In Focus: Alternator Technology

Updated Jan 6, 2010

Mitsubishi Electric Automotive America says most truckmakers have a good handle on alternator requirements.Mitsubishi Electric Automotive America says most truckmakers have a good handle on alternator requirements.

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.

Next should be the cables and the connections. If the batteries cannot get the proper power from the alternator or to the starter because of excess resistance in the circuit due to damaged cables, corrosion, loose or damaged connections, etc., the system will not function properly.

“Checking for proper cable connections in the charging system, as well as replacing old cables that are worn and create high resistance, can help ensure correct alternator life,” Braga says.

Bruce Purkey, president of Purkey’s Fleet Electric, says ground straps and connections are just as important as the positive side of the circuit.

Checking cables and connections is more important than many technicians realize. “It is not uncommon to see situations where the alternator or starter was replaced due to a no-charge or no-start situation when the real problem was the cables or the connections,” Stone says. In the normal course of replacing the starter or alternator, a good technician also will clean all connections before reattaching, apply proper torque to the connections, and replace a cable if it looks suspicious, he says.

“Typically, the replaced starter or alternator will seem to have fixed the problem, confirming the initial analysis that the component must have been defective,” Stone says. “However, when it is returned to the manufacturer for warranty analysis, it checks out just fine. This is the source of many denied warranty claims as NTF (No Trouble Found), which, in the end, doesn’t make anyone happy.”

Braga says that checking and replacing alternator belts, ensuring the correct belt tension, and using the correct alternator pulley and belts also will help ensure the correct alternator life. Purkey recommends using a belt tension gauge because a loose and slipping belt can create enough heat to boil the grease out of an alternator’s bearings, causing them to seize up.

The major alternator manufacturers all offer training materials to help technicians learn how to solve electrical system problems, and these documents often are available online. Also consult with suppliers to help prevent breakdowns, no-starts and denied warranty claims.