I don't know why I didn't see this long, long ago. It almost seems ridiculous now.

Let me start by saying that I have a Master's in Electronics Engineering and this is not an uneducated opinion. Not to brag, but for credibility.

First, the background story. Many moons ago, my Optima Yellow Top was going dead frequently on me. Got tired of that, and replaced it with an Odyssey, which is a $200 killer battery, one of the best deep-cyclers made. Lately, Odyssey has been going dead, and I've been having problems starting the car, and frequent manual recharging.

Meanwhile, I've had a Lightning Audio Strike 1F Cap installed since I gutted my system and re-did it in 2002. For those of you that like to do the math, that's 7 years ago. This thing is in there to provide instantaneous power to my 2 JL amps, including the 500/1 for the Image Dynamics 12" sub.

My system never quite sounded (bass-wise) the way I wanted it to, and I always attributed this to interior acoustics, not enough Dynamat, etc. Always seemed that as I turned up the bass, I'd get more, but it never seemed to have the punchy live quality I was looking for. Was it that I was only running one woofer? Hey, most people were impressed, and it wasn't like I had no bass. Also didn't seem like a flat response, but someday I'd get around to tweaking the 30-band Audio Control EQ in my trunk.

Well, over the weekend I decided to rip out the STIFFENING CAP, since it seemed like it would be the most likely culprit and cause of the dead batteries and drain while sitting idle in my driveway for a few days.

I WAS RIGHT. BUT THE REASON I'M WRITING THIS IS BECAUSE IT DOESN'T END THERE.

I'm happier than a pig in you-know-what that my battery no longer goes dead. BUT NOW MY BASS IS ABSOLUTELY UNBELIEVABLE. The frequency response has flattened out. I can hear every pluck of a bass in every song. Kick drums are dynamic and hit HARD. It's unbelievable, the only thing I did was YANK THE CAP.

Here's what's going on, and I'm sure it's happening to most of the other installs out there:

The theory says that you should install a large cap (1F per 1000 watts of amp power) immediately near your amp, and this provides instantaneous current for bass note spikes. That it may.

However, let's think about what happens immediately AFTER the cap begins to provide its stored charge (in the form of current) to the amp. The cap is now in a depleted state, in a very short time relative to the bass waveform (note) length. (More on this below.) But meanwhile, the battery and alternator are responsible for keeping the system (and capacitor) voltage at 12V or more, and so must provide current to CHARGE THE CAP.

That's right folks, the CAP has just become a major LOAD on the electrical system. And depending on how much charge/current was depleted from the cap on the attack of the first bass hit, this will determine how much current it will draw to charge it back up and replenish.

While it's replenishing, guess what component is not receiving all the current that your battery and alternator can provide - YOUR AMP. The cap is actually stealing current from your amp after it dumps its own.

The problem here stems from the sheer size of the cap, at 1 Farad. The time constant is relatively long. Time Constant T=RC, the series resistance times the cap value. The ESR, or Equivalent Series Resistance, of a typical 1F cap is 1.6 milliohms = 0.0016 ohms. This, of itself is small, but what must be added to this and accounted for is the series resistance of the wiring from CAP to AMP (for the discharge time constant), and more importantly, the series resistance from the battery/alternator to CAP (for the charge-up time constant).

The minimum value is (0.0016 ohms)(1Farad) = 0.0016 seconds = 1.6 milliseconds, but this time grows A LOT when we add in the series resistances of the wiring and connections as mentioned above. You can easily have 1/4 of an ohm in wiring and connections. That's .25 seconds, or 250 ms.

Now lets look at how much time this represents relative to the music and bass notes. A 100Hz sine wave has a period of 1/100 sec, or 10milliseconds. A 60 Hz sine has a period of 16ms. A 30Hz sine has a period of 33ms. Once the FIRST cycle of a LOUD bass attack occurs (you volume is turned WAY up), cap discharges, providing local current, but the low frequency bass cycles keep coming. OK, so you got one or two good cycles, but now the cap can't charge fast enough to continue to provide current, and is now A LOAD ON YOUR BATTERY/ALTERNATOR, AND IS COMPETING FOR CURRENT WITH....YOUR WOOFER.

