Why your Car Battery Charger Fuse Keeps Blowing? (+How to Fix the Fault)

For the most part, you can count on a car battery charger to quickly replenish the charge of your drained car battery unless there is an issue with the charger, such as when you’re unable to charge the battery because the charger fuse keeps blows and so does each replacement.

This post explains the likely reasons why the car battery charger fuse may keep blowing and what checks you can do to get it working reliably again.

What Causes the Fuse to Blow (+Tips to Fix it)

If the fuse keeps blowing, it may be because:

#1. The charger leads are accidentally reversed (reverse polarity) and connected to the wrong posts on the battery.

Check and confirm that you’ve connected the charger positive lead, usually red in color to the battery post labeled (+) and the charger negative lead, usually black in color to the battery post labeled (-).

Replace the charge fuse with another of the same type and rating (amps) and check if the fuse blows again.

#2. There’s a short in the car’s electrical system. This can be the case when you’re charging the car battery while it is still connected to the car’s electrical system.

If the car battery terminals are still connected, disconnect them and only leave the battery charger leads connected.

This eliminates the possibility of a short in the car’s electrical system causing the charger fuse to blow.

If the fuse remains intact after disconnecting the alternator terminals then this confirms that the charger and battery have no internal short. You’ll need to investigate and fix the short in the car’s electrical system.

#3. A faulty and shorting cell in the car battery. A car battery with an internal short draws an unusually high charge current and will cause the battery charger fuse to blow too.

Check if the charger fuse still blows when connected to another battery. If not, then it’s possible that the battery has an internal short.

Arrange to test the battery at an auto car repair facility and if faulty replace it with another.

#4. Faulty battery charger. It is possible that the charger has an internal fault, perhaps a shorting electrical component or the charger may have been exposed to water. Either of these can cause each fuse replacement to blow.

Should you Continue Using the Charger?

In some cases, the underlying fault causing the fuse to keep blowing can be fixed easily for example, if the charging leads were accidentally reversed.

Simply replacing the fuse and connecting the leads the right way may be enough to get the charger working reliably again.

As a first step, work through the suggested causes of the fuse blow listed above. If none solve the issue or if you have any concerns, contact the charger manufacturer for support.

If the fuse keeps blowing, and it is not the battery or the connections then you should probably consider investing in another charger.

It is usually not worthwhile repairing the charger as the repair costs may amount to about the same as a brand-new charger which comes with a warranty.

Consider the options and accordingly repair or replace the charger with another.

How to Tell that a Fuse has Blown

When the charge fuse blows, you may hear a popping sound. The battery charger status indicator will be off ( double-check that it is correctly plugged into a working wall outlet and that it is switched on.

What Happens When a Fuse Blows?

When the charge fuse blows, charging to the battery is immediately stopped as a safety precaution to avert the risk of damage or fire as there’s an excessive amount of current demanded from the charger than it is designed to supply.

How to Test if the Battery Charger Fuse Has Blown

Consult the charger user manual for the location of the fuse. Make sure that the charger is unplugged from the wall outlet and follow the manufacturer’s instructions to remove the fuse.

Use a multimeter to measure the continuity or low resistance of the fuse terminals. If the fuse has blown then the meter display on connecting the leads of the multimeter will show an open circuit.

Car Battery Fuse Size (Amps)

Battery charger fuse ratings (amps) vary from one charger to another depending on its amperage.

There is no one standard fuse size. Consult the owner manual for your charger for what replacement fuse to use.

Always replace with a fuse of the same type and rating as recommended by the charger manufacturer for the fuse to continue providing the necessary protection.

Do not use a fuse with a higher amp rating than that specified by the manufacturer!

Closing Thoughts

If the battery charger fuse keeps blowing, it could be a case of reverse polarity, a faulty battery, or a faulty charger.

Always replace the fuse with another according to the manufacturer’s specifications for fuse type and current rating (amps).

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