Author Topic: EEVblog #365 - ESR Meter Bad Cap Monitor Repair  (Read 45959 times)

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Offline Monkeh

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #50 on: October 06, 2012, 11:16:11 pm »
Yes, I'm poor. I do small things. I also have LOTS of other things to spend my limited money on. This is not uncommon.

There must be people on here willing to pool orders?

I suppose there might be. It makes things awkward if I'm just after a few bits.

What law exactly would you be breaking?
Anyone can be a sole trader 'trading as' a company name.

I'm not a sole trader. I do not trade, I do not keep records as a business, I'm not registered for self-assessment, I am not registered as self-employed..
 

Offline SteveyG

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #51 on: October 06, 2012, 11:17:55 pm »
Habitually lying?  ???

I am not a company. I do not have a company. I do not have company letterhead. Filling out the form claiming I am, I do, and providing something which is not real, is lying. And illegal, just FYI.
What law exactly would you be breaking?
Anyone can be a sole trader 'trading as' a company name.

I think he was implying that he'd be fraudulently saying he was a company when he wasn't in order to get a credit account. So fraud. But you don't have to to get a credit account.

I remember when I first ordered a CPC catalogue, they asked if I wanted to pay for future orders by credit card or pay monthly with a £250 limit per month even though I was 16 at the time. They said they would set the low limit of £250 because of my age. LOL. Still have the letter somewhere where they said I could change to a credit account at any time.

I work for a company now, so never use my personal Farnell account any more but they've still kept it open.
« Last Edit: October 06, 2012, 11:19:49 pm by SteveyG »
 

Offline Bored@Work

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #52 on: October 06, 2012, 11:21:21 pm »
Quote
Just because a person in Australia may have a harder time procuring quality parts, doesn't mean it's ok to teach a worldwide audience bad "habits".

The bad habit here is the naive assumption that parts are easily and cheaply available everywhere and that everyone can afford to pay more for shipping than the parts.

Waitaminute, yes? In the past Dave told us repeatedly how easy it is in Australia to order parts and get them delivered with free shipping. I am not sure if he talked about RS or Farnell/Element14, or maybe even both. And I am not sure if the free shipping included overnight shipping, but it really didn't sound like a problem at all.

It is maybe time that he orders a nice engineering sample kit with caps from a reputable manufacturer. Maybe he even finds a supplier who wants to sponsor him. Because I also think using these non-name stuff in the videos isn't cutting it.
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Offline SteveyG

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #53 on: October 06, 2012, 11:27:31 pm »
It is maybe time that he orders a nice engineering sample kit with caps from a reputable manufacturer. Maybe he even finds a supplier who wants to sponsor him. Because I also think using these non-name stuff in the videos isn't cutting it.

I find it hard to believe that as a hobbyist he doesn't have basic parts like capacitors to hand from previous projects or from personal component stores.

Offline PA4TIM

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #54 on: October 06, 2012, 11:30:20 pm »
Quote
I never tried it, but here's what i would do:
Put your cap in series with a resistor of a known value, say 100 Ohms. Now connect this to your Signal Generator using a rather high frequency of 100 kHz or so.
Now if you measure the Vpp coming out of the generator and the Vpp over the cap you should be able to calculate the ESR by using simple voltagedivider math.
Problably not very accurate but schould be enough to tell whether the cap is still ok or not.
Thanks, that seems to work. I get 4.8 Ohms for an old 160V 33uF cap, which is about right according to ESR tables.

ESR for a cap is most time given for Just one frequency. Most times somewhere between 100Hz and 1KHz. Many ESR meters meaure at 100 or even worse 200KHz.

