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In my project, I will be powering two 6V DC-motors with the tb6612fng dual motor driver from sparkfun. They have a stall current of about 3,2A. They are controlled by an esp32. My project will be solar powered and my solar power manager that charges a 10000mAh LiPo battery, supplys 5V 3A regulated power. I will use a step up converter to boost that 5V up to 6V for the motor driver. I will use a step down converter to get the 3,3V for the esp32. I heard there could be some voltage drops that could shut the esp32 down. I also heard, that a capacitor could be a solution to that problem. My questions:

  1. What will happen, if the motors are at stall or almost there? Would they do nothing, because my power supply can just supply 1,5A to each motor?
  2. In the case of the first question : Would the esp32 still get enough power from the power supply, or would all power go into the motors?
  3. Is it correct that a capacitor would help with the voltage drops? If yes, which one and how should I use it?

Thanks for your help!

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As you may suspect, the answer to these is "it depends".

1: Stall current for your motors is 3.2A, which is the peak output current of your controller. After a while, you will probably trip the internal thermal protection. Looking at page 6 of the datasheet, you might have thermal issues at 1.5A as well.

2: If the voltage on the 5V rail drops below the cutoff voltage for your 3.3V converter, you would see problems. If you suddenly lock the rotor of the motor, you might drop the voltage of your 5V rail enough to cause problems on the ESP32 side, but since that depends on the response of the 6V converter, 5V converter, and 3.3V converter, it's hard to tell if this will actually be the case.

3: Bulk capacitors could be used on all 3 rails: on the 6V rail to supply immediate power to the motors, on the 5V rail to help keep voltage constant as demand from the 6V converter changes, on the 3.3V rail to keep voltage constant if input voltage sags. The general best practice is to address these issues as close to the source as possible so I would start with electrolytics on the 6V rail. How much capacitance is acceptable is, again, determined by your converter.

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  • \$\begingroup\$ Hi, thanks for your answer. Would you suggest an other motor driver then? If yes, do you have a recomendation for a mosfet based one? \$\endgroup\$ Apr 20, 2023 at 17:04

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