​A Guide To Your Dodge Vehicle’s Alternator and How It Works

Alternators are some of the most robust components you'll find under the hood of a Chrysler product, as well they should be: everything from the spark plugs to the infotainment system depends on getting a steady supply of power from this automotive generator. Even if it seems to be working fine, a weak alternator can keep your battery from being fully charged, which can make the difference between getting to work and getting stranded during one of Chicago's infamous lake effect snow storm. 

The Components of an Alternator and How They Work

The alternator mounts on a bracket that lines it up with the drive pulley on the end of the engine's crankshaft. A belt runs from the drive pulley to the alternator pulley, spinning the shaft. This shaft rides on a set of bearings and has a magnetic rotor mounted on it. This rotor spins past a set of stators, large coils of wound copper wire. As the rotor passes by the stators, it excites the electrons in the copper, generating alternating current. That AC power is then fed into a rectifier. It contains diodes that turn the back-and-forth motion of the current into a solid, steady DC current. A voltage regulator that keeps the current at the voltage your vehicle needs, typically around 14 volts. From there, that electricity is sent through two connectors to the vehicle's electrical system.

Why Do Alternators Make AC Current?

Older vehicles used generators to make electricity, turning engine power into the correct current for the electrical system. However, DC generators are only efficient at specific speeds. An alternating current generator works well at a wide range of speeds, helping it deliver power to the electrical system no matter how fast the engine is driving it. As power demands increased, it made sense for auto manufacturers to switch over the AC generators paired with rectifiers to create a steady supply of DC power. We call this generator/rectifier combination an alternator.

How do Alternators Fail?

The case of the alternator has vents on the front and back to release heat from power generation. If these are blocked or the engine compartment is too hot, the alternator will fail. A cracked case can also cause the alternator to short.

Over time, dirt and heat can cause the bearings to fail, keeping the shaft and rotor from spinning fast enough to generate power.

Heat and vibration can cause splits in the copper wires that make up the stators. The alternator will still function, but with a lower output.

If the voltage regulator fails, the voltage can spike, overloading the electrical system.

How Can I Tell if My Alternator is Failing?

If the alternator isn't providing electricity, your vehicle can run for a short time on just the battery. A car battery will have a rated reserve time anywhere between a half hour and a couple of hours when running accessories, but this drops dramatically if it's being used to power the ignition system. As the battery drains, the voltage will drop, causing odd behavior of electrical components including flickering dash lights, dimming headlights and misfiring. 

Failing bearings will make a loud grinding or squealing noise under the hood while the engine is running. It also makes the shaft harder to spin: if the alternator is off the vehicle, spin the pulley. The alternator should be almost silent and should spin freely. If it takes effort to turn, or makes a grinding noise, the bearings have failed.

A bad regulator can increase the voltage of the power entering the electrical system, leading to burnt fuses and battery overheating that will quickly boil away the water inside. Sometimes, this also leads to odd behavior of accessories similar to a voltage drop, but it doesn't reduce the brightness of the headlights.

How to Test the Alternator

Using a multimeter, check the electrical system voltage while the engine is running. This can be done by setting the multimeter to the 20V setting and touching the probes to the battery terminals. If the terminals aren't readily accessible, contact the positive probe where the red wire connects with the alternator and the negative probe to a bolt on the frame. Do not ground the multimeter on the alternator, as this can cause a short. Ideally, the voltage should be within a few tenths of 14 volts. If it's 13 volts or lower, the alternator isn't producing enough power to drive electrical components and recharge the battery. If it's 15 volts or above, the regulator has failed, allowing the alternator to overload the electrical system.

If the voltage was low in the last test, there are three things that need to be checked before verifying the problem is the alternator: 

First, while the engine is running, look closely at the belt: it should be tight enough that it doesn't appear to be bouncing or vibrating on the pulley. If it's loose, the belt tension may need to be adjusted or the belt replaced so that enough engine power is being transferred to the alternator. 

Next, test the voltage while the engine is running above idle speed. If the voltage is where it should be, the idle speed may be too low.

Finally, shut the engine off and test the voltage. It should be close to 12 volts, but if it's closer to 10 in warm weather or 9 in very cold weather, the battery needs to be replaced. If you have a diesel that uses two batteries, both should be tested: one battery could be fine, while the other has a failing cell.

Which Alternator Do I Have?

For most models, Dodge fitted a single alternator model. However, if you have commercial vehicle like a van or truck, there may have been several alternator options to fit the expected electrical load from installed equipment. The easiest way to identify your alternator is to find the part number, printed on a tag at the center of the device between the two halves of the vented case. When the alternator is on the vehicle, this tag will be positioned either be at the top or on the side that's facing away from the engine.

Where Can I Get a Quality Alternator for My Mopar Vehicle?

MoparNow.com has all the OEM parts you need to keep your Chrysler, Dodge, Jeep or Ram on the road. We may be based in Chicago, but we can ship our parts across the country. Our search engine can find parts by part number, model information, keywords and even your Mopar's VIN. Our parts staff has over 80 years of combined experience, so we can answer any question you have from applications to shipping.