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Servo Leads Max Current

alexanderlohaus · 675

alexanderlohaus

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on: January 11, 2019, 01:05:11 AM
First of all, this is a great project! A big thank you to the people who made this! I'm currently working on improving the diffusion a little so I'll be sure to post my results here when I'm done. In the meantime, I have the following questions:

I got myself a 5V 7A power supply and the following servo extension leads: https://www.amazon.co.uk/gp/product/B073ZMHHLW
I'm wondering if the servo lead extensions used for this project can support that kind of current?
Also, am I correct in assuming that if for example I connect 9 LEDs, only 0.54A (= 9*0.06A per LED max) will flow through the cables?

Thanks!
« Last Edit: January 13, 2019, 01:14:20 PM by CdRsKuLL »



digitalgecko

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Reply #1 on: January 11, 2019, 02:57:24 AM
60ma is the maximum draw for one LED as per the specifications. This is assuming full brightness white is being shown.

I don't know the specs on the servo wires off hand so I cant comment on that. It should be noted though that with these LED strips you can inject power at any point in the chain to balance the current load, so for a particularly large display additional power points could be added. They would not need a nodeMCU just 5v



NotionalLabs

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Reply #2 on: January 13, 2019, 10:30:32 AM
This raises an excellent point - my servo wires are still on the way so I'm not able to measure them, but usually standard duty servo wires are 26AWG which can carry about 1A (assuming it's made of copper). Heavy duty servo wires are usually 22AWG which is rated for about 3A.

Depending on your build, the standard size wires should be good for up to 7/8 tiles if you're only using 3 LEDs per - I'm planning to use 9 per (and at least 9 tiles), so I'm going to need to find an alternative.

@CdRsKuLL - it might be worth us looking into this and stickying a post about it given that it's a safety issue that newcomers to electronics might overlook.

Jim

EDIT: In doing some more digging into this, I think I was a bit conservative in my original post - some resources suggest 26 AWG wire can carry around 2.2A and 22AWG can carry around 7A. These greatly depend on the construction of the wiring though (single core vs multi-core, how many strands, metallurgical content, insulation rating and type, etc). Once I get my leads I'll do some hands-on testing and update the thread.
« Last Edit: January 13, 2019, 12:10:00 PM by NotionalLabs »



CdRsKuLL

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Reply #3 on: January 13, 2019, 01:13:01 PM
Morning,


I'll make this a sticky. From the research I did I found a few posts saying standard servo wires are rated at 3A, but on testing it can actually carry up to 7/8A but did get warm.. Also, when I measured the current powering 16 tiles (48 leds) I found the below;


 Pattern
1 - 0.6A max
2 - 0.35A max
3 - 0.32A max
4 - 0.2A max
5 - 0.33A max
6 - 0.98A max
7 - 0.6A max
8 - 0.6A max


So, it depends greatly on what pattern is being displayed.  I'm using a 2A psu and I'm more than happy I'm running well within safety limits.


I think problems will arise when more than 1 led is used in each corner. If you go for three (9 per tile) then to do a 16 tile run like I have your looking at 144 leds compared to my 48.  So I would expect the amp's to be three times as much.. On pattern 6, that would be 2.94A, still not massive really but if showing all white that could be 8.64A.. very much borderline.


So there are quite a few variants going on really.  You could also limit the brightness to say 200 rather than 250.


My recommended limit would be 28 tiles / 3 leds per tile / 5v 5A supply... 


A nice LED / Tile / Power calculator would be nice :-)


The other thing I would mention is not all servo wires are the same quality.. which puts another spin on things as people will all end up with different products.  The safest way is to put a meter on your LED's once built and see what they are pulling. It's the only real way to be sure your happy with the install.


Steve
« Last Edit: January 13, 2019, 01:16:36 PM by CdRsKuLL »

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ARN

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Reply #4 on: February 11, 2019, 01:46:39 PM
I have 21 tiles (63 leds) set at the moment
I measured the power consumption with a kill-a-watt, set the color to full bright white and the draw was 10 watt, thefore ~5v@2A
This looks kind of good because in theory that max load could reach 18.9 watts.
Maybe I am missing something, but the result seems to point a consumption quite below the theorical one.
« Last Edit: February 11, 2019, 01:52:29 PM by ARN »



mannymiller

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Reply #5 on: February 11, 2019, 03:12:58 PM
Quote
I have 21 tiles (63 leds) set at the moment
I measured the power consumption with a kill-a-watt, set the color to full bright white and the draw was 10 watt, thefore ~5v@2A
To me that figure seems way to low.

I am running 10 panels with 9 leds per panel, so 90 leds.  its not so much the ammount of leds used, but the distance betweem them., 10 panels = almost 5.1 metres.

I build alot of projects using the ws2812b leds., some of my matrix use 16x16 leds ( 256 leds.) and i can use a 8 amp power supply without issues., yet on this project it struggled with 90 leds on full white (255), to fix this i did run a second 5v feed to my last panel to cure my voltage drop. ( see previous topic i posted)

i am now using a 10 amp power supply and can obtain full bright white without issue. if you are getting voltage drops, then something somewhere is going to get hot in a very short ammount of time.




 


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