First fake part :) - Page 1
Forum section: electronics / projects

author: WarSim
author_rank: Frequent Contributor
timestamp: October 05, 2013, 12:30:20 am
content: Well I can no longer say I have never been caught with a fake part now.I needed a super cap for my current project and found enough in my spares bins.They are marked NEC FYD .022f 5.5v. The stacked type from the earlier super cap days.Well they are actually are 220uf under 3.3v cap.No they are not aged, all the caps I have are the same. I have never seen caps age together in the same way and mimic valid cap specs.I must be samples for a project that didn't happen or I would have found out sooner.If I could remember the supplier I used to get them I would warn everyone but I don't.I have my favourite 5 sources now. I am going to assume it wasn't one of them.

author: Rufus
author_rank: Super Contributor
timestamp: October 05, 2013, 02:15:42 am
content: Quote from: WarSim on October 05, 2013, 12:30:20 amHow do you know that?

author: mariush
author_rank: Super Contributor
timestamp: October 05, 2013, 03:11:58 am
content: Some digital multimeters are limited to 220uF (have ranges like 2.2 uF , 22uF , 220uF).Most multimeters can't measure over about 10000uF so if you used a multimeter that may be your answer.You would have to use a particular circuit to measure them... for example.. i don't know... constant current load and measuring discharge time?

author: BravoV
author_rank: Super Contributor
timestamp: October 05, 2013, 03:20:40 am
content: Yep, agree with mariush, its way too large for normal dmm to measure it correctly.Since its so large, just rig up a constant current circuit and try measure the dV/dt, then use the basic formula to get the capacitance, not ultra accurate though, but should be enough. Been there and done that.

author: c4757p
author_rank: Super Contributor
timestamp: October 05, 2013, 03:28:58 am
content: Forget the constant-current circuit and use a resistor. Measure the RC constant.

author: BravoV
author_rank: Super Contributor
timestamp: October 05, 2013, 03:33:11 am
content: Quote from: c4757p on October 05, 2013, 03:28:58 amI guess this shows the diffrenece between a lame hobbyist vs a true electronic scholar.

author: WarSim
author_rank: Frequent Contributor
timestamp: October 05, 2013, 03:37:17 am
content: Quote from: Rufus on October 05, 2013, 02:15:42 amI used an LCR good up to 1f.And if it was over it's limit it says "over".Yes I did check with a 10f cap.

author: c4757p
author_rank: Super Contributor
timestamp: October 05, 2013, 03:38:44 am
content: Quote from: BravoV on October 05, 2013, 03:33:11 ams/true electronic scholar/lazy-assApplies to other fields as well."We will encourage you to develop the three great virtues of a programmer: laziness, impatience, and hubris." - Larry Wall

author: Rufus
author_rank: Super Contributor
timestamp: October 05, 2013, 04:44:10 am
content: Quote from: WarSim on October 05, 2013, 03:37:17 am0.022F at 100Hz is about 70 milliohms. The datasheet max ESR is 220 ohms. To an LCR meter at 100Hz it looks about 3000 times more like a resistor than capacitor. The inductance is probably significant too.I would charge one with a constant current (1mA from a 22k resistor and 22v from a PSU would do) and measure the rate of change of voltage with a meter and stopwatch. Maybe check with a different current in case it is leaky, especially if left discharged for years.Q = CV = IT.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 05, 2013, 06:14:10 am
content: This is the method used by NEC to rate their FYD super caps:Charge systemRc= 2000 Ohm for 0.022F capMeasure time constant to charge from 0V to 3.16V for 5.5V rated cap with 5V DC source.C=t/Rct should be around 44 seconds for this cap. Capacitance tolerance for a new cap: -20%/+80%.

