Post by thread:[EE]: Testing capacitors

OK, guys, thanks for the answers about the electrolytic capacitor. Glad to know I was right. Now, if I am not wearing out my welcome, one more question. A friend sold me a box full of old capacitors, resistors and TTL chips. He said that he bought them from some surplus place many years ago, but never had any need for them since it turned out to be more trouble than it was worth to go through a whole box looking for some particular value -- he would rather just go to Radio Shack and buy a new one. But I figure that I can use them in my lessons. Only problem is, I have heard that a capacitor will go bad after a certain period of time, and cannot think of a good way to test one, to see if it has gone bad or changed value. (A resistor I can check, of course, and a TTL chip I can check). Any good advice for someone on a low budget? Thanks, Bill

You can build a simple 555 timer circuit, and plug the capacitors in as the timing cap. If the value is approximately right, then the cap is probably ok. This gets a little more complicated with higher voltage caps, since they need to be re-formed after long storage without voltage. For electrolytics, you may see a tolerance range of -20% to +50% or even 100%. As caps age, they tend to decrease in value, I've seen them degrade to as little as 1% of their nameplate value.

On 12/23/05, Bill Kuncicky <spam_OUTkuncickyTakeThisOuTgmail.com> wrote: > OK, guys, thanks for the answers about the electrolytic capacitor. Glad > to know I was right. > > Now, if I am not wearing out my welcome, one more question. A friend > sold me a box full of old capacitors, resistors and TTL chips. He said > that he bought them from some surplus place many years ago, but never > had any need for them since it turned out to be more trouble than it was > worth to go through a whole box looking for some particular value -- he > would rather just go to Radio Shack and buy a new one. But I figure > that I can use them in my lessons. Only problem is, I have heard that a > capacitor will go bad after a certain period of time, and cannot think > of a good way to test one, to see if it has gone bad or changed value. > (A resistor I can check, of course, and a TTL chip I can check). Any > good advice for someone on a low budget? > If you still have your borrowed scope, you can make an RC filter and connect it to an oscillator, then check its -3dB bandwidth against the calculated one. If you don't have an oscillator, a computer with a soundcard will do. (Keep the value of R above 1K or so to avoid loading the soundcard's output.) I guess you could just use the AC-volts range on a DMM. But watching on a scope is better the first time, so you can see what's going on. It's the electrolytics that dry out after a while. But electrolytics usually have very loose specs, and are used in "bigger is better" situations. So small capacitance changes will go unnoticed. Regards, Mark markrages@gmail -- You think that it is a secret, but it never has been one. - fortune cookie

Jinx wrote: > > Many multimeters have a capacitance range > Not mine, though. It is a very cheap multimeter. :-( It actually came as a gift, along with some miscellaneous parts that I ordered, from Melvin Jones. Kind of like something which would come in a crackerjack box. But it serves. I have put my in-laws on notice that I sure would like a nice DMM to show up under the Xmas tree on Sunday morning. I have lots of shirts already. Since they would like their daughter to live somewhat better than she is presently living (although she is a good sport about things) they may just take that hint. :-) > > If the caps have been unused for a while (you said many years) I'm > sure some will need reforming. Don't put one in-ciruit with rated > voltage across it (aim away from face if you do ) without checking > first > Most of these capacitors (almost all of them) are ceramics. There are a few electrolytics, but only a few. I assume that the ceramics will not blow up, but only change value. (My wife, who tends to read my email over my shoulder, is now getting a bit worried about things blowing up). And how do you "aim" a capacitor? Seems like it would be about the same as aiming a grenade. > http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm > > and also read the pdf from the previous reply > > electrochem.cwru.edu/ed/encycl/misc/c04-appguide.pdf Yes, I will study both. Thanks, Bill

> > > Many multimeters have a capacitance range > > > Not mine, though. It is a very cheap multimeter. :-( Bill, you don't have to spend a lot to get basic functions. I have 3 meters like the QM-1320 from http://www.jaycar.com.au which are occassionally on special (NZ$24.95 last time). Three meters ? Isn't that just plain greedy ? Well, no. It's very useful being able to measure several things in a circuit (or two) at the same time. eg amperage in, voltage drops, etc. I have two scopes as well (both bought cheaply, but are good quality), a frequency meter and a logic analyser. That pretty much does me, although a digital storage scope would be nice too (makes big eyes, looks sad, rattles tin) > I assume that the ceramics will not blow up, but only change value They might drift a bit. If you stuff excessive voltage up a ceramic it will physically fail though. Most likely just crack, but that depends on just how excessive the voltage was > And how do you "aim" a capacitor? Seems like it would be about > the same as aiming a grenade The very few I've had go bang tended to blow the top off. At speed. Sometimes the bottom will go and a leg will come adrift. IOW, I've never seen the case split and crap go sideways But don't get me wrong Mrs Kuncicky, caps aren't inherently dangerous. They are more chemically complex than most components and you just have to treat 'em right

