RF Cap Claims?

dmeyer07 · Post by **dmeyer07** » Sat May 07, 2005 6:36 pm

http://www.rockfordfosgate.com/scripts/rightnow.cfg/php.exe/enduser/std_adp.php?p_sid=x6i*JVmh&p_lva=&p_faqid=417&p_created=1092178200&p_sp=cF9ncmlkc29ydD0mcF9yb3dfY250PTIzMCZwX3BhZ2U9MQ**&p_li=

What do you guyz think about these graphs, and performance tests...

Has a cap really done any wonders for your setup?

Jonathan · Post by **Jonathan** » Sat May 07, 2005 7:06 pm

"By providing intermediate power (small current bursts,) a Rockford Fosgate Capacitor reduces the pressure (current demand) on your electrical system."

Wrong. Now you have another load placed upon the electrical system, so not only does the amp draw current, but you now have to recharge the capacitor.

"Rockford Fosgate believes that in a car audio application the lowest possible ESR is required. Take the statement, “Current will take the path of least resistance.” For instance, the typical fully charged car battery (flooded) would have an ESR of 12-15 milliohms. All Rockford Fosgate capacitors have ESR’s of 14 milliohms or less, with most of them below 1.8. It would make sense that based upon the statement above, the lower the ESR, the more effective the capacitor will be. The larger the capacitor and lower the ESR, the less work the battery will have to do."

That would be a nice statement if the battery had a part in powering an amplifier, but in reality the battery should (optimally) have no activity when the car is turned on. Current should flow solely from the alternator and the battery will be in a charge state, and that is an example of current flowing from the point of least resistance, in which the alternator is the point of least resistance.

I would really like to see the type of power supply they used on that test to get those results, it really appears that they used a supply that is supposed to simulate a battery instead of an alternator. It appears to be a battery, and if that is the case, then that test is flawed from the get-go.

Fishy · Post by **Fishy** » Sat May 07, 2005 8:36 pm

Wrong. Now you have another load placed upon the electrical system, so not only does the amp draw current, but you now have to recharge the capacitor.

Not only that, but every time you charge a cap, regardless of its capacitance, ESR, or the difference in voltage betwen the initial and final states, the SAME amount of added energy that is stored is also dispersed as heat in the wiring. This is for an "ideal capacitor". Actual losses would be greater.

http://hyperphysics.phy-astr.gsu.edu/hb ... ng.html#c1

This is analogous to filling a gas tank while spilling at least half.

-Fishy

taylor17 · Post by **taylor17** » Sat May 07, 2005 8:52 pm

A cap can actually hurt you're electrical system.

Post by **GlassWolf** » Sun May 08, 2005 7:32 am

now capacitors aren't a "bad thing" per se. They do ahve their uses. They just don't help the charging system, and don't help with dimming lights etc as Jon and Fishy pointed out.
What a capacitor could do, is act as a filtering capacitor, smoothing AC ripple in the DC current from the voltage regulator's less than perfect bridge rectification of the alternator's AC output. The capacitor could theoretically at least, reduce transient response time, or propagation delay when the amplifier needs current quickly, provided the charging system is sufficient in the first place so it's not overtaxed in the process.
Remember a capacitor's voltage parallels the circuit voltage, so if your voltage rails are sagging due to a lack of current, the capacitor voltage is going to sag as well, which means it isn't going to help you if the lights are dimming when your bass hits.

I've seen people claim a capacitor stopped their lights from dimming, but in reality what was happening was the capacitor was smoothing the spiked demands for current, which stopped the lights from dimming suddenly by making them dimmer constantly.. thus masking the effects of an inadequate charging system.
Needless to say, most of these people end up replacing their car battery and alternator within a year or so due to failure and wonder why.
Spkrman uses battery banks with a stock alternator, which in his case is fine since he does SPL events where you're burping the system for 15 or 30 seconds with the engine off.. once the batteries are depleted (and isolated from the starter battery) the car can be started to recharge them with the stereo turned off, and no harm is really done, since the system isn't drawing large amounts of current while the batteries are recharging.

Audiophile · Post by **Audiophile** » Mon May 16, 2005 3:29 pm

I swear kiki, everytime I read something you say/write, I feel like a total dumbass. I really do. If I ever need advice I think I'd go to you first...such a fucking genius!

dmeyer07 · Post by **dmeyer07** » Mon May 16, 2005 3:39 pm

Ditto

dmeyer07 · Post by **dmeyer07** » Mon May 16, 2005 3:39 pm

There are a
lot of smart people on this board too.

Audiophile · Post by **Audiophile** » Mon May 16, 2005 3:41 pm

Hey David, how's it goin. Recognize me right? 92 ranger guy. Lol.
Did you ever hear about/know glasswolf? I may be a complete idiot and the guy's still here, but he was a damn genius too. Like 25 years as a master installer!

Edit: IM A FUCKING IDIOT! I just realized that KIKI & GLASSWOLF are one and the same! Wow...I guess I just knew him as glasswolf from Ecoustics...Maybe you remember me Glass--I was designing a blowthrough for my truck about 4 months ago?

Post by **GlassWolf** » Mon May 16, 2005 6:36 pm

yup I remember ya. sorry about the confusion there.
I've used GlassWolf since about 1995, but had to change nicks for EZboard, where this forum originated due to EZboard being retarded and seeing the word "ass" in my nick and disallowing it's use.. so out of lack of inspiration, I used my cat's name (one of them) here and it stuck here and on a couple other forums like CAF, but yeah it's me. Anyway, glad ya made it over here. I'm a lot more attentive here than I am on eCoustics. That board is just too busy to keep up with when I get busier in teh Summers.