For 33 uF at 100KHz the reactance is 0.048 ohm. If the ESR is 4.8 ohm a 100KHz that cap is so bad you can not even imagine. That is a D of 99.5 or a loss angle of 89 % ( 0% is an ideal cap, 90% an ideal resitor)

But if you measure at 1 KHz, reactance is 4,8 Ohm ( coincidence or are you just reading the meaurements the wrong way ?) a cap that meaures 4.8 Ohm is a D of 1, also not very good so to say ( 45 degrees loss angle) but if they state ESR for 100Hz Xc is 48.22 Ohm and then a ESR of 4.8 Ohm is a D of 0.099 ( or loss angle of 5.6 degrees) and that is not a bad cap.

So you see, three different frequencys, same ESR totaly different result. Now what was your frequency and what frequency in the datasheet of the cap ? ( or did you use those out of the blue tabels that are printed on ESR meters ?)

However the way with the squarewave works, i tested  it too,  but you must just measure the voltdrop over the ESR alone and that is often so small with regard to the measurement signal that it is hard to do. You realy must zoom in. But it gives an indication if you compare good and bad caps and use the right frequency it can be a quick go no-go test.

A cap has a selfresonant frequency, ESR is minimum there, capacitance and ESL are zeto Ohm. Below that ESR increasing upto almost infinity at 0 Hz and it incresase again after the SRF because the increasing skineffect. Besides that, your meauring an inductor above SRF.

100KHz or 200KHz is only usable if the cap is made for high switching speeds.

ESR is no magic, it is just plain network analysis and you need to know what you measure, to bad many people use  those ( much to expensive) ESR meters without knowing what they measure. And everybodys happy because a real bad cap shows itself ( one you would have seen in a second using your scope to meaure ripple) but a lot of caps that are not bad get replaced too, because at 100KHz almost all caps measure bad, so the result:
This was a good deal, the monitor works again because I found a lot of caps with high ESR.

The truth, you replaced a lot of caos, most however probably had good ESR, but lost capacitance or were leaking DC. But most important your monitor works again

About in circuit meaurement i will not even start ( I make enough enemie allready this way probably  ;) )

I measure ( and examine caps) ESR as a hobby, not while repairing, i designed an ESR meter, build several others, used vna's, bridges ect. Build capacitance meters upto 1 fF. Caps are very interesting.

I find bad caps most times by measuring with a scope for ripple ect. But after that I keep the bad ones and examine them for fun. From the many, many caps I measured ( the right way) only a very few ( like 5 out of 100) really had bad ESR. In smps most caps just lost capacitance, second place is DC leakage, third place ESR.

If a cap gets to hot ( bad design pcb or to hot housing) the water from the electrolyte vaporises and the electrolyte loses its capability to restore the oxide layer. Dielectrium dries out, capacitance decreases and it starts leaking DC, gets even hotter and pops open.

If there is dirt in the cap, or coroded electrodes ESR increases. It is important an ESR meter is not capable to measure Resistance direct ( like only a resistor), unless it measures phase angle because otherway you do not know what is R and what is jX. It is just measuring |Z|. And that is why they measure at high frequency, because most of them only measure |Z| and jX is small at those frequency.
A shorted cap will show a low ESR in that case. A good meter measures ESR upto pF ' s because the principle is the same. But the signal amplitude becomes high, |Z| is high. I need around 10Vtt to measure 10 fF capacitance at 1KHz with my homebuild fF meter. 1 pF is 160MOhm, an extreme good ESR for 1pF at 1KHz is 1600 Ohm. but at 100KHz Xc is just 1.6M so ESR for a real good capacitor is around 15 Ohm.

Now more realistic, most ESR meters stop at 1 uF. Xc is around 1.6 Ohm at 100 KHz, if D is good, say 1% loss angle, D is 0.017 so ESR is just 27 mOhm.  But 1nF is a jX of 1600 Ohm and the same D ( not unusual for 1nF) is 27 Ohm. This is within the range of most meters, so ask your self why they do not measure ESR of a 1nF ? Because they just measure Z, Rest my case  ;)

Damm, when do I learn not to react any more on ESR topics.
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
www.schneiderelectronicsrepair.nl  repair of test and calibration equipment
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Online mariush

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #55 on: October 06, 2012, 11:39:14 pm »
Look the point is...  this video brings nothing new compared to the previous video about fixing monitors.

