How to test a voltage regulator on a lawn mower

A faulty voltage regulator in your mower could spell problems for your battery including causing permanent damage to the battery.

For this reason, it’s important to learn how to test a voltage regulator on a lawn mower which luckily, is fairly easy.

Below we take you through the steps of examining if your voltage regulator is healthy or needing diagnosis.

How to test a voltage regulator on a lawn mower

You can use two different approaches for this: Either you test the regulator by reading its voltage via the battery or conduct a direct test.

We will start with the longer method.

1.     How to test a voltage regulator on a lawn mower via the battery

There is nothing complicated here…..

What we want to do is simply measure the voltage regulator’s voltages then compare with the regular readings when functioning properly.

Failure to reach the expected voltages will likely mean that you’ve got a defective regulator.

Step 1: Prepare your mower

Move your lawn mower onto a level, hard ground. Your driveway could make a nice working spot.

Step 2: Locate the voltage regulator in the mower

Look for the voltage regulator location in your mower.

It’s typically attached to the electrical system that re-charges the mower battery so finding it should not be a big problem (try to follow the wiring harness).

Of course, your owner’s manual could be helpful here if you’re struggling to narrow down to the specific point where the regulator is mounted.

Step 3: Safety preparations

Before starting, check that the ground lead is intact and firmly secured to the regulator (very important!).

Also, put on a set of work gloves.

Step 4: Set the multimeter

Change the multimeter setting to voltage.

In most cases, all you have to do is turn the dial on the multimeter (or press a button) and have it stand at the voltage position.

The ∆V symbol typically represents voltage though there are multimeters that use a V coupled with lines (above the letter) to symbolize voltage.

Tip: Be careful with this step because reading voltage with a setting (Ampere or Ohm) other than ∆V could kill the device.

Step 5: test for battery voltage

Your multimeter has two cords- one black and the other red, with leads or clamps connected to the end.

Grab the red lead and fix it to the + terminal on the battery.

Hold the black lead and place it on the negative terminal on the battery.

This test will tell you if your regulator is, in fact, receiving battery voltage.

You want to have a reading 12 volts or so if the battery is functioning perfectly and supplying enough charge.

Tip: In case there are no readings on the multimeter display, inspect the multimeter-battery connection as it’s often the cause of this issue.

Step 6: test for regulator voltage

If voltage is as expected, then test the regulator voltage itself with the multimeter.

To do this, first start the engine (It should be in the parking position).

Now give it some load, for example, by turning the headlights on.

Next, put the multimeter leads to the respective battery terminals and measure the voltage once more.

The voltage should now rise to about 13.8 – 14.5 volts.

Here is what it means if you get anything lower/higher:

  • Where the reading is less than 13.8 volts, your battery is slowly losing charge and you’re supposed to recharge it.
  • If it climbs above 14.5 volts, then your regulator is already damaged or will soon go bad.
  • You should still be concerned if there’s no change in the voltage since it might imply that the regulator is broken.

Useful tips

Below we share tips to help you navigate other probable occurrences that may arise during the test.

No reading

You may not get any voltage when testing the regulator voltage.

If you find yourself in this dilemma, you should focus on the other usual suspects at this point.

For example, there is a chance of the stator being faulty if you don’t get a reading (the diodes could have blown).

To be certain, test the AC output volts from the stator and replace the component or the involved diode and repeat the test.

Moreover, it may be as a result of a defect in the wiring- trace the wires and confirm that everything is right.

Jumpy voltage

At other times, the regulator fails to maintain a consistent voltage (try to hold the same engine speed when testing) on the multimeter.

Sadly, this is due to a ruined regulator for the most part and you have limited room for maneuver.

How to test a voltage regulator on a lawn mower- alternative method

A more straightforward way of conducting the test is by gauging the AC voltage on the two outer electrodes.

If the unit is fine, the multimeter should show 22 VAC or thereabout.

Note that the mower must be running.

The last step involves measuring the DC voltage between the + (middle) and – (ground) electrodes.

It should be approximately 14.25 VDC.

Failure in any of the two tests signals a troubled regulator.

What to do with if the voltage regulator is bad

The most effective remedy for a dead regulator is a replacement.

On a more positive note, replacement regulators/rectifiers are quite affordable and easy to install.

We suggest that you contact a dealer if your battery problems persist even after severally replacing the piece. 

Wrapping it up

The simplest way to test a voltage regulator on a lawn mower is by first measuring the battery voltage with the engine turned off then while the engine runs.

You should get about 12V followed by anything between 13.8 to 14.5V if all is well with the regulator.

But as we have seen, don’t be too quick to condemn the regulator as there are other suspects too including the stator.

Keep in mind that the best solution for a regulator that has been confirmed to be out of order is getting an exact replacement.

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