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Old 9th April 2006, 03:24 AM   #1
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Default Audio Cap ESR rating

Ok, what is considered a low ESR for audio use? I don't know if you have heard of the Alumapro carbon fim caps they are supposed to be purpose made for car audio but I am getting mixed reviews from people saying there ESR's are too high so they are useless for this purpose. Posted below is 4 .pdf files can someone look at this info and tell me what you think. I live pretty close to this company so I can always drop in on them but I found a 15 farad unit for a steal (impulse buy) and they are quite costly otherwise. Thanks for any and all help, Polo..


http://www.alumapro.com/docs/capcomps1001.pdf (Pg1)

http://www.alumapro.com/docs/capcomps1002.pdf (Pg2)

http://www.alumapro.com/docs/capcomps1003.pdf (Pg3)

http://www.alumapro.com/docs/capcomps1004.pdf (Pg4)
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Old 9th April 2006, 04:37 AM   #2
Eva is offline Eva  Spain
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The AC impedance chart has been spoiled with series inductance in the measurement setup to hide the low and flat impedance of the electrolytic up to at least 20Khz. Note how both plots show the same (test setup wiring) inductance (=rising slope) in the 10Khz range, despite capacitor construction is very different and they claim their capacitors to be "planar non-inductive".

Also, most of the statements on the text are wrong and demonstrate a quite high degree of misunderstanding of car amplifier behaviour. For example, anybody with some background should know that an amplifier playing a bass note at frequency F draws nearly all the current from the 12V supply at frequencies 2*F, 4*F, 6*F, but *never* at F. Thus, bass notes in the 20Hz to 100Hz range draw current in the 40Hz to 600Hz range, where electrolytics show their nicely low impedance.

Also, a 0.017 ohm ESR figure makes these capacitors almost unusable since a 100A pulse will already cause 1.7V drop inside the capacitor and 170W I^2*R instantaneous dissipation on its plates Battery and wiring impedance will be usually lower than 0.017ohms, thus preventing these capacitors from even providing any substantial amounts of current to the load.

I suppose that they have borrowed that "carbon" technology from memory backup capacitors, whose main features are very high capacitance densities at the expense of very high ESR and very low rated currents (they are only expected to provide a few microamperes).
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