5 Things You Need To Know About Your Heavy-Duty Alternator

Your alternator plays an indispensable role in the electrical system of your truck. It is the sole means by which all electric current is generated for charging your batteries, starting your engine, and powering all components on both tractor and trailer.
Open Front Semi Truck

Overview: Ensure Your Heavy-Duty Truck Alternator is Operating at Optimal Performance

Your truck’s heavy-duty electrical system is made up of the starting system and the charging system. Key components are batteries, the starter, the alternator, interconnecting wiring, and electrical relays. For maximum operating efficiency, specifically for your alternator, all parts of the system must be functioning properly. If they aren’t working top-notch, costly and significant truck downtime could occur.

At Wheelco, we get a lot of questions pertaining to your truck’s electrical system, specifically your heavy-duty alternator. That’s why we’ve decided to compile many of these questions and organize them into this post for you.

In this article, we will review:

  1. What Is A Heavy-duty Alternator?
  2. How Do Alternators Work?
  3. How Long Do They Typically Last?
  4. Discuss When It’s Time To Replace Your Alternator
  5. Testing & Inspecting Your Alternator

After we review the common questions, we’ll give you our top picks for alternator products, depending on your specific needs. We’ll also tell you why we back the brands we carry when it comes to your alternator.

Heavy-Duty Alternators 101 – What Is It?

Your alternator is a key component in the charging and starting system of your heavy-duty electrical system. It is the power plant to generate electricity for your trucks electrical demands. Charging batteries to deliver cranking power for your starter is one of the chief functions, and certainly one of the most important.

Simply put, alternator and battery start the semi-truck, and your alternator keeps the system charging to sustain the electrical system operation.

Heavy-Duty Alternators 102 – How Do They Work?

So how does the alternator work exactly? Without sounding like you’re about to get a lesson from your high school teacher, we’ll break this down simply.

  1. Whenever it’s running, the engine turns a pulley that’s attached to the alternator.
  2. This rotates a magnetic core inside the alternator called the rotor.
  3. The rotor spins fast – very fast. It is contained within a stator that’s lined with stationary copper winding.
  4. This spinning creates a magnetic field, which produces the power – power that the battery needs to stay charged.
  5. As your battery drains, the power created within the alternator is transferred to the voltage regulator which does exactly as it sounds. It “regulates” the amount of power being sent to the battery.
  6. This cycle is repeated as long as your battery needs power to stay fully charged.

Heavy-Duty Alternators 103 – How Long Do Should They Last?

The typical lifespan of an alternator is about 7 years or between 100,000-150,000.

Mitsubishi Diamond Gard alternators are designed to last and built to routinely last for as long as the first owner typically owns the truck or over 1,000,000 miles!

When properly maintain and used appropriately, alternators can last quite a long time. However, if not properly maintained, that lifespan can be cut dramatically. Let’s discuss, “What not to do with your alternator.”


Your alternator’s biggest culprit of shortening a typical lifespan can be heat.

Alternators produce heat, but they are also is surrounded by engine heat. This is often why you’ll discover that high-quality brands put a lot of technology and design into their alternators to help keep them cool.

Mitsubishi Electric

Mitsubishi Electric Patented electronics design and heat-sinking technology for cooler operation. Exceeds industry requirements for heat resistance.

Delco Remy 

Delco Remy employs the use of the alternator housing itself as a heat sink to dissipate heat.

Watch this YouTube Video to see the advantages of a brushless design. 

Improper Sizing

If an alternator is not big enough to meet the electrical demand of the application, premature failure may occur. Overloading will ultimately result in its premature failure. Your electrical system performance may suffer, even though your alternator is working harder. Your battery life will be reduced. Any number of electrical problems may occur if this continues long enough. This is why it’s important to get the correct replacement alternator for your truck.

Contact one of our experts if you have any questions with choosing alternators. We’d be happy to help with sizing questions.

Malfunctioning Batteries

An alternator is not a “battery charger.” They maintain batteries. If your batteries aren’t in good working condition, they can put a strain on your alternator

Poor Connections & Cables

Dirt and corrosion will inhibit the alternators efficiency and ability to maintain sufficient battery charge. Please ensure all of your connections are cleaned and secure and your cables are not corroded, have tears/breaks or have exposed, frayed wire for the lifespan of your alternator.

Heavy-Duty Alternators 104 – Signs You Need To Replace Your Alternator

Some of the same signs for a dead battery may actually be due to a failing alternator. When alternators fail to charge you may experience:

Dim Lights

One of the most common failing alternator symptoms is dim or flickering lights. This can be a sudden burst of bright light coming from your headlights or a dim or flickering dashboard.

Wheelco Quick Tip: If the truck’s headlights brighten suddenly when you amp up the RPMs, that's a sure tell sign your alternator needs replacement.

Engine Stalling

Your engine suddenly cuts power – while driving. If this happens, be sure to have your vehicle brought in to a service center right away. It could be an alternator issue. Typically a computer will shut down around 9.6v and below.

Service Engine Light

This may be obvious to some, but when the “Check Engine” or “ALT” light comes on, your alternator may be failing. However, some dashboards will show a battery icon lit up when it is in fact, your alternator that needs an inspection.

Squealing, Growling or Grinding Sounds

With age and frequent use, the serpentine belt is prone to stretching. It may not be spinning the alternator pulley effectively. This results in a lack of charge. This typically results in a squealing noise but can also sound like a growl or a grinding noise. Your alternator drive belt is also a key component to monitor and maintain.