At 12:41 PM 12/24/2005 +1300, you wrote: >http://www.jaycar.com.au > >Haha, I just saw the 20,00mCd red LED Monthly Special > >Was $3.95, now $3.95, save $0.00 > >How do they survive with price-slashing like that ? ;-)) Buy two for only $7.90!!! >Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" .....speffKILLspam@spam@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com ->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff

Ol electrolytics often tend to suffer from increasing ESR ("Equivalent series resistance")(Google knows). In many cases this is hard or impossible to detect using normal test instruments and an apparently good capacitor with high ESR can cause major problems. Here's a circuit for a "99 cent ESR tester" for use with an oscilloscope. You of course need a 'scope to use it BUT a 'scope should be something you aspire to add to your test equipment list as soon as possible. An oldish deadish baddish (choose any 3) one can always be acquired for very little or free and even one of those can utterly transform your test measurement life. Re cheap meters - in NZ the local large "Mitre 10" hardware chain stores have a multi metyer for $14 (~~$US10). It is extremely good for the money and better than some selling for 2 to 4 times as much elsewhere. it has a 200 uA range, diode tesrer, 10A range, plug in leads (unlike many ultracheap ones) and quite a lot more. Similarly priced and featured meters should be available elsewhere. RM

When I was much younger and much, much more foolish I liked to build multi-neon-bulb relaxation oscillator sequencers using free space wiring (parts just solder-tacked to each other without any board or chassis. I would power these creations with a direct (unisolated) half wave supply from the 120V line. Knowing that the sequencing rate was related to the supply voltage I decided to set up an "up-and-down" full wave supply to get twice the voltage. Not knowing/thinking about the fact that the output capacitor in the supply would see peak (rather than RMS) voltage left that poor device rather overstressed. When it gave out, it did so in rather spectacular manner, blowing out the end cap and then doing a reasonable impersonation of a rocket engine as it dragged the whole circuit across the bench at a pretty good pace. The excitement continued when the input AC line terminals then shorted out, resulting a very impressive spark, followed by darkness. I stood there in the dark, inhaling the stench of the exploded capacitor and the result of the monster mains spark, for at least a minute, wondering if my heart would ever slow down to normal again. Bob Ammerman RAm Systems

Would you mind actually attaching that circuit you you reference below? :-D On 12/24/05, Russell McMahon <apptechKILLspamparadise.net.nz> wrote: {Quote hidden}> > Ol electrolytics often tend to suffer from increasing ESR ("Equivalent > series resistance")(Google knows). In many cases this is hard or > impossible to detect using normal test instruments and an apparently > good capacitor with high ESR can cause major problems. > > Here's a circuit for a "99 cent ESR tester" for use with an > oscilloscope. You of course need a 'scope to use it BUT a 'scope > should be something you aspire to add to your test equipment list as > soon as possible. An oldish deadish baddish (choose any 3) one can > always be acquired for very little or free and even one of those can > utterly transform your test measurement life. > > Re cheap meters - in NZ the local large "Mitre 10" hardware chain > stores have a multi metyer for $14 (~~$US10). It is extremely good for > the money and better than some selling for 2 to 4 times as much > elsewhere. it has a 200 uA range, diode tesrer, 10A range, plug in > leads (unlike many ultracheap ones) and quite a lot more. Similarly > priced and featured meters should be available elsewhere. > > > RM > > -

Jinx, On Sat, 24 Dec 2005 12:41:49 +1300, Jinx wrote: > http://www.jaycar.com.au > > Haha, I just saw the 20,00mCd red LED Monthly Special > > Was $3.95, now $3.95, save $0.00 > > How do they survive with price-slashing like that ? ;-)) Perhaps they have very bad accountants? :-) I've seen a quantity discount where the 10-off price was more than buying singly - I actually wanted 10, so I had to order 5, twice... luckily their order processing system was as bad as their arithmetic, so it didn't combine them into a single order of 10. Merry Christmas! Howard Winter St.Albans, England

