Using a DVM please verify that there is approximately 100nF capacitance between GND tab and cooling plate.
The cooling plate is anodized so you must scratch or press the lead enough to ensure conductivity.
Following examples with FBL and SBL controllers:
Image 1-FBL23xx
Image 2-SBL23xx
In case you can't measure any capacitance then please place a capacitor between Controller GND and Earth (Cooling Plate/Motor Earth Wire), as the following figures show:
Figure 1 – FBL23XX Y Capacitor placement in the system
Figure 2 – SBL23XX Y Capacitor placement in the system
Capacitor:
• Film Capacitor: 0.1uF, 400VDC
• Suggested component: B32522E6104K189, EPCOS / TDK
• Link: https://gr.mouser.com/ProductDetail/EPCOS-TDK/B32522E6104K189?qs=rXlmONB1aiFy613UvkLeow%3D%3D
Back to back comparison below without and with the capacitor placement shows that the capacitor attenuates the chassis noise. Without the capacitor chassis is floating and jumps relative to the controller PWM. When the capacitor was placed this has highly attenuated.
