Maintaining an electric motor
  |  First Published: December 2013

I recently had the opportunity to spend two weeks working in the service department at BLA were my main focus was repairing Minn Kota electric motors. This gave me a really good insight into how these motors work and also what generally causes them to fail.

It may seem from the outset that this article is focussed around a specific brand, but in actual fact it is not. The points raised will be pertinent to the majority of the electric motors in the market place and if you adhere to some of them you may well increase the longevity of your motor substantially.

All manufacturers strive to put out the best possible product that they can, but ultimately they are at the mercy of the parts that they use. Some parts can be faulty when installed and to safeguard the consumer against this there are warranties put in place. Generally if a part is faulty then it should malfunction early in the motor’s life and the warranty will cover it.

The main issue that we found was a complete lack of maintenance when it came to electric motors. It seemed that the a lot of users bolt them on to their boats and then leave the motor to fend for itself. Please excuse me at this stage if you are not one of these people.

Now this seemed a bit strange because we service our cars and outboard motor, so why shouldn’t we do the same with our electric motors? Perhaps many people that buy them are not aware that they need to be looked at on the odd occasion. Therefore, here is a bit of a step-by-step process in keeping your electric motor maintained.

Check your prop

This would have to be one of the biggest cases of motor failure. The lower end of your motor contains an electric armature. At either end of this lower end there are rubber seals that guard against water ingress.

It is imperative to check that no line has found its way behind your prop on a regular basis. If you had the misfortune of picking up some line on your outboard propeller, you would know that it affects the working of the motor and if left would ultimately end up chewing your seal out and allowing water to enter your gearbox. Well an electric motor is no different.

The first seal sits directly behind the propeller and once you pick up some line it ultimately finds its way in behind the propeller and after some time will affect the integrity of this seal. There is a secondary seal behind the first, which acts as a backup, but at some stage it too could be affected by the line if left too long. It seems that there is a lot more line floating around in our waterways than we are aware of and it has a very frustrating habit of finding its way into our motors.

Try to make changing your prop a regular exercise. Remove the prop by loosening the locking nut on the front, slide the prop off and you can then inspect your shear pin (which stops the propeller from turning and safeguards it and your shaft from a hard knock). A good idea is to remove the shear pin, grease it, and your shaft and after replacing the pin slide your prop back on. This will keep all parts lubricated and, if you find yourself in a situation where you need to remove your prop at a later date, it won’t be locked up on the shaft due to excess corrosion. I like to keep a spare shear pin in my wallet just in case I find myself in a remote location and in need of one.

The interesting part was that after spending two days servicing motors I went straight home and did a cursory inspection of my motor. It was quickly apparent that I had failed at my attempt on maintenance. My propeller was quite tight and I struggled to get it off. There was a pile of braid behind it when I got it off and it had caused some slight damage to the seal. Fortunately I had caught it in time.


Most electric motors run on 12, 24 or 36 Volts. They need to be supplied with a good clean voltage for them to function properly. A surprisingly common issue that we found was incorrect voltage on a large number of motors shipped to the service department. Once the motor is placed on the test bench it is put through its paces to see what is causing the customer a problem. When no fault is found with the motor we place it in a test tank to run it under load. If it still runs fine after a reasonable amount of time, we look at ulterior causes. The main that we come back to is low voltage.

A large number of electric motors are used in salt water and this has a corrosive effect on any unprotected or sub standard wiring. A motor that was fitted a few months ago will need to have its wiring checked at regular intervals to ensure that no corrosion has set in. On several instances we were assured that the wiring was fine but once we inspected it and cut the heat shrink or insulation tape found corrosion or faulty joins. Joining plugs are great but still need to be inspected regularly as they may seem ok at a cursory glance, but once they are opened can be completely corroded.

Minn Kota have a wiring harness for their motors that can be purchased as an extra if you intended running your wires to the back of the boat. This will remove all the issues you may come across when joining wires, especially if you have limited knowledge of electronics.

If you do intend taking the DIY route then always try to use tinned wire and ensure that the grade is similar to that of the wire that the motor comes with, never smaller as this will only create voltage problems. Ensure that when you do join the wire that it is done correctly. Testing your voltage can also ensure that the motor is getting what it needs to function properly.

Lubricating sprays

Be wary of what you are using to coat your motor with to add protection. Some of these sprays contain chemicals that can be harmful to the circuit boards and wiring that control the motor due to harmful corrosive properties in the spray.

Some sprays are designed to combat rust and corrosion and will contain acids to attack these issues; unfortunately they may make the motor look healthier but can be doing more harm than good.


Your electric motor may need a bit more than a quick spray from time to time. The foot pedal can become a point of concern if not looked after. If you do want to give it a wash, especially after it has just spent a fair bit of time on the boat being towed back from a dusty environment, ensure that you allow it to sit up on its side after the wash. This allows any excess water to drain out of the pedal.

The problem is not the water but the dust that floats around in the water. If this settles down around the componentry inside the foot pedal then it can cause wear and tear, which will ultimately lead to product failure. I will actually dunk my foot pedal in some warm soapy water, give it a rinse with the hose and then leave it standing in an upright position against the gunnel of the boat to make sure that all the water drains out of it. In doing this I have never experienced any issues with my pedals.

Switch off power

Electricity can be a strange creature and find ways and means of creating surges or spikes even when inline fuses or circuit breakers are used. A good habit is to disconnect the power to your electric motor when it stands without use or when its battery is being charged. Some chargers do have voltage sensitive relays that regulate the amount of charge that is going into your battery, and will automatically switch off when your battery is fully charged. But once again these can malfunction and will tend to fry your electric motor’s components unless there is no power to the actual electric during charging.

Chargers that are fitted to outboard motors can also create a spike in power that can play havoc with electric motors. A separate battery used for your electric and a separate battery used for your cranking battery can stop this from happening. I have an on board Minn Kota charger on my tinny and am in the habit of parking my boat in the garage, unplugging the electric from the battery power and then plugging in my onboard charger. I will then switch the charger off at the wall the following morning once everything is fully charged.

There are other small things that you can do to your motor to keep it not only looking good but also working to its best, but these are really the major reasons for faults to occur. If you keep an eye on them then they will tend to keep looking after you on the water a lot longer.


Corrosion can compromise the effectiveness of your power supply from battery to motor. Do regular checks.


Braid is one of the major factors that contribute to lower end damage. Check your propeller and this shouldn’t happen.


When braid compacts, it results in seal damage. Even though there is another seal for added protection it can ultimately compromise the integrity of the lower end.


Once water finds its way into the lower end it’s only a matter of time before damage like this happens.


To remove prop, hold a pliers or spanner on the locking nut.


Turn the prop to loosen.


Once the nut is off you can remove the thrust washer similar to that on an outboard propeller and inspect the shaft and seals.

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