The only new addition is an ESR meter, which is an old one, no longer available commercially, and there's barely a sentence or two in the video about how esr meters work so there's barely anything educational about using the esr meter. Perfect opportunity to discuss capacitors, esr, why low esr is needed in that circuit etc wasted.

Dave is fixing a monitor so he went to the store and bought a capacitor.. it says LOW ESR on it so it must be true! It also says 105c so whatever, as long as it's 105c it must be fine.

So nice of Dave to look datasheets pointing out the 0.024 ohm impedance for the existing capacitor, but then he goes nowhere, he doesn't explain why this low esr is needed, and certainly makes it look like it's pointless to even bother with it because he goes straight to a no-name capacitor.

Where's the datasheet for that capacitor?  Oh, it's no name, crap, no datasheet available.  It is 105c apparently, but 105c what?  100 hours @ 105c? 1000 hours? Who cares brand name capacitors are 2000 hours @ 105c or even 7000-10000 hours @ 105c when Dave teaches us that any capacitor is good as long as it says 105c on it.

He didn't even bother to use the esr meter to test that no-name capacitor outside the circuit before installing it, at least to compare it to the datasheet of the old capacitor. After installing it, it shows the esr is about 0.04 ohm ... yeah, who cares it's TWICE the value the old capacitor should have been, it's good enough. The guys that made the monitors were probably STUPID when they decided they NEEDED LOW ESR capacitors there, how stupid were they for not saving a few more pennies by buying some more average capacitors.

No mention of ESR measurement being affected by capacitors being in parallel, just a mention that the esr meter can test capacitors in circuit. The youtube comments already show that, several people pointed that out.

Seriously, those Jaycar caps are so bad even the paint on the cover is breaking up in some places, just look at 15:00 in the video, there's holes in the paint... they're THAT good. What is that teaching people fixing their electronics? That they can just buy any crap fake capacitor from eBay or Dealextreme and everything will be fine?

Did this video really had to be rushed, that it wasn't possible to place an order on Farnell or somewhere and spend a couple of dollars on getting the parts before finalizing the video?

There should be a higher standard for these videos, they're not made by some kid on the kitchen table fixing his monitor. As it is now, I believe this video would be ok to post on a secondary eevblog channel, alterzone or whatever, not main channel where lots of people view these videos.

I can understand people like Monkeh who don't have a source of CHEAP quality parts and Dave should cater to this segment by pointing that it is possible to use cheaper components (pointing out potential problems that may come up when you're using these parts).

I just don't agree with him using poor quality, no-name parts, just because of laziness or impatience or unwillingness to wait for a few days for parts to arrive to do a proper video.
 

Offline IanB

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #56 on: October 06, 2012, 11:51:11 pm »
Look the point is...  this video brings nothing new compared to the previous video about fixing monitors.
It brings entertainment value with some education included. I enjoyed watching it.

Quote
There should be a higher standard for these videos
There "should"? It's provided to you free of charge. Watch it, or don't watch it. It's up to you. But complaining about things provided for free is not justified. Especially when they certainly take some time and effort to produce.

Quote
I just don't agree with him using poor quality, no-name parts, just because of laziness or impatience or unwillingness to wait for a few days for parts to arrive to do a proper video.
So make a better video and post it up on YouTube! I watched this video and previous ones and I learned very clearly that all capacitors are not the same. They have different specifications for ESR, voltage and operating temperature, and capacitors with the same nominal specification can vary widely in performance and durability between brands. Therefore choosing carefully is important. If I learned that then others could learn that too. Dave isn't making videos for 5 year olds, he is making videos for reasonably intelligent adults who can exercise proper judgement and make rational decisions based on information received.
« Last Edit: October 07, 2012, 02:57:04 am by IanB »
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Offline Bored@Work

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #57 on: October 07, 2012, 12:12:06 am »
What law exactly would you be breaking?
Anyone can be a sole trader 'trading as' a company name.