Finally, depending on the character of the bass notes, length, frequency, amp gain. headunit volume, the cap charge/discharge cycle length will have a time and frequency-dependent effect on the strength of the bass notes, altering the frequency response.

BOTTOM LINE HERE IS: Yank your cap(s) and try your system without. You may be pleasantly surprised as I was. Let the battery speak directly to the amp. Interior lights may dim, but for that case the solution is NOT to put a huge cap at the amp, but a much smaller one on the power supply wiring to the LIGHTS.

I also just found this tasty little tidbit, so check it out as well.:
http://www.installercentral.com/tech...think-it-does/

Jerry

 

It is soooooo pleasing to read a post like this!!!!

I am a MECP certified installer and personally, I do not use stiffening capacitors. Hey, if a customer wants one despite my advise against it...i'll install it for them. Heck, it's their money.

My advise is always to increase available amperage. Bigger or multiple alternators and multiple batteries.

There will be those that disagree with me, but your post really hits the proverbial nail on the head with one of the multitude of problems associated with capacitors.

 

This is not Earf shattering news, because it has long been understood that capacitors should be used to supplement an already stable system. For those who are consistently running their system at 11 (LOL!) and need quick bass response, capacitors are a total waste if the alternator is not feeding the system. I've said this many times here and on a few other forums, and it's never changed. Once a capacitor (or battery) becomes discharged or goes below the system voltage, it is a load - it's pure electrical fact.

One question I do have, though, Jerry, is how your capacitor could have been causing a battery to drain. If your alternator is keeping up with the system and charging the battery properly now, it should have been able to do this with a cap in line and not had a dead battery. I would be looking for something that may have caused additional drain, such as an amp staying on after the vehicle was shut off, in the chain. I've used capacitors many times in installations that were already fully functional to give a supplement and eliminate the disco lights, and they served that purpose, but never caused dead batteries.

Funny story to add, too - went in and had an alternator swap done in my old car because the factory one finally crapped out after 9 years (who knew??). Got a call from the shop wondering why the power lead might still be energized. They asked if I had additional batteries or anything in the car, because when they disconnected the battery it still had lights inside. Despite having the keys and full access to the trunk, the guy called me anyway, which I appreciated. I told him that yes, there was a capacitor bank in the back, and that he could pull the fuses out. He said when he went in there that he hadn't seen a setup like that and was amazed at how efficiently it was utilizing the space. I told him the custom buss bars were a gift from a friend and thanked him for the work on the alternator. He said when they worked on it they gave me a "little upgrade" and gave me a 160A unit instead of 130A. No complaints from me!

Big Mack

 

My guess on the battery drain factor, without having taken the time to measure anything, is that there was probably a minor leakage path through which the cap's charge was being bled off when the ignition was off, causing the battery to continually charge the cap to battery voltage. Wasn't bad if I started the engine every few days and recharged, but if I let it sit more than that, would usually result in not being able to start the car.

At 140K miles, I dunno how much life is left in my alternator, so I may need one soon, or a rebuild, etc. Got a good source Mack?

 

Im loving this entire conversation because it proves my point!!!!, Caps steal bass, and for those who say they've gained power from a cap, seriously need to reconsider their statement. Im puishing two Alpine Type R 10's on a Orion 1200D amp with NO CAP, and no one believes that all I have is 10's, because I beat out competition with 12's all the time and only one time with 15's although it was still a close call. All of them had caps installed and all of them were disappointed as I set their car alarms off as I rode pass lol.

engin ear....i'm seriously feelin your expertise here....

 

wow....good info...thanks!

 

Sorry it took me a bit to revisit this. Sounds like a good diagnosis to me.

The guys I dealt with were local to me, so it may be cost prohibitive to have them do the work for you, Jerry. I would look for a local alternator repair facility. I will definitely take my electrical problems (if any) to these guys, though, since they're right up the road from me. If anyone in Phoenix needs an alternator, the guys at Checkered Flag alts in Mesa are top notch. Very friendly, great pricing, and full warranty. They'll even do the work!

Big Mack

 

Great info coming from an EE