Can you identify these capacitors? - Page 1
Forum section: electronics / projects

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 04, 2018, 03:41:05 pm
content: Hi,Rummaging through a grab bag of ceramic capacitors, I came across some of the ones shown in the attached photo. There are no printed markings, just the colored top half. I don't have a good enough means to measure them but assume they are just a few pF.Thanks!

author: alanb
author_rank: Frequent Contributor
timestamp: May 04, 2018, 03:52:46 pm
content: Are you sure that it is a Cap and not a MOV (Metal oxide varistor)?

author: Benta
author_rank: Super Contributor
timestamp: May 04, 2018, 04:08:28 pm
content: Too small for a MOV (judging by the lead thickness). Could also be mica caps.

author: Gyro
author_rank: Super Contributor
timestamp: May 04, 2018, 04:17:12 pm
content: Wrong shape for Mica? (I've never seen one that wasn't approximately rectangular).Judging from the body vs lead size I'd say they are 1-2digit pF value ceramic disc.EDIT: ...or possibly temperature sensing thermistors? It might be worth a quick check for resistance.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2018, 04:25:57 pm
content: If there's no markings and no bandings then it's as good as a guess...That said, if the green dip is intended as color, I guess it could be 5pF.If you think unmarked ceramic discs are mysterious, wait til you see ceramic chip caps. They're never* marked.*Except sometimes they are, but they're rare.Tim

author: bob225
author_rank: Frequent Contributor
timestamp: May 04, 2018, 04:50:27 pm
content: Have you tried removing the green coating ?

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 04, 2018, 04:52:36 pm
content: Thank you all.They'd better be capsI bought a couple of grab bags some time ago. The dip color is brown to the naked eye (the phone lies.) I'll see if I can remove it.I was thinking 1pF. Seems quite odd, though.I'll check the resistance re. MOV.John.

author: Myrv
author_rank: Contributor
timestamp: May 04, 2018, 06:46:06 pm
content: How many of them do you have? You could try measuring a bunch in parallel to improve measurement sensitivity.Or if you have an Arduino* you could try making a (very) simple capacitance (time constant) meter. Something like this:https://www.arduino.cc/en/Tutorial/CapacitanceMeterTo measure 1 pF though you would have to change the above code to use micros() instead of millis() for timing and likely need an R value of 10 Megaohms or higher. Horribly inaccurate but if you have an Arduino lying around it would be simple enough to try.* Just checked the specs, a normal Arduino likely wouldn't be fast enough. Looks like a typical 16MHz Arduino ADC tops out at less than 77k SPS (not really enough to measure a 1pF time constant). . Although something like an Arduino DUE supports 1MSPS which could give it a fighting chance.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 04, 2018, 07:21:42 pm
content: It doesn't look like a cap to me, my guess is some kind of resistor, most likely a thermistor.I'll eat my shoe if it is a cap.

author: timpattinson
author_rank: Contributor
timestamp: May 06, 2018, 03:53:15 am
content: What equipment do you have? Just a DMM? Micro controllers?Sent from my SM-G930F using Tapatalk

author: TerraHertz
author_rank: Super Contributor
timestamp: May 06, 2018, 08:39:33 am
content: If you have lots of them, smash one. What do the insides look like?Also try heating one up, while measuring resistance. Does it start conducting at some temp lower than at which the thing is damaged?