Many types of medium-duty fleet vehicles, particularly vocational trucks and box trucks, have demanding electrical needs. They often operate at slower speeds, do a lot of stopping and starting, and operate a wide array of electrical accessories. This puts a big strain on the battery.

“Think about a box truck delivering to a gas station chain,” said Brian Thompson, North American fleet director at PHINIA, the BorgWarner spinoff whose product portfolio includes Delco Remy alternators and starters. “That truck will stop at one corner, go another mile or two, and stop again—often with its hazard lights on along with other accessories. In the summer the driver will have fans blowing in the cab. It all taxes the electrical system. A big part of the problem fleets can run into is that the batteries just don’t have enough time to charge.”

That potential issue is compounded if the alternator isn’t sized correctly, is past its useful life, or has been physically compromised. The last thing a last mile truck’s driver needs is to have to wait for a jumpstart during their shift, so we asked alternator expert Thompson to share the more about what medium-duty fleets need to know about this crucial part.

Eyes and ears on the alternator

According to Thompson, today’s alternators from top brands generally last a long time—often more than five years in many medium-duty applications, provided the fleet has spec’d a longer-lasting brushless-style alternator. That said, lifecycle can be shortened by excessive wear and tear, heat damage, overuse, exposure to water or other fluids, faulty parts, an overly tight serpentine belt, or overall faulty installation.

Drivers should be trained to watch and listen for certain symptoms that could signal an issue with the alternator, such as dim or overly bright lights, slow or malfunctioning accessories, and wining, grinding, or clicking noises emanating from the alternator. Those sounds could signal overly worn bearings or bushings, or an issue with the serpentine belt or pulley. Drivers may even notice a burning smell that may suggest an issue with the belt or wiring. These observations should immediately be reported to maintenance.

Speaking of maintenance, Thompson said fleets will often train technicians to run a tester on the electrical system during routine PMs. If there is a problem with the alternator, the technician will likely see signs of voltage fluctuations. Roughly a third of those cases are cable-related, according to Thompson.

“Crimps, corrosion, and loose connections are a huge deal,” he said.

In a lot of instances, however, Thompson said the alternator isn’t the root cause of the electrical issues a truck is experiencing. The alternator is part of a system, and issues with other parts of the system could be the culprit.

“The root cause is often battery-related, and I’m not pointing fingers at the battery manufacturers,” Thompson pointed out. “It’s just that in many of these medium-duty applications, the batteries are just not getting filled up. That’s where fleets start running into problems with jumpstarts. If you spec your system right from the start—including the batteries, alternator, and cabling—you should be in pretty good shape.”

Delco Remy’s 40SI High Output Brushless Alternator is available in output ranging from 240 to 320 amps, 160 to 190 at idle. Additionally, unique remote sense technology utilizes a second wire that reads the actual voltage at the battery to tell the regulator to increase its voltage output to compensate for the voltage charge loss, ensuring a constant 14 volts at the battery. Delco Remy said this feature can help reduce battery charge time by 50%.

Brushing up on alternator options

When spec’ing an alternator, fleets can choose either a brush-style or brushless model. Brushless alternators cost more, but also last longer. They are a good choice for fleets looking to keep a vehicle in operation for another five-plus years.

Brushless alternators can also provide a maintenance advantage. They have far fewer moving parts that can wear out. Additionally, they don’t have brushes that are known for trapping dirt and other contaminants.

“Fleets that buy based on ROI tend to lean toward brushless,” Thompson said. “When you weigh the cost out over the long-term and compare cost per mile, brushless looks really good.”

Fleets also need to pay close attention to output when choosing an alternator. In many medium-duty applications, Thompson said that means output at low speed. “Vocational and P&D assets aren’t hitting freeway speeds all the time,” Thompson reminded. “Low-speed output is critical on the alternator curve with these types of trucks.”

Thompson said Delco Remy’s 40SI High Output Brushless Alternator has become a popular choice in demanding medium-duty truck applications. It’s available in output ranging from 240 to 320 amps, 160 to 190 at idle.

“If you look at the history of an application and see a lot of jumpstarts or battery replacements, you may need to go to a bigger alternator like this,” Thompson said. “Then you need to make sure your cables are sized correctly for that alternator. It’s not unlike hooking a garden hose up to a fire hydrant. You’re still going to get water out of that hose, but not as much as you could.”

One challenge for vocational and P&D fleets is that there can be a lot of variability with respect to specific applications. For example, a box truck could be delivering in a downtown area one day, doing a lot of starting and stopping and idling. But the next day they are getting a lot more runtime out in the suburbs.

“You really have to size the alternator for the worst case scenario, unfortunately,” Thompson said. Fleets should identify which use case sees the most starts/stops, while also having the heater, blowers, and wipers all running on high, along with any other accessories. “Then, you always want a safety factor of 20-30% to make sure you have enough amperage going back to the batteries so they can charge back up,” Thompson added.

When a new alternator is installed, Thompson offered one final piece of advice.

“It’s important to recoat the electrical components to protect them from corrosion,” Thompson said, in reference to things like the connections on the D+ and ground. “We do a good job in the industry on the battery side, but not so much on the starter and alternator side.”

Taking that one simple step can help a fleet take an important leap toward ensuring the electrical system performance, reliability, and longevity its medium-duty assets require.