by The Roadie » Fri Sep 13, 2013 11:18 am
Huge capacitors should be put near the item that sucks the most amount of current that causes the voltage drop. The caps they sell for bass-thumpers are mostly snake oil in my estimation. The equivalent size motorcycle battery costs half as much as a huge cap, and is the electrical equivalent of 100 huge caps. Perhaps 500. I haven't done the math, but motorcycle batteries could and should be used in any application where the audio guys use caps, but they don't have the same "magic" snake oil qualities, or profit margins.
OK, now I'm annoyed at myself. Let's do the math I should have done a long time ago. A Scorpion gel cell (maintenance free) motorcycle battery I just found for $36 on-line. Capacity of 4 Amp-hours. Assume a constant discharge rate (not a good idea, but good for an estimate) of 1 Amp, and you start off with delivering 12W, tapering off to nothing after 4 hours. Average is therefore 6W X 4 hours, or 24 Watt-hours. The amount of energy in an item is measured in Joules, which is a Watt-second, so 24 Watt-hours = 24 X 60 X 60 = 86.4 KiloJoules.
Energy stored in a capacitor = 1/2 X C (in farads) X V squared. So let's say you had a 10 Farad cap for $100. The energy it can store (and remember, you won't get the total energy storage delivery out of a cap OR a battery if you're trying to prevent voltage drooping that causes headlight flickering) is about 980 Joules assuming 14V is on it when you begin.
So the battery is 88 times a better energy storage mechanism than the capacitor, and when you factor in the cost difference, it's 244 times as cost-efficient.
So my back of the envelope guess was in the ballpark.
Audio guys SHOULD be using small batteries instead of snake oil caps. There's a business model somebody could take and run with.