Wheelco Quick Tip: PM service should include inspection and replacement of your drive belt if needed. If you need any assistance choosing a drive belt, we’d be happy to help you find exactly what you need.

Dying Batteries

If your alternator isn’t working properly, your truck will quickly use up the reserves in your batteries. When replacing batteries, the alternator output should always be checked to make sure the alternator is delivering adequate current.

Electrical Issues

Phone charger not working? Power seats or window moving in slow-mo? Radio turns off suddenly? This lack of power is a sure-tell sign that your electrical system is not operating properly. While it may not be your alternator, your batteries themselves may be the culprit.

Wheelco Quick Tip: If you jump your vehicle, and the engine dies right after it’s jumped, it’s probably your alternator that’s failing.

Heavy-Duty Alternators 105 – Test & Inspect Your Alternator

Manually Inspect Your Alternator

To determine if it’s your battery or alternator that’s failing there are a few quick inspections and/or tests you can do.

  1. Visually inspect the cables at the back of the alternator, starter, and batteries.
  2. If no loose or broken connection(s) are found, the alternators can be tested using a voltmeter.
  3. An alternator that is running properly will have a reading from 13.6 – 14.2v when charging.

Wheelco Alternator Picks: Mitsubishi and Delco Remy

Have you determined your alternator needs repair or replacement? We’re here to help with product recommendations and technical service.

We recommend using Mitsubishi and Delco Remy to replace worn out/failed components. We’ve researched the most popular parts available for truckers so we can stock our inventory with the best. Our choice to recommend Mitsubishi and Delco Remy components factored in quality components, low cost of ownership, performance standards, truck application requirements, warranties, etc. We factored them all, including the cost and benefits of warranty options.

Best Warranty In The Business Alternator – Mitsubishi Diamond Gard

If you are looking for an alternator that is backed by their manufacturer, then you want Mitsubishis Diamond Power alternators. Why? If it fails with in the first three (3) years- for any reason – Mitsubishi pays. And when they say any reason, they stand by their word. Failure due to: manufacturing defect, worn mounting holes, loose pulley damage, fan damage, high vibration failure, solder re-flow, and failures due to excessive rust, oil, dirt, debris, water, etc.…

Mitsubishi Diamond Gard Key Takeaways

  • 3-year warranty
  • Unlimited Miles
  • No-fault, no exceptions
  • All new replacements (warranty reclocks – not prorated)

This is available in both the 160A and 200A alternator models.

Watch this YouTube Video to see all the benefits and features!

Recommended For The Long-Haul – Mitsubishi Diamond Gard 200A

Mitsubishi Electric HD 200A Alternators are designed to last over 1,000,000 miles! While many alternators start to fail after 100,000-150,000, Mitsubishis 200A was designed to last as long as the first owner has the truck. They didn’t take shortcuts when designing this alternator. It’s powerful even though it weighs in at 21 pounds and is only 8 inches long. This alternator delivers more charging amps at idle than most do at road speed! And with the innovative design exceeds industry requirements for heat, vibration and corrosion resistance.

Mitsubishi Diamond Gard 200A Key Takeaways

  • Delivering over 137 amps at idle
  • Patented electronics design
  • Heat-sinking technology for cooler operation
  • Reduced fuel usage

Replacement for Brush or Brushless Replacements – Mitsubishi Diamond Gard 160A

Mitsubishi Electric HD 160A Alternator is designed to fit most applications. In fact, a single DP A160 part number is a direct replacement for ALL Remy, Bosch, Denso, or Leece-Neville PAD-MOUNT HD Alternators since 1998 – brush or brushless.

Mitsubishi Diamond Gard 160A Key Takeaways

  • Exceeds 110 amps output at engine idle, 160 amps at road speed
  • Can replace a 2, 3, 4, or 5 wire system – no wiring harness change needed
  • Best in class efficiency of well over 60% provides reduced fuel usage
  • Remote Sense Technology comes standard

Recommended Brushless Replacements – Delco Remy Models

With a complete portfolio: From 70 to 450 Amp (12 and 24V). Brushless Alternators will last much longer compared to a standard brush alternator because it features fewer moving parts. Delco Remy has a variety of alternators to meet your specific application’s needs.  Work with one of our experts to help you find the exact alternator to meet your needs for your vehicle.

Delco Remy Models Key Takeaways

  • Rotatable starter drive housings
  • Electrical soft-start
  • Units available w/ Integrated Over Crank Protection (IOCP)
  • Units available w/ Internal Magnetic Switch Solenoid (IMSS)

Next Step: Schedule a Service or Talk to an Expert

Need assistance in choosing the right part, scheduling a service, or do you have more questions about our recommendations? Our aftermarket experts and service techs are ready to help you get exactly what you need. Simply text us, talk to us through chat, give us a call or stop by one of our stores today. We’re here for you however it’s most convenient.

About Wheelco Truck & Trailer

At Wheelcobeing customer driven is more than just a motto we live by. It means that our employees will do everything we can to best serve you, our valued customer.

Customer driven is more than just offering you advice, giving time-honored service or contributing the latest tech-support. It’s about being there—whenever and wherever you need us—in-person, over the phone or online.

Recent Posts

Video Tutorials

Browse Categories

Follow Us

More to explore

Contact Customer Support

Have a question and want to talk to a human? Get help from one of our a dedicated Customer Service Representative who know the industry. Our team helps customers like you get answers to their unique problems. Get help the way you want - Phone, text chat or email.


(800) 952.3674


Text Wheelco to 797979