SunSaver and ProStar Reliability

- ACCELERATED RELIABILITY TESTING
-
-- ProStar and SunSaver Controllers: July 1997 --
1.
Objective
Development HALT (Highly Accelerated Life Testing) is an intensive process to
uncover design and manufacturing weaknesses in an electronic product. The test
units are subjected to progressively higher stress levels by extreme temperature
transitions, vibration, and combined environments. The intent is to stress the product
well beyond normal operating conditions and determine the operating and destruct
limits of the product.
As each failure occurs, the failure is repaired so testing can continue to higher stress
levels. This allows a sequence of failures to occur up to the extreme stress limits.
The ultimate goal is to determine the root cause of each failure, and then correct each
failure mode. This process can allow the product to reach the fundamental limit of its
technology. This will dramatically reduce failures in the field due to aging or other
stressful operating conditions.
2.
Test Procedure
ProStar and Sun Saver controllers were tested by QualMark Corporation in July 1997.
A Morningstar engineer was present to repair failures and support the testing. Sandia
National Labs also provided support for this testing.
Before beginning the HALT testing, four controllers were subjected to HAST testing.
The HAST process is a relatively new test program, and it creates a high-temperature,
high-pressure and high-humidity environment in a QualMark test chamber. Two
ProStars and two SunSavers were placed in the chamber and powered up without
loads for 200 hours.
For the HALT testing, three ProStar controllers and two SunSaver controllers were
tested. To find the operating and destruct limits of the ProStar and SunSaver designs,
four groups of tests were done. These tests included the following:
• Thermal Step Stress
• Rapid Thermal Transitions
• Vibration Step Stress
• Combined Environment
Each controller on test was operated under load. The PV input was connected to a dc
power supply at 13.5 volts, and the output was loaded between 2 and 10 amps.
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