Electrical systems are great because they take a lot of the effort out of starting and operating a lawn mower. Well, that’s true until something goes wrong with the electrical system. For example, problems such as your lawn mower blowing a fuse when starting can be a common issue that, unfortunately, leaves your mower unusable.
So if your lawn mower keeps popping fuses when you start up the engine or try to operate one of its features, you’ll need to troubleshoot what’s going on. Here are 7 possible reasons why your lawn mower keeps blowing fuses.
Why Your Lawn Mower Blows a Fuse When Starting (The Short Answer)
Fuses on lawn mowers can blow for several reasons, resulting in unintended current flow. If current flows through an electrical circuit in a way that isn’t intended, then the circuit fuse will pop to protect the system. Here are 7 possible reasons why your lawn mower’s fuse blows when starting.
- Short Circuit
- Bad Ground
- Arcing Circuit
- Wrong Fuse
- Damaged Wiring
- Faulty Electrical Component
- Overloaded Circuit
7 Possible Explanations for a Lawn Mower that Keeps Blowing a Fuse
To figure out why your lawn mower keeps blowing fuses, let’s look at what is happening within your mower’s electrical system. These 7 possible explanations should give you a pretty good idea of where to begin your diagnosis.
Short Circuit
A short circuit happens when the positive current of an electrical circuit becomes grounded before it reaches its intended location. As a result, the short circuit has very little resistance. Therefore, current can flow at a high rate which is usually beyond the amperage of the fuse, causing the fuse to blow. So, if the positive side of the circuit can find a shorter route to the ground, say, a defective component, incorrect wiring, or a bare wire touching the frame of your lawn mower, then the fuse will more than likely blow.
Bad Ground
Bad ground is similar to a short circuit in that the current of the electrical systems will find an alternate route to the ground. Again, depending on the route, the current may find a path of lower resistance, which will allow the current to flow at a higher rate. Too much flow and the fuse will pop to protect the lawn mower.
Arcing Circuit
An arcing circuit is when the current can jump from one location to another through a spark. Typically this happens between bare wires, loose connections, or damaged connectors. For example, if you have ever connected a battery charge to a battery and had the connector spark, then this is electricity arcing.
So if the current arcs from one circuit to another, the fuse will pop if the current is moving too fast. For example, if a current passes through a 5 amp circuit and arcs to a 10 amp circuit, the current will be drawn at the higher rate and blow the lower rated fuse.
Wrong Fuse
A common mistake is using an incorrectly rated fuse in the electrical system. For example, a lawn mower starter motor will draw about 8-10 amps and requires a 10 amp fuse. So, using a 20 amp fuse will expose the starter motor to dangerous levels of current, whereas a 5 amp fuse will not be able to withstand the amp draw of the motor and blow.
Damaged Wiring
Damaged wires are probably the most common reason for a fuse to pop, or at least that’s the case on my lawn mower. It’s common for wires to rub against the lawn mower and cause the plastic insulation to wear away, resulting in bare wires. The end result is short circuits, arcing, and bad grounds.
Faulty Electrical Component
Sometimes, fuses that keep blowing can indicate a fault with one of the components on your lawn mower. For example, if your lawn mower’s starter motor has a damaged winding, the current can find an alternate route with less resistance through a short circuit.
Another example could be that the starter solenoid has overheated and is causing a short circuit. Either of these problems could result in your lawn mower blowing a fuse when starting.
Overloaded Circuit
Last on the list is an overloaded circuit. By this, I mean that one circuit pulls more amps than intended. For example, adding lights to a lawn mower on an existing circuit will increase the amp draw, potentially over the rating of the fuse.
Fixing a Lawn Mower That Keeps Blowing Fuses on Startup (4 Ideas)
Here are 4 quick fixes you can do if your lawn mower blows a fuse when starting.
Check the Connection
First, you want to check all the connections in your lawn mower’s electrical system, including the connections to the battery, components, and wiring harness. Next, make sure that none of the connections are damaged or loose. Also, check that the connections are not dirty or corroded.
Inspect the Cables
Next, you need to inspect the cables between each connection. Check that all cables have their plastic insulation intact so they can’t short circuit or arc.
Confirm the Fuse Rating
If your fuse keeps blowing, look in the user manual to make sure you are using the correct rated fuse. Also, you need to make sure that you are using a good-quality replacement fuse. I have used a few cheap fuses in the past that didn’t last five minutes.
Check Circuit Load
Next, you want to check anything you might have added to your lawn mower, such as additional headlights. Items like these should only be added to a circuit if your manual states that it is ok. Usually, there will be a couple of spare circuits on the fuse block of accessories for these types of modifications.
Diagnose the Lawn Mower Electrical System with a Multimeter
If you have run through the different tests and still have an issue, you’ll need to test your lawn mower’s electrical system with a multimeter. I have experienced electrical issues with my lawn mower where the visual inspections weren’t enough. So, testing with a multimeter is the next step.
Here is an example of how to find a short circuit on your lawn mower between the fuse holder and the ignition switch.
Test the Lawn Mower Run Circuit
- Turn the ignition switch off
- Remove the ignition circuit fuse
- Set your multimeter to DC voltage
- Connect the multimeter to both sides of the fuse holder
Results
- No voltage means no short circuit.
- Voltage present with the ignition switch off means there is a short circuit in the wire between the fuse holder and the ignition or in the ignition switch itself.
Test the Lawn Mower Ignition Switch
- Remove the connector from the ignition switch
- Remove the ignition circuit fuse
- Set your multimeter to DC voltage
- Connect the multimeter to both sides of the fuse holder
Results
- No voltage means there is a short circuit in the ignition switch. Therefore, the ignition switch needs to be replaced.
- Voltage present means there is a short circuit in the ignition switch connector or in the wire between the connector to the fuse holder. Therefore, this wiring section needs to be repaired or replaced.
Many different electrical systems make up a lawn mower. You can find all the systems in your mower’s electrical diagram. So, you can test each element to ensure power reaches the desired location at the required time.
Anytime power is present when it shouldn’t be, or it’s not present when it should be within a circuit, it means there is a defective component. Nine times out of ten, you’ll find a short circuit is the reason your lawn mower blows a fuse when starting.
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