Using two lithium-ion batteries to power three separate components with buck converters [closed]

Question

I'm trying to use two 7.4 V two lihtium-ion bateries connected in series to power an Arduino Due, a Buslinker, and two L298N motor drivers.

In series, the total voltage would be 14.8 V.

The 14.8 V will go into a power block splitter which will split this voltage to be used for three buck converters.

The buck converters will be used as follows:

• Buck1 to Arduino: 14.8 V -> 12 V
• Buck2 to BusLinker: 14.8 V -> 7.4 V
• Buck3 to two L298N motor driver: 14.8 V -> 12 V

After calculating the total voltage after the buck converters, it will be 31.4 V.

**First question: My total voltage input from the two lithium-ion batteries in series is 14.8V and my voltage being used is 31.4V. Can this configuration be used to operate it successfully or would I need to add two more lithium-ion batteries in series to make the input voltage 29.6V?

Has been answered: The total voltage consumption does not matter. In this case, the total current is what matters. Therefore, it seems that I could run everything on a single 7.4V 50C 2S Li-ion battery, since it can provide 260 amperes.

Second question: Am I wiring everything correctly in my schematic?

Third question: Is this a voltage issue? Is there not enough voltage to power two servo motors?

Has been answered: Indeed, it was due to the desktop power supply. The constant current was set to 3.3A. Once I set it to 4.5A, the two servo motors and the Arduino were able to run perfectly using the same 7.4V and shared GND.

Fourth question: The BusLinker board states that the voltage input ranges from 5-14V, but each servo motor requires 7.4V. Is it okay to supply 14V to the BusLinker board? Will the board regulate it to 7.4V for each servo motor connected?

TESTING PERFORMED

During individual testing, this is what I did:

• I used 7.4V from my power supply to provide power to the LewsanSoul Buslinker, which was connected to two servo motors. (Note that each motor requires 7.4V each.)
• I used a 9V battery to power the Arduino.
• The Buslink and the Arduino were connected as needed for the Tx pin, GND pin, etc.

Results: Each of the servo motors moved, but it would move sporadically. It was as if it was intermittently working.

When I disconnected one servo motor and just tested one servo motor, it worked well.

Also, when I looked at my power supply that was providing power to the servo motors, each time I moved the motors, it showed that the voltage dropped significantly. It dropped to ~2v.

Details:

• Li-ion battery:7.4V 2S 50C 5200mAh Link
• Arduino Due: 7-12V Link
• Buslinker: 5-14V Link
• L298N: 12V Link

EDIT 1:

1. Total current = 6.1A
2. Question for revising schematic: If I revise the schematic, then would it be okay to connect one 7.4V 2S 50C lithium-ion battery in parallel with one Arduino, two L298N motor drivers, and one Buslinker? In this case, will each load receive 7.4V and use the amount of current that it needs?

EDIT 2:

Updated Schematic to include GND

GND from Arduino pin is shared with (-)BUCK 2 and (-)BUCK 3

EDIT 3:

I redesigned the schematic. The circuit is being powered by one lithium-ion battery with no buck converters.

Let me know if this redesign is correct.

EDIT 3.1:

After reading some comments, it seems like the second schematic would be my best choice.

1. The buck converter won't be needed for the Arduino since the power that will supply the "vin" input will be stepped down to 5V.
2. The buck converter for the LewsanSoul BusLinker won't be needed since it only requires 7.4V and the 7.4V lithium-ion battery can provide it. Also, the 50C 2S lithium-ion battery can provide enough current to power each servo motor.
3. The buck converter won't be needed for the DC motor. I can run it on 7.4V. I don't need the DC motor to spin at the full 200 RPM.

Answer 1

With common GND, adding up supply voltages is pointless.
At different voltages, the most useful measure is added up power: voltage * current.

In the schematic, the only GND connection depicted is from Arduino to BLE module.
You write about more ground connections during tests, you probably are OK there, but the schematic is incomplete - I don't think it confusing.

Power supply voltage drops during tests are easily explained by the power supply not being in a position to cope with instantaneous demand. (With a (desk/lab) supply, this may be as simple as not increasing the current limit when going from one load to two.)
Unstable power supply easily explains erratic behaviour.

I don't see any "power" inductors on neither bus link nor debug board:
I expect neither to provide reduced supply voltage.

The voltage spec for the servo seems to be stated with an error, the same torques a claimed in the user manual for 7.4 V and 6 V, respectively - this is the range of voltages from many a "2S Lithium battery" from nominal to cut-off.

The one reason I see to use a voltage "higher than 2S" is the motors being too slow:

• use a contemporary motor driver
• use a motor specified for the speed needed at intended load and cut-off voltage/6 V - with a bit of room to spare

Answer 2

My total voltage input from the two Li-ion batteries in series is 14.8V and my voltage being used is 31.4V,

That's meaningless.

That's like saying "the total of your height (170 cm) and my height (160 cm) is 330 cm". That's meaning less. You're not standing on my head. As we are all standing on the ground, our height do not add up.

As all the voltages are referenced to the same ground, the voltages do not add up.