Car Battery Charger Not Charging: Everything You Need to Know

About Car Battery Charger Not Charging, It can be frustrating if the charger fails to charge your car battery.

That is why we have put together this article to help you understand everything about troubleshooting, testing, and repairing a car battery charger that won’t charge.

Troubleshooting tips for a car battery charger that won’t charge

If your car battery charger is not charging, do not panic or immediately purchase a battery charger replacement.

For instance, you should troubleshoot it first to determine if you can fix it.

Check if the battery is in good shape.

One of the reasons why your car battery charger isn’t charging could be that the battery itself is faulty. So, the first thing you need to try is to

  • Charge your battery using another charger
  • Or use your portable battery charger to charge a different car battery

If the second charger works or your battery charges the second car battery, the problem lies with the battery, and you may need to replace it.

Batteries below their voltage threshold

Some of the more popular “floating battery chargers” have a voltage threshold of between 8 volts and 11 volts.

Therefore, if the voltage of your car battery is below a certain level of the charger’s, the charger will not recognize a viable battery hookup and will not pass the current.

There are many methods to get around this; regardless of your method, you must disulfate it later.

The first method entails using a non-smart battery charger with supervision to cram current into the car battery, thus raising battery voltage.

And it would be best if you had a decent smart voltmeter to keep checking the car battery until it registers enough voltage on the smart charger before allowing the smart battery charger to take over.

The second method is where you do not have a ‘dump’ battery charger.

Therefore, you must connect the second battery parallel (-ve to -ve and +ve to +ve) with the bad car battery and then attach your battery charger.

Once the charger has put back some current, disconnect your car battery.

For instance, you should avoid leaving both car batteries connected for a long time because the good car battery may end up overcharged.

Check the outlets

The outlets can cause jump starter problems, and there are three ways you can use to determine if the outlets are the cause;

  • Connect another device to the outlet to check if it is working properly.
  • Hook the charger into a different outlet to check if it will charge the car battery.
  • Inspect the charger for any indications, such as if the power indicator is lighting up, emitting a sound, or receiving electricity properly.

Check the charger for signs of damage, dust, dirt, or corrosion

Loose or broken wires can also stop your car battery from charging properly.

Therefore, you must regularly check the battery cables for any signs of tear and wear, ensuring that the cables connecting the charger to the battery are secure and tight.

It would be best to inspect the prongs connecting to the clamps and outlets that will charge the car battery, ensuring that nothing is missing, broken, bent, and in great condition.

Corrosion stops the prongs of the battery charger from getting into contact with the car battery.

It also indicates that the charger has come into contact with water, which could have a shortage inside the charger.

Additionally, accumulated dust and dirt may be why your battery charger is not charging properly.

Therefore, clean the metal strips or contacts connecting to your device.

You can use a fine board to remove corrosion. Next, wait some minutes before trying to use the battery charger again.

Test a car battery charger.

Here are more details about the procedure for testing a battery charger;

Hook your battery charger into a nearby wall outlet

You should hook the power cable up to a nearby AC wall outlet, and the charger will start channeling electricity so that you can measure using a multimeter.

If the battery charger has a separate ON/OFF button, switch it to the “ON” position.

Attach the multimeter’s test probes to their corresponding ports

Most multimeters include a pair of detachable colored probes;

  • One red
  • One black

These probes measure the electricity flowing through the poles of the charger or battery.

Therefore, you should insert the black probe (negative) into the part of the multimeter marked “COM” and the red probe (positive) into the part marked “V.”

However, it is vital to note the following;

  • You can skip this step if your multimeter has in-built probes
  • Depending on the model you are using, the test probe ports may not be marked but instead color-coded.

Set your multimeter to “DC.”

Pinpoint the dial on the face of the tool showing the various testing modes.

Then, twist it until its pointer enters the “DC” range, resting on the next-highest voltage setting of the battery charger you will be measuring.

This will prepare the tool to test the charger, which supplies “direct current” or DC power;

  • “Direct current” means power flows straight from the device generating it to the receiving device.
  • You can use the “2V DC” setting to test a 1.5 volts standard AA battery.

However, you should always ensure the multimeter is set for the current type you are gauging at a higher voltage than your device’s. For instance, operating a multimeter on the wrong setting could;

  • result in more serious damage like an explosion
  • Overload it

Hold the black test probe against the -ve contact point on the battery charger.

If you are testing a receptacle battery charger, like the one used to reload rechargeable AA batteries, you should hold the probe to a part of the exposed metal on the charging chamber side labeled “-.”

