All_at_Sea
Well-Known Member
I need to show someone that the bowthruster works, but it is out of the boat. Can l run this out of the water without harm just for a short burst?
Testing bowthruster out of water
- Thread starter All_at_Sea
- Start date
Harry Brown
Well-Known Member
I did this and sheared the drive shear pin. It also caused the contactors to ark together, making it intermittently run by itself! I guess because of the lack of water resistance it span faster and drew more amps. I fixed it, but wont be doing it again though!
Ian_Edwards
Well-Known Member
Yes, I think you can, in short burst, it'll spin very fast and take along time to stop spinning because it has no hydrodynamic load on the prop'.
BUT, you need to be very careful to be sure that the prop' has stopped turning before you reverse it, the back EMF could damage the contactors. The motor will act as a generator whilst it's spinning with no power driving it, that can lead to very high voltages appearing on the motor terminals, because the motor is open circuit i.e. very high resistance. This happens even though the motor is serially wound and has no permanent magnets in it, there is sufficient residual magnetism in the laminations to generate quite high voltages when the motor terminals are open circuit.
Even with the prop' in the water you shouldn't reverse thruster quickly. Most thruster controller have a delay built in, to prevent this from happening, but the delay isn't long enough when the prop' is out of the water.
BUT, you need to be very careful to be sure that the prop' has stopped turning before you reverse it, the back EMF could damage the contactors. The motor will act as a generator whilst it's spinning with no power driving it, that can lead to very high voltages appearing on the motor terminals, because the motor is open circuit i.e. very high resistance. This happens even though the motor is serially wound and has no permanent magnets in it, there is sufficient residual magnetism in the laminations to generate quite high voltages when the motor terminals are open circuit.
Even with the prop' in the water you shouldn't reverse thruster quickly. Most thruster controller have a delay built in, to prevent this from happening, but the delay isn't long enough when the prop' is out of the water.
