I am living a nightmare trying to get my wheelchair motor controller to work reliably. My latest problem is with resistors - i'll try and be brief with my scenario:
I am using a mosfet H-bridge. The mosfets are being driven by an IR2113 high side mosfet driver. A PWM signal is generated by my microcontroller which is sent to the h-bridge to control the speed of my DC wheelchair motor. The mosfets are rated to 50amps, and my motor draws 7amps continuous (and not more than 15amps).
I have blown my mosfets too many times to count and so in desperation to prevent it happening again (at least while testing everything) I put 0.7ohms of resistance in series with my 24V battery. Very inefficient I know, but I would rather have a slightly slower motor than a repeatedly broken one. The reasoning behind this resistor was that even if my h-bridge shortcircuited through a fault in my code or whatever, the current would still be limited to 35amps which the mosfets could still handle. I also put a 15amp fuse in series with the resistors so that the fuse would still trip if there was a short circuit.
Now for the problem: I was working on something else for a few minutes when my resistors suddenly exploded. My microprocessor and motor controller were connected to power, but the motor was not running. I have an enable button and a line of code that prevents the motors from drawing current unless I am pushing that button - and that button was not pressed. The resistors which blew were rated to carry 10 amps continuously, so I am sure there must have been some short circuit which caused the resistors to blow. The weird thing is is that my 15 amp fuse did not blow - how could a short circuit not draw more than 15amps?
The above has now happened to me twice and I cannot think of any reason for it. The first time it happened I just replaced the resistors with higher power ratings and everything worked perfectly for a few days until now again. It makes no sense to me.
I will try to post a schematic of my set up as soon as I can, but in the mean time has anyone else experienced something like this?
Thanks!
I am using a mosfet H-bridge. The mosfets are being driven by an IR2113 high side mosfet driver. A PWM signal is generated by my microcontroller which is sent to the h-bridge to control the speed of my DC wheelchair motor. The mosfets are rated to 50amps, and my motor draws 7amps continuous (and not more than 15amps).
I have blown my mosfets too many times to count and so in desperation to prevent it happening again (at least while testing everything) I put 0.7ohms of resistance in series with my 24V battery. Very inefficient I know, but I would rather have a slightly slower motor than a repeatedly broken one. The reasoning behind this resistor was that even if my h-bridge shortcircuited through a fault in my code or whatever, the current would still be limited to 35amps which the mosfets could still handle. I also put a 15amp fuse in series with the resistors so that the fuse would still trip if there was a short circuit.
Now for the problem: I was working on something else for a few minutes when my resistors suddenly exploded. My microprocessor and motor controller were connected to power, but the motor was not running. I have an enable button and a line of code that prevents the motors from drawing current unless I am pushing that button - and that button was not pressed. The resistors which blew were rated to carry 10 amps continuously, so I am sure there must have been some short circuit which caused the resistors to blow. The weird thing is is that my 15 amp fuse did not blow - how could a short circuit not draw more than 15amps?
The above has now happened to me twice and I cannot think of any reason for it. The first time it happened I just replaced the resistors with higher power ratings and everything worked perfectly for a few days until now again. It makes no sense to me.
I will try to post a schematic of my set up as soon as I can, but in the mean time has anyone else experienced something like this?
Thanks!
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