So I am making a pair of wings that I want to light up in programmed patterns.
Previously I have only ever used always on LEDs connected straight to a 9v or AA batteries… I kinda want to level up and make it so the wings can catch fire, so I know that means a lot more LEDs and programming, and generally electronic stuff… So maybe I am jumping into the deep end seeing as it has been 20 years since I did this at school or used a breadboard…
I am looking at WS2812B LED strip. 5v, 100 lights per metre. 30Watt per metre.
Attached to an ESP8266 Dev board with WLED.
I understand that it is best to run the power to each end of the LED strips.
So a few questions… What sort of wire do I need to buy to run the power to the far end of the strip?
I tried looking but couldn’t find a clear answer, with the ESP8266 devboard, how many LED strips can I plug in? So rather than 5m doing a long loop connected to the board, cut it into 6 lengths, and all 6 shorter strips connected to the board?
Battery… So my understanding so far, and digging 20 year atrophied math skills out… To work out the amps needed for the battery it is amps = watts/volts. So 30wx5m, 150watts. 150/5v = 30amps.
So the battery would need to put out 30amps to power the lights… Is it even possible to get a wearable battery that size? If so, where? (I can’t find many batteries that display the amp).
What would I need to do to wire a battery like that in? I did see something about being able to reduce the power needed… I think.
I could drop to 60lights per metre, which I think would bring amps down to 18.
If you’re cutting the strip into 6 shorter strips you may get away with powering it from one end just fine.
Amps
I remember the 144leds/M strips were 5A per meter so this math feels about right.
Some good news is that it’s only 30A if your rocking full brightness white on every single LED.
30A of batteries feels like a lot to carry but if you can write code that ensures… maaaaaaybe a little less that that you won’t need an Arabian Camel following you around to carry your wine-skins full of lithium.
You’re writing some code that emulates fire so I claim that many of the LEDs in your gird are going to be off anyway to form the shape of the flame.
If there is a battery solution to this I’ll leave it to the CE to make a product recommendation since they will be familiar with the stock and your options.
AAs have 2 AmpHours right? Battery backpack? … do it?
Design
Bit of a trade off here. I believe that 6 separate strips will be easier to power with batteries since there unique draw will be smaller. This will make it easier to debug since you can treat each strip as it’s own machine.
In exchange you’ll be running six Data Pins from the ESP8266 which will take a little more code because you’re trying to print a coherent image. That’s a trade off I would take but that’s a personal preference.
How flexy does this need to be?
If you don’t need these to flap in the wind would you consider working with something like this?
Lastly, @Murray125532 had some cool thoughts for me when I asked a similar question last year.
I haven’t gotten to the code yet, still working on physical limitations at the moment.
(I am kinda assuming I can do basically anything with some degree of hair pulling)
I found a battery that should do it… RC toy batteries using, 18650s!
The only time full brightness will be used is for my “competition” program, which will be lights rise slowly to absolutely as high as possible (angel entrance should be like high beams), hit high white for a moment, shift to gold, then a darkening red, then into the flame effect.
Lucifer falling, basically
So it will only be at full brightness for 10 seconds of the 6 hours I’d ideally want the lower lights on.
I have found a 12V, 30A max discharge, 10A max continuous discharge, with 20,000mAh. 10cm x 7cm x 6cm, 750g battery.
So from that I assume I would get 20mins of full max white
Or an hour tops of normal use.
I’ll recalc with the 60 lights per metre instead… And try and get more time
I can also carry a spare of that battery
Are there any other ways to reduce the power used?
And what should I use to step down a 12V battery to 5V?
That 20AHr would be at the 20 hour rate, ie; 1A or 1000mA. At 10A the capacity will be reduced. Not quite sure of the curves for LiPo but quite drastic for lead acid batteries,
A switch mode buck converter but with a high current rating.
The good news is that the 20Ahr is quoted at 12V. It will be somewhat more at 5V if using aforesaid switch mode converter.
At 12V 20Ahr = 240Whr
At 5V 240Whr = 48Ahr
Allow conversion efficiency of say 85% we are left with 40.8Ahr @ 5V.
So you are a bit better off than you thought. BUT don’t forget that is for a 20hr discharge rate or 2A. Derate for higher discharge rates. You will have to find some curves find out what the derating is.
Cheers Bob
That is not necessarily true. You can connect the power to six individual strips but there is nothing stopping you connecting the Data is series and as far as software is concerned it will be one long strip controlled by one pin.
Cheers Bob
Okay, so made a few modifications to what I am looking at based on feedback here, and the further reading that sparked.
