Monitor recapping and low ESR

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sandord
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Monitor recapping and low ESR

Post by sandord » Mon Oct 08, 2018 1:52 pm

I'm planning to recap two Commodore 1084S-D2 and a 1084S-P1 monitors.

I've assembled part lists for both (they are quite different in internal design) and I've selected Panasonic or Nichicon where ever I could.
I also tried to select low ESR caps as much as I could. About 1/3 of them are low ESR now on my list.

I don't really understand what low ESR means, something like low internal resistance that lowers when the caps warm up. I've just naively assumed selecting low ESR parts would be a good thing to do.

I'm wondering through, low ESR really important in CRTs? Most things I've read are about high frequency switching power supplies.

I think of my parts are ESR type, do you guys think it is safe to use the parts I've selected or should they like, all be low ESR or is it not important at all?

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Re: Monitor recaps and low ESR

Post by exxos » Mon Oct 08, 2018 2:01 pm

I found this article which quickly explains it, albeit not very well I think...

https://www.digikey.com/en/articles/tec ... acitor-esr

The image may look confusing but I will try to explain little better..
article-2016september-simple-explanation-of-fig1.jpg
article-2016september-simple-explanation-of-fig1.jpg (55.87 KiB) Viewed 361 times

What the image represents is series resistance and inductance internally in the capacitor.

For example you have to imagine a capacitor in series with a 1 ohm resistor for example and then in series with small inductor. The higher the resistances the lower the current capability is of the capacitor and the greater losses as it equates to.

You have to imagine if you passed one amp through a 1 ohm resistor it will of course get warm. This is the same heat output which is happening internally in the capacitor. Of course heat is bad and reduces life of components. So we want this as low as possible. This is your ESR (equivalent series resistance) of the capacitor.

Reducing this figure as much as possible means capacitor can run more efficiently and deliver higher current while increasing its life expectancy due to less internal heat buildup. So basically, the lower the ESR the better.

In terms of ESL (equivalent series inductance) it is a similar thing and you want this as low as possible. Inductance is bad because current demand ends up being slower the higher the value is. For example if you had a electrolytic and did not cut the legs and had 1inch lead length on the bottom of the capacitor to the PCB, you would increase the inductance which basically makes the capacitor more sluggish to react to current demand.

Rolled capacitors are inherently bad design in most respects. You have to imagine that the length of the internal foil layer, if rolled out could be about to a meter long. This is why generally Axial capacitors are bad because of this. Of course similar problems with any rolled up capacitor. And of course we can only choose the best current specifications on the market currently. Things have improved a lot in recent years of course.

Generally flat plate stacked capacitors are better by far. Basically because all the plates are common and on each side of the capacitor so all the plates are in parallel making much shorter connections to each plate than having a capacitor which is rolled and having a meter long foil layer.


This is what a parallel stack capacitor looks like..
cap5b.gif
cap5b.gif (4.47 KiB) Viewed 355 times

Versus a rolled one...
roll.JPG
roll.JPG (18.81 KiB) Viewed 355 times

Of course we are pretty much limited to rolled capacitors anyway. But this is why I generally use ceramics now in things which are 100uF and less performance so much better than electrolytic's.

Such topics can actually turn into a very long complicated one.. But I hope this in a nutshell summary helps give you an basic idea what is going on..
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Re: Monitor recapping and low ESR

Post by IngoQ » Mon Oct 08, 2018 2:24 pm

Wow, this is a really great explanation... hopefully, as time comes, you might feel inspired to write some more :)
Ingo :geek:

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Re: Monitor recapping and low ESR

Post by exxos » Mon Oct 08, 2018 2:31 pm

IngoQ wrote:
Mon Oct 08, 2018 2:24 pm
Wow, this is a really great explanation... hopefully, as time comes, you might feel inspired to write some more :)
Thanks.. Actually trying to find a proper App-Note on it all... It is actually a massive topic and I'm sure manufacturers have already wrote volumes on all this..
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Re: Monitor recapping and low ESR

Post by IngoQ » Mon Oct 08, 2018 2:39 pm

"some more" as in "some more (and different) explanations on varying subjects", not neccesarily more about this one ;)
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Re: Monitor recaps and low ESR

Post by sandord » Mon Oct 08, 2018 3:36 pm

exxos wrote:
Mon Oct 08, 2018 2:01 pm
...
Thanks a lot for your explanation, it's actually very clear! I've learned a lot of new stuff (I have only very basic understanding of electronics).

Going back to my original question, I understand that low ESR is better but I can't find low ESR variants for all of the parts (at least not at Mouser.com).
I have no idea which of the original parts were already low ESR (the service manual doesn't mention anything about it).

I guess basically my question is: is it probably that there are caps in these monitors are absolutely must be replaced by low ESR caps?

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Re: Monitor recapping and low ESR

Post by sandord » Mon Oct 08, 2018 3:51 pm

If anyone is interested, I can post the part list, schematics etc.

