Right Sizing Alternators: Longer Battery Life Starts with Choosing the Right Alternator

As recently as a few years ago, a standard alternator with an output of 130 amps at 12 volts would probably serve the needs of most regional and vocational truck fleets and operators. Long-haul truck fleets and operators might need an alternator with a slightly higher output of up to 140 to 150 amps at 12 volts for high hotel loads. But stricter federal emission standards, local anti-idling restrictions and the choice of truck operators to run more electronic devices have changed all that.

“Fleets and truck operators who’ve experienced problems with short-lived batteries would do well to rethink their choice of alternators,” said Everett Seymoure, global manager for TRP Aftermarket Parts. “TRP and its network of authorized dealers, which include Kenworth and Peterbilt dealerships, recommend truck fleets and operators take a closer look at the components drawing power from the truck’s electrical system. We’ve found that when truck operators and fleets experience lower than expected battery life, they’re usually using alternators with inadequate amp output.”

Emission control systems on newer engines draw more power from electrical systems for passive and active regeneration cycles, especially SCR technology engines that meet 2010 EPA emission standards, Seymoure said. Plus, the engines using SCR or EGR technology run at higher temperatures, which can play havoc on alternators not rated for those higher temperatures. Tighter tolerances and extremely high-pressure fuel injection system mechanisms can also tax the starter motors and, by extension, the batteries. Since many state and local jurisdictions restrict idling to five minutes or less, drivers must turn off and restart their engines up to 20 or 30 times a day or more. That places even more strain on the batteries, he added.

In choosing the right size alternator, Seymoure said operators should first calculate the electrical loads or amp-hours per working shift and rest period. Make note of all electrical components, including the emission control system, gauges, air conditioner, headlights, tail lights, cab marker lights, fog lights, and van or trailer lights, and the amps each of them draw respectively during the working and rest period, he added. Multiply each of those amps with the number of hours the components operate in their respective working or rest period to determine their electrical loads or amp-hours.

Add up all of the electrical loads and then calculate a reserve for battery charging by multiplying that total by 20 percent. Add the total electrical load and the reserve together and that determines the minimum amount of output the alternator should produce, Seymoure said.

“Cost will certainly impact the truck operators’ choice in alternators, but they shouldn’t shortchange themselves in capacity since that will only shorten the lives of their batteries,” he added. “While rebuilt or remanufactured alternators can save money, they may not have been originally designed to withstand the higher temperatures common in newer engines.”

Another consideration is choosing whether to purchase a brush alternator or brushless alternator. While a brush alternator is cheaper, a brushless alternator lasts much longer, generates a more consistent amp output and operates at a lower temperature. That’s because in a brush alternator, the current that’s generated with the alternator’s rotating magnetic core and stator is carried away through tiny bristles, which can eventually wear out, Seymoure added.

A brushless alternator is actually composed of two alternators — the main alternator and the exciter mounted end-to-end on one rotor, he said. Electricity is generated by moving a coil through a magnetic field. The coils are charged with protons and electrons as it moves through the field. As these molecules collect, electrical current is generated and the electrons are sent through the coil and into the wires of the alternator.

TRP features the RE022 brush series of alternators offering 150 amps of power and a one-year warranty and the RE 555 brush series of alternators, providing 160 amps an a one-year warranty. TRP also has the RE035 and RE036 series of brushless alternators. The RE035 features 140 amps of power and a three-year warranty and the FE036 features 170 amps of power and a three-year warranty. TRP’s line of brushless alternators also feature remote sensing capability, which can help compensate for cable voltage drop through accurate voltage readings and further extend the service life of the truck’s batteries, Seymoure added.

Through remote sensing, TRP alternators measure not only the power they push through the truck’s electrical system, but also the power being delivered to each of the batteries. A remote sensor at the battery terminals measures how much electricity is actually being delivered. If the sensor reads a power drop at the battery terminal compared to the power the alternator is generating, the alternator automatically increases its output until the battery has reached its specified charge.

“Truck operators need cab comfort systems and electronic devices that make the truck a more agreeable and productive work environment,” Seymoure said. “All of these things tax batteries and alternators to their limits. That’s why today’s truck fleets and operators need robust alternators like those offered by TRP.”