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Old 13th December 2010, 09:13 PM   #701
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If you can get the standard size caps, I would be getting those, but that is just my opinion.
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Old 13th December 2010, 09:15 PM   #702
EUVL is offline EUVL  Europe
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You should not compare caps with different capacitance, as then the ripple current is not the same.

So let's take 39000uF 25V, with 12A ripple current at 50C.

TS-UQ has a current ratio of 1.63, and about 60,000 hrs.
TS-HC has a current ratio of 2.07, and about 120,000 hrs.

So I guess in this particular case, it is worth using the 105C cap.

The curves are taken from Krummer data sheets.
Not sure if they can be universally applied to all cap makes.

So use it with care.


Patrick
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Old 13th December 2010, 09:25 PM   #703
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Thanks Patrick

I know what I will be using. I have seen enough capacitor failures to know that using 85 degree caps is asking for trouble. Anyway it was nice to see these graphs and to make sense of them.
I don't want to scare people off from using 85 degree caps though if you can get them for a good price.
If you can get the 85 degree caps for half the price of the 105 degree caps then I would get the 85 degree caps.
If not, my suggestion would be to get 105 degree caps.

Last edited by Melon Head; 13th December 2010 at 09:33 PM.
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Old 13th December 2010, 11:37 PM   #704
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Contrary to your experience, I have no bad experiences with 85C caps even in Class A amps running at 60C heat sinks.
Especially, the ones I have from BC Components have retained their capacitance over the years very well.

In theory, there is a factor of 2 between 60,000 hours and 120,000 hours.
In practice I don't think my transistors will last 120,000 hours (which is 14 years continuous non-stop).

Of course you are all free to choose what you want.
I am not going to recommend any, other than good brands like Panasonic, BC, EPCOS, etc.

I have not tried Krummer, but they seem to be well received in German DIY forums.


Patrick
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Old 14th December 2010, 08:02 AM   #705
Luke is offline Luke  New Zealand
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I have very rarely seen cap failures in amps period. Even in 30 year old amps, it seems to be the outputs and drivers that fail.
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Old 14th December 2010, 08:55 AM   #706
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I wasn't specifically talking about amplifiers. For the record I have not had any type of amp failure (touch wood).
I was talking about electronic equipment in general. I am constantly getting lab equipment repaired and all of the cap failures have been 85 degree caps. None of the cap failures have been 105 degree rated caps.
Hence, this is the reason for my bias towards 105 degree caps.
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Old 14th December 2010, 11:46 AM   #707
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Looking at Euvl "Krummer" graphs, the important factor, that I see, is to keep the capacitors cool !
You do this by ensuring they are in the bottom of a well ventilated case and by ensuring that the applied ripple current is well below the maximum rated ripple current.

Doing both of these, you can expect quarter of a million hours of use from any temperature rated capacitor.
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Old 14th December 2010, 04:03 PM   #708
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If those are the design criteria, then maybe you shouldn't be building Class A in the first place.




Patrick
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Old 15th December 2010, 08:35 AM   #709
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Lifetime model for Panasonic Snap-in's :

http://www.ndb.com.tw/files/panasoni...C%E5%BC%8F.pdf


Patrick
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Old 16th December 2010, 04:42 PM   #710
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For all that remember post 550

Have a good Lough

Quote in full so not to confuse matters.
I have no problem with open technical arguments. You should know.

> Where you see volume content I am referring to pigment to binder ratio. There are also some level of volatile solvents (not included in the volume) which evaporate once applied.

That is cheating.

> However you can combine the two different types of particles in different ratios to get thixotropic flow properties as well as the benefit of high thermally conductive particles such as diamond.

> So you might end up with 20% diamond and 50% thixotropic particles.

That is exactly the same as what I meant by bi-modal.

If all particles are perfect spheres of the same size, and you can pack them by hand in the tightest possible manner, you can fill up about 65% of the volume. The rest of the space you can now fill up with a particle size (smaller spheres) about a factor of 10 smaller. Again if you have perfect packing, you would fill up say 50% of the remaining 35%, giving you a theoretical fill factor of 80%+.

That is theory. In practice, the particles are not spheres, they are not all the small size, and they do not pack themselves into perfect filling geometry. So a bi-modal mix will get you slightly above 70%. Extrusion is good for packing, compared to the like of isostatic pressing or slip casting, in that you have some lubrication effect of the molten plastic, plus the extremely high extrusion pressure which helps to pack the particles as tight as possible.

The Kerafol 82/86 is not the best they have in sheer thermal performance. I have tried other stuff which are better thermally. But they have such high filler content and hence so fragile that they break into pieces in your finger. So I thought I wasn't going to recommend the public to use any of those.

There are ways to get even better performance (e.g. doubling the pad size by soldering a 3mm copper plate to the TO247 of twice the footprint, and using a larger piece of Kerafol). But you need to know what you are doing. And at a dT of already 3C (with the 2SK1530, so about 4C for TO247), the gain is at most 2C for all the trouble.
Patrick

There must be sometink wrong with 5mm cooper 3 apparently is much better as oviously capacitance dont count anymore.

Have a nice day

Al
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