That depends on the laws in your country. If I would suddenly claim to be a business or sole trader, the tax authorities would hunt me and I would be in trouble for not having registered the business. And if I would register a business the tax authorities would hunt me, too. And if I would use an exception in the local law for liberal professions, which here does include some engineering work, I would again be in close contact with the tax authorities. Because they really don't like the tax exceptions for liberal professions, because there is much abuse going on with them.

I sometimes do consulting as a side job, but I do it via a company in a neighboring country. They employ me for the work, do the legal stuff in their country, get a share of the profit (bastards), and I correctly declare the money I get from them as income earned in a foreign country. A country for which we happen to have a taxation agreement with, so I don't get taxed twice. And all that still does not make it possible that the local Farnell or RS want to deal with me. Because for them I am still a hobbyist, and here they refuse to deal with hobbyists.
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Offline tom66

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #58 on: October 07, 2012, 12:32:21 am »
No point missed.

I don't have the money to easily justify a £20 minimum order or spending more on delivery than the parts. What does that suggest about how much I'm likely to spend a month, and as such my eligibility for a trade account?

Buy caps from eBay.

Would normally be considered unwise if you were getting them from dodgy sources. But I know several sellers who sell genuine capacitors in the UK. If you need a list, ask me or anyone else.

I also live about a mile from Farnell's trade counter, and that only has a £5 minimum order. When I was working in my internship, my company had a business account with Farnell, and could order anything with no minimum order, no shipping charge. I ordered many batches of £2-£3 in caps overnighted by UPS.

If Maplin sold decent caps at their local stores with even a 100 or 200% margin, I would drop Farnell in a heartbeat and often go down there for caps. But they'd rather sell disco lights. Wonder how long that'll work out for them.
« Last Edit: October 07, 2012, 12:35:58 am by tom66 »
 

Offline Pentium100

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #59 on: October 07, 2012, 01:10:16 am »
I buy caps in my local electronics store and I usually get the good ones. Last time I bought some caps (for a PC power supply) I got ones made by Nichion.
Then again, there are 4 electronics stores in one street, maybe competition keeps them from stocking crap brands (of at least the low ESR caps, I got some Samxon and Aishi normal-ESR caps, but don't really care since they are used in linear power supplies).
 

Offline EEVblog

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #60 on: October 07, 2012, 01:19:28 am »
Waitaminute, yes? In the past Dave told us repeatedly how easy it is in Australia to order parts and get them delivered with free shipping. I am not sure if he talked about RS or Farnell/Element14, or maybe even both. And I am not sure if the free shipping included overnight shipping, but it really didn't sound like a problem at all.

They both used to be free overnight delivery by courier.
Now they charge for it again. But you can also go to the trade counter and pick them up in Sydney.

Dave.
 

Offline Monkeh

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #61 on: October 07, 2012, 01:25:07 am »
No point missed.

I don't have the money to easily justify a £20 minimum order or spending more on delivery than the parts. What does that suggest about how much I'm likely to spend a month, and as such my eligibility for a trade account?

Buy caps from eBay.

Would normally be considered unwise if you were getting them from dodgy sources. But I know several sellers who sell genuine capacitors in the UK. If you need a list, ask me or anyone else.

I do. I'd definitely appreciate a list of decent sellers, though.
 

Offline EEVblog

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #62 on: October 07, 2012, 01:35:11 am »
Yes, that's an important thing that wasn't mentioned at all in the video and it's important.
If capacitors are in parallel, when testing a capacitor the ESR value reported will be much lower, it can fool you into thinking a capacitor is still "good enough" to leave it there, and a few weeks later your monitor is broken again.

Yes, I should have mentioned that.
But BTW, if you were paying attention you would have noted that none of the caps I measured were in parallel.

