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Noise Suppression Case Study

Many of you will know that I tend to bang on about motor noise suppression, my stern lectures are often met with a resigned smile and promises to fit some in the future. Well this week we had a really interesting case that highlighted the importance of taking this seriously.

The Lord Raglan is a tourist boat running on the Brecon Canal. It is unusual in that it has a rudder, motor, and propeller at each end, it doesn’t turn around in the narrow canal, the helmsman just turns off one motor, locks one rudder and goes to the other end to drive back.

It has a single battery bank feeding one Pro-360-HV and Lynch LEM-200 motor at each end. At one end the installation has been fine, but at the other end there have been three controller failures. We spent a day there this week looking to figure out what was causing the problems.

As soon as we opened the engine bay at the problem end the cause was apparent – there were no noise suppression components fitted to the motor. However these were also missing from the other end which did not have problems, so what was the difference?

Looking into the routing of the motor wires we found that they had been run directly on top of the battery wires feeding the problem controller. The motor wires are carrying a large current that is being switched on and off very quickly, this, along with the lack of noise suppression was inducing noise into the battery wires for the controller and causing mosfet latch-up to occur.

The solution was to fit an extra section of trunking to allow the motor wires to be routed away from the battery wires, and also to fit noise suppression components to both motors.

Looking forward to going for a cruise now that it back working as it should.