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We all know that capacitors are necessary to the proper functioning of any HVAC system. Yet, some in the HVAC industry have elected to make capacitor selection decisions based primarily on price. After all, they only cost a couple dollars, so if you can get them for a few cents less, then that amounts to some savings you can bring to your bottom line, right?
Here’s what you need to know: All capacitors are not created equal! Using low-quality capacitors can result in significant damage to your customers’ systems, and can also cost you hundreds of dollars per year in service callbacks - not to mention damage to customer relationships, wear and tear to on-call technicians, and reduced profitability.
Let’s take a look at what capacitors do and how they’re made, so you can better understand the importance of using high-quality capacitors.
THE ROLES OF A CAPACITORCapacitors are a very important component of modern HVAC systems, as they are used in ac motors to provide starting torque and to improve the motor’s running efficiency. For both functions, the capacitors are connected in series with the start and main windings of the motor.
Depending on the function of the capacitor within the ac motor circuit, it can be called a start capacitor or a run capacitor. The start capacitor provides the motor with the torque needed to move the motor from standstill, and then automatically disconnects itself from the circuit. The run capacitor helps to maintain the rotational field under optimum conditions, helping the motor to run more efficiently at a higher power factor; it remains connected at all times. This is the reason it is called a run capacitor.
These capacitors generally are found in single-phase ac motors. This is because a single-phase ac source rises and falls from zero very rapidly, and the capacitor helps by producing a current-to-voltage lag on the windings. Since this current builds up more slowly, it gives time to the motor armature to react to the rotational field.
Capacitors are sort of like batteries - both store electrical energy, but they work differently. A battery uses chemicals to produce electrical energy and release it very slowly through a circuit, sometimes taking several years to disperse all the energy (in the case of a watch battery, for instance). A capacitor, which stores energy in the form of an electrostatic field, generally releases its energy much more rapidly - often in seconds or less. This can make a large, charged capacitor extremely dangerous if used or handled improperly.
THE IMPORTANCE OF CAPACITOR QUALITYThe Electronic Industries Association (EIA) issues quality standards for capacitors. EIA-456 provides standards for metalized film dielectric capacitors intended for use with, among other things, ac motors. The reliability test outlined in EIA-456 is a Highly Accelerated Life Test (HALT) in which a set of capacitors is subjected to 125 percent of their rated voltage and 10o°C above their rated temperature for 2,000 hours. For example, a capacitor that is rated at 5uf/440 vac, with an operating temperature of 70°C, is tested at 550 vac and 80°C for 2,000 hours. This HALT test simulates 60,000 hours of field life. If you estimate 5,000 hours of capacitor operational time per year, a 60,000-hour capacitor could last approximately 12 years in the field. EIA-456 calls for a first-year failure rate of no more than 0.50 percent.
High-end HVAC manufacturers/OEMs adhere to EIA standards, and thus require capacitors that meet EIA-456. Unfortunately, some capacitor manufacturers, while claiming that their products adhere to EIA-456, use poor-quality materials and/or flawed manufacturing processes.
If one compares any two capacitors in the industry, the initial readings for both capacitors will more than likely reflect the ratings specified on the capacitor label. Based upon the initial readings, it would seem that both are good capacitors. However, it’s in the rigorous HALT testing that capacitor quality can be determined more definitively.
In February 2010, capacitors from one domestic supplier, one offshore supplier, and Genteq were placed side by side and tested against EIA-456. In tests that ran upwards of 2,000 run-hours, the failure rates of lower-quality capacitors was 7-12 times greater than that of higher-quality capacitors - literally, only a savings of a few pennies for a much reduced run time.
When capacitors do not meet the performance ratings specified on their labels, and when used with motors in HVAC systems, they can severely damage the motors by:
• reducing the speed of the motor, which:
– increases the motor’s temperature;
– causes bearing wear and insulation breakdown; and
- increases the noise;
• lowering the motor’s efficiency, which causes additional energy consumption and costs for the customer;
• creating improper operation of the entire equipment, which:
– results in improper cycling;
– increases system noise; and
– provides unwanted stress on other system components.
Needless to say, a motor is expensive to replace.
A PENNY SAVED IS NOT A PENNY EARNEDBargain brands may have the same labeling and claim to meet the same standards as more expensive capacitors. However, they may contain poor-quality materials and may be manufactured using processes that yield lower quality and reliability. This combination of poor quality materials and inferior manufacturing processes may significantly reduce the life of a capacitor. In short, cheap capacitors may fail faster.
There also is a safety perspective to consider. In the last few years, customers have asked Genteq to perform failure analysis of bargain capacitors that have exhibited safety-related conditions such as wiring overheating and melting, capacitor case bursting, and melting of the terminal assemblies of the capacitor, all of which may be attributable, depending on the circumstances, to the use of lower-quality materials.
In approximately the last three to four years, many contractors and OEMs have made capacitor selection decisions based primarily on price. Now, however, there is a growing realization that capacitor quality is very important and that lower-quality capacitors may damage both HVAC systems and customer relationships.
David Allen, owner of Allen’s Air Conditioning, Inc., Tuscumbia, Ala., began looking at his company’s processes and procedures to determine ways he could keep the company profitable when the business slowed last year. In reviewing the company’s callback logs, he was surprised to see the number of return visits his technicians were making associated with capacitor warranty claims. He did his own research, and discovered that he was losing hundreds of dollars in callbacks to replace faulty capacitors. Through intensive research, David has decided that installing high quality components for his customers provides the best overall return for him and his customers.
Publication date: 10/18/2010