Quote
I'm otherwise really disappointed.
Dave, considering so many people watch your videos, and you know they're gonna recommend them to others, it's really not a good idea to keep using crap no-name capacitors and excuse yourself saying that's all you have.

Why? I pointed out that I was replacing them with unknown caps (not necessarily dodgy, just unknown brand to me).
I am not in the repair business, I had no idea I was going to make another video on this, it just happened. I wasn't going to wasn't going to wait few days and order some brand name caps from Farnell that cost maybe $20. Sue me.

Quote
Also, considering a few capacitors in that area have failed, there's really no excuse for leaving those other capacitors on the board, even though they still measured good, you can never know how long they're going to remain good.  A name brand capacitor is half a dollar, even less, no reason to be cheap with that.

Yes, there was a reason. I didn't have any more caps, and I wanted to finish this impromptu video and head home.
You may not think that's a good enough reason, but I do.
I win, because it's my video  :P

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You should be more responsible about this, you're just encouraging people to make poor quality fixes.

Rubbish. I am telling people to use quality known caps. Just because I don't have them to hand to do an impromptu repair does not mean I am encouraging or endorsing poor quality fixes. This is not kindergarten, people will understand this just fine.
Some people might very well want to do an impromptu fix to just get it working again. Or test that that's the actual problem before deciding to spend more money on quality caps they might not have in stock.
It's a perfectly reasonable video IMO.
I made it clear what I was replacing and the consequences of it.
If you don't like it, and want to correct me, post a follow up video and I will happily link to it.

Dave.
 

Offline EEVblog

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #63 on: October 07, 2012, 01:54:51 am »
And quick fixes using the only components you have to hand 99% of of the time always end up being permanent.

What's wrong with that if it's your monitor?
If it fails again in short order (unlikely actually) then you know to use better quality ones next time. No big deal.
If it doesn't fail and gives you many years more service, then you did a worthwhile fix.

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I agree with your comments - replacing all of those capacitors with Panasonic FC caps wouldn't have cost more than a few pounds/dollars from Farnell and they'd normally deliver next day for free.

Farnell no longer deliver free, and it's a long drive, not that there was time anyway.
And I was not going to wait to finish the video, that's not my style. It was another simple "is it the cap at fault?" repair video.
So you got what I had.

Dave.
 

Offline EEVblog

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #64 on: October 07, 2012, 02:05:33 am »
I find it hard to believe that as a hobbyist he doesn't have basic parts like capacitors to hand from previous projects or from personal component stores.

Top quality brand name high value, high temp, low ESR caps designed for SMPS I don't really consider "basic parts" that you'd have in your hobbyist junk bin.
I'm not in the repair business, nor do I roll my own high power SMPS's that often. There is a ton of stuff I don't have in my junk bins.
YMMV
BTW, I do happen to have a couple in the bins, but they were not the right type in these cases.

Dave.
 

Offline EEVblog

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #65 on: October 07, 2012, 02:17:06 am »
So make a better video and post it up on YouTube!

I'll even post it as a follow-up video!
But of course, the people who complain are never the ones who actually make their own content...  ::)

This video blog has always been in the style of "what's happening in the lab today", or "what I'm thinking about today". Hence you got another quick impromptu repair video, and it was quite valid for me to use whatever brand low ESR cap I had on hand to see if that monitor could be fixed.
I could have talked for another hour on selecting the best capacitor for the job and reading datasheets etc. Was that appropriate to this video? No, it's wasn't.

Quote
I watched this video and previous ones and I learned very clearly that all capacitors are not the same. They have different specifications for ESR, voltage and operating temperature, and that capacitors with the same nominal specification vary widely in performance and durability between brands. Therefore choosing carefully is important. If I learned that then others could learn that too. Dave isn't making videos for 5 year olds, he is making videos for reasonably intelligent adults who can exercise proper judgement and make rational decisions based on information received.

There is a LOT to choosing the capacitor as you say, and it really deserves it's own video, and it would likely be fairly long and detailed.
And even if I did that I'd still get complaints that I missed something, or didn't explain something right, or didn't cater for this situation etc etc.

