Alternators, 2
Page 46
If you've noticed an error in this article please click here to report it so we can fix it.
GENERALLY speaking, the alternator needs less maintenance than the DC generator. The brushes on a dynamo carry the full output of the machine, but on the alternator the brushes only carry the exciting current for the coil on the rotor. The slip rings are simpler than commutators and wear on alternator brushes should be less than those fitted to dynamos so modern alternators are very reliable and any faults which may develop are more likely to be caused by lack of knowledge or carelessness by someone working on the vehicle while it is in the workshop. The following precautions must always be taken:
OPolarity. It is essential that the battery leads are not reversed. On most vehicles the length of the leads are such that this mistake can't be made, but connecting the leads the wrong way round, if this is possible, will severely damage any semiconductor devices in the alternator, even if the leads are only connected for a split second.
• The battery should not be charged with a fast charger unless the battery leads are disconnected.
• A second battery connected into the system by jumper leads to aid starting the engine, must be connected in parallel (that is, positive to positive and negative to negative).
• Polarising an alternator is not necessary and, if attempted, serious damage will result.
• When any electric arc welding is being done on the vehicle, the battery and alternator must be disconnected.
• There must be no "flashing" to earth, either intentionally, to see if a current is present, or accidentally, by allowing tools to short circuit from a live terminal to earth.
• Excessive heat will damage diodes or transistors. They must be properly protected when soldering. by using a pair of pliers to act as a "heat sink". Semi
conductors must not carry current when out of position, as heat which cannot be dissipated in the normal way will damage them.
• Certain types of timing lights used to check ignition timing on petrol engined vehicles can cause damage to the alternator if they develop a fault. It is better to be on the safe side and use a "slave" battery for this purpose rather than the battery fitted to the vehicle.
• • The engine must not be run with the alternator leads disconnected.
• The battery earth terminal should be disconnected befo the alternator is removed or fore its cables are disconnect from its terminals. {This is good safety precaution whi any work is being done on vehicle).
Alternator drive pulleys a generally smaller than tho fitted to dynamos, to give ti higher speed at which altern tors run, and this smaller pult gives a smaller arc of contact f the driving belt.
The alternator has a great output than a dynamo, so a cc respondingly heavier load placed on the belt.
So it is important that a br approved by the manufactur of the vehicle be fitted and that is adjusted according to t, recommendations. As a genet rule there should be half an in (13 mm) of lateral movement a point midway between ti longest portion of belt betwer two pulleys.
Belts which are run too tig will cause excessive wear on 9 alternator bearings while or which is too slack will slip.
by Precept