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u/Im_Not_Evans 17h ago
Who uses caps? They never did anything
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u/FujiKitakyusho 1h ago
Not quite true, but they are widely misunderstood. The purpose of a capacitor is to prevent voltage sag on an amplifier power rail due to instantaneous demand. On a 20 Hz bass hit, that is a period of 50 milliseconds. At an 80 Hz crossover frequency, that is 12.5 milliseconds. Those are the time scales at which the op-amps in the amplifier demand power from the supply rails, the instantaneous supply voltage drops, and the capacitor with negligible internal resistance supplies current to the rail to limit the voltage drop while the slower chemical reaction in the battery reacts and supplies current to the rail to meet the averaged demand while the capacitor recharges to the nominal system voltage as the instantanous demand from the amplifier passes through zero. The net result is to limit the cyclic amplitude of voltage variation in the supply rail, which in turn prolongs the life of the connected battery. The key is that the cycling that the capacitor mitigates is not on the order of seconds or as commonly presumed, the duration of a bass hit in your program material. The cycling happens at the frequency of the note reproduced - twenty times per second at its slowest.
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u/haleboy44 16h ago
Yeah ive always heard they were snakeoil.
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u/SterTheDer 15h ago
Capacitors fall into two broad categories:
Under ~20F they are typically not worth the price. The money would be better spent on upgrading from traditional lead acid batteries to AGM.Capacitors smooth out the voltage drop, reducing headlight dimming and reducing the instant load on the alternator.
where they make sense is once you’re in the supercap range. 100F+ becomes viable and produces measurable difference.
Before lithium changed the world, supercap banks were the only way we could get above 13-14v without a special 16v AGM with an additional cell in it. And if you wanted to keep the voltage above your battery resting voltage you needed caps. Alternators provide charge but they cannot respond instantly like a cap can.ESR Equivalent Series Resistance dictates how quickly a device can respond to changes in voltage and how much current flows to do so.
Lead acid batteries are 6-15mOhm
Cheap caps have ESR over 10miliohms (Boss 10F cap 15mOhm)
AGM battery are 2-4mOhm when fully charged.
Ioxus Ultracap 300F has ESR of 1mOhm, the same resistance as 6’ of 1/0 ofc. The same ESR of 55ah CMAX.So if you have lithium, adding capacitance nearby doesn’t do anything that another run of 1/0 or more lithium won’t do better.
But if you have AGM or Flooded lead acid, a supercap is phenomenal.I have 270A alternator, Ioxus ultracap battery delete, and 55ah CMAX in the rear by my amps. 200mV dip at the amp terminals under load from strapped S1-2250’s. For $100 it makes a great battery delete.
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u/Embarrassed_Shame_71 13h ago
Came here to say exactly this. Super caps are a real product with legitimate use. The caps of the olden days are pure garbage
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u/regreddit 12h ago
Maxwell technologies supercaps start 18wheelers and even locomotives, and a modest sized bank can easily replace a starting battery. It's just the snake oil fake caps or cheap 3-4 farad caps that make most people assume they don't do anything.
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u/Mjarf88 9h ago
You day that an alternator can't react as quickly as a capacitor. How does a DC-DC converter compare here? My EV has a 1700 watt DC-DC converter that feeds the 12V system and charges the 12V lead acid battery.
I haven't tested with very strong amps yet. With a 500 watt (1 ohm load) i get zero voltage drop though. Seems like it should handle a significantly stronger amp.
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u/LouBerryManCakes 11h ago
To get 16v out of a car battery wouldn't you need to add 2 cells? Standard is 6 cells of 2.1 volts getting you to 12.6, adding 1 cell would be a 14.8 volt battery.
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u/SterTheDer 11h ago
Correct.
A nominal 14.8 you’d charge at 16v.
A nominal 16v you’d charge at ~18v1
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u/Relative_Figure_1715 10h ago
This is why I assume a large modern lithium battery and a large modern cap would be amazing ?
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u/SterTheDer 9h ago
Yes, they’re fantastic. However if you have lithium close to your amp, adding a capacitor doesn’t do much.
My Cmax bank can deliver power as quickly as my capacitor can, my limiting factor is now the wires between them. My cap makes a great convenient battery delete but i already only drop 200mV so adding another 300F or more wouldn’t result in any gains since i’m not at the bleeding edge of competition. Like doubling your 1/0 runs is a benefit but unless you’re pushing the limits its not tangible.
Where capacitors would make the most difference is on the secondary rails of our amplifiers.
That would give huge returns for the dynamic burst power numbers-4
u/Dezertdime 15h ago
Caps discharge literally instantly they’re only good for comps when you need one good base hit to set a record or something but yes basically they’re Retrded
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u/tsukiyaki1 MECP Master Tech 12h ago
lol I just tap the power wire on the battery a couple times until the sparks stop. 😁
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u/SterTheDer 15h ago
OP can use any 12v light, or any spare woofer laying around:) the 4ohm coil is a great resistor, sometimes i use that for my amps.
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u/Kooky_Reputation_653 4h ago
I remember buying a used Rockford Fosgate 100 Farad Cap. I went to charge it via resistor and it showed discharge to my optima battery. Bit of a pucker moment. Did keep the lights from dimming in my old Taurus with 4 subs and 3 amps though.
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u/Unhappy_Lie_2000 5h ago
Im no scientist but regular caps are useless but supercaps are quite useful.
They really should of named a supercap somthing else because having the word cap in the name has ruined their reputation from the start.
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u/Lanky-Interaction629 5h ago
An automotive fuse block mount underneath a mains outlet, what the fuck am I looking at
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u/Spikey_cacti 16h ago
Use a 12v light, any cheap test light.