If your electric lawn mower won’t run, it could be down to a faulty power rectifier. The power rectifier is a small electron part that provides the right type of power to your mower’s motor. Without a working rectifier, your electric lawn mower is never going to run. So what is a power rectifier, and what are the symptoms of a bad power rectifier on a lawn mower? Well, let’s dive into this blog and find out.
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Symptoms of a Bad Power Rectifier (Overview)
Occasionally, the diodes inside a lawn mower power rectifier degrade, causing irregular power supply to the motor. As a result, the electric motor will intermittently start and stop. But, typically, a lawn mower power rectifier will either work or it won’t, resulting in your mower failing to operate its electric motor.
What is a Lawn Mower Voltage Rectifier?
A lawn mower voltage rectifier is a small electronic device made up of a series of diodes that convert AC power (Alternating Current) into DC power (Direct Current). The diodes will convert the entire AC waveform into DC or just half the waveform. The outcome of both types of diodes is that the current will only travel in one direction. This single direction of current is what makes the direct current. Without the diodes, the current would continue to switch back and forth, otherwise known as alternating.
Because lawn mower motors need DC power to operate, the voltage rectifier aims to take the incoming AC power from an outlet and convert it to DC. If a DC motor receives AC power, the internal spinning components would simply rock back and forth a few degrees and not spin.
Do All Lawn Mowers Have Voltage Rectifiers?
Only lawn mowers that use an AC power supply, such as corded electric lawn mowers, use voltage rectifiers. Electric lawnmowers powered using batteries do not need rectifiers as batteries are DC voltage. So, if your battery lawn mower has a few issues, it’s definitely not because of the power rectifier. The cause for your electric lawn mower stopping will be something else.
Difference Between a Rectifier vs. Regulator
It’s common to hear the terms rectifier and regulator in the same conversation and get confused about the difference. Typically, this is because people either get the terms mixed up or simply use the words incorrectly. Adding to this confusion, you will sometimes find rectifiers and regulators within the same physical component, as some devices use both, such as motorcycles.
So, what is the difference between a power rectifier and a power regulator?
You already know that a rectifier converts AC to DC. So, what about the regulator? Well, a regulator regulates power. For example, if your gas-powered lawn mower uses a battery to start the engine, then it has a stator attached to the flywheel, which generates power to recharge the battery. Now, because stators produce a varying voltage, you need something to regulate/limit the voltage going to the battery. Basically, the regulator ensures that the battery doesn’t receive too much voltage. This is because overcharging or charging with a power supply that is too big can cause battery damage and can even cause a battery to explode.
Why Do Power Rectifiers Go Bad?
The main cause of a power rectifier going bad is overheating. When converting power from AC to DC, the rectifier generates a considerable amount of heat. To prevent the rectifier from overheating, you’ll typically find them attached to a small heat sink. This is a passive heat exchanger that pulls the heat from the rectifier so that it can naturally dissipate from a larger attached surface.
How Does a Bad Power Rectifier Affect Your Lawn Mower?
You’ll usually find a thermal paste between the rectifier and the heat sink. The thermal paste is a substance that ensures a good connection between both components. So, if your rectifier becomes loose, the connection will be lost. Basically, the thermal paste will have no effect, and the heat sink won’t work. If this happens, your lawn mower rectifier will heat up very quickly and burn out.
Why Do Power Rectifiers Become Loose?
Normally, the vibration in your lawn mower can loosen off the screw attaching the rectifier to your mower, breaking the connection. It’s not uncommon to find a rectifier flapping around under the motor cover where it has become loose. Also, the thermal paste will, over time, dry out and become less effective.
What Else Can Cause a Bad Lawn Mower Rectifier?
Lawnmowers need good airflow to help disperse the heat from the rectifier. Vents in the motor cover and the airflow generated by the rotation of the motor help keep the motor cool. So, keeping the vents clear of debris is vital to ensure an unblocked path for the cool air to enter and hot air to escape the motor housing. For example, if your lawn mower sucked in grass clippings and has blocked vents, the heat can’t escape. So, even if the heating sink is correctly attached and working, the rectifier will still overheat and burn out.
