Why Capacitors go bad

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halifaxhops

halifaxhops

It's going to get stupid around here!
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As you can see capacitors are just insulated very thin aluminum wrapped in a roll. I have found that when they short the plastic between the wraps kind of non insulates and throws the capacitance off. When they open usually the spring washer looses tension so it will no longer makes contact. Hope it helps.
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<< weird when I first saw this post there was no picture of described condensor so I assumed we were talking electronics.sorry to muddy the waters!>>

capacitors dry out. The dielectric dope in them just dries out then they short internally and blow their tops...literally. They are like foil and wax paper wrapped in a roll, eventually the foil shorts to the other foil layer. See the swollen tops? Find a non-op flat screen TV and I can almost guarantee there are a few of these on the power board, .50 a piece.
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^^This is true of what is called electrolytic caps but automotive ignition caps are "paper." Or more modern ones, probably plastic dielectric. No "electrolytic" and therefore they should not "dry out."

They more likely go bad because of moisture intrusion, or heat damage
 
In the context of the automotive lexicon, what happens in other devices doesn't matter. The most common fault of an automotive condenser not doing it's job is not controlling current at the points, causing contact material transfer.
 
pishta said:
? Find a non-op flat screen TV and I can almost guarantee there are a few of these on the power board
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Funny story about buldging caps...

I read some time ago that a guy working for a capasitor manufacturer decided to steal the formula for how the caps were built. He then went to work for another company and they got the formula and produced millions of caps. Shortly there after buldging caps became a thing. Turns out first company kept a part of the formula secret so everyone who uses the stolen formula is in for trouble. Thats the way i remember it. Wikipedia has a slightly diferent accounting
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Vibration and heat cycling, plus in rush currents degrade wound architecture capacitors. Even paper capacitors have some sort of dielectric that could leak out.
Most electrolytic capacitors become leaky current wise, especially at higher voltages.
 
Lots of different types of capacitors & lots of different failure modes depending on type. Google “Partial Discharge Testing” for some fun reading if you are an electro-nerd.
 
Dana67Dart said:
Funny story about buldging caps...

I read some time ago that a guy working for a capasitor manufacturer decided to steal the formula for how the caps were built. He then went to work for another company and they got the formula and produced millions of caps. Shortly there after buldging caps became a thing. Turns out first company kept a part of the formula secret so everyone who uses the stolen formula is in for trouble. Thats the way i remember it. Wikipedia has a slightly diferent accounting
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**** China.
 
I heard same story, Rubicon were good so the guy stole their successful formula minus 1 stabilizing agent. Good ones: Nichicon, Panasonic, Sprague and my favorite ELNA (silks) for audio path.
 
Just the last couple days I've sawed the tops off bad Johnson/ Evinrude "condensers" and "redneck" replaced them with poly film caps. "We'll see" how they hold up
 
Way back in my teens we had a window air conditioner in our house. It stopped working & I figured out that the run capacitor was bad. It was a big honking electrolytic. It was a hot day, so I went rummaging through electronic parts we had in the basement. We had a lot. I came up with a two section paper wound capacitor. Didn’t understand the difference between AC & DC capacitors back then. It was the same value & voltage, but alot smaller, but I thought “what the heck, let’s give it a try.”

I hooked up to the ac, hanging out the front. It started right up. I was standing in front of the ac cooling myself off, very proud of myself. About 30 seconds later it exploded violently, sending paper flying everywhere. Scared the crap out of me. I was covered with paper shreds. That’s when I learned about different types of capacitors….
 
Actually AC ones are not electrolytic. They are normally oil filled although there are some specialized electrolytic AC caps. "None polarized" is what you want for AC. If there is a polarity designator, you do not want that on AC
 
I bought some off the internet and they had no marking on them. But I just looked at some more I bought and they have the - on them. So I'm good on that question but have another one. What's the best way to test them? Thanks.
 
Photos? Part no's? If they aren't marked they MAY be non-polarized.
 
Dana67Dart said:
Industrial espionage happens everywhere even in the US.
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Keep telling yourself that when the power goes out or the bombs start falling or the economy starts dumping, and China is behind it.
 
The problem with "modern tests" is that they do NOT CHECK for high voltage leakage which is a huge problem with old condensers/ capacitors and sometimes with low quality "modern" replacements. The only "simple" (but not cheap) way I know of is to obtain an "old school" cap checker which HAS a LEAKAGE test. This type of test actually applies high voltage to the cap and checks leakage under those conditions. I toss most outboard caps not because of the value (capacitance) --which is MEANINGLESS if they have leakage---but rather because they are in fact "leaky"

I have a pair of old Eico testers which I'm hoping to "refurbish" as well as an older model Heathkit. The Heathkits especially, and especially the newer models--have gone absolutely nutcase on egag for price

My Heathkit is an older model like this photo I "stole" of the internet

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The Eico's are very similar in construction and operation to the Heath

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67Dart273 said:
The problem with "modern tests" is that they do NOT CHECK for high voltage leakage which is a huge problem with old condensers/ capacitors and sometimes with low quality "modern" replacements. The only "simple" (but not cheap) way I know of is to obtain an "old school" cap checker which HAS a LEAKAGE test. This type of test actually applies high voltage to the cap and checks leakage under those conditions. I toss most outboard caps not because of the value (capacitance) --which is MEANINGLESS if they have leakage---but rather because they are in fact "leaky"

I have a pair of old Eico testers which I'm hoping to "refurbish" as well as an older model Heathkit. The Heathkits especially, and especially the newer models--have gone absolutely nutcase on egag for price

My Heathkit is an older model like this photo I "stole" of the internet

View attachment 1715812620

The Eico's are very similar in construction and operation to the Heath

View attachment 1715812621
Click to expand...

I have a fluke 87 which has a capacitor test on it but I haven't figured it out.
 
I had a motherboard capacitor fail in my computer tower a few years back. It sounded like a shotgun blast going off and a puff of white smoke came out from the back of the case.
 
LO23M8B said:
I have a fluke 87 which has a capacitor test on it but I haven't figured it out.
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To my knowledge none of the modern solid state testers have a leakage test. I have a couple of "china" testers which can VERY accurately give you the capacitance value down to very small values, and therefore quite useful. But for automotive caps leakage testers are far and few

The "Bruno" tester I use has one, as do the old "Merc-o-Tronic" testers of which I have two "non working" ones

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