Please see latest posts for the currently relevant info.
I've been developing a motor controller for myself for some time now, mostly designing one rather than buying one as a learning experience. Have had success so far, but I've got a question in regards to using a capacitor as a snubber across the drain and source of the MOSFET in the controller. The controller is being designed for up to 144V DC, I've tested it so far at 12V, and plan on slowly working up to the full 144V, to prevent sudden instantaneous death of components if something were connected incorrectly. Anyways - The capacitor I've connected across the drain and source is a 1uF polyester capacitor rated for 250V. C3 in the scmatic below is that capacitor.
Capacitors C1 and C2 in the schematic below are placed right on the positive and negative terminals of the motor, and hub to the frame of the motor. They are ceramic disc capacitors rated for 1KV. C1 is 4x 22nF capacitors in parallel, as well as C2.
First, before I added the 88nF worth of capacitors across the motor terminals and before the polyester capacitor was added, this is how the waveform looked:
Then, after adding the 88nF capacitors across the motor terminals (The extended ringing eventually fades out to nothing):
And finally, after the polyester capacitor was added across the MOSFET:
The motor leads are also fairly long ~2ft in length, so this may be part of the problem as there may be stray inductance.
What I'm actually wondering is... is this actually an acceptable solution to the overshoot or should I put a reverse biased diode across the MOSFET instead... or is there another, better solution available?
EDIT: At this time, I am revising the snubber across the drain and source of the MOSFET by adding a resistor to help dissipate the current. I've opted for a 1K resistor and will go from there. I will edit this post with more information once I've done this. User ebp has also suggested that the motor terminals being twisted will cancel out stray inductance in the wires leading to the motor. I will also be doing this.
EDIT 2: I redesigned the controller to reduce parasitic inductance as much as possible. Most of the above post is irrelevant at this point. The layout is significantly more simple and leads have been shortened a good amount, as well as placement of components more conveniently placed closer to each other. Positive and negative bus bars have also been placed close to each other.
The MOSFET has been switched out for an APTM50AM24SC, and the Diode has been switched out for a BYT261PIV-400.
I've been developing a motor controller for myself for some time now, mostly designing one rather than buying one as a learning experience. Have had success so far, but I've got a question in regards to using a capacitor as a snubber across the drain and source of the MOSFET in the controller. The controller is being designed for up to 144V DC, I've tested it so far at 12V, and plan on slowly working up to the full 144V, to prevent sudden instantaneous death of components if something were connected incorrectly. Anyways - The capacitor I've connected across the drain and source is a 1uF polyester capacitor rated for 250V. C3 in the scmatic below is that capacitor.
Capacitors C1 and C2 in the schematic below are placed right on the positive and negative terminals of the motor, and hub to the frame of the motor. They are ceramic disc capacitors rated for 1KV. C1 is 4x 22nF capacitors in parallel, as well as C2.
First, before I added the 88nF worth of capacitors across the motor terminals and before the polyester capacitor was added, this is how the waveform looked:
Then, after adding the 88nF capacitors across the motor terminals (The extended ringing eventually fades out to nothing):
And finally, after the polyester capacitor was added across the MOSFET:
The motor leads are also fairly long ~2ft in length, so this may be part of the problem as there may be stray inductance.
What I'm actually wondering is... is this actually an acceptable solution to the overshoot or should I put a reverse biased diode across the MOSFET instead... or is there another, better solution available?
EDIT: At this time, I am revising the snubber across the drain and source of the MOSFET by adding a resistor to help dissipate the current. I've opted for a 1K resistor and will go from there. I will edit this post with more information once I've done this. User ebp has also suggested that the motor terminals being twisted will cancel out stray inductance in the wires leading to the motor. I will also be doing this.
EDIT 2: I redesigned the controller to reduce parasitic inductance as much as possible. Most of the above post is irrelevant at this point. The layout is significantly more simple and leads have been shortened a good amount, as well as placement of components more conveniently placed closer to each other. Positive and negative bus bars have also been placed close to each other.
The MOSFET has been switched out for an APTM50AM24SC, and the Diode has been switched out for a BYT261PIV-400.
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