Dumb capacitor question - Page 1
Forum section: electronics / beginners

author: MyHeadHz
author_rank: Regular Contributor
timestamp: May 08, 2018, 08:38:44 am
content: I know that 1 farad (F) is quite a lot of capacitance. So, 1 F capacitors, like the one below, are big.Why do I see so many capacitors that have such high values (sometimes hundreds of Farads) that are so small? (likethis one)I must be missing something very basic and obvious here...

author: agehall
author_rank: Frequent Contributor
timestamp: May 08, 2018, 08:56:04 am
content: Correct me if I'm wrong (and I probably am!) but isn't that due to different construction and different constraints.The first one you show is a huge cap for use in 12V systems while the other one is limited to 5.5V. That makes a big difference...

author: ggchab
author_rank: Frequent Contributor
timestamp: May 08, 2018, 09:00:02 am
content: The small one may also have a high ESR that limits discharge current and would be totally useless in the case of a car audio system.

author: BravoV
author_rank: Super Contributor
timestamp: May 08, 2018, 09:11:26 am
content: Also ... some of those car audio bling-bling cap are just fakes, they put much-much lower capacitance capacitor in there and put into bling container to impress.

author: MyHeadHz
author_rank: Regular Contributor
timestamp: May 08, 2018, 09:19:10 am
content: hmm. I foundthis articleand now I'm even more confused. Are *all* of the car audio capacitors gimmicks?

author: BravoV
author_rank: Super Contributor
timestamp: May 08, 2018, 09:23:49 am
content: Not all though, but lots of car audio stuffs are not far from audiophool's stuffs.

author: MyHeadHz
author_rank: Regular Contributor
timestamp: May 08, 2018, 09:38:08 am
content: I found another more convincing articlehere. It is really starting to sound like car audio capacitors are 100%marketing BS. It really seems like a large capacitor would just add some spikes and dips, but overall lower the total power throughput to an amp- that is to say the "area under the curve" would overall be less. Does anyone have a scope and one of these capacitors to test it?

author: Whales
author_rank: Super Contributor
timestamp: May 08, 2018, 10:29:33 am
content: The big fellow is probably a standard electrolytic capacitor, whilst the smaller banggood one is a 'super capacitor'. Different chemistries, magnitudes different power densities, presumably the supercaps end up cheaper however.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 08, 2018, 10:53:53 am
content: The only way to know if these Auto-Phool caps are the real deal is to bench test them before and after install in a vehicle,or use with some high current A-B switchand running the audio hard before and after, with engine revving at standard driving RPMwith test gear attached EVERYWHERE...oscilloscopes, current clamps, multimeters etcand the listening test, which may not mean much with semi-nuked fatigued ears cringing at high levelsOTOH, if you've got a beefy car battery with excellent CCA ability, I can't see what the cap is going to do except perhaps give the battery and alternator a headache

author: GerryBags
author_rank: Frequent Contributor
timestamp: May 08, 2018, 12:41:51 pm
content: The problem with things like these huge "audio" caps is that, once the price has got that audio premium on it, who is going to test it impartially and tell us if its a waste of money? Any professional reviewer owes more to the manufacturers who send them free stuff to "review" than they do to their audiences, as their audiences are never going to pay them well enough for their reviews that they would be able to pay for all review items as a normal customer so they become reliant on being in the manufacturers' good books for material to review.Customer reviews are not really that reliable unless you personally know that customer, due to the very Human reaction of not wanting to find negatives with a product they've just shelled out a large amount of money for. People value things more that have cost them more. Think of someone paying several million for one of Damian Hurst's half a sheep's head in formaldehyde... of course it's effin' art! It's the best art there is, it's WORTH millions!

author: Old Printer
author_rank: Frequent Contributor
timestamp: May 08, 2018, 12:57:01 pm
content: Considering the noise (music?) that comes out of them, I would say the "Bling" factor is about 100%. Kind of like this UniT bench dmm.

author: rstofer
author_rank: Super Contributor
timestamp: May 08, 2018, 03:16:27 pm
content: Quote from: Electro Detective on May 08, 2018, 10:53:53 amIf the battery is under the hood and the amplifier is in the trunk, the cables regardless of size, have resistance and inductance. Placing a capacitor (or even another battery) right next to the amplifier can prevent sags in supply voltage caused by the resistance and inductance. there's also a limit to how large the cables can be and still get them routed to the trunk. It's pretty clear that #10 AWG isn't going to do the job. I don't know what size cable is usually used.I'm not into audio at any level so I wouldn't know if the capacitors are real or not but I kind of understand what they are intended to do.Put a scope on the DC input to the amplifier and crank it up. Add the capacitor and see if there is any difference in the trace.

author: GerryBags
author_rank: Frequent Contributor
timestamp: May 08, 2018, 04:19:34 pm
content: I would like to hook that 1F cap to a huge inductor in a tank circuit and see how low a frequency oscillation I could get. I've fancied messing about with LF and ELF antennae, as I'm up in the mountains, and they either have to be huge or active and I was thinking this would be a good way to load one with a useful amount of power.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 09, 2018, 12:07:05 am
content: Quote from: Old Printer on May 08, 2018, 12:57:01 pmIt's win win mate, UNI-T has left lots of tool/parts storage space to make the product a must buyand you could in theory squeeze in a pair of 1 FARAD caps to boost the meter's DC performance, especially in buzzer and diode modes...Quote from: rstofer on May 08, 2018, 03:16:27 pmI'm very familiar with auto and hi-fi audio and test gear etc and always understood what these addon caps 'should' do and the sales pitch angle that accompanies such products etc,but whether that equates to any REAL audio benefits and doesn't burden the vehicle electrical system doing it, is debatable till demonstrated properly and unbiased.Some products may be legit, and others great retail 'mark up' duds with joules of bling and eye candy factorI'd like to test a few of these thoroughly under all conditions and see if they trigger or peak on the Stereo BS Meterbut pulled the plug on good car audio for many reasons,some being that competing with road traffic noise and being aware of danger at high music levels is a no no (lots of speeders and donkeys on ice or medication, and distracted phone junkies on the roads here)Even parked somewhere at night doesn't work for long, as the battery gets drained, and one better have a reserve battery in the boot to bail you out to start the engine.FWIW 'most' partners don't care/can't tell the difference, and in most cases they can't operate a nice system, and happy with simple ON/OFF and Volume controls, so why bother?I'm happy enough with whatever sound system comes stock in the vehicle, do a check that everything is wired correct and works, no flat battery to think about for a while,and sounds pretty good with great dynamic music and over compressed Autotuned noise, indie, rap, metal and R+B drivel.The only way to know if these caps are a worthwhile investment or yet another Auto-Phool wank, is if a member here or Youtuber with test gear and a pumping car rig with a good fresh car battery, and stable alternator to begin with (both items load tested first by an auto electrician if not up to speed with that),with solid connections and appropriate gauge wiring, wants to set it up and test itActually you don't even need to install the sound system in the car for the sake of testing, just have a high powered car audio rig assembled on a garage benchand hook it up to the car as close as possible, get the right inline fuse/s in place, keeping the wiring as short and thick as possible, ensure all the test gear is isolated or floating and SAFEand make sure you have a large fan running and the garage door isWIDE OPENduring the proceedings !

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 09, 2018, 04:24:54 pm
content: Quote from: Electro Detective on May 09, 2018, 12:07:05 amSomething isn't right about that unit. It seems to be missing the inverse-squared gravimetric attractor.