For some time now I have been looking at buying an electric lawnmower. I don’t need it, really. I just want one. One issue I’ve run across, however, is that people have left them out in the rain and have wondered if they had ruined their fancy yard machine. Like any other electric tool, an electric lawnmower doesn’t do well with exposure to water. I’ve been reading up on this and here’s what I’ve learned.
Here are 3 steps that you should take if you left your electric lawn mower out in the rain:
- Take apart your lawnmower to expose the motor.
- Get the motor and wiring as dry as possible.
- Apply electric contact cleaner
- If your motor wiring has lost insulation resistance, use a megohmmeter to test and reestablish the resistance of the wire windings around the motor shaft.
Whether you have an electric push mower or one of those really cool robotic mowers like the WORX Landroid (link to Amazon), you’ll want to keep it out of the rain as much as possible. However, accidents can and do occur.
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If you act quickly, you can often prevent a rain-soaked electric lawn mower from being irreparably damaged, so you need to know how to dry it out correctly.
How Electric Lawn Mowers Are Designed
Because of its sensitivity to moisture, your lawnmower’s motor will be housed inside a water-resistant casing that’s likely made of plastic or metal. Despite this. an electric mower isn’t, by any means, impervious to water damage from being left out in the rain.
Often, these cases are designed with vents that allow air to flow in and out, which helps keep the electric motor from overheating while in use. These openings also allow water to reach the lawnmower’s protected motor and wiring if it’s exposed to rain for long periods.
The battery casing is also made to be water-resistant, but, to allow the battery to be removed and replaced, the covering sits on a hinge that allows the compartment to be open. Gaps in connection can eventually allow water through that can damage the battery as well.
Beyond just the damage water can do to the motor, excess moisture will also cause the battery connectors to corrode, which interrupts the energy supply from the battery to the mower’s motor.
As a result, the lawnmower with either run with diminished power or may not turn on at all. Make sure as soon as you realize your lawnmower has been caught in the rain that you start the drying process.
How Condensation Can Damage Your Electric Mower
Exposure to rain isn’t the only way that the elements can cause water damage to your electric lawnmower.
Even if you live in an area with little rainfall, widely fluctuating temperatures can result in similar issues. As the temperature drops as night, water can easily condense on the underside of the water-resistance casings around the motor and battery.
To best protect your electric lawn mower’s longevity, make sure to always store it in the garage to minimize the risk of condensation-related damage.
If that’s not an option in your home, you can purchase a weather-resistent shed (link to Amazon) to store your lawnmower and other electrically-powered tools that would have the same problem.
Another thing to keep in mind is the condition of the grass when you use your lawnmower. Your owner’s manual will have the most specific recommendations for your model.
A good rule of thumb is to never mow the grass with an electric lawn mower if you can step on the grass and leave a footprint behind due to the wetness of the grass.
How Water Damage Affects An Electric Mower’s Wiring
Once water or moisture has accumulated on your motor, it can seriously undermine the intended function of its wiring and power delivery.
That’s why it’s so important that you avoid mowing wet grass. If the power interruption occurs while the lawnmower is in use, you can risk electrical issues and personal safety.
Electric lawnmowers use electrical energy from its power source (the battery) to generate mechanical energy via the rotation of its motor (source). The wiring that transfers electricity to the motor is usually made from copper and is wrapped around its center column.
These wires are insulated to protect against short circuits, but when they come into contact with a lot of water or repeated exposure to moisture, the insulation becomes ineffective.
Then, a short circuit of the power occurs, which means that electricity is diverted from where it’s supposed to go within the mower.
Fortunately, if your lawnmower was simply left in the rain, there’s no risk of handling it unless you turn it on. You’ll eventually need to do so as part of the repair process but you’ll have an opportunity to dry it off first.
How a Short Circuit Can Damage the Motor
As short circuits often result in an excess amount of energy being routed to the wrong place in the electrical system, water exposure can result in significant damage to your lawnmower’s motor (source).
The excess current will cause the parts to overheat if the lawnmower is turned on in this condition.
This can even result in white smoke being produced if the lawnmower is run as the high amounts of electricity sent into the motor will cause it to burn, especially if your lawnmower model has a brushed motor.
The smoke is generated because parts of the motor are being burned by the excess, diverted electricity, which can result in harmful fumes as well as a potential electrical fire or electrocution if the mower isn’t turned off.
If you are concerned that your electric lawn mower has been exposed to water or high levels of moisture, do not turn it on to check how it operates.
How to Initially Dry Your Lawn Mower
To salvage your electric lawn mower after leaving it in the rain, you’ll need to get the motor as dry as possible immediately. This can be accomplished in a few different ways, including using compressed air, a blow dryer, or a fan to air dry and blow away remaining moisture.
Refer to your owner’s manual to see how you can remove the water-resistant casing around the motor and expose it for you to dry off.
Drying out the motor won’t necessarily be a simple task, especially if your mower was in the rain for a long time.
In some cases, it might be best for you to leave your motor out to dry. The drying process can take up to 8 hours or more.
Additionally, if your lawn mower’s wires have become wet enough to weaken its insulation, you need to use a device called a megohmmeter (link to Amazon) to measure the current resistance of the outer coating on the motor’s wiring.
This will tell you whether you need to take further steps to dry the wiring based on the readings.
Apply Electric Contact Cleaner
After leaving the mower to dry, it’s a good idea to disconnect the battery and apply an electronic contact cleaner like BW-100 (link to Amazon) to the connection terminals and any other electrical connections. You can use grease or lubricant if you prefer. You just want to make sure that connections are clean and moisture-free.
How to Restore the Insulation Resistance of the Wiring
After you’ve got your lawn mower’s motor and wiring rid of most excess moisture, you will need to restore the motor wiring’s insulation resistance to make it safe to use again.
If you are not familiar with insulation resistance and how a megohmmeter works, I suggest you watch this YouTube video that takes time to fully explain this.
Don’t start this process before using enough time and/effort for most of the water to be removed. Applying even a small amount of current to the wiring can diminish the voltage capacity and the lifetime of your lawn mower’s battery.
Start to measure the insulation resistance until the wiring has been dried to the point that the megohmmeter measures 100,000 ohms value for its insulation resistance.
If the measurement is too low, you’ll have to keep waiting for the wiring to further dry on its own. Once you have the right reading, you can use the device to run a small amount of current through the motor.
To determine how much current you will need to apply to the wiring, you will need to reference your lawn mower’s owners’ manual. You should be able to find a copy online using your model number if you don’t still have access to your copy.
Inside the owners’ manual, the manufacturer will have listed a voltage, called the nameplate voltage, that tells you a range of voltage at which your lawn mower’s battery operates, with the highest number for a battery at full capacity.
You can apply 10% of this voltage to help dry the wiring and restore its insulation resistance without the risk of overwhelming the motor.
After each time you apply current, re-test the insulation resistance of the wire winding around the motor shaft.
Once you’re done, you can reattach the motor compartment and your lawnmower should be ready for use. You may have to repeat this step several times before you’re done, so be patient and work methodically.
It is very important to keep an electric mower out of the rain but if it happens, these are the steps that you’ll need to go through.
If you are unable to effectively dry the motor and wiring and get the mower running, it may require professional servicing. Contact your manufacturer or the dealer where you purchased the mower for guidance.
In your are in the market for a new electric lawnmower, consider a self-propelled model like this one:
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