Electrolytic Capacitor kit for repairing TV, Laptop etc?

[helius]

It may depend on where you are, but in the relatively affluent US, repair shops for "more modern equipment" have largely gone out of business. The TV/radio repair shop used to be a familiar sight in the mall or the phone directory, but they are very rare now, so most "modern equipment" is being scrapped rather than repaired.

[Siwastaja]

General purpose elcap series do not typically report ripple current rating at 100kHz, only at 120Hz, but if it is rated/simulated/measured @ 100kHz, it tends to be roughly half of the ripple current rating of a similar sized "low ESR" type.

Given that even the low ESR types tend to be quite stressed in SMPS circuits, replacing with one with only half the ripple rating, the result seldom lasts very long.

But of course, no one says an SMPS design must use a type labelled as "low ESR". One with high enough ripple current rating is obviously enough. Similarly, you don't actually shop for a "low noise opamp" or a "high performance DSP", instead you buy one with the numbers you need.

Ripple current rating and ESR of course go hand-in-hand. Given same I_ripple, lower ESR means less internal heating. Other parameters affecting this is the surface area of the capacitor, internal heat conduction from the core of the capacitor to the outer sleeve, and the details of the electrolyte, how quickly a certain temperature degrades it.

Ripple current rating exists solely so that you don't need to understand the internals of the capacitor, model the heating and then try to find out how much ripple current you can put through it. Just look at the table and you are given the number you need for your design, directly. This is handy.

Low ESR types are easily available in 5000-8000 hour ratings @ 105degC, this specification is actually the ambient temperature (around the capacitor, not around the complete device) and at rated ripple current. It follows, it's fairly easy to derate the operating temperature and/or ripple current so that 5000 hours becomes 50000 hours. The practice of derating is widely understood and known and supported by documents from the capacitor manufacturers, so a 5000 hour rating does not mean the capacitor is actually supposed to only last for 5000 hours, not at all. Like always in engineering, you need to know what the numbers mean.

"Repair people" tend to have strong biases. In reality, repair is a tiny tiny business compared to manufacturing new units to replace broken stuff. If you and your friends like to repair your broken devices, you are missing the 100000 average Joes who just ditch them.

[rsjsouza]

You would be very surprised to see the vast amount of people that performs repairs in Amigas, Apples, early PCs, old monitors...

IMHO you overestimate that grossly, confirmation bias. A few enthusiasts who do that relatively often and some very rare random jobs done by others. In comparison to repairs of more modern equipment, it's just a miniscule amount. Unless person states intention to repair exactly those, it's not even worth consideration.

I never compared with modern equipment, so this is a moot point.
In my experience, the amount of people that are interested in maintaining these equipments is quite large, even if they outsource the repair work (which is still imposes a demand on regular capacitors, which is the subject of this thread). You don't know the entire world.

All of them with ancient SMPS circuits.

I did not say they don't have it.

Neither I suggested the opposite.

[wizard69]

What I don't see stressed enough here is the fact that you will likely never have what you need in the kit.   On top of that a good portion of the kit will just age and eventually become a problem because of that.   Al the technical discussions in this thread are completely true but the number one point for me is the waste of money that kits of Electrolytic Capacitors are.   Even worse is the temptation to put that kit to work, because you spent all that money, on bodged installations that likely will not be reliable.   Bad voodoo very bad VOODOO!

Now that is in the context of a repair lab.   A designer might have use for a kit but then he will have a good idea what he expects to be designing and how a kit might fit.   Even here it often makes more sense to simply buy the right parts to fit the design.

The story might be a bit different for other capacitor technologies.   Ceramic capacitors will likely last for ever on the shelf, but even here I can't see buying a kit in the hopes that it would have the right chip when you need it for repair work.   Again a different story on a hobby or design bench where the projects can be varied.

Beyond all of that if you really want to make up an on going inventory; simply order more parts than the last repair required.   At least then you know you have a use for the parts.   As a business you would want to keep your inventory concentrated on stuff that will move out the door fairly quickly.   In other words keep stock focused on stuff that drives the business and avoid tying up cash in stock that will not generate revenue quickly.   Sorta JIT thinking, though I don't see JIT as ideal for a repair shop, it isn't like you will know what you are working on from one hour to the next.

So baring all of the well reasoned points earlier in this thread I just see kits like this as a bad business move.   There are far better things to tie your cash flow up in.

[Jwillis]

Pretty much every thing others have said . But the biggest annoyance with electrolytic cap kits for me is getting a bunch in the kit with voltages you never use .This of course depends on what type of electronics that interests you. Better to get good E caps as you need them . You really don't save much getting cheap ones from unknown sources . I've not had any problems with E caps from Ebay and they have tested fine but I can't really say how they will perform as they age .
Just my opinion.

[wizard69]

"Repair people" tend to have strong biases. In reality, repair is a tiny tiny business compared to manufacturing new units to replace broken stuff. If you and your friends like to repair your broken devices, you are missing the 100000 average Joes who just ditch them.

Sadly much of what you said is correct, however it would do us a lot of good to try to change the mind set with respect to repair.   Part of the throw it away mentality has come from the rapid advancements in compute technology which made old computers obsolete pretty quickly.    That rapid obsolescence is no longer the case, a smart computer purchase can last for years now for many users.   Repairability just means a device will last even longer.

On the flip side I worked with a guy for years that had a computer repair business on the side.   Most of his repairs involved reinstalling Windows and fixing other OS related issues.   Actual repairs would be at the sub assembly level.   However when products have known failure points that are easy to address one can save a lot of money over the board swaps that large computer companies do.

In the end capacitor replacements can be a win win situation when it comes to repair.   It is something that usually is easy to diagnose, fairly cheap to repair, and makes the customer happy when charged far less than a board swap when going through the manufactures support.   In a nut shell I really see repair as something that needs to be focused on more as it is good for the economy, good for the environment and keeps some cash out of the hands of the largest corporations in the country.   So yeah lets do cap replacements right so that repair can maintain a good public image.

[Zero999]

What I don't see stressed enough here is the fact that you will likely never have what you need in the kit.

I agree. That has been my main arguement: it's highly unlikely any of the capacitors will fit, so you'll be tempted to bodge. Often I will use a capacitor from my kit to piggy back on to a faulty capacitor, to prove the circuit works, when it's replaced, then I'll by a new one, in the correct case size for the propper repair.

On top of that a good portion of the kit will just age and eventually become a problem because of that.

I have not found this to be the case. I have some very old capacitors in my capacitor assortment which I salvaged from some old toys/radios/TVs, when I was a child (yes I know it's not advisable to use second hand capacitors, but I didn't know any better back then and it was one of the few sources I had) and guess what? Many of them are perfectly fine, even though they're over 30 years old. For prototyping it's a good idea to keep a stock of the most commonly used electrolytic capacitor values, at least 10µF, 100µF and 1000µF, which are handy for decoupling and output filtering on power supplies, but I try to stock electrolytic capacitors in the E3 values, i.e. 10, 22 and 47, from 2.2µF to 10 000µF, for general prototyping purposes.

[Renate]

I've been surprised at the level of disapproval here.
Yeah, it's all fine to say that a part should only be replaced by its exact equivalent (after checking with the manufacturer to make sure there hasn't been an engineering change order).
Maybe some of you should go look in at the scrap recycling center and see how many TVs and monitors there are there.
Would a quick replacement cap that gets another 5 years of life out of some of them be such a bad thing?

Ok, if I were fixing a spectrum analyzer I would be more picky about a replacement part than a $99 Walmart TV.

And yeah, for some of us, the hassle of ordering a single part would be a hassle.

[wraper]

Would a quick replacement cap that gets another 5 years of life out of some of them be such a bad thing?

