Hi all
I have been asked by a colleauge to work on a pwm dc motor speed control for a 55lb electric trolling motor.
My friend claimed that the motor draws 25amp however online specs say 50 amps.
When I built the speed controller I built it in a power electronics board (5x parallel mosfets and diodes) and a controller board ( a 12f683 micro with an analog to do the pwm work).
Originally my friend had a crude pwm generator switching some mosfets which failed when a back emf diode failed short circuit and now I hear that it has 'let the smoke out' again and I suspect that my new board has done the same again.
I have 5 x IRLF34N Mosfets switching in Parallel (each with there own 10 ohm gate resistor) and to protect against back emf I have 2 x diodes in parallel with the motor. (the diodes arent anything fancy 1N series if I remember correctly)
It seems to be that the back emf diodes will be happy to work for an hour or so then they fail short circuit.
How do I choose suitable back emf diodes so I will not keep having these problems?
I dont know if it makes any difference but the switching frequency is around 15Khz
Many Thanks
Bruce
I have been asked by a colleauge to work on a pwm dc motor speed control for a 55lb electric trolling motor.
My friend claimed that the motor draws 25amp however online specs say 50 amps.
When I built the speed controller I built it in a power electronics board (5x parallel mosfets and diodes) and a controller board ( a 12f683 micro with an analog to do the pwm work).
Originally my friend had a crude pwm generator switching some mosfets which failed when a back emf diode failed short circuit and now I hear that it has 'let the smoke out' again and I suspect that my new board has done the same again.
I have 5 x IRLF34N Mosfets switching in Parallel (each with there own 10 ohm gate resistor) and to protect against back emf I have 2 x diodes in parallel with the motor. (the diodes arent anything fancy 1N series if I remember correctly)
It seems to be that the back emf diodes will be happy to work for an hour or so then they fail short circuit.
How do I choose suitable back emf diodes so I will not keep having these problems?
I dont know if it makes any difference but the switching frequency is around 15Khz
Many Thanks
Bruce