Are Your Capacitors Stale?

A capacitor is a pretty simple device, basically a couple of rolled up sheets of aluminum foil or metalized film with paper or plastic between them. Any practicing service tech will tell you that service calls involving dead capacitors  are common. Technicians that have been around for a few decades will also tell you that capacitors die a lot more now than they did twenty years ago. This is because the newer capacitors use a different electrolyte. The electrolyte in the “good old style” capacitors was polychlorinated biphenyl, PCB. PCB causes cancer, so it is no longer used. The newer capacitors are smaller and less expensive than the older PCB capacitors, but they are not as robust. The two most common causes of capacitor death are heat and over voltage. However, there is another less known cause: old age. Many capacitors have a shelf life. I have seen shelf lives listed as little as one year. The oxides on the metalized film break down when the capacitor is not in use, weakening the capacitor. They tend to self-heal during use. That is why a capacitor that cannot sit on the shelf for longer than a couple of years can last for ten years in use. 

Always check the capacitance of any replacement capacitor with a capacitor tester or the capacitance scale on a digital multi-meter before using the capacitor. It may have already died of old age before you install it! Although a capacitor is a simple device, it is an extremely important part on most air conditioning systems. A bad capacitor can kill a system’s compressor. To protect your reputation and your customer’s equipment, only use capacitors that can pass the EIA-456 Highly Accelerated Life Test. The HALT test subjects a set of capacitors to 125 percent of their rated voltage and 10˚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. Two links for more detailed information on capacitors are  

Aerovox

Genteq

Determining which capacitors to stock on your truck is another problem. There are so many sizes of dual capacitors that it is nearly impossible to have all the necessary sizes. American Radionic, AMRAD, has a solution – a multiple capacitor with enough sizes to cover nearly any application. Better yet, they will send instructors sample capacitors to use in your lab. These are great for demonstrating the effect of connecting capacitors in series and parallel. Their web site is AMRAD

Fundamentals of HVAC/R has coverage of capacitors and their effect in circuits in  Unit 29 Electrical Power and Circuits, Unit 30 Electric Motors, Unit 33 Control Circuits, and Unit 83 Troubleshooting Refrigeration Systems. Unit 30 of MyHVACLAB has an interactive exercise on determining capacitance and a video on testing capacitors. Unit 83 has an interactive exercise on testing capacitors. 

Simplify Parallel Calculations

The total resistance in a parallel circuit is difficult to calculate because it cannot simply be added as in a series circuit. However, the total current flow in a parallel circuit is easy to calculate. It is simply the sum of the currents for all the individual loads. The famous parallel formula for resistances in parallel uses this concept.  Dividing the resistance of each load into 1 calculates the current draw for each load at 1 volt. Adding these fractions gives the total current draw of the entire circuit at 1 volt. Since resistance can be calculated by dividing current into voltage, dividing the total circuit current at 1 volt into 1 volt gives the total resistance. I confess that I have used and taught this formula for many years without knowing why it works. Once I understood the reason behind the formula, it seemed far more logical and less imposing.  Did you know that this works for any voltage you choose? We can use this to create a simpler parallel calculation. 


I find that many of today’s digital students struggle with the fractions, common denominators, and all the trappings that go with fractions. One solution is to convert the fractions to decimals. But the decimal numbers you get when dividing whole numbers into one are always several decimal places to the right of 0, causing another own sort of confusion. My suggestion is to choose a voltage at least equal to the highest resistance; preferably, twice the highest resistance. That way, all the answers will have at least one whole number. This not only makes the answers easier for the students to deal with, it makes the decimals to the right of 0 less significant, so lopping off a few won’t have as big an impact on the final answer.


 For example, with resistances of 15, 20, and 30 ohms choose 60 volts. Instead of trying to add 1/15  + 1/20 + 1/30  or their decimal equivalents, you are adding 60/30 + 60/20 + 60/15. Most people can add 2 + 3 + 4. Then, divide this total current, 9 amps, into the voltage we used, 60 volts, to get 6.6 ohms total resistance. OK, so I stacked the deck a bit. Another teacher’s trick – if you get to choose the questions, why not choose questions that make your life easier. After your students are adept at these “easy” problems, have them measure the resistance of some actual devices and do the calculations. This is where choosing to make the calculations easier really pays off. Anybody can make simple things difficult – the trick to teaching is to make difficult things simple. 

A Story of Personal Courage

Have you ever wondered how you would react in the face of personal tragedy? I have. When I read about tragedies in the paper or hear about them on the news, I find myself wondering “What if..?”  Fortunately, I have never found out. Soon the business of the day drowns out my musings, and I return to the business at hand. However, the closer to home the tragedy is, the more difficult it is to dismiss. 

Just before the start of this past summer quarter, my friend Bruce Arnold lost his 18 year old son Tyler in a motorcycle accident. Tyler was preparing to study air conditioning at Athens Tech and study with his dad. Bruce works in the field and takes classes in the evening. Bruce was so excited about his son going to school to study the trade he practices.

Only a parent can truly understand the feelings parents have for their children. You really cannot fathom how much you have been loved or how much of themselves your parents invest in you until you are a parent. When you are a teenager your parents unending questions about where you are going, what you are doing, and who you are going to be with are an incredible annoyance. Their interest in every detail of your mundane school day is perplexing. The reason is simple: parents have more interest in your safety and success than you do.  

Nobody celebrates your victories and accomplishments more than your parents. I have been teaching longer than most of my students have been alive, and I know that my mother is still my biggest booster. I have a 20 year old daughter and a 15 year old son, and I know I get far more excited about their accomplishments than my own. That is why I know there can be no greater pain than losing a child. Truthfully, I hope I never learn what it feels like.  

Bruce returned to school and completed his summer coursework. He explained that he felt compelled to come back to school because Tyler was so proud of his dad for going to college and so happy to be going himself. Many of Bruce’s friends counseled him to “put it behind him” and “go on with his life.” He couldn’t. Instead, he started a non-profit scholarship foundation in his son’s memory. He hired a lawyer to create the non-profit foundation, established a bank account for the foundation, started a web page to advertise his foundation, and is out personally raising money for the foundation. His goal is to raise money so other young men and women can realize their future, fulfilling their parent’s dreams. If you would like to learn more about Tyler or the scholarship foundation established in his name, go to http://www.thetylerbrucearnoldscholarshipfund.com/index.html   

Where Do YOU Belong?

You can tell a lot about someone by looking at who they hang with. The people and organizations you spend time with help form who you are and advertise to the world what you really think is important. I believe finding where you fit in is important. You may have heard people talk about networking: not a connection between machines, but a connection between people. Spending time with people that have similar interests and developing your common interests. Some of the benefits are obvious, like making valuable connections to folks that can help you. However, I believe part of the power of networking is that you find a group of people whom you enjoy being with. The truth is that most people are more inclined to put effort towards helping someone they know and like. Being with other people who share your interests makes all your activities more meaningful. Disneyworld is no fun by yourself; a big part of the magic in the magic kingdom comes from having fun with your family.

Joining an industry organization gives you immediate access to a group of people with similar interests. There are many groups organized around different aspects of the HVAC/R industry. There is a group for HVAC/R Technicians – RSES; a group for trades students – Skills USA; a group for Air Conditioning Contractors – ACCA; a group for HVAC/R Distributors – HARDI. If you teach HVAC/R you have some common interests with all of these groups. Every one supports HVAC/R education with resources and material. Trying to participate in all of these would probably not be possible for most of us, but joining and participating in one is doable for even the busiest folks. I suggest exploring what all of these groups have to offer, finding where you belong, and taking the plunge.

Each organization has an annual meeting where you can network with other HVAC/R folks, participate in training, see the latest in HVAC/R technology, and just have fun. If you have never been to a national HVAC/R convention, an opportunity coming up would be the National RSES Conference in Tucson, Arizona November 9 – 13.

Here is a partial list of HVAC/R organizations with links to their web sites where you can learn more about each one.

ACCA – Air Conditioning Contractors of America

ACTE – Association for Career and Technical Education

AHRI – Air Conditioning, Heating, and Refrigeration Institute

HARDI – Heating, Air Conditioning, and Refrigeration Distributors International

HRAI – Heating, Refrigeration, and Air Conditioning Institute

HVAC Excellence - Heating, Venitlating, and Air Conditioning Excellence

NAOHSM – National Association of Oil Heating Service Managers

PHCC – Plumbing, Heating and Cooling Council

RSES – Refrigeration Service Engineer’s Society

Skills USA