DENSO outperforms competitor alternator in quality test

DENSO tested an alternator from an anonymous Brand ‘X’ against the DENSO Design Standards (DDS) adhered to by our own OE quality alternators for the aftermarket. The tests rigorously examined the alternator’s performance, durability and welding composition. The Brand X alternator failed all three tests whilst the DENSO alternator outperformed the standards each time.


For the test, the alternator was hot stabilised at 5,000rpm for 30 minutes, then a speed sweep was carried out, from 1,000rpm to 10,000rpm in 60 seconds, at 25°C and 90°C ambient temperatures. Rpm values were related to alternator revs, for which 1,800rpm represented approximated engine idle speed and 5,000rpm represented approximated engine normal driving speed.

In order to receive a passing score, the alternator had to meet or exceed the DENSO Design Standards (DDS) for output amps in each of the four testing scenarios.

In each test, Brand X’s alternator output fell below the DDS. In addition, Brand X’s alternator rotor resin melted, a common cause of premature failure.

In contrast, the DENSO alternator exceeded the DDS in all scenarios.

20180416_S3_Alternator Benchmark Bulletin _1


For the durability test, DENSO used an ‘up and down’ analysis, which involved acceleration and deceleration between 0 – 22,500 rpms. The alternator was tested at 90°C in 20 second cycles, with 1 second for acceleration, 9 seconds at 22,500rpm, 1 second for deceleration and 9 seconds at 0rpm.

In order to pass the test, the alternator had to be electrically operational with a maximum 10% output reduction after 45,000 cycles. There could also be no mechanical damage present such as fan welding detachment or cracking.

Brand X’s alternator electrically failed after only 1,227 cycles due to rotor coil wire breakage; therefore, the test could not be completed. After disassembly, interference between the rotor O/D and the stator I/D was also noted due to rotor claw pole deformation and field coil fusing point resin crack. This demonstrates an extremely short lifetime for the Brand X alternator, equivalent to approximately 6 months in service.

The DENSO alternator, in contrast, showed no signs of failure until approximately 90,000 cycles, equivalent to more than 15 years in service. After 130,000 cycles, mechanical damage may occur due to failure in the fan welding.

Welding composition

In the final test, Brand X’s alternator was tested to analyse the chemical composition of the welding alloy using Scanning Electron Microscopy (SEM) — used to provide detailed, high resolution images — and Energy Dispersive X-Ray Analyser (EDX) — used to identify the elements that make up the sample.

In order to comply with not only DDS but also with European legislation, welding should be lead-free. However, despite this, the test found lead and tin present within Brand X’s welding alloy.

European legislation bans these heavy metals from use in parts such as alternators due to their poor mechanical strength and low melting points which pose a fire hazard. In the past, nearly all welds contained lead, but safety concerns have increasingly dictated the use of lead-free alloys.

The use of soldering to join the stator phase and rectifier terminal as well as the regulator frame also reinforces the poor quality of Brand X’s alternator.

In contrast, DENSO uses tungsten inert gas (TIG) welding for the SC Alternator stator phase and spot welding for the regulator frame, always with lead-free alloys.

DENSO SC Alternators

DENSO introduced its first automotive alternators in the 1960s and since then, has pioneered a variety of new alternator designs capable of producing more electrical power more efficiently, yet in a smaller, lighter unit. In 2000, for example, DENSO introduced the world’s first SC (Segment Conductor) alternator using a rectangular conductor for its stator coil. By raising the winding density (space factor) from 45 percent to 70 percent, DENSO was able to make the SC Alternator 20 percent lighter and achieve 50 percent higher output than a conventional type.

Today, DENSO SC Alternators are the first choice of the aftermarket for their high standards of performance and trouble-free repair.

Find out more

Further details of DENSO’s alternator range are available online, on TecDoc or from your local DENSO Aftermarket contact.