Minn Kota Maxxum power loss

[gcornelisse]

I recently ran my 4 year old Minn Kota Maxxum trolling motor for about 5 minutes or less at just about 100% power. When I let off the button on the foot pedal, lowered the power down to about 30% to fish and then touched the button again, the motor was dead. Of course this happened on a gas restricted lake. Go figure! Huge thanks to the guys who helped tow us back.

I got it back home and we opened the lower unit to find both brushes were stuck in their channels. Using a small flat-head screwdriver they only needed a little nudge to be freed. I slid the brushes out to clean them up and get the channels clean of any dust and grit, leaving them connected by their leads. I reinstalled the brushes, and they seem to slide relatively clean and free of any hangups. I didn't see anything in the lower unit that looked damaged or burned.

There was no evidence of water leakage, but I reassembled the lower unit with all new Minn Kota o-rings and seals using a little light grease to keep the seals from pinching or rolling when putting everything back together. I was careful to realign the motor housing using marks I had made before taking it all apart.

I also inspected all the wiring from the 3-prong plug, through the pedal and down to the brushes. I found a little resistance in the wiring from corrosion inside the plugin. I cut back the wire insulation to get clean copper and replaced the plug with a brand new one, exactly the same. A final resistance test indicated a lot of improvement.

Since having the boat out again, there seems to be about 20-30% less power/thrust, maybe more. The the prop spins smooth and free by hand. Having fished with this trolling motor for more than 4 years, I've become very familiar with using it at different percentages based on the conditions... wind, current etc. Previously, running it at 100% was virtually uncontrollable from all the torque. Now 100% is super easy, even with the cable tension backed off. I used to troll the banks between 20-30% power and now I'm using it in the 35-50% range. I think the loss at the higher end is even greater. So, something is still not right.

Does anyone have an idea what I should be testing, looking for, or parts I should be replacing at this point?

Thanks in advance!

 

[Silvertip]

Could it be the battery is no longer up to the task?

 

[gm280]

Not sure how the trolling motor is built. But if there was anyway to remove the field magnets or winding, did you possibly but it back together with the fields reversed. Meaning what once was forward is now installed the opposite. Like turning the fields 180 degrees and installing them. Because it could be a timing issue with the armature and filed windings. They are installed at certain positions in relationship to the brushes so the motor has its maximum torque... Just asking?

 

[gcornelisse]

The batteries are only about 1.5 years old, and out fishing maybe a dozen times. I keep them on a good quality battery tender at all times. I bet most of the time I never really run them down past 50%. I'm just not out that long and I don't push the trolling motor that hard. But, I am suspicious. I cleaned the terminals at the beginning of the year, but maybe I need to pull them out and get them tested. I would not be shocked if they come back with a clean bill of health. I got 5 years out of the previous set and these still look like they came out of the box. No corrosion.

The trolling motor lower unit is super easy to take apart and reassemble. There aren't that many parts and I only pulled apart minimum to get at the brushes. There's really no way to reverse anything unless I started disconnecting wires, which I haven't at this point. And I'd expect it to spin the prop the wrong direction. I also marked the outer housing parts with each other so the timing would be the same or very close after putting it back together.

That's why I'm a bit stumped. Unless I really burned something out that I can't see when it first died, I can't imagine that I damaged anything.