39 ft sailboat - 20kw motor - loud knocking at 12.5kw & above

Motor: ME1917, 10kw, two in the system for a 20kw system

Sevcon: gen4 48v 450a, two in the system, one connected to each motor.

Issue: between 12.5-14kw and above, the motor makes a consistent knocking sound https://photos.app.goo.gl/xk3efbB36ySjgGL3A

When we isolate the motors, it seems that one sevcon (on port) works normally and allows a single 10kw motor connected to it to run at full capacity (~11.7 kw). But using the starboard sevcon results in whichever motor is connected dying at about 2.5kw.

Hypothesis is that the starboard sevcon is for some reason triggering an overspeeding fault breaking mechanism (breaking torque). When it's on one motor, the motor stops running. When both motors are running, the port controller pushes through the breaking mechanism which causes a knocking.

But, there are no error messages or error lights. And going at least than 25% of an individual motor's capacity should not be overspeeding. So wtf is this happening and how can we fix it?

It also might be that one sevcon unit is leader & other is follower, which is why the motor cuts off when run on only one sevcon (the starboard being the follower in this case), but then why the knocking? And why doesn't either motor knock when independently run at full speed?

Any help appreciated.

I've seen that sin/cos encoders can suffer from noise and the knocking looks like an out of sync issue. Do you have any way to read out or log the sin/cos signal from that controller while having the knocking?

Unfortunately we do not, sevcon's reader is bonkers expensive and we haven't even found mechanics or electricians that have one.

If anybody has the software and lives on the west coast of North America, we could come sail to you to and consult the oracle.

Hardware-wise, you could try to ensure the encoder wiring is shielded and isolated from the phase wiring, all the way from encoder board to controller input connector. That would help isolate from electrical noise problems.

If you use a shield (braided cover, foil, etc) on the encoder harness, only ground it at the controller end.

BlackberryHikes said:

Unfortunately we do not, sevcon's reader is bonkers expensive and we haven't even found mechanics or electricians that have one.

If anybody has the software and lives on the west coast of North America, we could come sail to you to and consult the oracle.

Click to expand...

I think that all you need is an oscillocope and someone who can use it. Maybe you can even find help here with an ad under "help wanted"

BlackberryHikes said:

Motor: ME1917, 10kw, two in the system for a 20kw system

Sevcon: gen4 48v 450a, two in the system, one connected to each motor.

Issue: between 12.5-14kw and above, the motor makes a consistent knocking sound New video by Nora Daly

When we isolate the motors, it seems that one sevcon (on port) works normally and allows a single 10kw motor connected to it to run at full capacity (~11.7 kw). But using the starboard sevcon results in whichever motor is connected dying at about 2.5kw.

Hypothesis is that the starboard sevcon is for some reason triggering an overspeeding fault breaking mechanism (breaking torque). When it's on one motor, the motor stops running. When both motors are running, the port controller pushes through the breaking mechanism which causes a knocking.

But, there are no error messages or error lights. And going at least than 25% of an individual motor's capacity should not be overspeeding. So wtf is this happening and how can we fix it?

It also might be that one sevcon unit is leader & other is follower, which is why the motor cuts off when run on only one sevcon (the starboard being the follower in this case), but then why the knocking? And why doesn't either motor knock when independently run at full speed?

Any help appreciated.

Click to expand...

When the motor is running, use a multimeter to measure the voltage and current of the motor at different speeds as a basis for fault analysis. The initial judgment is that the power supply is insufficient, followed by the controller part.

BlackberryHikes said:

Sevcon: gen4 48v 450a, two in the system, one connected to each motor

Click to expand...

Are these connected to each other in any way ? ….you mentioned “Leader and Follower” ?
..if so why ?
Common throttle?
Do the motors drive a common prop shaft ,…or separate props ?
and i guess a common battery pack for both controllers ?..what capacity ?