[Henry '06]

Morning guys, I recently installed a stiffening capacitor. I charged the capacitor correctly, what's happening is the capacitor is charged on start-up of the car, not too long after the audio is turned on, the cap goes to 0 and never charges back to 12-14v.


How I ran, Battery-fuse-cap-amp.

Ground-cap-two separate grounds. trunk hinge area.

 

[Z09B4U]

This is a parallel circuit. On the positive side the battery, capacitor, and amp are all connected. Same on the negative. It is impossible that if the capacitor is properly connected as you describe that it could read zero volts and the amplifier work.

With one meter lead on a good ground check the capacitor connector positive. The voltage should be the same as at the amplifier positive connector and at the fuse.

With one meter lead on the fuse you should have the same voltage at the negative capacitor connector and the negative amplifier connector,

 

[Henry '06]

correct, that's how I have it. the initial power wire that was connected to the amp, now goes to the cap. I have a 2ft power wire that connects from the cap to the amp.

 

[Z09B4U]

I do not want to start a capacitor/no capacitor debate. But if the capacitor is going to do as much as it can it should be within inches of the amplifier to reduce power lost in the wires.

The capacitor also should be connected to the same negative lead as the amplifier.

 

[Henry '06]

There right next to each other @Z09B4U . I will just remove the cap for now......It was fine before introducing the cap, I also installed Gary's big 3 already.

 

[91ss]

Post what 'capacitor' you have. If it has a voltage display, it's more than must a real cap. And in all likelyhood, you won't want the display always on draining the battery when the car isn't running. That's all that might be happening.

 

[Henry '06]

Belva BB1D 1.0 Farad is the cap I purchased. I thought I had a bad cap and did an exchange and I had the same symptoms. Cap starts at 14.1v when the car is running and the stereo is on, slowly it drops to 0.0 and no audio comes out the speakers since the cap has been depleted. Cap shows 12.4 when the car is on accessory.

 

[91ss]

Doesn't make sense. Do you still have the charge resistor in series with the cable to the battery?

 

[stonebreaker]

Exactly what problem are you trying to solve with this capacitor?

 

[storm9c1]

I'll let him speak for his reasons of using a capacitor.

But my 2 cents is that some people feel that the long wire run through the fuse to the trunk has enough voltage drop to be noticed during peak amp conditions (ie: when the bass hits), especially when using low ohm speaker setups. The theory is that the capacitor is supposed to absorb the voltage sags and make the audio cleaner. I'm not going to get involved in whether our ears can hear such things. Nor am I going to remind people that most high-end amps already contain large capacitors anyways. I'm just saying what I know.

This technique goes all the way back to the '80s and '90s. I remember building diode isolators for those systems to eliminate any backfeed into the car from the capacitor so the amp got full power. Again, I can't say if anybody could actually hear the difference, I just helped a guy out who was designing and installing high-end systems at the time. A hobby/business in that I am no longer involved. FWIW, large capacitors were very expensive then.

In this particular case, since everything is in parallel (assuming it is wired properly), if the amp shuts off after the cap is discharged, then the fuse feeding the cap/amp from the battery is blown or the connection is poor. That is the only logical explanation. The capacitor is likely charging via backfeed through the amp somehow but once music is playing, it's not being fed by the battery at all. So it quickly discharges.

A capacitor has the ability to draw a lot of power when discharged (and first connected). It's a dead short until it approaches a charges state. Unlike a battery, a capacitor tries to charge instantly, possibly drawing hundreds of amps. Unless there is built-in inrush circuitry. If there is such circuitry, I'd say something is defective. Or there is some in-rush detection problem with it.

What gauge wire is going to the trunk? Are you sure the fuse is not blown?

Disconnect everything from the power lead coming from the battery including the cap and amp, in the trunk. Use a test light to draw power from the lead. Not a multimeter. It needs to have some load on it. Using an old headlight bulb would be even better to test whether it can draw more than a few milliamps. You can buy a test light at Harbor Freight. You can get an old fashioned headlight bulb from a junkyard. Good luck.

 

[stonebreaker]

Sounds like the capacitor is a band-aid for a too small alternator.

 

[storm9c1]

Sounds like the capacitor is a band-aid for a too small alternator.

On a general level, yes. On a more technical level, an alternator (of any size) cannot respond to the transient sags fast enough that an amp would demand. And some feel that affects sound quality. As I mentioned, good amps already have large capacitors inside. So this is fiercely debated.

Edit: Correction/Clarification: You have at least 3 layers of transient "delay" of voltage drop to overcome: 1) the battery's ability to deliver transient current over transient sags, 2) the alternator's ability to detect and respond to the transient sag, and 3) the wire, fuse and connections running from the battery to the amp causing voltage drop therein. A capacitor at the amp can respond instantly to smooth all of these out. At least that's the theory.

 

[stonebreaker]

Yeah, but on the other hand, the capacitor's adding additional load. The guy mentioned that the capacitor is gradually discharging after he turns on his system. I'm not an audio guy, but in his particular case, seems like the capacitor is just dragging the system down.