MaxPower Bow Thruster open circuit

[ericoh88]

I need your help.

Just bought a traditional full keel with a cut away forefoot 44' 15 tons sailboat in May. Yesterday was the second time I took the boat out. Used the bow thruster to starboard to help in getting out of marina.

When I came back in the afternoon, tried to turn to starboard to enter my berth, there was no response. I missed the entry.

At night I remove the v berth stuff, open the panel covering the motor - there was strong burnt smell. The plastic cover melted on the side. Upon inspection, I can see the right side aluminium L plate melted. This L plate connects the relay from the +12V house battery supply to the motor for MaxPower Series 100 (installed in 2003 in Fort Lauderdale by PO) . The house battery is supplied through a Plastimo On/OFF switch at the bulkhead.

There are 4 studs on motor housing 2 poles for turning to starboard and 2 poles for turning to port. . The relay has 2 studs for +12v house battery. One for starboard and the other port side.

Disconnected the relay from motor by taking off the one L plate for port and a melted L plate for starboard.

Tested the Joystick, all the relays are working fine with a multimeter as well.

I use a thick cable to supply +12V to the +12V pole on the motor which gave a spark and no motor turning sound. Same result for the port side on the motor.

All this testing were done at night while motor is still warm.

This morning, I dived in the water and check the blades in tunnel. Had some small growth, blades move easily with my hand turning it. I was expecting to see a rope or plastic bag stucked inside. Nothing.

With better sunlight in the v berth I checked the motor now with supply +12V to the starboard and port terminals. Nothing. No spark. No motor turning. Use multimeter to test the 2 poles for starboard side. Open. Checked the port side. Open.

This unit does not have any sensor alarm for heat/temperature that can cut the supply.

The relays is mounted on the side of the motor housing. I removed both the relays and motor housing.

I can easily turn the gear on the top of the tunnel.

I took the motor and relays to the dealer in Singapore who said he can't do anything except he suggested I buy a new motor.

Anyone can help me here with suggestion to see if I can recover this unit without spending another boat bucks.

My question is :-

1. Is a bow thruster such a delicate item? I only use it to turn into the marina 3 times. Twice the first time and yesterday once to get out. Please share your experience.

2. I find it strange the installation did not include a breaker except from the mains battery a 300 amp fuse or a temperature sensor as alarm or to cut the +12v supply until the motor cools down. The dealer said only the new models (which he did not carry any stock) have temperature sensor on the motor housing .

3. Now the motor 2 sets of winding are giving open circuit. What is the next best thing I can do?


4. After repairs/replace a motor, what can I do to prevent another incident like this one again?

Please share your comments, suggestion and experience.

Appreciate all your inputs.

Thanks.

Eric

[ericoh88]

I strip the MaxPower Series 100. Took out the rotor and stator. Checked everything and found that there were no burnt marks. Everything look clean.

Looks like the motor should be working fine.

Installed all the parts back and tested the motor. Not turning. Refer to the wiring pictures with the relay.

AH! The battery +12v goes to stator to create the magnetic field. Out another terminal to the rotor then back to the -12V.

The motor turn! Swap the +12V to another stator post. Motor turn another direction.

What happened was when I removed the L aluminium plate, there was no more closed circuit.

Looks like the aluminium L plate saved the motor when it over heated.

I am going to add some protection circuit. Ordered thermal cutouts to sound an alarm at 120C/248F and cutout at 140C/284F. Will install the sensors at both the L plates.

Of course, I will a circuit breaker Blues Seas 200 amp. The manual suggested 300 amp . May have to add another 100 amp later if this trips too often.

Not so intimidating after all.

Eric