Keep your alternators out of trouble: Proper charging depends on spec'ing, maintenance
Today’s trucks have more electronics than ever, and they cruise at lower rpms, so more careful alternator spec’ing likely is in order. Fleets should use the appropriately rated alternator for their applications to ensure the longest possible life for the device, says Orlando Braga, Denso’s senior engineer.
Most truckmakers have a good handle on actual requirements, says David Stone, heavy-duty executive director for Mitsubishi Electric Automotive America. “Specifications have changed to accommodate the engine system changes as a result of new emissions regulations,” Stone says. “Output requirements have increased, and heat tolerance capability has increased.”
Truck manufacturers have calculated the required output levels necessary for all of their truck configurations, and have made the best choice the standard offering, Stone says. “The best advice is to let the truckmaker decide which alternator is best, and not spec off standard.”
When spec’ing, fleets also need to consider which basic design to choose: brushed or brushless. The customer makes that decision relative to their situation based on several considerations, Stone says. Lower-cost brush-type alternators bring with them shorter life, lower reliability and increased maintenance, while more expensive brushless alternators offer longer life, higher reliability and less maintenance. Output levels are nearly the same for both, Stone says.
“By design, a brushless alternator lasts longer than a brush-type under the same conditions,” Braga says. “However, brush-type alternators tend to be less expensive, though they also have a shorter warranty period.”
Another consideration is the power curve versus the rpm of an alternator’s output. The Denso brushless alternator has a “Y” connection on its stator coil as opposed to a delta connection, Braga says; the “Y” connection is designed to facilitate higher output at a lower rpm than the delta connection.
“Denso believes that most customers will benefit by having an alternator provide higher output at lower rpm based on current customer demand and use,” says Braga, who recommends checking with a sales engineer to make sure the alternator has the correct output characteristics at the cruise rpm for which the vehicle is geared.
Keeping them charged
Once spec’ed properly, how do fleets keep alternators delivering? Rule number one is to remember that the electrical system is just that — a system where one bad part always drags down the rest.
Batteries are a relatively perishable item, and their ability to accept and store power efficiently deteriorates with use. Alternators frequently become overloaded by deteriorated batteries, ultimately causing failure.
“As with alternators, fleets should check the condition of their batteries regularly and discard batteries that no longer take a charge or show physical wear,” Braga says. Stone agrees, saying that the charge-start system cannot function properly with batteries in poor condition. “Any analysis of the system should start with the batteries,” he says.
