How to Test a Cordless Drill Battery Charger

How to Test a Cordless Drill Battery Charger
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How to Test a Cordless Drill Battery Charger

No matter how good your cordless drill is, it seems inevitable that sooner or later there will be battery issues. Either the battery won’t charge, or it won’t hold a charge and runs down too quickly. In that instance, it’s important to figure out whether the issue is with the batteries, or with the charger, so you can determine where the problem is and what needs to be repaired or replaced.

Difference Between a Voltmeter and a Multimeter

While there are a few ways to test a battery itself without a voltmeter, you cannot test a battery charger without a voltmeter or a multimeter.

As the name suggests, a voltmeter measures the amounts of volts in a circuit. For most battery charges, this device is sufficient for testing, since the charger will be rated in volts.

A multimeter is a more complex device, because it can measure volts and amps. Many multimeters also measure resistance and capacitance, among other things. Multimeters are useful for a wide variety of measurements when testing circuits, and are preferred by professionals.

Voltmeters and multimeters have different settings for AC or DC. Remember to set it for AC to test a charger, and DC to test a battery.

How to Test a Cordless Drill Battery Charger with a Multimeter or Voltmeter

  1. Look at the label on your battery charger to determine the voltage rating. It will always be printed somewhere on the device.
  2. Set your multimeter to the charger’s voltage rating or higher. For example, for a 12 volt charger, set your multimeter to 12 volts. For a 20 volt charger, set the multimeter to 24 volts.
  3. Then plug your cordless drill battery charger into an electrical outlet.
  4. Touch the multimeter’s black negative probe the metal terminal at the base of the charger (the terminal will usually be marked with a minus or negative indicator).
  5. Touch the multimeter’s red positive probe to the metal contacts at the base of the charger (this terminal will usually be marked with a plus or positive indicator).
  6. Read the multimeter. The voltage reading on the multimeter should be at least slightly higher than the voltage rating of the battery. Generally speaking, the voltage on a charger will be higher because chargers deliver more volts than the minimum in order to charge a battery quickly.
  7. If the multimeter indicates fewer volts than the charger is rated for, or gives no reading at all, the charger is faulty.

If you have tested and know that your charger is working properly, but your batteries won’t hold a charge, that is a common issue in NiCad rechargeable batteries, and they can be repaired without being replaced.

How to Restore a NiCad Cordless Drill Battery

Nickel-cadmium (or NiCad) batteries are extremely popular in cordless drills, because they are extremely powerful, and deliver consistent power for the entire charge of the battery, rather than dropping off over time. However, these batteries tend to want to store and discharge only as much power as was used in their previous charging and discharging, a fault that is commonly called “memory.”

Today, many NiCad batteries are advertised as “memory free,” but they all tend to have the same problem. When the battery is used lightly, either by being left on the charger for long periods, or being left idle for long periods, cadmium inside the battery forms crystals. These crystals grow as the battery is unused, and their sharp edges cause the battery to discharge and short out. In other words, to restore a NiCad battery and help it to accept a charge again, you need to break these crystals.

To restore a NiCad battery in a power drill, there are two simple ways to do it.

One method is:

  1. Place the clean, dry battery in a clean, dry, plastic freezer bag and place it in the freezer overnight.
  2. Once the battery is frozen, remove it from the plastic bag. Wipe it clean and dry if there is any moisture or frost on the battery.
  3. Tap the base of the battery firmly against a workbench. One firm tap will break the crystals. Allow the battery to reach room temperature before charging and using it normally.

Another method is:

  1. Charge the battery to full capacity
  2. Place the battery in your drill, and use a vise grip or other tool to hold the trigger on the drill so that it operates continuously
  3. Allow the drill to run until the motor stops, then release the vise
  4. Wait a half hour or so, then pull the trigger again. The drill motor will probably start again, so allow it to run all the way down again.
  5. Keep allowing the motor to rest for a while, and then running the motor down until the drill won’t start at all, and the battery is completely empty.

Completely draining the batteries breaks down the crystals to their original state. After the battery is fully drained, you can charge and use it as normal.

To prevent power loss and keep NiCad batteries functioning properly, they should be charged to capacity and drained completely every 2-3 months. If you regularly use your drill enough to completely drain the batteries, you will keep NiCad batteries in peak condition for longer.

Conclusion

There is nothing more frustrating than having battery problems with a cordless drill. Fortunately, not all battery problems require expensive solutions. A multimeter is an inexpensive device that you will probably use more often than you expect, particularly if you are maintaining a home or involved in DIY projects. And NiCad batteries don’t always need to be replaced just because they won’t hold a charge.

Knowing how to diagnose and manage battery issues will help you get more use out of your cordless drill, and save you time and money. Your cordless drill should always be charged up and ready to go when you are, and with a little bit of troubleshooting, it always will be.

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