In the past I have tried a few times to review our data and come up with a planned component replacement / rebuild for the alternator. I found that in most cases the original alternator would last 120,000 to 150,000 miles at the time of its first failure. Upon further investigation subsequent failures occurred around 20,000 to 70,000 miles. This makes it difficult to try to determine a planned component replacement schedule for the alternator or charging system.
Upon talking with a couple of my colleagues it was suggested that we may need to check into defective remanufactured alternators. I may agree that some of the alternators may have been defective but not as many as I was sampling for the report. With the particular industry we are in, it is common to make cuts to the maintenance department by hiring inexpensive help with lack of automotive repair experience. I have identified where poor performing charging systems place undue stress on the alternator causing premature failure.
Charging system performance
It is a good idea to check your alternators performing by 1) checking for excessive resistance in the charging system circuits that would decrease current flow and affect charging system performance; 2) cleaning connections and making sure they have good contact to improve charging system performance. This step would help resolve resistance issues.
For an example I will refer to the diagram above when talking about performing voltage drop tests. A lot of Automotive Repair Technicians are not familiar with the voltage drop test and get a little confused when shown the test because the digital multi meter is usually hooked on the same side of the circuit, either insulated or ground. For example if we hold the black probe on the negative battery terminal (3 in Diagram) and the positive probe of the DMM on ground (4 on diagram). This would confuse some Technicians because there wouldn’t be a voltage reading. Technically there should not be a voltage reading. When performing these tests you want the DMM on the lowest voltage scale. At this point you want to place this circuit in an operating condition by starting the vehicle. Upon the vehicle running you want to capture the reading while the engine is running for the first few seconds while the alternator is putting out a high current to start charging the battery. If there is resistance in the circuit some of the current will not flow as a result showing a voltage on the DMM.
For the ground circuit you should not have more than .2 volts or 200 millivolts. This would be pretty much for all circuits in the charging system. With such voltage drops you will see a lack of performance in your charging system. Depending on some voltage drops, the charging system will try to compensate causing the alternator to put out 15 or more volts while only getting 13 volts at the battery and to power stuff in the vehicle, hence poor efficiency. And the alternator is working so hard at that higher voltage that the alternator will prematurely fail. Therefore when replacing an alternator or regulator that has failed I would recommend:
- Checking voltage drop on the insulated supply circuit, ground circuit and insulated circuit to the regulator.
- Clean and tighten connections to reduce voltage drop.
- Check field voltage specs and determine if alternator current flow is in sync with the field terminal voltages.
In most newer vehicles today you may find that they don’t have regulators. Car and van manufacture’s are using the vehicles ECM to control the alternators charging output. This means that engine, body and chassis grounds are more important than ever. Make sure you have good grounds and that connections are clean and tight. With proper maintenance you should have a long lasting and efficient charging system.