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Revision as of 20:16, 27 May 2020
This page covers the mechanical and electrical problems that can arise with domestic paper shredders.
Paper shredders are simple electromechanical devices but a fairly powerful motor is required to operate the shredding mechanism, and that power can break things internally.Problems can be divided into mechanical and electrical, but your first task might be to determine which it is in your particular case.
- Always unplug before opening the device.
- Keep fingers, hair and loose clothing well away from the mechanism.
Principles of operation
There are two types of shredder: strip-cut and cross-cut. Strip-cut shredders simply cut the paper into narrow strips which, with patience, could be reassembled. Cross-cut shredders are considerably more secure as these chop each strip into many short sections.
The shredding action is accomplished by two interlocking sets of circular cutterrs which rotate in oposit directions. The paper is drawn in between them so cutting into strips. In a cross-cut shredder, the circular cutters also have spikes which break up each strip.
The cutters are driven by a fairly powerful motor (always an AC/DC motor) through a gear chain to reduce the speed and increase the torque. A switch controls power to the motor. This is normally a 3 position switch with off, forward and reverse positions. The reverse position can be used in the case of a jam, to feed the paper back out again. In this position, the connections to the field winding of the electric motor (or to the brushes) are reversed, causing it to run backwards.
A mechanical or optical sesnsor detect when a piece of paper is inserted into the feed slot, only allowing the motor to run when this happens.
If there is no life in the shredder the first thing to check is the fuse in the plug. This isn't often the problem but is very easily checked.
It's possible the motor may have burnt out, in which case signs of overheating should be obvious. Even if it looks good, use a multimeter to check the resistance of the motor field windings and the resistance of the rotor measured between the brushes. Check that the commutator is clean and not pitted from sparking, and that the brushes are in good order.
There may be a thermal cutout attached to or inside the motor which could have tripped. If it's open circuit and provided it's accessible it should be replaceable, though it may not be easy to work out what temperature rating the replacement should have.
Problems with the paper detect mechanism may not be easy to detect unless indicated by obvious burning or a swollen electrolytic capacitor, but fortumately they are fairly unusual.
If the problem is still not apparent you will have to check for continuity from the plug, through the switch and the motor, and back to the plug.
Jams are very common, and may be due to feeding too much paper in at once or a foreign object such as a paper clip. Some shredders are designed to tak CDs and DVDs, but feeding one into a shredder which is not designed to take it may well cause a jam or the motor to overheat.
Double-check that the device is unplugged before going anywhere near the cutters. The first thing to do is often to remove as much shredded paper from the cutters as possible. Often, it gets wrapped around them. If there's any other cause of a jam you should now be able to see it.
Not uncommonly, a jam or heavy use can cause one of the gear wheels to be stripped. This should be obvious, but there is little that can be done about it.
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