Dave.
 

Offline EEVblog

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #66 on: October 07, 2012, 02:59:35 am »
The only new addition is an ESR meter, which is an old one, no longer available commercially,

Wrong.
Perhaps you missed the link I posted to Bob Parkers page that has links to no less than two companies still selling his design ESR meter.
BTW, WTF would you complain about that for anyway?
Would you have also complained if I used an oscilloscope or multimeter you can longer buy?

Quote
and there's barely a sentence or two in the video about how esr meters work so there's barely anything educational about using the esr meter.

Umm, using an ESR meter is exactly what I showed. Zeroing the meter, measuring the cap, and comparing it to the datasheet and/or a typically expected value. What more do you want on using an ESR meter?
(yes, I forgot to mention parallel caps)
Please provide a list of all the things I left out on using an ESR meter, because there must a be lot of them given that there was "barely anything educational" in my video.

Also, perhaps you missed the link I posted to Bob Parkers page that has the full construction and design article for how his ESR meter works, complete with pretty diagrams.

Quote
Perfect opportunity to discuss capacitors, esr, why low esr is needed in that circuit etc wasted.

This video was not entitled "ESR meter and capacitor tutorial". The video had exactly the content is claimed to have.
If I do a future video on the topic I'll link it in.

Dave.
« Last Edit: October 07, 2012, 03:06:11 am by EEVblog »
 

Offline david77

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #67 on: October 07, 2012, 03:06:49 am »
+1 Dave.

Some people are lucky enough to live in a country where Farnell happily sell to anyone. Some of us aren't, so getting hold of Panasonic caps is not as easy as it should be.
Personally I couldn't justify a minimum order + postage for a few caps worth maybe 4-5 Euros, so would have to go to the local electronics store and get whatever they have. This of course is supposing there still was a local electronics store - the nearest one is 50km away.

I have some experience running a small local electronics store, so let me tell you why they usually don't stock the top brands of cap suppliers:  You can't easily get hold of small quantities of them, I'm talking about 100s quantities. Panasonic won't even talk to you. Buying from RS or Farnell is not an option, they're just too expensive. You can't buy a cap for 25ct and sell it for 50ct, that simply doesn't work out. As a small business you need to make a decent margin on this stuff. I'm talking about margins well over 500%, that has nothing to do with greed it's simply trying to stay in business.
So in my case I had to settle on Yageo caps, they are easily available from wholesale distributors in reasonable quantities and at a good price.
Of course one could order Panasonic caps in huge quantities at a similar price but that's not economically viable for a small business. Let's say we need about 50 different caps to have a good selection, let's also assume Panasonic have a MOQ of 1000/value. That's 50000 caps, how and in what time does the local dealer shift that? Let's also assume Panasonic charges an average price of 50ct per cap (Wildly optimistic! The large values are realtively expensive.) so we're looking at a bill of 25000 EUR. Just not possible for the small shops, they can't afford stock like that.
 

Offline reagle

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #68 on: October 07, 2012, 03:08:22 am »
Dave,
the video was fine- a nice mix of being entertaining and providing something new- for example the ESR meter from Bob and where to find it. Anybody with a long list of complaints should just go do something themselves and see that it is better, instead of wasting Dave's time on the threads like this  ;D

I just did an exactly the same thing- friend stopped by with a dead monitor, I searched in my bins, picked something more or less suitable and he went home with a live monitor. I did write down all the caps , so if/when these die, I'll simply order the "proper" ones from DK/Mouser. But that when may be never..
« Last Edit: October 07, 2012, 03:10:08 am by reagle »
 

Offline EEVblog

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #69 on: October 07, 2012, 03:12:40 am »
I just did an exactly the same thing- friend stopped by with a dead monitor, I searched in my bins, picked something more or less suitable and he went home with a live monitor. I did write down all the caps , so if/when these die, I'll simply order the "proper" ones from DK/Mouser. But that when may be never..

*gasp*
You'll be hunted down by the capacitor Nazi's! :o

Dave.
 

Offline reagle

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #70 on: October 07, 2012, 03:18:50 am »
Well, naturally I had him sign a disclaimer!

Quote

*gasp*
You'll be hunted down by the capacitor Nazi's! :o

Dave.

Offline JoannaK

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #71 on: October 07, 2012, 04:10:06 am »
also as anyone here saw the interest of esr meters, dont forget to visit my esr repository page
where you can find (almost) all free, DIY, analog, digital and commercial esr meters.

http://kripton2035.free.fr/esr-repository.html

thanks.

For the record .. there are at least two sellers not on your ESR list..

http://clientes.netvisao.pt/greenpal/evb1.htm
http://dx.com/p/100khz-1-7-lcd-auto-ranging-esr-capacitance-meter-black-1-x-6f22-157241?item=4

So for the "Mariush" .. Those are available and on quite many places. And if someone like DX sells a thingie, I'd expect many other chinashops have those too.
 

Offline kek

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #72 on: October 07, 2012, 04:33:46 am »
Dave - these are great video's, keep em comming.

I picked up this meter off ebay <see attached>. I paid $80 for this as well as a seperate cap meter.

Haven't really put it though it's paces but first impression makes me think it'll do it's job just fine. It's got a picmicro inside with a programming header  if it needs to be repurposed. The pic shows a 100 ohm resistor being measured.

Dave, you should come up with your own version of an ESR meter before your next ESR meter video. I'm sure you'd sell quite a few!

Ken
 

Offline SgtRock

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #73 on: October 07, 2012, 04:35:01 am »
Greetings EEVBees:

--I much appreciated the views of the data sheets, I was not quite sure if the impedance was the same thing as the ESR, duh, now I am. And a new character has been born the Capacitor Nazi - "No farads for you"

--My friend Dieter says, what with Dave charging more and more for videos where he does not stop, make a Digikey order and resume a week later, Dieter from now on is only going to watch videos by Hauptmann M. Dieter also notes that Dave did not hold up his right hand and recite Ohms Law, which is nearly as grave an offence as the failure to discuss capacitors in parallel.

"He was born ignorant, and has been losing ground ever since."
Fred Allen 1894 1956

Best Regards
Clear Ether
 

Offline Wytnucls

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Re: EEVblog #365 - ESR Meter Bad Cap Monitor Repair
« Reply #74 on: October 07, 2012, 04:41:28 am »
Quote
I never tried it, but here's what i would do:
Put your cap in series with a resistor of a known value, say 100 Ohms. Now connect this to your Signal Generator using a rather high frequency of 100 kHz or so.
Now if you measure the Vpp coming out of the generator and the Vpp over the cap you should be able to calculate the ESR by using simple voltagedivider math.
Problably not very accurate but schould be enough to tell whether the cap is still ok or not.
Thanks, that seems to work. I get 4.8 Ohms for an old 160V 33uF cap, which is about right according to ESR tables.

ESR for a cap is most time given for Just one frequency. Most times somewhere between 100Hz and 1KHz. Many ESR meters meaure at 100 or even worse 200KHz.

For 33 uF at 100KHz the reactance is 0.048 ohm. If the ESR is 4.8 ohm a 100KHz that cap is so bad you can not even imagine. That is a D of 99.5 or a loss angle of 89 % ( 0% is an ideal cap, 90% an ideal resitor)

But if you measure at 1 KHz, reactance is 4,8 Ohm ( coincidence or are you just reading the meaurements the wrong way ?) a cap that meaures 4.8 Ohm is a D of 1, also not very good so to say ( 45 degrees loss angle) but if they state ESR for 100Hz Xc is 48.22 Ohm and then a ESR of 4.8 Ohm is a D of 0.099 ( or loss angle of 5.6 degrees) and that is not a bad cap.

