Why my project powering choice isn't working?

Projects General Guidance
1

I have a circuit that has:

1x ESP32 C3 mini
2x WS2812 LED bars with 8 leds each (16 LEDs total)
1x MT-3608 Step UP converter

My idea was to power it from 2x AAA rechargeable batteries (~2.4V) raising it to 5V using the step-up.

I assume the circuit will need ~1A to work (16*60mA max for the LEDs + ESP power consumption + Step up loss). The AAA batteries capacity are around 1000mAh. So, one could suppose the circtuit could work for about an hour.

However, this is what happens:

  • when using 2x AAA rechargeable batteries (ESP lits, LEDs doesn't work)
  • when using 2x AAA alcaline batteries (ESP lits, LEDs doesn't work)
  • when using 2x AA rechargeable batteries (ESP lits, LEDs doesn't work)
  • when using 2x AA alcaline batteries (LEDs lit once, sketch halts)
  • when powering the PCB with a breadboard power supply module that offers 700mA, no step-up, it works.

2xAAA batteries was on the limit, but 2x AA should work ok and it doesn't.

Questions:

  1. What am I missing?

  2. This circuit is supposed to go on a bike, so size matters. What batteries should I use instead?

2

What is your aim for the project ? How long do you want the batteries to power the circuit?

3

Use the lights as brake sign, etc...

+-1 hour

4

Based on the power consumption of your circuit. This battery should be able to power it for around an hour. These are the 3.7V 2000mAh li-ion batteries

image
image800×800 48.4 KB

5

Output power of stepup = 1A x 5V = 5W
Input current is 5W/2.4V = 2.1A

Can your batteries actually supply that much current?
Considering they are AAA probably not.

6

Ok, this is a 18650 battery. I´m gonna give it a try and report back.

7

Thanks for the tip Jim.
The AAA definitely can't. The AA should be on the edge, which is what I observed on the bench.

8

You need to read the datasheet for the battery to see what the maximum continuous current draw is.

9

Well, I'm just coming back to report. So, the 18650 battery worked!
That's why I´m marking post #4 as the solution.

Jim's contribution at post #5 was important for me to understand why:

Output power of stepup = 1A x 5V = 5W
Input current is 5W/3.7V = 1.35A

As the 18650 voltage is closer to the output voltage, less current is needed to achieve the same power, which makes the 18650 (3.7V) a better choice than 2xAA or AAA (2.8-3V). Also, the difference voltage between output and input (5V-3.7V=1.3V) still respects the Step-up converter specs (diff > 0.5V).

Regarding the battery datasheet I was unable to find it. The battery I have is marked as GoldPower and there was no info on their site about the datasheet.

If we just assume the maximum continuous current draw is 1C, my battery can provide 2.2A, which is now bigger by far than the 1.35A needed.

Thanks @jim-p , thanks @UjanDatta

10

That is usually the case but for some batteries it can be much much higher, even for the 18650s

11

There is more to electric circuits than "volts".