On Fri, 23 Dec 2005 18:08:09 -0500, Bill Kuncicky wrote: >... > (My wife, who tends to read my email > over my shoulder, is now getting a bit worried about things blowing > up). And how do you "aim" a capacitor? Seems like it would be about > the same as aiming a grenade. Tantalums, maybe, but electrolytics tend to blow through the "top" - large ones have proper vents sealed with rubber, small ones have an X-groove cut in the top so they open there, like a ringpull can. If you're really worried, Mrs. Kuncicky, there's always the metal waste bin trick - make him place one on the desk and put the target device in it, and stand back! Anyway, gardening and DIY are much more dangerous activities than electronics, so think yourself lucky :-) I had a worrying incident about a week ago - in my living room, where a lot of my computer equipment and some electronics is located, there was a loud "crack" sound, that could easily have been a small capacitor exploding, but I have no idea where it came from, and everything in the room is still working! I wonder what it was? :-# Merry Christmas! Howard Winter St.Albans, England

On 25 Dec 2005 at 13:57, Howard Winter wrote: > I had a worrying incident about a week ago - in my living room, > where a lot of my computer equipment and some electronics is > located, there was a loud "crack" sound, that could easily have > been a small capacitor exploding, but I have no idea where it came > from, and everything in the room is still working! I wonder what > it was? :-# I had a very similar incident last month. I was working late, two in the morning when a loud "crack" sound almost pulled me out of my chair! No smoke, no strange smell, no stop working equipment, nothing. After inspection, every piece of hardware was ok. It took me one week to discover two 25A blown fuses on one of my UPS. Of course, two shorted MOSFETs too... They seems to be fired at the same time. Mark Jordan

Howard Winter wrote: > I had a worrying incident about a week ago - in my living room, where a lot of my computer equipment and some > electronics is located, there was a loud "crack" sound, that could easily have been a small capacitor > exploding, but I have no idea where it came from, and everything in the room is still working! I wonder what > it was? :-# A Christmas cracker of course! Regards, Rob -- Rob Hamerling, Vianen, NL phone +31-347-322822 homepage: http://www.robh.nl/

Hi Howard, I had a similar incident about a year ago. I was asleep and woke up to a loud crack followed by a sizzle. I thought sure that a wall-wart or something similar had bit the dust and was going to be smoking but when I jumped out of bed and turned on the light, there was no smoke or smell or any other sign of what had made the noise. Initially, I hypothesized that it was probably the sound of a power surge heard through my PC speakers (which were on and powered by a wall-wart), but months later I found my answer: I opened up a hand-held shortwave receiver to discover that one of its AA cells had opened up and was leaking. I was surprised that it was so loud! Merry Christmas to all! Sean -- Copied Text -- I had a worrying incident about a week ago - in my living room, where a lot of my computer equipment and some electronics is located, there was a loud "crack" sound, that could easily have been a small capacitor exploding, but I have no idea where it came from, and everything in the room is still working! I wonder what it was? :-#

There's a guy where I work who keeps a stash of firecrackers at his workbench. One of his favorite things to do is to wait until someone is bent over working on some delicate thing involving the possibility of a large short-circuit (like something with large lead-acid batts) and then sneak up behind them and drop one of the crackers. It is done at least once to every new employee :-) Sean -- copied text -- Howard Winter wrote: > I had a worrying incident about a week ago - in my living room, where a lot of my computer equipment and some > electronics is located, there was a loud "crack" sound, that could easily have been a small capacitor > exploding, but I have no idea where it came from, and everything in the room is still working! I wonder what > it was? :-# A Christmas cracker of course! Regards, Rob

----- Original Message ----- From: "Howard Winter" <.....HDRWKILLspam.....h2org.demon.co.uk> To: "Microcontroller discussion list - Public." <EraseMEpiclistspam_OUTTakeThisOuTmit.edu> Sent: Sunday, December 25, 2005 2:57 PM Subject: Re: [EE]: Testing capacitors | On Fri, 23 Dec 2005 18:08:09 -0500, Bill Kuncicky wrote: | I had a worrying incident about a week ago - in my living room, where a lot of my computer equipment and some | electronics is located, there was a loud "crack" sound, that could easily have been a small capacitor | exploding, but I have no idea where it came from, and everything in the room is still working! I wonder what | it was? :-# Have a look at your motherboard... regards Enrico