MT3608 Modules in parallel

Other Hardware General Electronics
1

Hi everyone,

I’m planning to build a Bluetooth-controlled car using an ESP32. I currently have two Li-ion batteries and I want to use them to power the car. My plan is as follows:

  • Connect both batteries to two separate TP4056 modules for charging. I’m thinking of using the same input power source to feed both TP4056 modules.
  • The OUT of each TP4056 would then go to its own MT3608 boost converter, boosting the variable 3.7–4.2V up to 12V.
  • Finally, I want to connect the VOUTs of both MT3608 converters in parallel to power my L298N motor driver.

My doubts

Is this setup possible?
Is it safe to connect the outputs of two MT3608 converters in parallel like this?

Schematic

Schematic_Bluetooth_2025-11-07
Schematic_Bluetooth_2025-11-071169×827 20.9 KB

2

Absolutely not.

Output voltage of those will never be exactly same. The converter with the higher voltage will attempt to supply nearly all of the load current, while the other one will do very little work, or may even be damaged if a reverse current flows into it.

If one converter/battery can comfortably supply the current needed, you could try that by placing diodes to both outputs to prevent back-flow.

But what's the point of this setup?

3

Sounds like a good space heater with those L298N drivers. Step 1 is NO to parallel operation or battery connections, put the batteries in series. Second get some MOSFET drivers, www.polulu.com is a great place to look

4
  • Explain how you came up with the +/- wiring connections :roll_eyes:

IMG_4285
IMG_42852107×727 123 KB

5

-out of the TP4056 is the current protected output of the negative terminal of the battery, which is shorted to the other TP4056's current protection circuit and vice versa via the ground traces of the MT3608 modules.
Not sure how that's going to end when you have an overload.
Leo..

6

Two or three cells on series and a 2S or 3S charger seems a better solution.
This one seems to also have a cell balancer for a 2S pack.
Leo..

7

I wanted to charge my car with USB-C (I am a beginner, I don’t know many options…)

8

Sry… Wiring mistake…

9

Can I connect the OUT of the TP4056 in series with the other TP4056 then to a MT3608. Is it safe?

10

Yes, but only if you use two separate 5volt supplies (two mains power bricks).
Powering them from a single 5volt supply (or PC/Laptop) will create a short.
Leo..

11

Hi, @decisivelloyd1234

Can you please post spec/data of the batteries?

Thanks.. Tom.... :smiley: :+1: :coffee: :australia:

12

18650 3.7v 3800mAh battery

13

Hi, @decisivelloyd1234

Motor specs?

Tom.... :smiley: :+1: :coffee: :australia:

14

What was your reasoning for connecting the boost converters in parallel?
Was it because you thought it would give you more current?

How much current do you think you need?

There could be a very simple solution

15

Those are fake, no such thing as a 3800 18650.

16

Ya, i thought i would need around 3A in total from the batteries

17

The usual hobby gear motors... 60RPM one, idk its current specs.

18

image
image271×218 39.1 KB

19

The best 18650 batteries from Panasonic and LG arrive to 3600mAh.

I have serious doubts that some local brand makes cells with higher capacity. But the big question is: are they safe?

20

The easy way to tell is to weigh them. Look up the chemistry (LiPo, LiFePO4, LiIon or some other) and do the math. Yes you need to guess the packaging weight but the fakes are really light.
Brand means nothing if fake.
Yes, real batteries are 3600 at it's maximum, but most are in the mid to low 2,000's.
I assume you have a professional charger that can do a proper capacity test.

As far as safety, the only Li battery that ever went bad for me was an Anker. I and many thousands of Rvers sleep on LiFePO4 batteries but a few weeks ago I saw a report of LiFePO4 batteries going up in flames so bottom line, NO all Li batteries can be unsafe under the right/wrong circumstances.