Power plan with neopixel advice

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Draculen
 
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Power plan with neopixel advice

Post by Draculen »

Hello,

I have a portable project which requires me to power 400 neopixels. I have 100 pixels on each pin of my feather express board but I know one little lipo from the feather isn't going to be enough to power all 400 pixels. What product would I need in order to inject more power into the circuit without breaking all the pixels?

And can another power source/battery be wired in at the same side of the circuit?

If i can use another lipo would it even get a charge if it's only wired in from the + side of the circuit?

Originally I was going to have the lipo battery from the feather plus a 12v battery holster with a buck converter to step the voltage down but am totally lost if that is even possible or what the wiring would look like.

Thanks in advance

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dastels
 
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Re: Power plan with neopixel advice

Post by dastels »

I advise you start by reading through https://learn.adafruit.com/adafruit-neopixel-uberguide.

And, you are likely correct about needing additional power. If you only light up a handful at a time you might be OK with the LiPo. Each NeoPix4el can require up to ~60mA (that an RGB NeoPixel set to full brightness white). That doesn't sound like much, but it adds up quickly. For example, if you lit all 400 at full brightness white, they'd require 24A. It's not likely you'll be doing that (unless you want to blind everyone in the area) so the requirements will be somewhat lower. Anyway, that guide goes over options for powering, and is generally the best place to start if you're doing anything beyond basic usage with a handful of pixels.

Dave

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adafruit_support_bill
 
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Re: Power plan with neopixel advice

Post by adafruit_support_bill »

And here is another guide well worth a read: https://learn.adafruit.com/sipping-power-with-neopixels

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dastels
 
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Re: Power plan with neopixel advice

Post by dastels »

I was trying to find that one. Working to minimize the current requirements is the step, especially with a battery powered situation.

To answer your other question, only a LiPo connected to the Feather will charge when the Feather is powered by USB.

Dave

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Draculen
 
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Re: Power plan with neopixel advice

Post by Draculen »

That's definitely useful information. Thank you!

I suppose if only the lipo plugged into the BAT pin can charge could you wire two lipos to the same pin or would that be wayyy too much power going in? I have the pixels at half brightness and probably will not go higher then that.

If I wanted to use a disposable battery to help with power, if I'm reading the guide correctly i should be able to to wire the positive of a 12v battery holster with battery to a buck converter (to step the voltage down) and on the other end of the buck converter, that is where it would wire in to the neopixel array(unless I'm missing an extra step like a capacitor to ensure when it turns on the voltage is controlled correctly)?

I apologize for the million questions, this last step of my project has been putting me at a stand still! Thanks

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dastels
 
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Re: Power plan with neopixel advice

Post by dastels »

Yes, battery -> convertor to get 5v -> V+/Gnd of the NeoPixels. That Gnd also connects to the Feather. A cap can be a good idea to absorb any initial surge when the strip powers up. Read the uberguide I linked regarding best practices.

Trying to charge 2 LiPos will likely cause problems.

Dave

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Draculen
 
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Re: Power plan with neopixel advice

Post by Draculen »

Fair enough. You guys always have invaluable information. Thank you for the assistance!!!!

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Draculen
 
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Re: Power plan with neopixel advice

Post by Draculen »

Last question I promise.

The buck converter I have is 5v at 3a. Is this ideal for 400 neopixels when stepping down 12v? Or is this the wrong setup for a neopixel array this large

https://drive.google.com/file/d/1T_lR81 ... p=drivesdk

If my calculation is right all 406 pixels should be 28 amps in total(woah!)

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adafruit_support_bill
 
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Re: Power plan with neopixel advice

Post by adafruit_support_bill »

That 28A is a worst-case estimate. Your actual requirements will likely be less. But still quite likely to seriously overload a buck 3A converter - which is inviting problems. Is there any reason you need to start with a 12v source? Powering everything directly from 3.7v LiPos would be simpler.

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dastels
 
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Re: Power plan with neopixel advice

Post by dastels »

Or 5v from a USB powerbank... or multiple, each powering a different segment of the strip. But then you need to use a level shifter to boost the data signal to 5v.

Dave

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Draculen
 
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Re: Power plan with neopixel advice

Post by Draculen »

I may be able to use a cylindrical power bank. The form fit is why I chose 12v because it packs a punch and they are super tiny.

If I can use another Lipo bill, what kind of pinout would that look like? I doubt I can have 2 lipos charging directly off the JST or BAT pin but it most certainly would be ideal!
The pixels themselves will only be at half brightness if that would make a difference in power consumption.

For more context, with all 400 neopixels along a 3.5ft cosplay sword I was going to wire in the other battery source at the top, drill a hole in the PVC pipe (to keep the blade from wobbling like a noodle) and running wires down the pipe so the battery holster could be changed from within the hollowed out cylindrical hilt at the bottom.

Another Lipo is preferred if it can be charged directly off the board and not have to be disconnected once it dies(but totally do-able if needed!)

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adafruit_support_bill
 
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Re: Power plan with neopixel advice

Post by adafruit_support_bill »

We have LiPo batteries as big as 10Ah: https://www.adafruit.com/product/5035
The pinout is the same as all the other LiPo cells we stock. You can charge it from the Feather - but it would take a while since the charger on-board the Feather is limited to 100mA charge rate.

Another approach would be to use one of our Mini charger boards for a 500mA charge rate. https://www.adafruit.com/category/575
You could add an SPDT switch to switch between run and charge mode.

Or you could use the Mini charger with one of the ItsyBitsy boards. https://www.adafruit.com/?q=itsybitsy&sort=BestMatch
These are similar to the Feathers, but without the on-board charger, so there would be no need for the switch.

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Draculen
 
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Re: Power plan with neopixel advice

Post by Draculen »

Bill thats extremely interesting! Especially the Lipo that can supply the required mA but at the appropriate voltage.

I guess my main concern switching to this power method is if its one battery/power source near the microcontroller.
Would the voltage still drop near the end of the array?

the LED's themselves are very close by and the electricity does not travel through extremely long wires (The project itself is 3.5 feet long feeding 2-4 different pins)

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adafruit_support_bill
 
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Re: Power plan with neopixel advice

Post by adafruit_support_bill »

3.5 feet is not a very long distance. The limitation is the resistance of the power and ground traces on the strip. To avoid voltage drop, 400 pixels will require power to be supplied at more than one point along the strip. I'd run extra power and ground feeds to the middle and end of the strip also.

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Draculen
 
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Re: Power plan with neopixel advice

Post by Draculen »

Okay, im sorry if this is a super dumb question but how would the wiring be if its coming from the same power source?

+ and - side of the neopixels going into the micro-controller

(Neopixel Array --> Microcontroller)
1 extra wire coming out from the microcontroller for +
1 extra wire but also from ground

those extra wires then go further up the array and are then tied into the Neopixel array (near the end and possibly the middle) but the extra wires are spliced

Extra - and + wires going into - and + from the middle of the array but also wired again in order to power the next neopixels up the array?

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