How much power I should supply for 7 Segment display using WS2812B

Projects General Guidance
1

Hi,

I want to make a 7 segment clock and each digit uses 21 WS2812B LEDs

The LED strip had 2 extra wires for 5V and ground (see red and white)

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I have a 5V 10A buck voltage regulator

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I will connect mains power to the buck converter and then connect output of buck converter to the first digit JST. I will then use the red , white wires and connect to a electric connector blocks and connect the output of each to a digit

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Is this setup safe ? Is the power amps safe or am I supplying too many amps?

please advice

2

Each LED at maximum brightness (white color) consumes 60 mA, so your digits would consume up to 1.26A.
You can connect up to 7 digits without problems.

3

You can't supply too many amps. The LEDs will draw whatever current they need so it is possible that you don't have enough Amps

Do you have 4 digits only?

4

yes 4 for now and may be 5 after I get more leds ( max 5 digits).

Agreed that the consumer ( LEDs) take whetever they need , and is not based on what we supply.

Is my setup ok ? I am not daisy chaining the digits, if I am using the right words.

5

not sure why you specifically mentioned white colour. I checked google gemini and it scared me for AMPs and I bought a 5v 15A converter too.

6

The buck converter accept a maximum of 24v DC !

7

The converter you show need 12-24V input not mains voltage.

8

You can daisy chain the data line, and connect each digit with 5v + GND.

9

I understand data in and out. my question is abour power.

10

I agree that I was not clear . I wanted to add the "adapter" to connect from electrical terminal to buck converter

11

What is it's voltage and current?

12

I am using the right adapter like a laptop charger that outputs 12V and 2A output.

13

A better idea would be to use a 5v adapter and ditch the buck converter.
21 digits at 60mA Max = 21 x 0.06 = 1.26 A max x 4 = 5..04 A, so a 30W 5v Adapter should suffice.

14

Depending on the brightness of the LEDs that may be cutting it close. I would use 2.5A or more.

Which Arduino are you using?

15

If i would design what you want to achieve, (i have thought about something similar) i would actually use 12v WS2811 strip, with 3 LEDs per pixel, and have the actual 7 segments and use a 12v PSU (and maybe a small stepdown for the MCU)

16

Hence added the buck converter.

Arduino is NodeMCU ESP12E.

I will use upto 95% brightness depending on sunlight brightness.

I am not making this for a 5 minute youtube video but for a clock that will be on 24 hours x 365 days !!

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17

The Clock will never have all LEDs on at the same time (unless it shows 88:88 in pure white)
A single switching PSU will behave in a predictable way, if it can not provide the current, the voltage will drop, which in turn will reduce the current draw of the WS2812b 's . Older coil based transformers will burn out.
What will happen with the PSU + Buck-converter combo is not as predictable. Will the PSU stay at the maximum wattage ? will the buck-converter overheat ? who knows.
If the PSU will brown out due to excess current draw, it will drop below the 12v minimal input voltage of the buck converter.
A single PSU solution is preferred even if it breaks, you break only 1 part.

18

I understand and I have to consider the (LEDs) worst case scenario. ( as mentioned in the chain I may add another digit)

LEDs are 5V...so cannot use my 12V PSU. (though you did not say that)

I have a 5V mobile charger, but it is only 1.2A or 1.5A

I want to design this properly.

20

For 21 pixels per digit you need 21 x 0.06A = 1.26A and for 5 digits, that’s 5 x 1.26A = 6.3A maximum, power is 5V x 6.3A = 31.5 Watts.
So the 12V supply needs to provide at least 31.5W / 12V = 2.63A.

That is assuming everything is 100% efficient. Assuming worse case efficiency of 80% then the power for the 5V buck is 31.5W / 0.8 = 39.4W and the power for the 12V supply 39.4W / 0.8 ~ 50W

So the 12V adapter current rating should be around 50W / 12V = 4.2A

You should also include a 100uF cap for each digit

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21

Thank you

I learnt a new formula. I just checked one of my laptop charger, it is 130W , output = 19.5V and so 6.7Amps

But this is not suitable for me, as I need 5V.

So I want to understand if I can use a 12V adapter connect it to buck converter to make it 5V and the amps as generated by the converter and use a 100 micro farads capacitors.

please confirm