When replacing LOW ESR cap with some random general purpose cap, likely will get you less than a few months of life. And as I already said, basically any LCD TV or monitor will have low ESR capacitors. As of laptops, you're not likely to find any electrolytic caps in anything made in last 15 years. And even in a rare case when there is one or two, unlikely to be a reason of failure.

[Dacke]

Ok, if I were fixing a spectrum analyzer I would be more picky about a replacement part than a $99 Walmart TV.

It's not just TV's and monitors,  switch mode supplies are in literally everything now.  Low ESR caps are par for the course.  I do a lot of SMPS repair,  and it's rare that I would use gen purpose caps for anything but audio circuits,  testing,  and prototyping.  As wraper has stated,  you will not get "a few years" of life from a gen purpose cap being used in these power supplies,  you would get weeks or a few months at best.  I speak from experience and it's annoying as hell to go back into something you've recapped only to have to do it again in 2-3 months,  even if it's just something I'm repairing for myself.

[Siwastaja]

If the original, designed-in-by-a-professional part failed in a few years of use, don't expect 5 years lifetime out of random parts. You need to do better, not worse.

I don't repair that much, mostly I design, but personally, some 15 years ago I "repaired" a PC PSU with a general purpose "I have this on my self" elcap which had the correct voltage, temperature and capacitance ratings, and it lasted in the circuit for about 1 month until I had to order proper low-ESR caps so this isn't just theoretical talk.

[TimNJ]

Not to  but another two reasons:

1. ESR of output caps often plays a large role in ripple suppression. GP caps might have 5...10x ESR of a low ESR cap. As power supplies are commodity items, they are built to a price, and usually don’t have a ton of margin with respect to their output ripple specifications. So, put in a GP cap and you might be very far out of the specification. Will it cause problems? Maybe. Maybe not. Might look fine at first but start doing weird things once you really start to use it.

2. Depending on the topology the ESR zero of the output capacitors play a role in the feedback loop stability. Change it too much and you risk instability. Granted, most current-mode control (and similar) power supplies (these days) are pretty robust and easy to keep stable, but it is still not a good practice.

[wizard69]

I see this "lets buy a kit of parts" mentality in all sorts of technical pursuits.   One example I just ran into  is a guy ordering O-ring kits for pneumatic repair and only using three sizes out of the kits.    I say kits because he had 5 kits of assorted O-rings with every kit missing the same three sizes of O-rings.   The fact is he could have ordered several hundred of those 3 O-Rings and not spent the money that one kit cost him for 10 of the needed O-rings.

So the issue of kits is not something that is a problem just in the electronics repair industry.   It is wasteful in just about any repair activity.    Note: that I'm saying this in the context of a repair activity or business.   It is a different story for an R&D operation but even there you need to be careful.   

Beyond that if your income stream involves repairing common item it may pay to buy a know failure item in bulk.   Often with a bulk purchase you are still paying far less than the inflated prices seen in kits.   

Maybe I'm triggered by this subject but I don't see the point in kits, often they are ordered by lazy people or people that don't know any better.   You are almost always better off ordering the correct part for item to be replaced.

[CatalinaWOW]

I see this "lets buy a kit of parts" mentality in all sorts of technical pursuits.   One example I just ran into  is a guy ordering O-ring kits for pneumatic repair and only using three sizes out of the kits.    I say kits because he had 5 kits of assorted O-rings with every kit missing the same three sizes of O-rings.   The fact is he could have ordered several hundred of those 3 O-Rings and not spent the money that one kit cost him for 10 of the needed O-rings.

So the issue of kits is not something that is a problem just in the electronics repair industry.   It is wasteful in just about any repair activity.    Note: that I'm saying this in the context of a repair activity or business.   It is a different story for an R&D operation but even there you need to be careful.   

Beyond that if your income stream involves repairing common item it may pay to buy a know failure item in bulk.   Often with a bulk purchase you are still paying far less than the inflated prices seen in kits.   

