Tightly- controlled design and manufacturing processes at Aerovox Corp. reduce risk of film capacitor failure
By Ed Lobo, SVP/CTO, Aerovox Corp., New Bedford, Massachusetts
Electrical capacitor failures due to excessive temperature, voltage, high duty cycle, and wear are well recognized and understood. However, such failures can be accelerated by defective manufacture or design, improper installation, shipping damage or environmental influence. Capacitor failures (during use) of some consequence have occurred, resulting in significant expense and, at times, liability for U.S. device manufacturers.
To explore the consequences of premature failure in the field, this article provides examples of capacitor failures in four application areas: HID lighting, power factor correction, after-market motor run, and defibrillators. It then [assigns, suggests] possible causes [due to design or manufacturing shortcomings]. Last we describe practices in place at Aerovox Corp. that virtually eliminate unexpected failures, and ensure continual performance and long life in use.
Low cost capacitor sources may increase failure rate
Rigorous US manufacturing processes deliver superior quality both here and in US-owned plants abroad by adhering to US manufacturing protocols. Aerovox, for example, has established standards that ensure any product is produced at the same quality levels, whether it’s made in the U.S., China or India.
While lower cost sourcing can be attractive to reduce total cost of manufacturing, there can be an increased risk of failure due to product designs that are not well validated, use of materials that are not always compliant, and processes that are neither robust nor consistent. Additionally, “offshore” can bring with it other issues, such as logistics, shipping damage, communications, exchange rate, etc.
HID lighting capacitor failures result in costly field replacements
Manufacturers of lighting systems and ballasts typically provide a warranty for field replacements. If a capacitor fails, manufacturers bear the cost of expensive third party repairs and replacements.
Low cost capacitors available from some sources, especially outside the US, typically fail within 12-24 months when 90+% should survive 8-10 years.
At Aerovox, capacitor design enhancements and process developments, including certain electrical characteristics of the metallized dielectric system, have been combined with advancements to the very critical encapsulation process. These have significantly improved the long term performance and life in these high temperature capacitor applications. These enhancements were achieved by utilizing comprehensive DOE’s and validated by long term accelerated life testing at EIA RS-456-A conditions, as well as SALT (Super Accelerated Life Testing) testing, which was developed by Aerovox to quickly and effectively eliminate variables. Accelerated life testing by a major customer has confirmed the enhanced Aerovox design outperformed their previous supplier
Motor run capacitors must survive hot, humid environments
As the number of days with abnormally hot weather increase during the summer months, climate-control systems are exposed to greater than normal use. This increased usage places more stress on the capacitors within these systems, which are often the source of system failures.
Many HVCR and HVAC OEM manufacturers had shifted to Asian motor run capacitor suppliers to gain price advantage. In the aftermarket, however, contractors have noted a significant problem with Asian products, especially in hot and humid environments such as the U.S. south and southwest.
Contractors making maintenance calls under warranty incur significant expense if capacitors fail prematurely or repeatedly, requiring multiple service calls. They are increasingly replacing Asian made capacitors with U.S. made products, and some are exclusively using Aerovox motor run capacitors to reduce their out-of-pocket warranty expenses.
Each Aerovox motor run capacitor is filled with patented, environmentally-friendly Epoxidized Soybean Oil. This patented formula traps and suppresses unwanted contaminants to prevent premature failures and ensures high reliability and capacitor performance. A proprietary impregnation process with vacuum and heat cycles ensures complete removal of moisture, resulting in superior capacitance stability and long term reliability. Each Aerovox capacitor undergoes 100% electrical testing prior to shipping.
Power factor correction capacitors affected by workmanship
Early life failures and qualification test failures on low voltage PFC capacitors made in Europe have been experienced by a number of U.S. manufacturers. Investigations into the reasons for these failures suggest they were related to poor end spray connections to the capacitor windings, poor lead connections to the capacitor windings, or a workmanship defect.
Aerovox has avoided these issues by using high quality materials and meaningful process controls, backed by extensive process validation testing (pulse testing at high peak currents). The quality of the Aerovox products, whether made in New Bedford or at our factory in China is further supported by an extensive accelerated life test program comparing the performance and life characteristics of Aerovox PFC capacitors compared several other major suppliers. Recent testing to IEC 60831-1 & 2 standards comparing Aerovox Euro style capacitors and a like rating from others revealed the other brands failed after 750 hours at 115% rated voltage compared to Aerovox capacitors continuing to run after 1500 hours at 125% rated voltage.
PFC Life Testing Results
|SUPPLIER||RATING||PART #||LIFE TEST CONDITIONS||LIFE TEST RESULTS||RESULTS AFTER PULSE TEST||RETURNED TO LIFE TEST|
|Supplier E||30 KVAR525 VAC
|_||600 VAC50оC||750 hrs.4 of 4 OK prior to pulsing||4 of 4 OK @ 750 hrs. with pulsing||3 failed before 1500 hours; 1 OK @ 1500 hrs.|
|Aerovox||40 KVAR480 VAC||EPFC040F33N||600 VAC50оC||750 hrs.All passed per EIC 60381-2||Testing continues||Testing continues|
|Aerovox||25 KVAR480 VAC||EPFC025F33N||600 VAC50оC||750 hrs.All passed||4 of 4 OK @ 750 hrs. with pulsing||4 of 4 OK at 1500 hrs. of testing|
A major recall of defibrillators made by a prominent medical device manufacturer and an associated FDA warning last year resulted from failures in components due to moisture ingress in high humidity environments. The company was cited for failure to perform adequate design validation, specifically failure to conduct the validation testing protocol at high humidity as stated in the operating specifications.
Aerovox quality assurance and life testing protocols are designed and extensively tested to encompass the extremes of possible operating environments and conditions. High voltage failures of this nature are are averted by testing at the worst case operating conditions.
Aerovox’s new-generation dry cap defibrillator capacitor is recognized as the most reliable defibrillator capacitor design in the world. A recent study performed on over 180 randomly selected defibrillator capacitor models showed a survival (Fitted Weibull Survival Plot) of 99.93% after 10,000 rated joule shots and 100.00 % survival after 5000 rated joule shots. That means zero defects during the life of the capacitor. Aerovox monitors outgoing quality and continuously selects samples from its production operations to track quality and reliability. Aerovox also performs extensive qualification testing on new capacitor models. We not only test at maximum operating voltages, but at the worst case environmental condition as well. This is to insure that you the customer will not have a capacitor failure in the device due to high humidity or high temperature of operation.
Expert design and rigorous, standardized manufacturing processes make Aerovox capacitors amongst the most consistently reliable in the world. Life testing conducted by Aerovox provides proof of performance and long life in use.
Quality and reliability issues have occurred in Asian and European produced products that have caused significant problems in a number of applications. Superior U.S. manufacturing standards, combined with expert engineering design, are making U.S. made capacitors, such as those made by Aerovox Corp., more attractive on a cost-performance basis.
Author’s Note: For further information on the global market for paper and plastic film capacitors go here-