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12-07-2008
Hi everyone.
I have an old 1 farrad accucap that I was considering installing when I get new subs. Only problem is that there is no indication on the cap which set of terminals is +and-. I have not used it in a few years and can't remember which is which. Is there a way to check this with a multi meter or something? Thanks for any help!
12-07-2008
my suggestion is don't even use it. they don't really do anything.
12-07-2008
I have it already, it can't hurt anything to have it and The display is kinda cool, so if I can figure out which way it hooks up properly I would like to use it.Originally Posted by jasonball
12-07-2008
Actually, it can. Once it becomes discharged (after the first hit), it will do nothing but add a load to your alternator instead of helping it.
12-07-2008
So what purpose do they really serve then? Just wondering. A friend of mine has a 5 farrad cap on his system which consists of 1 3000 watt power accoustic amp 2 12 p accoustic subs and an alpine 4 channel and the lights still dim on bass hits?
12-08-2008
A cap can be very helpful with minor light dimming/voltage drop situations, as it stores power and discharges it very quickly...much quicker than a battery. A cap is essentially a battery, but it can charge up much faster, discharge energy much faster and take a lot less toll on your charging system overall (not to mention it weighs a fraction of a batteries weight)....any more than a 1-2f cap is useless, and likely will start to over-tax your charging system (much like additional batteries)...the absolute one and only thing that makes power is an alternator, batteries and caps simply store power... so if your low on voltage upgrade your alternator!
As for your cap, i really can not see there being no markings unless the stickers got peeled off or something??...hooking up a cap backwards can be dangerous, so i would look into the make and model try pulling up some information on it, perhaps e-mail the company.
12-09-2008
Bragging rights? Not much else.
12-08-2008
use a test light and ground it to you cars chassis and touch the probe to both ends. whisch ever on lights up is the pos.
like it has been stated it WILL cause damage. they are pointless besides for the display. i have one in my competition truck only for the voltage gauege. it is hooked up with 14 awg wire.
12-08-2008
[quote=reinke;112550]use a test light and ground it to you cars chassis and touch the probe to both ends. whisch ever on lights up is the pos.quote]
That will only work if the cap has a charge
I say toss it out. you can probably take the digital volt meter off of it and wire it in anywhere.
12-08-2008
usually a capacitor will hold some of its charge no matter what. you only need 1 volt to turn a test light on.
12-09-2008
He said he hasnt used it in a few years though. I guess it's worth a try
12-09-2008
Well caps do serve a useful purpose, even in automotive applications. The one big thing they are good at as stated already is power storage. Thats why they are used so widely in audio applications, they fill the gap where the battery/alternator cant keep up, but they do have limits and as mentioned you can get one big enough that it could potentially put too much of a load on the alternator.
The next thing they are good at is filtering AC noise out of an electrical system. In a car that is powered by DC that is a really good thing, particularly with all the AC noise that can be introduced into the system by various components. Anyone ever hook up an oscilloscope to an automotive system? It can be quite loaded with AC noise.
Usually with capacitors, they are marked in some way. Smaller circuit board one have a lead that is longer than the other or marked on the part itself in some way. In larger ones, Ive seen + and - signs stamped into the terminals themselves.
Another way to determine it (someone already mentioned the test light) would be to also try using a multimeter set the measure DC voltage. The red lead is positive, the black is negative or ground. Touch the two terminals, when the voltage reads a positive voltage (i.e., not -12 or something like that) then the terminal the red lead is touching is the positive terminal.
Capacitors can recharge themselves on the static electricity in the air. In electronics school we were taught to keep a resistor across the terminal of large capacitors. At that time a large capacitor was 200,000 micro farads. I can only imagine the charge full farad or multi-farad capacitors can store from just the static electricity in the air.
Ive seen a 100,000 micro farad capacitor arc pretty darn good from just the charge built up from static.
12-10-2008
I finally found the markings under the terminals. Caught it in just the right light to see them. No idea why they would be so difficult to find since it would be dangerous to hook it up wrong. Thanks to everyone for all the info!
12-10-2008
yeah, you'd think they would make that easier to see.
12-16-2008
_nick_ and Synthetic posted the most useful and accurate info in this thread IMO. A multimeter is the best way to go about testing something like this. I imagine that the diode test on the meter would work quite well and quite safely for a capacitor
12-16-2008
Diode test would do nothing. A capacitor is an open no matter how you test it. You will never get continuity since there is no continuity.
Small caps inside the electronics for filtering are good. They also make up part of band-pass filters. Using them to supplement power is a waste. Sorta like putting a bandaid on a broken leg. If you alternator can't keep up, you should put the money towards a higher output alternator.
12-16-2008
actually a secondary battery would be a better moved. his stock alternator has roughly 25 extra amps that are not needed at speed. he would see a better imporvement if he picked up a kinetik or a powermaster battery.
12-16-2008
Second battery is worthless too. Batteries are 12v. Usually the car's electrical system is above that. So, the battery won't do anything until the alternator is strained and the system's voltage drops to 12v. Then the batteries will keep it from dropping any lower until they are dead. Only problem is that when the load lifts now the batteries are drawing current as they try to recharge.
The only real answer to the problem is a better alternator.
12-19-2008
all i have to say is DAMN your a dumb ass. adding a second battery will give him more reserve. a battery with a CCA rating of 600amps is like adding a 100 farad capacitor. what you are saying is that the battery in the front of every vehicle serves no purpose then.
12-20-2008
Yeah, I have a few years of college level electronics courses. I repair complex electronic equipment every day for the Air Force. I must be a dumb ass. Thanks for letting me know.
When the vehicle is running, the battery is supposed to be charging and doing nothing else. So, as long as the engine is running it does serve no purpose, and if it does your alternator requires upgrading. If the battery did have a purpose during engine operation (other than to recharge itself off the alternator), then removing it with the engine on should have some effect. Guess what, you can take the battery out with the engine running and the car is none the wiser. The only reason a battery has to do anything with the engine running is when the alternator can't handle the load and its voltage drops. Then the battery has to step in and supplement it.
The battery's purpose is to start the car and power the electronics when the engine is off. Not when the engine is running. If you don't understand a basic parallel power supply circuit, then perhaps you should hold off on the name calling.
The problem with adding any supplemental power source (like another battery or a cap) is that once that source is tapped at all, it becomes a load on the alternator. You get a nice string of hard hits from your stereo, and now your cap is dead. From now on, until you turn down the volume or pause the music, the cap is putting more load on the alternator than before since it's trying to recharge. Similar situation with adding a second battery, or relying on the factory battery to supplement the alternator.
So, it comes back to the fact that the only real solution is to get a better alternator. Any intelligent questions or do you want to go back to name calling?
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