author: WarSim
author_rank: Frequent Contributor
timestamp: October 05, 2013, 06:46:25 am
content: Quote from: Rufus on October 05, 2013, 04:44:10 amI know the cap is not as it is marked.It was going to be used as a power backup for the PIC during power source testing and changes. The cap lasted for 100th of the calculated time. This is What caused me to test the caps which revealed an calculated value of 100 times less, and a voltage threshold lower that spec'd. Which was verified when I tested it with my LCR meter.Yes if I had not already completely tested the caps before I made my initial post, I would certainly do it now. But seems I do not say I know when I am guessing I can assure you I performed many test already, and all test results proved my claims.Thank you for your advice, all the suggested test where completed before my initial post. If someone has a theory how these 10 caps can have charge and discharge curves of a 220uf cap (I made several loads for such purposes), exhibit break over at 4v, test as a 220uf cap (on one LCR meter, my second tester on my 87V can't), Have an ESR measurement on the LCR 1000th of the spec (the expected value range of a low voltage 220uf cap), act as a 220uf cap in it's intended cct and still be the cap as marked please enlighten me. I accept that I didn't list all the test I did before posting, originally I did not think it was needed.The cct has been redesigned to use two 2.2mf 10v caps. They take more room than wanted but they are on hand. Hopefully I won't need to make room for a third. I calculated I needed 97ms max and these give 87ms. Testing thus far has shown cycle times measured in the 40 - 60ms range. So unless I can't find the space I am going to stick with these GP caps.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: October 05, 2013, 08:09:26 pm
content: Quote from: BravoV on October 05, 2013, 03:33:11 amImho you are shooting from the hip and there is a big probability that the bullet will hit the foot. With a constant current it is possible to detetermine C in a short time with good precision. Waiting for the RC constant to come takes a looong time and is influenced by leakage (in case of fake or faulty super cap) and measuring on a "flat" part of the slope. Very interesting problem. Somebody should open a time-nut & volt-nut style thread on this and compare the methods to ppm level

author: AndyC_772
author_rank: Super Contributor
timestamp: October 05, 2013, 08:47:18 pm
content: If it's an electrolytic cap, measuring parts per million is a waste of effort... parts per part would be enough!

author: quantumvolt
author_rank: Frequent Contributor
timestamp: October 05, 2013, 08:58:14 pm
content: Quote from: AndyC_772 on October 05, 2013, 08:47:18 pmWell - that shows the difference between engineering and science ... I used to waste my time on getting cash, booze and women. Now studying the user manuals for Agilent's more than 10 grand LCR meters is more rewarding

author: c4757p
author_rank: Super Contributor
timestamp: October 05, 2013, 09:08:17 pm
content: Quote from: quantumvolt on October 05, 2013, 08:09:26 pmYeah, but a resistor is more than enough to tell apart 22mF and 220uF.

author: WarSim
author_rank: Frequent Contributor
timestamp: October 05, 2013, 09:08:28 pm
content: Seems I started this thread I must now say I was wrong.Because of this discussion I decided to retest the caps. Today when I started testing I noticed something new. It would resonate at two different frequencies. So I investigated.The caps will charge as expected but has a second internal capacitance that causes huge oscillations. I was measuring these oscillations as it's primary capacitance. The oscillations seem to be proportional to the charge rate and my original test where at 10ma oscillations where equal to my test voltage. Charging at 2ma enabled me to see the second charge curve. So i now think these are 22mf super caps but all have big issues. I have never seen a super cap that will generate over 100% noise so I did not suspect this.I have no idea if it is poor design or these samples have been equally damaged in some profound way. I may disassemble one to find the issue. My first suspect is the stacks are not bonded and moisture I greased and corroded the mating surfaces and created the second capacitor. And something else happened to cause the ESR to test lower.As a result they are not fake parts only parts too horrid to use. And I was fooled by it despite my testing. Next time I know to charge test at rated, mid and low currents.

author: WarSim
author_rank: Frequent Contributor
timestamp: October 05, 2013, 09:10:40 pm
content: Quote from: c4757p on October 05, 2013, 09:08:17 pmI do realize your suggestion was given as a workable option not knowing what resources or knowledge I have. I do appreciate your help.

author: WarSim
author_rank: Frequent Contributor
timestamp: October 05, 2013, 09:48:21 pm
content: Well I took one apart.The case is a can over a base plate with a Teflon tub. Introduces capacitance but unlikely the problem.The element is a black stack of layers, layer margins where quite messy but straight. No idea what it's made of but I has to be conductive. Maybe it is the resistive network to maintain cell balance. It is a possible cause if it is causing intermittent resistance changes and un predictable inter layer capacitance.The cells are encapsulate inside as layers of gel, Teflon, and a grey conductive material. I don't know anything about this, and I couldn't get into thus part cleanly.So anyone what kind of nasty chemicals I just got exposed toIn conclusion unlikely it was contamination. My only suspect is the only thing I could see. Sloppy cell buildup with respect to the conductive rubber outer layer that I think is the balancing network.Well lucky for me none of my other super caps exhibit these issues, so I will just toss these ones. I have no idea how low of a charge or load I have to go before they are usable. I suspect well under 1ma. I would rather rive up the $25 than mess with them.

author: Zero999
author_rank: Super Contributor
timestamp: October 06, 2013, 05:06:09 pm
content: How about building an astable 555 circuit with the capacitor and measuring the output frequency?

author: WarSim
author_rank: Frequent Contributor
timestamp: October 06, 2013, 09:17:04 pm
content: Quote from: Hero999 on October 06, 2013, 05:06:09 pmThey are an oscillator without a 555 timer.