Why Stators Fail Did you ever wonder why alterna- tors make a charac- teristic whine as they churn out amps? Or why some _alterna- tors are noisier than others? Let me share a true story. A dealer- ship technician called me (this hap- pened in 1993) and asked if I would check a charging system for him. He confessed up front that he and the dealership were desperate and price was no object if I could help them. They had a 16-month-old, S-10 Blazer with close to 20,000 miles on it. The alternator had been changed seven times, not because of a charging prob- lem, but because the owner complained it was noisy. The tech wanted to know if I could suggest anything that might help satisfy the customer. The owner had filed a complaint under Florida’s Lemon Law, and the dealership had one last chance to correct the “problem” or they might have to buy the vehicle back at full price. Under the law, an arbitra- tor makes the final call. I listened to the CS130 very carefully, checked the battery, cables, amperage output, charge voltage, and ripple voltage. Of course the dealership had already done this several times. The alternator was working perfectly and it sounded very normal to me. The tech agreed, but could anything be done? While you ponder that, let’s go back to the original questions. Where does the noise come from? The stator is com- prised of a stack of circular steel plates, riveted tightly together. Notches are cut around the inside of this stack and wire is wound through these notches in a pat- tern. The pattern can vary depending on the particular alternator, but the princi- ple is the same. As the strong magnetic field, created by the rotor coil and poles, is moved around inside the stack, the electrons in the wire are induced to move. The more amps we make, the stronger the forces required and the greater the movement. Even though the stack of laminations is riveted tightly together, vibrations from the magnetic force cause them to move as well. The noise we hear is coming from the lami- nations as the electro-magnetic forces cause them vibrate against one another. Most of us have turned an alternator pulley by hand on the test bench while the field was turned on and felt the strong resistance as each rotor pole passes a set windings in the stator. The force you feel is what it takes to push the electrons. At higher speeds and amperage, the force becomes even greater. That is why stator windings must be tightly locked in. If the wires can move, they will. The result will be internal shorts as the insulation is rubbed right off. We have all noticed that some alter- nators make more noise than others. A number of factors affect the volume of the output whine, but the simplest way to control the sound coming from the stack is to enclose it inside the housings. Is it any wonder that the noisiest alter- nators also happen to be the ones with the laminations fully exposed? One of the reasons Delphi covered the stack in the 130D was to cut down some of the noise from the CS130 (and complaints from customers like the guy with the S-10). Most automotive alternators being made today have stator windings that are at least partially enclosed. As amperage and noise have gone up, some manufacturers have also resorted to staggering two sets of wind- ings in one stator. The vibrations are still there, but they have been dampened because the windings overlap one another. Ford has done this with the 4G and 6G series alternators. We are sure to see more of this in the future. Heat is also a prime reason for stator failures. We all know not to use an alter- nator to charge a battery, but what about your customers. “The battery is brand new” or “I just charged it for two hours” are two common answers I hear all too often. My suggestion is they let the vehicle idle for two full minutes with no electrical accessories turned on. Then touch the stator (if it is a 2G or CS130) or the side of the alternator with the back of a finger. It should be warm, but not hot. If you cannot hold your hand there, the battery is not charged enough. If you have checked temperatures of your alternators with a heat gun, you know it is the stator that heats up first and it is the stator that normally runs the hottest, even hotter than the rectifier. At least that has been my observation. A CS130 stator at maxi- mum output will exceed 300 degrees F in just a few minutes. So, could anything have been done to quiet down the S-10, short of installing a 130D that was not in production yet? Not that I’ve been able to think of. If you have an answer, let me know. While I’m sure this case has long been since settled (hopefully not in favor of the customer), I still wonder what I would have charged them if I had come up with a solution. They did tell me: “price was no object.” Bob Thomas is owner of B & H Electric, Jacksonville, FL.