Hi all,
I'm workng on a project using 3 WS2812B matrices. Each one 32 by 8 pixels, so a total of 512 pixels. Assuming a possible 60mA max draw if set to white, that's a possible over 30A!
(Edit. Wrong quick maths- Used just 2 panels for my prototype, this is 3 panels so 768 pixels, 46A. So even more of an issue, will see what it looks like with my breadboard build, but hoping I can get away with setting 9A max- so notionally 3A per matrix- not sure if that changes wire gauges etc...)
Too much.
I set a max amp setting (6A) in SW, which should do the trick, but I want to be extra cautious and build in Hardware protection, for both a current limit, and short protection- drawing a few amps per panel might get melty worst case, and cause a short- which I believe isn't good for a construction of plastic and wood. As I'm building this as a gift for a friend, I'm being extra cautious wrt making sure I don't give them something that might burn their house down.
So, first of all, I'll be powering each of the three matrices indepentantly- This will make sure that all those 6A (Or the worst case 30..) doesn't go down one wire to all matrices. Then, I will be soldering together the 3 5V injectors spread out across the matrix- one at start, middle, end. So the hopefully ~2A going to each panel will actually be split across 3 power delivery wires- 22AWG cable should be fine. I've attached a photo to show the back of my matrix- matrices horizontal here, so I will be connecting the top row of 5V's, the middle, and the bottom, and each of those will independantly go to the power board.
Each matrix 5V line will plug into a pin on my power distribution board (Pictured). Simple layout, 5V barell plug in, using a DC PSU rated for 5V@10A. Top is a 5V to 3.3V voltage regulator, to directly feed the ESP32, other 3.3V peripherals, into a 3.3V and ground pin rail. Despite my care to make sure the toal current is split for entry to the matrices, you can see that ultimately this is still all going through relatively small 22AWG cable on the protoboard, and into a line of pins.. It's a single point of failure though...
Bottom, is so far just grounded bottom line of pins (also linked to the 3.3V ground line for common ground), and you'll see I've left a space where i haven't linked up the 5V heyween the barrel and the 5V pin rail, where I had intended to wire in a toggle switch.
I think now though that in that space I will put some overcurrent and short circuit protection.
So here's the question;
What is best to use for this overcurrent/short protection? I want to avoid building my own, as per them many tutorials online, partly because of space constraint here, and partly because I'd rather just shove in an all in one COTS component it it's only a few quid.
Simplest I know would be a fuse- But I quite like the idea of a 5V relay/cutoff switch for both overcurrent draw and short protection- Then if it's a semi-regular occurance, it can reset itself and continue operation once it's calmed down, without replacing a fuse.
As above, I've played with a maximum current setting in the SW already, and found I can get the matrix to do everything I want at 6A max current (Though that's what it operates at, with that hard limit set, so it would pull a lot more if I let it.) based on this, I'll use a 6 maybe 7A limit for the over currnet protection.
So I've seen a few COTS devices that will do this, such as;
This 20A one on ebay
And I've found the same at 2A. Nether meeting my current needs.
I've also seen a lot of these type of things;
Aramox-Overload-Protection-Overcurrent-Protector
which seem to be designed for cars- look like car fuses. This seems to be the funciton I'm looking for, and there seems to be an 8A version, and also apparnetly does short circuit protection. Is this the same thing as above, just in a little black box and made for the cars? Could be ideal- And I guess I can solder this straight to the board, or fine a plug. Could this just be the simple solution?
I've also just found these 'PTC' devices, described here;
PTC devicies on Sparkfun
I'm not quite sure how that can do everyting i need that is otherwise done by s eries of transistors, reistors, and/or relays... maybe they're just for low current- seems too easy...
The final alternative, is to put one of those cheap ebay 2A devices at the input to each matrix. Can't workout if that's safer or not- Higher fideltiy control, but there'd still be 6A going through one cable at all times between the power board and each 2A device..maybe that's not too bad. I do prefer the idea of having all my power safety stuff in one place on my power delivery board though. I like the idea that if anything's going to get hot and melty, it's within this one single point of failure, and not nestled between some sheets of plastic in my matrix housing.
Any suggesitons on which type of device best suits my needs? And overall if my approach here is okay? That is to put a single device on this board for the 5V power, and that 5V ~7A connection point to the 5V pin rail is okay? I can re-do another way if this is not considered appropriate.
(Note, the always on 3.3V power line is a delibarate choice, to keep my ESP32 always on- and it'll be a realtively low current draw, so keeping it sperate from the 5V protection stuff).
Here's some pictures;
Hopefully I've explained all this okay, sorry for all the words- maybe I'm overcomplicating it, but as said, just being cautious.
When it's all done I intend to write a fully detailed instructable which I'll link here. It's basically just your standard smartmatrix type dispaly running WLED-SR for audio visulations, but I've blinged it up with some additional controls, relevant code modules and far too many pixels.
Thanks for any help,
Edd.
32 x 8 x 3 = 768. And the current would be around 45A.
