FastLed project with 3.3V pin

Projects Programming
1

Hello Everyone!

Me and my colleague have created a FastLED project using WS2812B.

It contains 14 LEDs. These are split into a 6-LED and an 8-LED group.

The 8 LED group operates from the 5V pin. The 6-LED group uses the 3.3V pin.

Brightness is set to half (127).

As I know the LEDs shouldn’t work from the 3.3V pin but the 6-LED group works fine so far with it. I also tried White color. (but brightness is still 127).
I worked on the project 6 hours. During this time the 6-LED group was ON lots of times. But not more than 5 mins at once.

What do you think?
Can the 3.3V bear a full-white setting with half brightness for a longer time?
I’ve read halving brightness halves the power consumption.
Instead of 60 mA it consumes 30 mA. That’s 6*30 mA = 180 mA altogether.

3.3V pin max power is 150 mA in theory.
However I think the design allows a bit more than described in the data sheet.

Opinions?

2

A decent 5V power supply can power everything. Why split it over 5V and 3.3V?

You forgot to mention which (Arduino) board you're using.

My view on that:
It uses on average less power; but peak power is still that 60 mA.

3

I am using Arduino Uno.
I read the 5V pin max power is also just 500 mA.

If I count with 30 mA/LED then 14*30 = 420 mA works with the 5V pin.
But with 60 mA/LED it also goes over the 500 mA limit.

Based on my experiences above (6 hours work - no problem) does it mean it will probably work on long-term?

Or it’s only a matter of time and some LEDs are going to die in the 6 group?

4

You are powering led from 3.3V pin and your data line is VCC of your board, in case of Arduino, 5V. Not really something Ws2812B LED was designed to handle.

5

I am using Arduino Uno.

6

It's not good practice generally to power LEDs from arduino pin. It's out of specs to power them at 3.3V. But It's even more out of specs to feed data at 5V while powering at 3.3V.

7

There is a fuse on the board to protect the USB port of the PC; that is where the 500 mA comes from. If you don't use the USB to connect to a PC you can use a power supply and provide power on the 5V pin; don't use both at the same time; that same 5V can be used as power for your LEDs.

8

Thank you for the answers so far.
Two questions left:

1, Can I make safe the 3.3V pin using the setMaxPowerInVoltsAndMilliamps function limiting the current to 150 mA?

Cable is already soldered to the 3.3 pin.
I can modify this but first I’m interested in the above workaround.

I guess the 8 LED-group wouldn’t work this way. But let’s give it a try.

2, Can I use a Powerbank as power supply for the Arduino Uno?
As I know phone chargers charge with 1A.
So I guess a Powerbank should be close to that.

9

the issue isn’t the LEDs themselves, it’s the supply current that might stop by being overdrawn.

10

I’ve changed the max mA to 150 and the max voltage to 3.3V in the FastLED.SetMaxPower….() function.

It still works. Is it safe this way?

11

The 5volt pin can provide 500mA - 50mA for the Uno itself = 450mA. If you draw 150mA from the 3.3volt pin, then that 450mA is reduced to 300mA, because the 3.3volt regulator steals it's current from the 5volt pin. The Uno is a tough cookie, but you should have a spare Uno handy.

A lower voltage on the LED strip causes red-shift, because the blue LEDs needs a higher voltage. Feeding a 5volt-logic signal into a strip while powering it from 3.3volt can cause phantom-powering, which can blow up the first LED. So better also have a spare LED strip handy.

Powering both strips from the 5volt pin of the Uno, with reduced brightness and a 1000uF buffer cap and 330 ohm resistor should be safer than what you're doing now.
Leo..

12

Why are you so fixated on using the 3.3V pin? It makes no sense for all the reasons already mentioned.

13

The LEDs are part of a thing. And this thing would be a present.
I don’t have the tools to change pins cause the time is short.

But I don’t want to give it to somebody if it’s not safe.

I think I’ll show this thing to the people but will not give it to them.

I can modify the pin later then.

14

Yes use a power bank but stay below the max rated Amps of the power bank and run all the strips on 5V.

15

You don't need any special equipment to splice 5V wire to two or chain it from the first strip to second one.

16

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