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I have recently taken over for a guy who retired from my company and I am working on getting a prototype that he designed back in 2016 up and running.

We are using two 3.6 V 18650 batteries to power the system and attempting to run a brushless DC motor using a boost board to drive the motor at 9-14 V. The boost board is separate from the h-bridge and the MCU but connects to the board with a direct trace straight to the h-bridge.

The problem is that when I run the whole system together, I can't get enough current to the motor to reach our torque spec, even when running off a power supply.

The weird thing that I can't figure out is that the system works when I use two power supplies (7.2 V, 20 A limit), one to power the MCU board which has two voltage regulators to 5 V and 3.3 V, and the other to the boost board. When I use the two power supplies I can draw the 10-ish A I am looking for. When I use just one power supply and run the system, I am only able to draw roughly 6 A.

Any ideas of why this is happening, and any possible solutions?

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    \$\begingroup\$ I suggest you draw a block diagram and find the missing low impedance ground. for a split supply. Sounds flakey by the description for a signal that requires high SNR and high BW. \$\endgroup\$ Commented Jan 13, 2022 at 16:20
  • \$\begingroup\$ Sounds like the batteries cannot deliver the watts needed for everything. Try a bigger battery pack (more in parallel). \$\endgroup\$ Commented Jan 13, 2022 at 16:45
  • \$\begingroup\$ its not a battery problem. I am using power supplies and not drawing enough power. Also the batteries we are using are rated for 15A continuous draw \$\endgroup\$ Commented Jan 13, 2022 at 16:56
  • \$\begingroup\$ Really need a diagram here and need part numbers. Where is the voltage regulation happening? A BLDC won't fare well when connected directly to the batteries. \$\endgroup\$ Commented Jan 13, 2022 at 20:25

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