How To Diagnose Power Tool Problems

Stator and rotor of a 3-phase motor: 0.75kW, 1420rpm, 50Hz, 230-400V AC, 3.4-2.0A. Photograph taken by Zureks.

Lets start our journey to find the glitch. To locate our fault, we’ll track the electricity flow from the tool’s power source to the tool’s motor, checking the main components along the way.

Beginning with the power cable, simply ensure that you don’t have any breaks or cuts; these will prevent the current from flowing to the power tool and its motor. If all looks great with your power cord, our next step would be to look at the tool’s brushes. Although the power switch is the initial landing point for the tool’s electrical current, faulty brushes are much easier to discover, and are also more commonly the culprit in a poorly performing power tool, so, for now, we’ll skip the switch and proceed with the carbon brushes.

If your carbon brushes don’t fully make contact with the armature’s commutator bars, it will cause a poorer performance and might contribute to difficult start-ups too.

To begin with, there are a few factors causing your brushes and commutator to separate: heavy wear, tear, or not-so-springy springs. Make sure that the carbon block of your brush’s body is touching the commutator. Next, heat damage will prevent the brushes from conducting to their fullest capacity. Check for melting, burning, or discoloration.

When any of the above happens, the brushes should be replaced quickly to avoid damaging the tool’s other components. It is in the nature of damage, particularly heat damage, to radiate to neighboring parts within your power tool. So, if your brushes have been severely damaged, I suggest you immediately inspect the armature for similar signs. Nevertheless, if all looks great, you may check your switch.

I say “may” simply because a damaged switch will generally prevent the power tool from starting altogether rather than just reducing the overall power of the tool. Despite its unlikelihood, it is still possible for heat damage or even a severely worn switch to cause decreased performance. Heat damage will look like burning, charring, melting, or discoloration of the switch body, the cables, or the wire insulation. Since heat damage may not always be evident, it might be helpful to replace the switch anyway, especially if you know that the switch has been overloaded or exposed to moisture.

Also, and because I am nearly certain the issue doesn’t lie in your switch, we’ll continue on to the tool’s more significant components, the armature and the field coil. If your armature or winding are ruined, you might also see smoke or sparks coming from the tool. When there’s smoke or sparks coming from the power tool, you almost certainly have a burnt armature or field coil. As you recall, if your brushes are burnt it is also an indicator of armature damage, which if left unchecked will quickly spread to the winding.

First, inspect the armature’s commutator to ensure the bars form a totally smooth circle. Any bumps or pits in the circle will damage the brushes, leading to poorer or no electrical conductivity. Replace the armature. Any discoloration on the commutator are also signs of heat damage, reducing its conductivity and the tool’s overall performance.

If the commutators are ruined, and especially if they have any observable heat damage, it’s important to also inspect the rotating part of the tool. Here, heat damage will again look like burning or melting or discoloration of the insulation or wires or of the armature assembly. Keep in mind that a damaged assembly will truly act as cancer in your power tool. It will quickly spread to the other elements and will soon reduce the tool’s ability to perform.

If the armature is damaged, it’s also necessary to inspect the winding. Although generally reliable, the field coils can be damaged by heat. This is caused by over-heating, over-loading, abuse, etc, and will affect your tool’s performance. As with your armature, heat damage will look like melting, burning, or discoloration of the coil field’s wiring, insulation, or of the assembly itself. Bear in mind that both the field and armature are extremely vital parts in your power tool.

Remember also that damage is like cancer on your power tools, which will continue to spread and worsen if not eliminated. Replace your damaged parts early to avoid greater, more expensive damages later on. Thus, if any part, particularly the armature, is severely burnt, it is important to inspect the tool’s other elements as well. Additionally, if you know the tool was over-loaded, it’s always prudent to check the whole tool for any signs of damage.

Essentially, if your tool is feeling a bit slow, I’d say head directly for the brushes, this is usually where the weak point lies in a poorly performing power tool. If after checking and replacing any necessary components, your power tool still feels sluggish, take it to a licensed service center for professional checkup.

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