I have never heard anyone claim that a capacitor will eliminate electrical noise, and light dimming should not be an issue with ballast controlled lights.

Not the same use we are describing. Power supply vs Frequency filter

Would a capacitor remove alternator whine from my old amp?



Buck Pomerantz from Crutchfield on 10/1/2019
Tiaan, That kind of noise is usually caused by a loose ground or power connection. A capacitor will have no effect on the noise.

(Stole this from a crutchfield forum on Stiffening caps)

A properly installed power cap will reduce noise coming in on the power input. Very few (if any) ppl who install a power cap are doing so to reduce noise but the cap still does it.

Poor grounding is not the only cause of noise. A perfectly grounded system can still pick up noise when the audio wiring acts like antennae.

If the head lights are dimming, a power cap is just a (poor) band-aid and doesn't actually fix the root cause of the problem.

If the "noise" is actually slight ripples in voltage, it will smooth them to a certain degree, but this is not "Audible noise".
I have not seen a single article that states that a stiffening cap will help reduce noise. Not even from a manufacturer trying to sell them.
I would think that if it were in fact a benefit of using a capacitor, every manufacturer would shout it from the rooftops to try to sell one more unit.
In my opinion, Stiffening caps are snake oil, and if your sound system is ridiculous enough that you need additional help, a second battery, or upgraded alternator may be in order.

As I said, power caps are not installed for noise filtering. A filtering cap should be be installed as close to the equipment as possible - all power caps I've seen are installed in the engine compartment. But it still provides some filtering.

Most manufacturers already have quite a bit of noise suppression designed into their products (on power and audio). They know the units will be operating in an electrically noisy environment. If you need to add caps for noise, you have a problem elsewhere (eg, speaker wires run too close to the ECM, faulty voltage regulator, etc).

On this, we agree. :tiphat: