Intro: What Is a Bad Capacitor?
A troubling trend in our technological society today is when good capacitors (caps) go bad. Perhaps this is a phenomena that you have heard of somewhere in passing, but do not know as much about as you'd like to?
In which case you have come to the right place! Because in this article I will endeavour to discuss when good caps go bad, and how you might spot the bad caps for yourself too.
Step 1: What Are Bad Caps, and Why Should I Care?
A bad capacitor is an electronics component that over the course of its life has turned to the dark side. It is evil now and is no longer serving its intended purpose in life. It is a hazard to all other electronic components that are relying on it functioning properly now too. In short, it is broken. We will soon learn it is a short. Here is one that my tester thinks is a diode. Good caps will never read as diodes.
Step 2: Let's Try to Read That Cap Again, Shall We?
In this image I have flipped the cap around in the test clips and read it again. Now it is coming up as a capacitor, and we can see readings related to capacitance too. Let us take a moment to decrypt the readings the meter is displaying now.
Reading across we see; 1-||-3 Vloss=34%
On the next line is shown; 943μF ESR=2.2Ω
1-||-3 are the test points the meter has found a component on
Vloss is the amount of voltage the meter has measured that the capacitor has lost.
943μF is the capacitance the meter has measured of the capacitor. 943 micro Farads.
ESR=2.2Ω is the measured Equivalent Series Resistance (ESR) of the device under test.
Well, you may ask, Why is any of this so bad? To begin with it is a 2,200μF capacitor so 943μF is not even close to its marked capacity. But that is not the worst of it. A voltage loss of 34% is terrible! This part is leaking electricity like a sieve. Which is not what capacitors are supposed to do at all. Quite the opposite in fact. Capacitors are supposed to be able to store electricity. They are supposed to have the capacity to store an electrical charge. Hence their name. The ESR measurement is pretty bad too, but not nearly as out of spec as the Vloss.
There is a lot of talk about ESR, so if you are interested in that I suggest you browse the web for additional information on that topic.
Step 3: How Can I Spot a Bad Cap?
You may not have one of these fancy meters at your disposal. But the good news is bad caps often appear bad visually! So you can just see that they're bad. OK so what are the telltale signs of a bad cap? Well, bad caps typically have a domed, or swollen top. Sometimes really bad caps can leak their electrolyte out of themselves too. Then you may see this brown crust around the capacitor, or perhaps on it. It often looks somewhat like a dried coffee stain.
In this image I have tried to photograph the slight bulge on the top of this bad capacitor. It is easier to see in person than in my picture. A good cap will have a very flat top. Any bulge is a bad sign.
You can also use some deductive reasoning to find the more likely places in circuits where caps may go bad. Capacitors that are placed under heavy stress are more likely to go bad than caps worked less hard. So power supply filter caps go bad often. The power supply is often where the power comes into equipment. You may see buck boost coils there, a diode bridge, heavy switching MOSFETs, and things like that. All of those items are a bad influence on impressionable caps, and can make them go bad.
Step 4: Why Should I Care About Bad Caps?
A fair question. Realize that a few inexpensive capacitors can be the difference between your expensive electronics working, or not. I had several caps go bad in my flat screen TV, and when they did it would no longer come on! $4 of parts replaced brought a $1,400 TV back to life. I bought my TV when they were more expensive than they are today.
Yes, I was extremely ticked when my TV seemed to die at such an early age too. But when I resurrected it I was happy then!
So you too could suffer from early infant mortality of your expensive electronic devices, just like I did. Bad caps cause a lot of electronics to fail long before they should today. This is a huge issue. Any electronics that you have that plugs into a wall outlet has filter capacitors in it. When they go so does your whole piece of equipment then too.
If you can spot bad caps for yourself you can fix this equipment for yourself too. Saving you hundreds, if not thousands of dollars. Over what repair, or replacement costs may add up to.
Step 5: Enough About Bad Caps Are There Any Good Caps?
Yes there are! Not all caps are created equally. The Japanese make a superior capacitor than what is available from some other parts of the world. When you buy replacement caps it pays you to spend the few pennies extra and get these better capacitors for yourself too.
In my capacitor testing I have found that the absolute best capacitors I have run across are manufactured by Rubycon. Rubys are some fine capacitors. Although Nichicons are no slouches either. These are called Jap caps. No slur intended. Because they are the very best caps you will find today. They generally do not cost much more than the inferior ones do either.
But if you are a manufacturer buying tens of thousands lots of capacitors then pennies add up I suppose. Still what is going on is a grave injustice to all of humanity. Expensive equipment dying prematurely over such an insignificant cost difference is a travesty.
Step 6: For Folks Curious About My Meter
Someone is bound to ask, so I might as well say something about the meter I used in this post. I am using something called an "AVR TransistorTester by Karl-Heinz Kübbeler". There are a number of models available from the Far East. The first one I purchased was called an LCR-3 (now going under the name of Mega328 Transistor Tester). Sometimes it is referred to as the "graphical meter". Because it has a larger screen that it draws the parts out on graphically. Unfortunately the designers of it took some license with how they made the circuitry. This makes the meter less accurate as a result. (I have thought about trying to rectify that but I am not sure if I can due to a lack of firmware availability)
I learned all of this later as I researched the topic more myself. So then I bought a kit that I assembled my "AVR TransistorTester by Karl-Heinz Kübbeler" clone from myself. I might as well supply a link to that here now too, because people are likely going to ask for that as well.
I am in no way endorsing that company, I am merely providing information people may want. But honestly I think the whole deal is pretty sweet. I am extremely satisfied with my meter today too. Here is a link to the original open source project all of these meters were derived from
Which is in German, but you can translate it. Anyhow, the meters are pretty neat and anyone with even a passing interest in electronics would be wise to get one for themselves. They are an awesome deal for what they are. They will help you pinpoint bad caps even better too. Because not all bad caps look bad.