System:
Headunit: Kenwood DDX 6019
Speakers: F: Polk/Momo MMC6500, R: Polk/Momo MMC650
Sub: JL 10w1v2 in WickedCas corner magic box
amp: Phoenix Gold R.0:5

Headunit is in, the rest I will be installing in a few weeks. Do I need a cap or will I be ok without one? System is not extreme and I don't operate at very high volumes.

 

what kind of power is your amp?

 

You will not need a cap.

 

Cool; didn't think so, just wanted to be sure. Thanks.

'nother quick question: I'm running a UR pulley and stock battery; will I have any kind of power delivery issues?

 

I'm running a UR pulley and OE battery as well...I have a 700 watt amp and don't have any issues. (The volt drops from 14 to 10~12 while at idle and volume turned way up - I just increase revs to 1K and it goes back to normal)

-Peter

 

Ok, well I don't really crank the volume, so hopefully I'll be fine.

Does your drop in voltage have any negative effect if you don't rev it a bit?

Here's the amp I'm getting:
http://www.millionbuy.com/phgr905.html

 

This would be a sign that you probably need a cap.

 

really? I didn't think it was too much of a concern - I've only had it happen once. I barley turn up my music that loud while at idle...on that occasion, traffic was super bad and I was bored out of my mind (my normal 30 minute commute took close to 3 hrs!)

-Peter

 

It's an indicator that your alternator cannot keep up and you're putting additional strain on it, which isn't good. If you're dropping down into the 10's and 11's at any point, I would highly recommend a cap of some sort. No need for anything major, but better safe than prematurely replacing your alternator. With the power the both of you are running ( Im not sure what type of amp you have, but phoenix gold is pretty efficient) 1 farad should be fine. There is a scale to go from but I don't know it off the top of my head.

And FYI, your pulley's aren't helping the situation. One of the trade-offs unfortunately. I wanted pulleys myself but opted to wait and see what I was pulling power wise. Now that I downgraded, I will probably do the pulley set-up this winter since I have more than sufficient power.

 

Rule of thumb. Install a 1 Farad cap when you reach 1k watts. Add an additional farad for every 1k watts after that.

 

Well, I'll start without one and see how it goes. I can always add one later, if needed. Thanks for the input, guys.

 

What happens once the cap is drained? Its gotta recharge somehow...just more strain on the alternator. It is good for a small burp in power but after that it is just one more strain on the system.

The only advantage that I could see to using a cap would be for filtration but thats overkill.

I say ditch the cap. Like Driven1 said, you are straining your alternator when you drop bellow 14 volts. If you want to stop that completely...upgrade alternators.

 

You have the wrong impression of what the purpose of the cap is to an electrical system. Yes caps do drain, but the purpose of it is to regulate not completely power and recharge. It is meant to take the jolting and pulsing loads of an aftermarket stereo (typically the bass, b/c it requires quick loads of power when operating) and recharge at a steady rate. The quick loads are what drops your voltage, not a steady pull which the battery buffers even more before it effects the alternator (i.e thats why many stero guys switch to a mirine or dry cell).

Like judging from what "MustGoFastR" said, Im willing to guess that he listens to rock? This is because he saw the volt meter drop over an extended period of time at a high level and the quicker pulses of rock music take less draw but the rate at which they were occurring was more than the output of the baterry and alt.. So in this case a cap would help buffer and disperse the load when he listens to it loud at an idol.

If he were to listen to rap music the draws are larger (due to frequency) and the distance between the draws is longer as well and the pulsing isn't as quick But the battery can recharge between the longer pulses(hense, you frequently see pulsing lights).

Typically you will only need to swap an alternator and upgrade when you are running applications requiring 0 guage wiring and possibly multiple batteries.

 

A cap is a filter. I agree that it aids in filtering out the jolts of current drawn by the amps. However, a long nasty square sin wave at 50hz(al la lil john) will kill the voltage on even a dry cell battery without a problem.

I listen to rock and my voltage stays constant. When I switch to something with synthetic bass lines, the voltage drops because those long 50-70 hz bass lines draw a ton of current.

 

You're ,missing the point man. You just stated what I just told you in different words.
And you're cap isn't big enough if that happens when you're listneing to lil john. You must also take into consideration the efficiency of your amplifier. You put crap like off name brands in your car (from the flea market), most likely that amp will draw considerably more power to make the same power a nicer amp would draw. This has to do with the quality of the circuitry and the amount of technology put into it.

I can crank my stereo (full dolby digital 5.1 surround, 4 tv's, One kicker twelve, two Audiobahn amplifiers) all day in neutral for hours with minimal to 0 volt drop. Granted I did a slight overkill using the 5 farad Aluma pro C.A.P.

Remember this doesn't apply to vehicles with 1000's of watts. This applys to relatively normal applications.

12V class is OVER.

 

I am not attacking your explination because the use of a cap in a car is not clear cut. I do have a full understanding of capacitors and the RC functions associated with them(charging and discharge functions). Capacitors do no discharge and charge in a linear fashion as you described(steady).

Are audiobahn amplifiers considered good quality to you?

Compare this:

to this:


Which looks better to you? Both have nearly the same rated power.

 

To the OP, you do not need a cap for the install you described. The stock charging system should be able to keep up with your demands. I personally don't see a need for a cap ever. A second isolated battery, now that's another can of beans to open and they have their uses in the car audio realm, but again, not for the system you described (unless you plan on running your system for long periods with the engine off). The factory alternator has ABOUT 15 amperes of headroom over the stock draw. I say about because it all depends on what you have on at any given time (headlights, radio, etc.). If your amplifier is going to draw more than that, then think about upgrading the charging system in the near future. Keep in mind that the amplifier is only going to draw its full amperes at full volume during peak musical throughput when tuned right.

I come from the school of thought that a cap is a band-aid for a bigger problem - a weak alternator. Some people install caps to fix dimming headlights. this is a band-aid, not a fix. To properly fix such an issue, save the money you would have spent on a cap and buy a high output alternator and a nice battery (Exide Orbital is my fave, but the Optimas are good too). A cap may "filter" the spikes, but the same strain is on your charging system, so to YOU it appears as though the charging problem is fixed, when in reality it still exists.

Your charging system upgrades should be in the order of the following if you are having troubles:
1) Verify the power & ground wire you are using is sufficient for the amp draw you have with your amplifiers.
2) The big 3 - Google it if you don't know what it is.
3) Switch to a gel or dry cell battery.
4) Upgrade to a higher output alternator.

Again, this applies to the "average Joe's" intall under, say, 1000 watts who is going to listen to the stereo for their own enjoyment with the engine running (i.e. 90% of the people who install an aftermarket audio system).

 

Can't go wrong with a cap though.

 

Wow, lots of info. to digest here. Well, if I experience power issues, I certainly have a nice list of options to go about rectifying it.

Next question:
I'll be running 12 ga speaker wire to the sub, but are the factory wires adequate to run the front and rear speakers? I know I'll have to run new wiring from the amp, but was hoping just to tap into the factory wires at a convinient spot, rather than running the new wires all the way to the speakers. The amp will be pushing 50W RMS x4 at 4 Ohms.

 

The factory speaker wires should be sufficient. Do yourself a favor when you splice into them and solder and shrink tube them.