Maybe I'm triggered by this subject but I don't see the point in kits, often they are ordered by lazy people or people that don't know any better.   You are almost always better off ordering the correct part for item to be replaced.

If repair is your business, and if time to repair is not an issue I totally agree.  For those at remote locations, or homeowners, or hobbyists the answer is no where near as compelling. 

The O-ring kits are a great example.  I have a couple, in different materials for different purposes.  And as you correctly state I have over a decade or two of ownership used less than 5% of the kit contents.  By the time I die I am sure that more than 85% of the O-rings will not have been used.  But the gasoline saved by not having to drive down to a local store (in my case about 40 kM away) those few times a usable O-ring was in the kit paid the entire price of the kits.  And the time saved not having to make that drive or order over the internet when local sources don't stock the correct part (more often than not) has its own value.

For professionals where time to repair really matters (just about anyone supporting an assembly line, a mine or something like that) it makes sense to ignore the general purpose kits and figure out what parts are used in the machinery you are supporting.  And then stock up a kit of those parts, being sure to re-order as they are used.  Your associate buying the pneumatic kits would have done well to take that approach, assuming that his salary in doing the research didn't cost as much as the kits.  Probably the best economic answer is to buy a few kits to keep things up and running.  Those kits will then teach you what you use and you can then order those parts in quantity.

[perieanuo]

hi,
big no no
I just keep revolving capacitor stock from serious suppliers, tme farnell & company
if you have ONE returning repaired TV in warranty cause one new&non-conform capacitor, the time and gas money you loose undo all the profit and pleasure gained

[Zero999]

I see this "lets buy a kit of parts" mentality in all sorts of technical pursuits.   One example I just ran into  is a guy ordering O-ring kits for pneumatic repair and only using three sizes out of the kits.    I say kits because he had 5 kits of assorted O-rings with every kit missing the same three sizes of O-rings.   The fact is he could have ordered several hundred of those 3 O-Rings and not spent the money that one kit cost him for 10 of the needed O-rings.

That doesn't mean kits are always bad, just that that person was a fool for buying a complete new kit, rather than just ordering the O-rings to replenish it. Take my kit of E3 capacitors for example. When I run out of a common value such as 10µF, I don't buy an entire brand new kit, just a pack of 10µF capacitors! 

[wizard69]

I see this "lets buy a kit of parts" mentality in all sorts of technical pursuits.   One example I just ran into  is a guy ordering O-ring kits for pneumatic repair and only using three sizes out of the kits.    I say kits because he had 5 kits of assorted O-rings with every kit missing the same three sizes of O-rings.   The fact is he could have ordered several hundred of those 3 O-Rings and not spent the money that one kit cost him for 10 of the needed O-rings.

That doesn't mean kits are always bad, just that that person was a fool for buying a complete new kit, rather than just ordering the O-rings to replenish it. Take my kit of E3 capacitors for example. When I run out of a common value such as 10µF, I don't buy an entire brand new kit, just a pack of 10µF capacitors! 

There are many factors to consider here.   In this case I was addressing what appeared to be somebody getting started in the repair business apparently on a shoe string.   Buying a whole kit of electrolytics just makes no sense to me in that context.   It is a big expense for stuff you may never use.   Repair is a business where you have to carefully watch where your money goes to have any prospect of staying in business for very long.

As for other activities that is something that each engineer will have to decide for themselves.   A kit of parts might make sense if you are engaged in R&D, product design or the like.   Even there I'd have to suggest that one be careful as you can easily end up with a big out lay of cash better spent elsewhere.   

I'm not against kits nor against the idea of organization in some contexts I just think kits of electrolytics can be wasteful starting out in a repair business.   That comes down to the idea that your chances of having a good fit for parts replacement is slim.   If you are going to have inventory, it is best to build that inventory around the stuff that you commonly see on your bench.