Part 3 of 6 – Identifying Starting & Charging Systems
Most of the time all of the power for the electrical system is delivered by the use of an alternator when the engine is running. The only time that this isn’t the case is when current capacity of the alternator is exceeded, which may happen at very low idle speeds with all the electrical accessories turned on. Alternators are rated by their amperage output, so when it comes time to select one it’s important to know how many amps the electrical system consumes.
There are two reliable methods of determining the electrical system’s requirements. One is to add the advertised requirements of all components together. Generally all electrical items will have their supply demands included with the instructions. Another way is to use an inductive ammeter with a “peak hold” function clamped around the battery cable while the car is running. While the latter method would be more accurate since it would be testing the electrical system as a whole in real world conditions, it’s not always the most practical. The point is that when everything is turned on at the same time, the amperage demands on the electrical system can be surprisingly high. So selecting the right alternator is important.
Bigger is Better!
Alternators are rated by their maximum output, a good rule of thumb is to pick an alternator that has 20 percent more capacity than the total demand of the electrical system. Another critical factor is the gauge of the charge wire from the alternator to the battery. The basic rule here is bigger is better. Eight-gauge is usually recommended for alternators in the 85 to 125-amp range, six-gauge for 125-150 amps, and four-gauge for anything larger. Going larger than necessary isn’t an issue, but going smaller definitely is. Using smaller gauge wire than recommended can cause electrical damage to your car‘s components.
Next Week: Identifying Starting & Charging Systems – Part 4 of 6