Multi-Tool: Excessive Sparks From Motor

The armature is the power-producing part of the motor and is the only moving part. If your multi tool is producing excessive sparks, it could be caused by the armature. To check the condition of your armature, you will need to access it. Remove the collet nut, collet and unscrew the front cap. Remove the brush caps on the side and take out the brushes. Remove the screws and separate the two halves of the housing. Remove the power cable connector. Take out any screws holding down the motor assembly and pull the motor out. Separate the motor from the switch and circuit board. Slide the armature free from the field and then clean the armature with electrical contact cleaner, wiping it dry. Inspect the armature for burn marks, indicating excessive sparking. If there are burn marks on the armature, you need to replace it. You can also check its condition as well.

There are three tests to use when checking an armature. The first is a continuity test. With the armature removed from the unit, stand it up on a bench. Attach one end of the ohmmeter to the shaft, for ground, and the other to the bar on the commutator. Move the probe to each bar on the commutator, checking all the bars. If the ohmmeter shows a reading on one of these bars, this indicates a short and a bad armature.

The second test is a bar-to-bar test, determining resistance. Attach one probe to the bar on the commutator and the other probe on the bar right beside it. There will be a specific reading for this, depending on the design of the armature. But, most importantly, there is not a large fluctuation here between the values, indicating a fault. If there is an increase in resistance, this will indicate there is a broken, or burned out, wire in the coil. If the resistance drops, the there is a short. Move around the commutator, checking each bar.

The third test is the 180-degree test. Attach the two ends of the ohmmeter on the commutator bars, directly across from each other. There will be a specific set of readings for this, depending on the design of your unit. Once again, what is important is that there is not a large fluctuation in values, which would indicate fault. If there is an increase in resistance, that would indicate a broken, or burnt out, wire. If the resistance drops that would indicate that there is a short. Continue this test on all the bars. If an armature fails any of these tests, it is recommended that you replace it.

Slide the armature into the field. Connect the switch and the circuit board and install into the housing. Reinstall the hold-down screws and the power cable connector. Secure the two halves of the housing back together. Secure the front cap back on and install the collet nut and collet. Reinstall the brushes and caps.

Excessive sparks from the motor can be caused by worn carbon brushes. Wear on carbon brushes are caused by the constant contact they have on the commutator. To check the condition of the brushes, locate and remove the brush caps on the side of the multi tool, pull out the brushes and inspect. Brushes measuring 1/8 of an inch, or less, are worn and need to be replaced. Uneven wear of brushes, or damaged brushes, need to also be replaced since they can cause excessive sparks. Install the brushes into the multi tool and secure the brush caps.

The field, located around the armature, is an electromagnet used to generate a magnetic field in an electromagnetic machine. To inspect the field for excessive sparking, you will need to visually inspect it. Remove the collet nut and unscrew the front cap. Locate and remove the brush caps on the side and remove the brushes. Remove the screws and separate the two halves of the housing. Remove the power cable connector. Take out any screws holding down the motor assembly and pull the motor out. Separate the motor from the switch and circuit board. Slide the armature and field apart from each other and then clean the field with electrical contact cleaner, wiping it dry. Inspect the field for burn marks, indicating excessive sparking.

Replace the field if burn marks are present. You can check the condition of the field by performing a couple of tests. Using a multimeter, you can check the field for continuity. Set the multimeter to the ohmmeter and place a lead on each end of the coil in the field. You will have to perform this test for each coil in the field. If the reading is infinity for one, or more, for the coils, then the field is bad and requires replacement. If there is a major variance between the coils, then the field needs to be replaced. Slide the armature into the field and then connect both the switch and circuit board, installing them in the housing. Reinstall the hold-down screws and the power cable connector. Join the two halves of the housing back together. Screw the front cap back on and reinstall the collet nut. Finally, reinstall the brushes and caps.

The switch controls the flow of electricity to the motor. Over time, the switch will wear out and when this happens, it can produce sparks. To check the switch, remove the collet nut and front cap. Remove the brush caps on the side and pull out the brushes. Separate the two halves of the housing. Remove the power cable connectors and then take out the screws holding down the motor assembly and pull the motor out. Slide the armature out of the field and separate the field from the switch. Remove the wires by inserting a small pick next to the wire and pull out the wire and pick together. Inspect the switch for burn marks, or melting, indicating sparking and overheating. Install a new switch, if you notice any of these conditions. Install the wires into the switch by just pushing them in. Slide the armature into the field. Connect the switch to the motor and place everything back inside the housing. Install the hold-down screws. Join the two halves of the housing together. Install the front cap, collet nut, brushes and caps.