So you see, three different frequencys, same ESR totaly different result. Now what was your frequency and what frequency in the datasheet of the cap ? ( or did you use those out of the blue tabels that are printed on ESR meters ?)

However the way with the squarewave works, i tested  it too,  but you must just measure the voltdrop over the ESR alone and that is often so small with regard to the measurement signal that it is hard to do. You realy must zoom in. But it gives an indication if you compare good and bad caps and use the right frequency it can be a quick go no-go test.

A cap has a selfresonant frequency, ESR is minimum there, capacitance and ESL are zeto Ohm. Below that ESR increasing upto almost infinity at 0 Hz and it incresase again after the SRF because the increasing skineffect. Besides that, your meauring an inductor above SRF.

100KHz or 200KHz is only usable if the cap is made for high switching speeds.

ESR is no magic, it is just plain network analysis and you need to know what you measure, to bad many people use  those ( much to expensive) ESR meters without knowing what they measure. And everybodys happy because a real bad cap shows itself ( one you would have seen in a second using your scope to meaure ripple) but a lot of caps that are not bad get replaced too, because at 100KHz almost all caps measure bad, so the result:
This was a good deal, the monitor works again because I found a lot of caps with high ESR.

The truth, you replaced a lot of caos, most however probably had good ESR, but lost capacitance or were leaking DC. But most important your monitor works again

About in circuit meaurement i will not even start ( I make enough enemie allready this way probably  ;) )

I measure ( and examine caps) ESR as a hobby, not while repairing, i designed an ESR meter, build several others, used vna's, bridges ect. Build capacitance meters upto 1 fF. Caps are very interesting.

I find bad caps most times by measuring with a scope for ripple ect. But after that I keep the bad ones and examine them for fun. From the many, many caps I measured ( the right way) only a very few ( like 5 out of 100) really had bad ESR. In smps most caps just lost capacitance, second place is DC leakage, third place ESR.

If a cap gets to hot ( bad design pcb or to hot housing) the water from the electrolyte vaporises and the electrolyte loses its capability to restore the oxide layer. Dielectrium dries out, capacitance decreases and it starts leaking DC, gets even hotter and pops open.

If there is dirt in the cap, or coroded electrodes ESR increases. It is important an ESR meter is not capable to measure Resistance direct ( like only a resistor), unless it measures phase angle because otherway you do not know what is R and what is jX. It is just measuring |Z|. And that is why they measure at high frequency, because most of them only measure |Z| and jX is small at those frequency.
A shorted cap will show a low ESR in that case. A good meter measures ESR upto pF ' s because the principle is the same. But the signal amplitude becomes high, |Z| is high. I need around 10Vtt to measure 10 fF capacitance at 1KHz with my homebuild fF meter. 1 pF is 160MOhm, an extreme good ESR for 1pF at 1KHz is 1600 Ohm. but at 100KHz Xc is just 1.6M so ESR for a real good capacitor is around 15 Ohm.

Now more realistic, most ESR meters stop at 1 uF. Xc is around 1.6 Ohm at 100 KHz, if D is good, say 1% loss angle, D is 0.017 so ESR is just 27 mOhm.  But 1nF is a jX of 1600 Ohm and the same D ( not unusual for 1nF) is 27 Ohm. This is within the range of most meters, so ask your self why they do not measure ESR of a 1nF ? Because they just measure Z, Rest my case  ;)

Damm, when do I learn not to react any more on ESR topics.
I used a generic table, as there is no brand name on that cap, which was harvested from a 20 year old top of the line CRT Sony TV.
I fed a 5Vpp square wave at 100kHz (50% duty cycle) through it with a 100 Ohm resistor in series. I also measured an AC current of 47 mA on the circuit. Noticed 240 mVpp on the oscilloscope across the cap, which gives me an ESR of about 5 Ohm for that old cap, applying Ohm's law. Not sure if this is the right procedure, but that cap could be out of tolerance, being so old.
 


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