How to Test a Power Rectifier on a Lawn Mower
The easiest way to test a lawn mower power rectifier is to check the input/output using a multimeter. For example, a typical corded electric lawn mower has a rectifier with 120v AC input from the outlet and a 12v DC output to the motor. By testing either side of the rectifier with a multimeter, you should quickly be able to determine if your lawn mower rectifier is bad or not.
A second way to test the rectifier is to check for continuity between the negative and positive connections. If your multimeter shows a connection (Continuity) between the negative and positive connections, your rectifier has an internal short. This is typical of a burned-out rectifier.
Before performing these tests, disconnect the motor after the rectifier. This is to prevent the motor from accidentally spinning the blade. Also, remember that you’ll need to pull the start lever to complete the circuit to the rectifier.
How to Replace a Lawn Mower Voltage Rectifier (My Guide)
Once you have determined that your lawn mower rectifier is bad, you’ll want to move on to installing a replacement. Here are the steps you can follow to install your new rectifier. Let’s take a closer look.
- Disconnect the Power Supply – First, disconnect your lawn mower from any connected power supply to ensure the electrical system is not live.
- Remove the Motor Cover – Next, using a screwdriver or a nutdriver, remove the cover that protects the motor. This is where you’ll be able to locate the power rectifier.
- Remove the Rectifier Mounting Screw – Remove the mounting screw which attaches the rectifier to your lawn mower.
- Detach the Heat Sink from the Rectifier – Next, pull the old rectifier from the heat sink and position it to one side.
- Clean the Heat Sink – Using a cloth, wipe any old thermal paste from the heat sink so that the surface is clean.
- Apply Thermal Paste to the Heat Sink – Apply a liberal coat of new thermal paste to the heat sink, ensuring that you cover sufficient area for the replacement rectifier to attach. An ⅛’’ covering should be sufficient.
- Position the New Rectifier – Next, press the new rectifier onto the heat sink, making sure that the screw-hole through the rectifier and heat sink line up.
- Secure the Rectifier – Secure the new rectifier and heat sink to your lawn mower using the previously removed screw.
- Swap Over the Wires – With the new rectifier in place, remove the wires from the old rectifier and attach them to the replacement. I suggest you do one wire at a time to avoid mixing up the connection. Also, refer to the replacement rectifier documentation to ensure you make the right connections.
- Disconnect the Motor & Test the Rectifier (Optional) – If you choose, you can test your installation to check if the new rectifier is functioning correctly before you replace the cover. If you do decide to test before replacing the cover, disconnect the motor and connect the power supply. Repeat the in/output voltage test to confirm 120v AC in and 12v DC out. Once complete, remove the power supply and reconnect the motor.
- Replace the Motor Cover – Next, replace the motor cover and secure it into place using the screw you originally removed.
- Test the Lawn Mower – Finally, connect your lawn mower to the power supply and test out your lawn mower.
Tools, Parts, & Materials to Install a Replacement Lawn Mower Rectifier
To complete this repair, you will need a few tools, parts, and materials on hand. Here’s a list of everything you need, including links to example items.
- Screwdriver Set
- Nutdriver Set
- Thermal Paste
- Shop Rags
- Multimeter
- Replacement Lawn Mower Rectifier (Lawn Mower Specific)
Electric Mower Won’t Run (Not The Power Rectifier)
So what do you do if you have tested your mower’s power rectifier and discover that it’s not the cause of why your electric lawn mower won’t run? Well, you’ll need to check other components that might be causing the issue. Like What? Well, several different parts can prevent an electrical lawn mower from starting. Here’s the common problem that I would check.
- Incoming Power – Check that the incoming power is working.
- Cables & Extensions – Check the cord and extension are in good working order.
- Electrical Connections – Ensure that the internal electrical connections are not loose or corroded.
- Thermal Cut-Off Switch – Make sure that the thermal cut-off switch is functioning correctly.
- Motor Brushes – Check that the carbon brushes are working and not worn down.
- Power Switch – Check that the power switch is functioning when operating the start lever.
- Power Lever – Check that the power lever engages the power switch.
