I am trying to drive a 23-pole pair(i.e. 46 poles) BLDC motor using an LV8139 pre-drive, the output of which is fed to drive the 3 half bridge MOSFETs. I managed to connect the correct phase sequence(out of the 6) between the motor and driver.

The pre-drive IC basically provides a hardware solution for 120 degree and 180-degree commutation(sine wave). It requires a DC control signal to vary the speed of the motor, which I am doing via a potentiometer. Here is the link of the datasheet for the same

https://www.onsemi.com/pub/Collateral/LV8139JA-D.PDF .

Now there is literally zero material on the internet about this chip but I am able to use it to drive the motor. I do have a few problems though:

1.) Mostly I need to give a physical push (by hand) to the motor before it starts to rotate normally. I feel that this is an issue of the hall sequence. But once the external push is given, the motor starts normally.

2.) The specification says that motor will rotate in 120 degree mode till a certain speed and then it will jump to 180 degree sine wave. However I don't see any such transition i.e. the commutation is 120 degree always.

I searched about the first issue on the internet and found some suggestions to add a high value capacitance across the power supply to provide sufficient initial current, but the issue persists. Any suggestions are appreciated. Thanks & Regards

  • \$\begingroup\$ What are the motor specs? What voltage are you running it on, and how much current does it draw? Can you show us the hall placement on the motor? Do you have an oscilloscope to show the timing? \$\endgroup\$ Dec 2 '19 at 7:13
  • \$\begingroup\$ It is a 48 volt 3 phase motor. There are 23 pole pairs(rotor). It draws about 2.1Amps per phase. I didn't dissambled the motor but I assume the hall sensors are placed 120 degree apart( mechanical angle). Also I saw the three hall sensor output to check fo the sequence. And was able to confirm the 6 signal sequencing. \$\endgroup\$ Dec 2 '19 at 7:18
  • \$\begingroup\$ Kv, Kt, rated current and power? It's possible you have a hall sensor configuration that isn't quite right. Make a chart of all possible combinations and try each one in turn. What bulk capacitance do you have now, and what is your power source? Can you show us the schematic and a photo of the controller? \$\endgroup\$ Dec 2 '19 at 7:35
  • \$\begingroup\$ @BruceAbbott , I am not sure about the Kv and Kt however the motor has following specs:- 400-600 rpm at no load torque: 37NM Max torque: 72NM this is basically a scooter motor with a rim size of 10 inches 1Kw and 48volt as suggested above and I tried the combination of motor phases, do I need to do the same with hall sensors too?wouldn't it be redundant?I will add a link of the schematic... \$\endgroup\$ Dec 2 '19 at 8:45
  • \$\begingroup\$ so there's 69 poles on the stator? \$\endgroup\$
    – Jasen
    Dec 2 '19 at 9:09

two theory:

  • the motor requires a high starting torque because of the motor load. See if you can start the motor without a load or apply a higher CTL signal at startup.
  • The hall sensors are not correctly aligned with what the motor driver expects, check the "Timing chart" in the datasheet vs the motor's datasheet.

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