However, some multimeters feature input ports that plug certain kinds of power supply jacks into the multimeter.

Touch the red probe on your battery charger’s +ve contact point

You must insert the probe’s tip into the barrel at the tail end of the power supply jack, which carries live current.

Next, hold the probe to the exposed metal part on the side of the charger’s contact point marked “+.”

If the poles are accidentally mixed up, your multimeter can display a _ve or no reading.

So, you need to switch the probe’s position and try again.

Check the number on the multimeter’s screen

This number shows the DC power voltage your battery charger is outputting.

For instance, it should output at least an equal voltage to the car battery one is charging, which helps restore them to their full capacity promptly.

If the charger’s voltage is well below the recommended output, invest in a new battery charger.

However, you should check the user manual included with the battery charger if you are unsure how much voltage it supplies.

Charging the car battery

Charging the car battery

Repairing a car battery charger

To repair a car battery charger, you need the following tools and materials;

1.Soldering kit
4.Wire snips
5.Alligator clips
6.Bridge rectifier

Open the case

One major challenge you can encounter while opening the case is the security-type screws, which have thread poking in the middle of the slot and the nut outside.

However, if you do not have the right screwdriver, you can push on the two slots using two smaller screwdrivers.

Besides, the screws are generally not very tight, which makes it easy to open the case.

The top leather strap is held in place with rivets. T

herefore, to keep it in place, you need to wiggle the case, which allows you to open it without removing the leather strap.

Check the circuit and its operation principles.

You should use a multimeter to check all the connections to learn how a battery charger is built and works.

You need to measure voltage in different sections of the circuit.

For instance, the transformer is connected to the main input on the primary side, and there is a middle tap for 6 volts of output on the secondary winding.

Therefore, three wires are coming out of the secondary winding;

  • Two wires are soldered to the voltage switch, mounted on the top
  • One wire goes directly to the bridge rectifier

The switch should be connected to the other rectifier’s input where on its supply, the -ve wire was connected through a metal strip that acts as a current shunt, and the +ve wire was directly connected.

The charging indicator is wired across the current shunt and measures the voltage drop when more current is drawn to charge the car battery.

Test the output of the transformer.

To confirm that the transformer is working properly, you need to remove the transformer from the circuit and measure the output on the whole winding and half-winding.

If the voltage is around 8 volts on the half-winding and about 16 volts on the whole winding, then the transformer is okay, and the issue is elsewhere.

Bridge the rectifier wiring.

You need to check the bridge rectifier wiring by measuring each diode separately.

However, since its construction is exposed, the diode may develop a relatively large voltage drop, which cuts the output in half on the car battery charger.

Therefore, you must remove it by desoldering all the wiring and replace it with a new rectifier that can hold up to 50 Amps.

Suppose you have never worked with these types of bridge rectifiers.

In that case, you can make the mistake of assuming the wiring placement because one of the positive and AC output connections is labeled, and the other two are on the same side as the labeled ones.

However, they are diagonally opposite.

Besides, when you first connect a wrongly connected bridge rectifier to the battery charger, the diodes can short the output and release the magic smoke.

Therefore, always check the datasheet to learn more about bridge rectifier wiring.

Install the new bridge rectifier.

The new bridge rectifier is smaller than the old one, making it easier to install.

If you do not have wire crimps to add connectors, you can directly add solder to the pads on your new rectifier and solder the wires.

You need to solder one lead from the transformer to one of the rectifier’s AC pins.

Likewise, you should solder the other two leads to one of the switches.

Next, solder the other two contacts on the switch to the diagonally opposite side of the bridge rectifier to the other AC connection.

Solder the output lead on the other pins where the +ve wire is soldered directly to the bridge rectifier, and the -ve wire goes first to the -ve connection on the rectifier through a resettable fuse.

Assemble the charger

After making all electrical connections, you should return everything to the case and wiggle with the wire mesh on the outside to make it flat and sit correctly in the dedicated slot.

Then return the screws to place and tighten them using a regular screwdriver.

Next, use your two small screwdriver technique to complete the tightening.

Test and enjoy!

Finally, measure the output of your car battery charger.

For instance, the output of the 12V battery type charger should be 14 volts, and 8 volts for a 6V car battery type charger.

Battery cables

Battery cables


Troubleshooting the exact cause of your battery charger not charging can be your best bet to discover an ideal solution that works.

Contact Cloom for help with your cable problems.