Given the light will be behind several layers of EPE foam, it will be quite diffused, and the pattern does need the lights to be different colours every 1cm, like the 5v led at 60per m, every 3cm, like a 12v 60p meter but controllable in groups of 3. So different light every 3cm rather than 1cm is an easy change for decreases amps needed.
So looking at either WS21815 (individually addressable) or WS21811 (addressable in groups of 3),12V LEDs, 5m string, 60p/m.
That is 18watt/metre
So that should be 7.5amps (much better than 30!)
On the battery above 20aH, and using 7.5amps, it should last 2 hours 40mins at full power.
So I would be right to assume it would last 6hours if it’s switched between sometimes off, usually low light red/yellow, and once or twice for 10sec at full bright white.
If I switch to those 12V lights can I still use the ESP8266 Dev board?
It’s more a matter of I can cover space better if I have 6 1m strips heading out from the dev board, rather than having a continuous 6m long snake.
So I assume all 6 pieces would need to be attached to the devboard that way. Unless I can wire att 6 strips onto the same pin somehow? (Sorry, I am still getting linear/parallel/etc mixed up)
Yes. It doesn’t matter which LEDs you are using you can’t power them from any controller board that I know of. You have to power them directly from the supply (battery etc). It is the Data line that you connect to the controller and the Ground (negative) connection also is a common point.
You are not reading my reply. I have already told you the 20Ahr is at the 20hr rate, ie; a discharge rate of 1A. The capacity has to be derated for higher discharges. By how much depends on the battery chemistry.
Don’t know how the 30A became 7.5A but I leave you to sort that magic.
Cheers Bob
Hi MostlyReallyMatt
You have to connect LED power directly to the supply as stated above That can be 6 strips in parallel.
It is the Data you connect in series like this
Data pin - to - strip1 DIN.
Strip 1 DOUT - to - Strip 2 DIN.
Strip 2 DOUT - to - Strip 3 DIN
and so on to strip 6
and write the software to look at it as 1 continuous strip with X number of LEDs.
I don’t know but this could simplify the software instead of trying to write to 6 individual strips.
Cheers Bob
Don’t forget the grounds (data and power) pins have to be connected together.
Hi
Ah, you changed strips. I missed that or my old grey matter got confused.
Same number of LEDs, same power. The advantage of 6 strips is you reduce the voltage drop over a long length and have a far better chance of having almost equal voltage on each LED. Over 5M you can have a fair voltage drop under high current conditions, the tracks on the strip are not that thick so you will have less trouble of this nature with shorter strips connected to the power in parallel.
Cheers Bob
So my Math maths?
I have saved myself a big power issue?
What sort of wires should I be using to run from the power to each strip? My understanding is they’d need to be a thicker copper? To stop it heating up to much with the amount of amps coming through. And the wires in the strip and cheap connectors is quite thin?
If so, specific recommendation like I know nothing
Hi MostlyReallyMatt
18W @ 12V = 1.5A. Quite manageable. No need to go overboard so I would say 20 or 22 Gauge would be OK as long as you are not running it for dozens of metres. If you had what you might think is a long run you could go up a bit in size but you can keep it decent as I don’t think it will be super critical.
They can get away with thinner wires in the connectors because they are short and would not have much in the way of voltage drop over the short length.
Your maths has nothing magic about it. Different strips.
Cheers Bob
Ah Peukert’s Law, haven’t seen that referenced in a while.
C = (I ^ K) * T
Where C is effective capacity in amp-hours, I is current draw in amps, T is time in hours, and K is Peukert’s constant for the cell.
You can visualise this in the graph below, where the higher your draw is above 1A, the lower the effective cell capacity, dropping much faster for cells with higher Peukert’s constant values:
LiPOs, LI-IONs, NiMH and SLAbs all have varying K values (essentially how much the effective capacity changes versus a change in current draw), most of the time it is between 1.05 and 1.5 depending on the chemistry the internal resistance of the cells, with the higher values indicating a faster drop-off in effective capacity.
From memory SLA batteries are particularly bad at this (K is 1.1 to 1.3-ish, while it is usually less than 1.1 for most LiPOs,) and is one of the many reasons most modern electric vehicles and large scale drones use lithium based cells.
The tldr of this is that if you’re trying to supply a relatively heavy current load, large LiPO cells are almost certainly the way to go in order to get a decent effective capacity (such as for these strips you’re trying to power).
Hi Matt
That should work.
One thing you need to make sure of. On the 12V to 5V converter the negative or ground MUST be connected through. That s the ground on both sides of the converter MUST be the same connection. If it is not connected connect it. This is a requirement so the data line has a ground return to the controller .
Cheers Bob
SWEEEET
