Capacitor Codes

Uncle Krunkus

I know I should know this, but, I just found myself double guessing the nature of capacitor codes! Shocked

According to my intuition, and a couple of descriptions on the net, a three digit code is the same as a resistor code, ie; 1st digit, 2nd digit, Multiplier, as picofarads.

But, there is never an example of a code which ends in 0!
Now if a code is 220, that means it must be 22pF. But wouldn't it be clearer to just put 22 on it? Without the 3rd digit we know it's not EIA and must therefore be literally 22pF.
However, if that were the case, then 220 would have someone believe that it may be 220pF.
Oh God! You can see where I've confused myself can't you? I certainly can! Embarassed

Oh, how shameful! Uncle Krunkus, great stripboarder from another planet, who has recently branched into beautiful PCB designs, doesn't know how to read capacitor values!!!! Surprised

I have a feeling this means that some of the styrene caps I put in the ASM-2 are actually 10* smaller than they are supposed to be!! No wonder it was so hard to get it adjusted exactly right!!!

Let this be a lesson to all you who have recently started playing with electronics, and are feeling a bit thick 'cos it's taking a while to sink in. Even people who have been doing this stuff for years are still learning the basics!

Broadwave · Posted: Thu Aug 02, 2007 3:50 am Post subject:

I agree, as someone who has just got into electronics, I find Cap codes VERY confusing. I have a conversion chart that I keep referring to (so many pf's = so many uf's = so many n's etc.). One major mistake I made recently was ordering a stack load of 0.01uf caps for de-coupling, but I ended up with 0.01n (10pf)... no so useful Mad

Very frustrating - especially when you've waited 3 weeks for an order to arrive!

Andy.

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

I have quite a lot of polystyrene in stock but don't have many that use the 3-digit code with a 0 at the end. Every one of them that has a 0 is stamped with the actual value. 2700, 3300 and 10000 don't cause any confusion, but I do have a bunch of 100pF ones that just say "100". These are, however, really 100pF. I bought them brand new as such and my cap meter confirms they are 100pF.

I only have a handfull that use the 3-digit code; 361, 681.

With most polystyrene caps you can tell from the size what capacitiy range it's in. A 10pF one is much smaller than a 100pF one.

Uncle Krunkus · Posted: Thu Aug 02, 2007 4:10 am Post subject:

Now I've just found some very similar styrene caps, with the same brand on them "DIEL". They have 3900 printed on them. Now this must be 3900pF yeah? Now does that point to the idea that these styrene caps have the value in pF printed on them? Does that mean the 220 is, in fact, 220pf? I'm so confused!!

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

It's likely that 220 is just 220pF. But just check them with a meter and you'll be sure.

Uncle Krunkus · Posted: Thu Aug 02, 2007 4:17 am Post subject:

I just tested one which has 390 printed on it. My cap meter is not great, but it did show .14nF with nothing connected, and .74nF with the "390" across it. So that must be in the "order" of 390pF.

And I'd just finished moving most of them to new spots!

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

Yes, that's certainly nog 39pF. My cap meter is just as bad, reading 180pF for the 100pF ones, but at least it tells me it's not 10pF.

Uncle Krunkus · Posted: Thu Aug 02, 2007 4:32 am Post subject:

psylux · Joined: May 15, 2007 Posts: 44 Location: Dallas, TX

This is a perfect reason to throw everything on the (cap) meter. I shelled out a little extra for a DMM with a decent cap tester.

A similar situation a newbie (not me, stop staring at me, I told you it wasn't me) can get into is the decade band of 3 and 4 striped resistors. You get used to red being 1k and sometimes its 10k, its late at night, you've been drinking and 'bam' you wake up in the back yard.

23isgood · Posted: Fri Aug 03, 2007 12:39 am Post subject:

This is a great thread. I'm always struggling with caps. I hate it when you buy a capacitor assortment, and all the caps come all mixed all up. Its pretty bad with ceramic caps trying to decipher their values. So can you guys recommend a good cap tester? Are they built into a DMM? While on the subject can anyone point me to a good tutorial on how to use a volt meter?

Check out this web page. It has an excellent cap code chart. I use it every time I'm checking caps. I just downloaded the page to a folder on my pc so I can use it when I'm not online.

http://www.bobknarley.com/synth/capcodes.html

v-un-v · Posted: Fri Aug 03, 2007 1:39 am Post subject:

Uncle Krunkus · Posted: Fri Aug 03, 2007 7:41 am Post subject:

One thing I have learned is that the cap meter on your DMM is a relative thing. ie; the meter itself, and the probes you have attached at the time will have their own capacitance. You need to notice what this is before you connect across the cap, then check what it is with the cap across the probes, and take the original figure away. (caps in parallel are added together) Depending on the value you're measuring, it can make a big difference to the level of accuracy.