Electric Drill: Excessive Sparks From the Motor

The armature is the power-producing unit of the motor and is located inside the field of the motor. To replace, or clean, the armature, begin by removing the screws securing the case of the drill together, then separate the two halves of the case. Locate the brush holders and remove them by gently pulling the wire up and maybe using a small screwdriver on the other side for even lifting.

Remove the spindle and chuck assembly from the drill, then lift the motor assembly up and slide the armature out of the field. You can clean the armature with an electrical contact cleaner, if it has a heavy build-up of dirt and grease on it to improve performance.

To check for a bad armature, you can perform the 180-degree test. With the armature removed from the unit, stand it up on a bench. With an ohmmeter, attach the two ends to both sides of the commutator to measure the resistance of the windings. As you move it around the commutator, the reading number is not important. You are looking for a consistency in reading, indicating the windings are good. If it varies, radically reading zero, or open circuit, then the armature is not good. Another test is reading. If the ohmmeter reads a zero, or open circuit, then that indicates a bad armature. The last test is a bar to ground test, which is done by placing one end of the ohmmeter to the tip of the shaft on the armature and the other to the commutator.

If the armature is bad, install a new one. Install the armature into the field. The field will have a notch on it, indicating the front. Reinstall back into the drill housing, then reinstall the spindle and chuck assembly back in the case. Reinstall the brush holders in the case by using a small-blade screwdriver to hold the brush down, giving you clearance on the commutator. Ensure all wires are back inside the channels and out of the way. Finally, reassemble the case back together.

The brushes ride on the commutator, applying electricity to the armature. If the brushes become worn, or wear unevenly, they can cause excessive sparking. To check the brushes to see if they require replacement, remove the screws securing the case of the drill together and separate the two halves of the case. Locate the brushes and remove them by gently pulling the wire up and maybe using a small screwdriver on the other side, for even lifting. The brushes should not be 1/8 of an inch, or less, from the brush holder. If they are, or are getting close, replace them. Push the tab on the brush holder to remove the brush. Insert the new brush into the holder. When reinstalling into the drill, use a small-blade screwdriver to hold the brush down, allowing you to reinstall it. Make sure all wires are back inside the channels and out of the way. Now, reassemble the case back together.

A field coil is an electromagnet used to generate a magnetic field, in an electro-magnetic machine. Over time, this part can build up a lot of heavy dirt, as well as overheat, which can lead to problems such as sparking.

To check the field, remove the screws securing the case of the drill together and separate the two halves of the case. Remove the brush holders by gently pulling the wire up and using a small screwdriver on the other side for an even lift, if needed. Remove the spindle and chuck assembly from the drill. Disconnect the spade connectors on the motor and lift the motor assembly out of the case. Separate the armature from the field by pulling the armature out. Inspect the field for burn marks, indicating sparking.

You can use a multimeter to check the field for continuity to see if it has shortened. Set the multimeter to an ohmmeter and place a lead on each end of the field. If the reading is infinity, the field is bad and requires replacement. If the field is good, looks fine, but is dirty, then clean it thoroughly in thinner and dry completely before reinstalling.

Install the armature in the field – the field will have a notch on it, indicating the front. Place the motor back in the drill and reattach the spade connectors. Install the spindle and chuck assembly back in the case. Reinstall the brush holders using a small blade screwdriver to hold the brush down, giving you clearance as you reinstall them on the commutator. Ensure all wires are tucked inside the channels and out of the way. Close the case back together and secure it tightly with the fasteners.

The springs are housed inside the brush holder and keep pressure on the brushes, allowing the brushes to ride smoothly and evenly on the commutator. If these springs lose tension over time, they will have inadequate press, which will lead to sparking between the commutator and brushes. To replace these springs, remove the fasteners securing the two halves of the drill together. Locate and remove the brush holders. To remove them, you can gently pull up on the wire. Push down on the brushes and check the pressure. If you suspect they are weak, remove the brush by pushing down on the tab on the side of the holder, then pull the brush and spring out. Install the new spring and brush in the holder, ensuring they lock on the tab. Next, install them back in the drill using a small-blade screwdriver to hold the brush down as you reinstall it. Put the case back together and re-secure it with the fasteners.

The holders support the tension spring for the brush as well has holding the brush in place on the commutator. Any physical damage to the holder, or a heavy build-up of dirt on the inside, can interfere with the free motion of the brush and may result in sparking. Since the commutators are not always perfectly round, the brushes must move in and out of their holders to maintain effective contact.

A visual inspection and testing of the free action of the brush with the fingers are sufficient to reveal proper operation of the holder. Remove the screws securing the case of the drill together, then separate the two halves of the case. Locate the brush holders and gently remove them by pulling the wire up and maybe using a small screwdriver on the other side for even lifting. Look for any physical damage to the holder and check that the brushes are free to move up and down. If any of these symptoms are occurring, replace the holders.

Push the tab on the brush holder to remove the brush. Disconnect the wire on the brush and attach it to the new holder. Install the brush into the holder and make sure the tab locks in place. Use a small-blade screwdriver to hold the brush down, allowing you to reinstall it back on the drill. Ensure all wires are back inside the channels and out of the way. Finally, reassemble the case back together.