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Re: Monitor recaps and low ESR

Post by exxos » Mon Oct 08, 2018 3:55 pm

sandord wrote:
Mon Oct 08, 2018 3:36 pm
I guess basically my question is: is it probably that there are caps in these monitors are absolutely must be replaced by low ESR caps?
I would basically say no.. Because capacitors from years ago simply likely not going to be as good rating as they are now... But In terms of low-voltage power supply capacitors, I would always suggest and recommend going for the lowest ESR value possible. The capacitors will perform better and last longer.

I posted something about similar relating to recapping power supplies.. That some cheap capacitors are simply not designed for switchmode use. They can actually heat up rapidly and even explode. Generally if the manufacturer does not quote any ESR figures at all, you can pretty much just assume it is a bad capacitor, and generally I would just avoid that manufacturer altogether. But generally if you stick to a top leading brand should basically be okay... But not in all cases...

As most know, I recommend Panasonic capacitors as the values I use are generally one of the best in the market.. But this does not mean Panasonic make the best capacitors in all values and voltages. Larger capacitors like 10,000uF mark which I use in my power supplies, are generally EPCOS. Because they make really good capacitors in that range and are actually a good price.

There is one other thing to take note with low ESR values.. Is that low voltage capacitors for example 63V and below, may have quoted ESR say 20mR or less. It is generally very good... BUT..

In terms of higher voltage capacitors such as 400V , low ESR mean something different can actually be 1ohm.. This basically looks terrible for a "low esr" capacitor, but for higher voltages, resistance is actually still classed as low ESR. Simply because some high voltage capacitors could literally be 3ohms - 10ohms for example.

So for general advice, go with one of the top brands such as Panasonic, Rubycon, epcos etc. look at the datasheets and just get "feel" for what is the normal ESR for whatever particular capacitor you are looking at.. And go with one of those..

When I choose capacitors, literally go through every manufacturer, with all variations of voltage and values which will work in my application to find the best overall capacitor versus cost. It actually can take several days just choose if you capacitors when I look around.. And of course I am literally looking for the best specifications at the best price.. That takes a lot of time..

Of course older equipment, these are a lot more forgiving with what you can use. Just please don't go with the cheapest capacity you find which physically fits and is the same ratings.. Just look at the datasheets at the ESR/mA figures.. To feel for which is generally a good range choose one of them.. There is no need to generally look through every manufacturer unless you really want to go literally the best in all cases.. That of course will take a great deal of time and is probably not worth it for older equipment..
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Re: Monitor recaps and low ESR

Post by sandord » Mon Oct 08, 2018 5:46 pm

exxos wrote:
Mon Oct 08, 2018 3:55 pm
When I choose capacitors, literally go through every manufacturer, with all variations of voltage and values which will work in my application to find the best overall capacitor versus cost. It actually can take several days just choose if you capacitors when I look around.. And of course I am literally looking for the best specifications at the best price.. That takes a lot of time..
It has taken a day and a half of my time already, so I know what you mean! I'm not looking for the best selection but I want to be sensible, hit the middle ground or something.
exxos wrote:
Mon Oct 08, 2018 3:55 pm
Of course older equipment, these are a lot more forgiving with what you can use. Just please don't go with the cheapest capacity you find which physically fits and is the same ratings.. Just look at the datasheets at the ESR/mA figures.. To feel for which is generally a good range choose one of them.. There is no need to generally look through every manufacturer unless you really want to go literally the best in all cases.. That of course will take a great deal of time and is probably not worth it for older equipment..
Looking at my current list and having added the lifetime and ESR specs, I'm starting to see a picture... I see a few caps that I definately want to see upgraded to something better.

One thing that caught my eye was that Panasonic low ESR caps list impedance and their normal caps list dissipation factor.

Untitled.png
Untitled.png (9.14 KiB) Viewed 312 times

I'm wondering how to compare the two, as non of both types list both values (at Panasonic at least).

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Re: Monitor recaps and low ESR

Post by exxos » Mon Oct 08, 2018 5:58 pm

sandord wrote:
Mon Oct 08, 2018 5:46 pm
I'm wondering how to compare the two, as non of both types list both values (at Panasonic at least).
I'm not really sure what you are trying to compare to what ?

The lifetime run of the capacitors and some other factors you should probably not be getting into right now...

For example, the hours capacitors run for at worst case operation, such as running it at maximum temperature continuously its maximum voltage rating also continuously.. Is such cases the capacitor will last around 5,000 hours for example.. But this does not mean the capacitor is no good have to those hours.. That our figure was true, the capacitor would only last half a year.. But obviously they can last many years..

Example taking Atari power supplies like the SR98 etc, the low-voltage capacitors are constantly being heated up by the heatsink.. So thereunder constant abuse which is why they fail.. Technically the same capacitors was a greater distance away from the heatsink such as couple of centimetres.. They would be subjected to a lot less heat, and last year's longer.
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