteries, I understand that 8A is a substantial current for any small battery. On another hand - it's jus maximum possible current for the case when all leds are white.I'm building a lightpainting stick - images probably will have a black background and the leds will not be on for long - several seconds max per one picture.

author: johnnyfp
author_rank: Frequent Contributor
timestamp: January 12, 2014, 01:45:12 am
content: WS2812 are cool. I'm using a load of them in my projects. But at 144 In series, not sure you'll get the refresh rate of the strip high enough to light paint. You may want to split the strips serial line into two or three, to improve performance. It would be good to know if you achieve good results at 1 continuous strip.Looking at putting a POV project together using these. But plan on splitting the line into 4 to get the refresh rate up. It also allows me to split tge psu into 3 or 4 smaller units.So maybe that would be a better option.Split the psu into smaller rated parts, yes you'll have more components. But it will be manageble and duable without the need for expensives and large inductors and switch mode ic's

author: peter.mitchell
author_rank: Super Contributor
timestamp: January 12, 2014, 10:42:40 am
content: light painting doesn't need that fast of a refresh, in the right environment, exposures can be up to several minutes long... that said, it does make things easier...also, a lm2596 most certainly wouldn't be able to handle this kind of application, the internal switch would cook, that and it doesn't switch fast enough, you'd need a massive inductor.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: January 12, 2014, 04:05:35 pm
content: Something you could consider, depending on how you plan to position and mount the strip:You could cut the strip into shorter segments, to isolate the +5V rail, and then re-join the ground and data signals to their original connections. You could then run individual wires to the +5V of each segment and power each by its own lower current +5V supply.It may be easier to buy or make a number of lower current supplies than one big high current supply.Controlling the resulting strip would be the same as if you had used a single supply.

author: miceuz
author_rank: Frequent Contributor
timestamp: January 12, 2014, 04:29:10 pm
content: Quote from: johnnyfp on January 12, 2014, 01:45:12 amI'm yet to determine that. From quick calculation i get 800 kHz / 24 bits / 144 leds = 231 Hz refresh rate. It's ok for lightpainting.My biggest concern is if I would be able to read from SD card fast enough to pipe the data into the strip. I'm going to use LPC1343 72MHz micro. I'll use SPI data line @ 6MHz for data transfer, seems to be within timing tolerance margins, but I've seen on the net that led controllers might be picky to overall cumulative errors. SPI has 8 frame write buffer on the micro, so I'd get 10uS to prepare data for the next pixel. That's 720 clocks at 72MHz - seems like plenty, but again SD card and FAT library overhead...Thanks for the multiple dc-dc converter idea, but the battery still would have to provide substantial amount of juice.

author: bgsteiner
author_rank: Contributor
timestamp: January 12, 2014, 06:44:43 pm
content: this is one of my go to resources for lithium based batteries. They come in all shapes voltages and sizes you can buy a ready made 5v pack or build your own. They also have balance charging boards so you will be covered there. You would be better off getting a multi cell pack so you don't have to use a boost converter. You will find that the LIiFePO4 batteries will generally be able to handle higher amperage.

author: miceuz
author_rank: Frequent Contributor
timestamp: January 12, 2014, 07:13:39 pm
content: errrr... forgot to add an URL?

author: johnnyfp
author_rank: Frequent Contributor
timestamp: January 12, 2014, 07:17:08 pm
content: I usehttp://www.batteryspace.com/lifepo4cellspacks.aspx. But I'm sure there are a load of others out there.Get a couple of Cylinder ones. Put them in serials and mount it like that. That way you can use them as a handle (That's if you light painting by hand and not using a Plane or Drone).

author: bgsteiner
author_rank: Contributor
timestamp: January 12, 2014, 09:56:27 pm
content: sorry used bb code but it didnt stickhttp://www.batteryspace.com/

author: poorchava
author_rank: Super Contributor
timestamp: January 13, 2014, 12:19:02 pm
content: I think you have 2 options:LiPo cells are available with very high constant discharge currents. Some can be constantly discharged at over 50C, so getting 8A from one cell is not a problem. Efficiency is a problem, so for a boost converter you'd probably need synchronous converter (i.e. mosfet instead or in addition to a schottky catch diode). Those would have to be fairly low Rds MOSFETs. Most likely you will not find a fully integrated solution, but rather a controller that needs external power devices.second option is to use 2 or preferably 3 cells in series as input. @ would technically do, but voltage can go as low as 3V per cell which gives you 1V of headroom, and that's kinda low. Plus you would be working on much lower input currents which is always nice.Additional merit behind buck converter is that if a boost converter switch fails short, you have a Vin-GND short limited only by Rs of the inductor. Buck converter does not have this problem, as shorted switch will result in Vout=Vin. Failed buck converter can kill the led strip, but a failed boost converter can short out a LiPo, which is much, much worse.

author: Raymond75
author_rank: Newbie
timestamp: April 30, 2014, 08:15:56 am
content: Many of the older neopixels can be powered by 3.7v lipo battery,but it is not really guaranteed. Of the various neopixels that I have,the 60LED/M WS2812B stripbe powered by a 3.7v lipo battery, though I need 5v. Now that strip is happy being signaled from a 3.3v processor like the Teensy or Gemma.

author: miceuz
author_rank: Frequent Contributor
timestamp: April 30, 2014, 12:50:10 pm
content: Yes, I've tried to run it directly from an old Nokia 3.7V battery and it works reliably. As I'm driving pixels from UART I've powered up an inverter from the battery so that signal high voltage is the same as power. I'm using WS2812B pixels.One annoying thing though is that pixels do a random glitch when powered on for the first time, so I can't really power them down while not in use. I produces a visible line on a photo.