First of all, what does a voltage regulator do on a lawn mower? Well, it’s a little box of electronics that helps with your lawn mower’s charging system. So, if you are dealing with a dead/bad battery, you could be looking at a symptom of a bad voltage regulator on your lawn mower.
To diagnose this, you’ll need to inspect what’s happening inside the regulator and test the diodes and resistors. I know this might sound a little daunting at first, but it’s actually pretty simple once you know the steps. So, with your multimeter ready, let’s take a look.
What Does a Voltage Regulator Do on a Lawn Mower? (The Short Explanation)
The voltage regulator is the device that converts AC power from your lawn mower’s stator into DC voltage before it reaches the battery. In addition, the voltage regulator controls the voltage level so that only a safe amount of power reaches the battery. The voltage conversion is called rectifying, and the voltage control is called regulation.
Symptoms of a Bad Voltage Regulator on a Lawn Mower
The main symptom of a bad voltage regulator on a lawn mower is a charging system that doesn’t work. So, if your lawn mower’s battery keeps losing charge, then there is more than likely a problem with the regulator. As a regulator goes bad, it loses the ability to output enough voltage for your lawn mower’s battery to charge effectively.
For example, if your lawn mower battery usually sits at around 12.6v when it’s fully charged and is only receiving 10v from a bad voltage regulator while your lawn mower is running, then your battery will lose charge while it is in use. This is because the 10v isn’t enough to keep the battery charged up to 12.6v. So, even though your battery is still receiving charging voltage, it’s not enough and will die.
How to Test a Voltage Regulator on a Lawn Mower (2 Steps)
If you notice that your lawn mower battery is not charging properly, you’ll first want to diagnose the voltage regulator. Testing the voltage regulator will confirm if it is at fault or not. So, let’s go over how to test a voltage regulator on a lawn mower.
Understanding the Voltage Regulator Wires
Once you have located your lawn mower’s voltage regulator, you’ll see three wires coming out of the side of the unit. Two wires connect to the stator, and one goes off toward the battery. The two wires from the stator are the input AC voltage, and the single wire is the output DC. The AC input should be labeled AC & AC, whereas the connection to the battery should be labeled B+.
Testing the Voltage Regulator Input Voltage
The first step in testing a voltage regulator is to test the incoming voltage to make sure that the input power from the stator is correct. If the input voltage is right, then it means any output issue is down to a bad voltage regulator.
Steps to Test the Input Voltage of a Lawn Mower Voltage Regulator
- Disconnect the two cables from the voltage regulator labeled AC
- Connect one of the probes on your multimeter to one of the cables labeled AC coming from the stator
- Connect the second probe on your multimeter to the second cable labeled AC coming from the stator
- Set your Multimeter to DC Voltage
- Start your lawn mower’s engine
- Review the multimeter reading
Equipment Needed to Test a Lawn Mower Voltage Regulator Input
- Multimeter with AC voltage reading ability
Your stator output voltage will vary depending on your specific lawn mower. Therefore, it is best to look up the output voltage specifications in your mower’s manual so you know what voltage range you should expect from your stator.
For example, if you have a stator on your lawn mower that should have a range of 24-30 VAC, then your multimeter should read something between these two numbers. So if the incoming voltage is within range, you can then move on to the next test. Just remember to have your lawn mower set to full throttle so that you are getting the maximum output from your mower’s stator.
Testing the Voltage Regulator Output Voltage
The next test is to check if your lawn mower’s regulator is giving out enough voltage to charge your lawn mower battery. So, let’s review the steps you’ll need to follow to test the voltage regulator DC output.
Steps to Test the Output Voltage of a Lawn Mower Voltage Regulator
- Connect the stator wires to the voltage regulator (AC&AC)
- Disconnect the B+ wire from the voltage regulator
- Set your multimeter to DC voltage
- Connect one probe of your multimeter to the B+ terminal of the voltage regulator
- Connect the second probe of your multimeter to your lawn mower’s frame to ground the circuit
- Start your lawn mower
- Set the throttle to maximum
- Review the multimeter reading
Again, you need to double-check your lawn mower’s voltage regulator specifications to verify the correct output range. But, generally, you’ll expect to see a reading of around 15v or so volts. Basically, it should be above 12.6V so that there are enough volts to charge the battery. Anything lower, and you’ll know your voltage regulator isn’t outputting enough volts and it is faulty.
Equipment Needed to Test a Lawn Mower Voltage Regulator Output
- Multimeter with DC voltage reading ability
Your Options If the Voltage Regulator Does Turn Out to Be Bad
If the results of your voltage regulator test indicate a good input AC voltage and a bad output DC voltage, then you’ll have diagnosed a bad voltage regulator. So, you’ll need to install a new voltage regulator to get your battery up and running again. Let’s take a look at the steps required.
Steps to Install a New Lawn Mower Voltage Regulator
- Disconnect the stator cables (AC&AC) from the voltage regulator
- Disconnect the battery connection (B+) from the voltage regulator
- Remove the bolts that secure the old voltage regulator to the lawn mower
- Position the new voltage regulator onto the lawn mower
- Reinstall the bolts to secure the new voltage regulator to the lawn mower
- Connect the stator cables (AC&AC) to the new voltage regulator
- Connect the battery B+ cable to the new voltage regulator
Tools & Parts Needed to Install a New Voltage Regulator
- Small Socket Set
- Replacement Voltage Regulator (Mower Specific Part)