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The attached Schematic uses 6 N Channel Power Mosfets "IRL3303". I have wound my inrunner bldc motor with 180 windings per phase using a 26 Gauge Magnetic Wire. My motor is a 6 pole 2 magnets machine. The encountered problem is defined below.

3 Phase Current Driver Schematic

Q. The mosfet being used has a Vgs Threshold as 1V. Arduino outputs are being used to power the mosfets(state-machine). Even at 15V VCC the drawn current by the motor is around 0.6AMPS. I have checked the winding connections seperately and it draws 2Amps at around 3-4V. My resistance per phase is around 5ohm and inductance 1.5mH. I have no clue how to fix it. Your input would be really appreciated. Thanks

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  • \$\begingroup\$ "Even at 15V VCC the drawn current by the motor is around 0.6AMPS. I have checked the winding connections seperately and it draws 2Amps at around 3-4V", now what?? Does it draw 0.6A at 15V or 2A at 4V? You didn't mention the speed of motor, and if your state machine follows the rotor position - do you have any feedback like hall sensor or back EMF to give you the switch position? \$\endgroup\$
    – Marko Buršič
    Commented Mar 26, 2016 at 8:12
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    \$\begingroup\$ What do your high side drivers look like? You can't just connect the upper FETs to Arduino pins. \$\endgroup\$
    – user16324
    Commented Mar 26, 2016 at 12:13

1 Answer 1

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You are most likely not driving the high-side MOSFET with enough voltage to turn it on. You need to have VCC+1V or more at the gate to turn those on fully. Typically you would use a gate-driver IC to do this, which has a built-in boost circuit (bootstrap circuit).

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