NECO NM692 Electric Motor Stopping

[BO]

Hi,

I have a NECO NM692 system 24V motor that has been converted to work with a Raymarine Evolution ACU400, EV Sensor, Rudder Feedback Unit and P70S Control Unit. It is standalone, not interfaced with anything.

Everything works, for a while, then I notice that the wheel is not moving and the rudder position indicator is not scrolling. Then I get a "Drive not Responding" error message and bleeping alarm. It happens about an hour or so in, with engine running.

I have checked the clutch, solid 24V supply and the motor is getting 7 - 9V when turning, measured at the ACU400 output red and black wires to the motor. The voltage changes plus / minus depending on rotation direction. It's a 24V system, so I assume the turn force is low, hence the voltage is low. Would this be a correct assumption, if turn forces are high voltage will increase up to 24V? Raymarine gave me a series of tests and they have specific voltages for clutch and rudder feed back stated in the test, but for the motor test, they just said measure voltage, no figure for expected voltage. All the tests work out fine, hence I am sure the Raymarine equipment is doing what it is supposed to do.

My main question. The NECO motor has two carbon brushes, which I have not inspected yet. If these brushes were sticking, or had worn right down, could this explain why the drive just stops responding because the voltage isn't getting to the commutator. Maybe after a while rotating too and fro, the wear level breaks contact, but later after vibration, they reengage slightly to work again. I haven't tried the hammer tapping test yet to reengage stuck brushes as the motor access is difficult when sailing.

Just trying to narrow down my options as it could be a quick fix. I am loath to spend money on the NECO motor. If it something like insulation break down at temperature, then I may buy a modern motor to replace it.

Look forward to your advice.

Alastair