Factors that Affect the Lifetime of an Alternator

Our vehicles work hard for us, oftentimes under less than ideal conditions. Though the engine is mostly protected from the harsh elements, parts like the alternator are exposed. Without a working alternator, your vehicle will only run as long as the battery has a charge, which is not long under normal working conditions and electrical demands.

Your Alternator’s Number One Enemy

The major environmental factor affecting the life of your alternator is heat. Heat is the bane of most electrical equipment as it increases electrical resistance, which means parts or devices must work harder to produce the same output. In addition, excess heat puts strain on electrical component packages, mechanical parts and lubrication.

An alternator itself produces a lot of heat, especially when fully loaded. It absorbs heat from the engine too. As an alternator warms up, it typically loses 10 % efficiency by the time it reaches normal operating temperature. The additional work of the alternator places strain on the drive belt and engine as well. Over time, this strain can reduce the life of belts or bearings.

Proper Alternator Sizing

For cost reasons, all manufacturers, industrial and personal, ship their vehicles with the minimum size alternator that supports the stock electrical system. However, over time as the alternator leeches some of its working capacity, the entire system can suffer.

Furthermore, if the vehicle’s full load prevents the alternator from maintaining a full charge on the battery, then battery life may suffer and a weak battery means the alternator must work even harder. The electrical system begins to fall into a deadly spiral.

To test if your alternator is underpowered, use a voltmeter on the battery terminals to see what its output is at full electrical load at engine idle. If the voltage at the battery drops below 12 volts with everything turned on, a larger alternator is recommended.

Fortunately, a properly sized alternator will supply all your vehicle’s electronic needs without voltage drops, which means both the alternator and your vehicle’s equipment can expect a longer life.

Correct Spin Ratio

A less common cause of alternator inefficiency and shorter life span is a mismatch between the size of the drive pulley and the alternator pulley. Most alternators like a ratio of 3:1, which means the alternator spins three times as fast as the engine.

Alternators do not work efficiently at idle until they reach 2,400 RPM and suffer damage if their full RPM exceeds 18,000. At a 3:1 pulley ratio, those speeds correspond to 800 and 6,000 engine RPM, respectively, which is a normal range for most commercial vehicles.

To check the ratio, simply divide the diameter of the drive pulley by the diameter of the alternator pulley. Usually an incorrect ratio is corrected by changing the alternator pulley size.

Keeping Your Alternator Happy

To ensure a vehicle’s alternator has a long and happy life, ensure it stays clean and free of debris, the battery is in good condition and the alternator’s output is sufficient for the full electrical load it must support. If your vehicle’s electrical equipment shows signs of voltage drop, have the system checked soon and strongly consider installing a larger, new or remanufactured alternator.

If you have any questions this blog did not answer about alternator life expectancy, contact us by phone, email or fax today.