Auto Stereo & capacitors.

[DarrenFishtrain]

Helping a local kid install his big-boom stereo he got for his birthday.
Whenever his bass amp hits a hard note; everything dims. He got a 2 farad capacitor. We're running all the wires direct from a battery to the stereo, amps, etc. (ie: not using any "common body metal grounding" -- all directly to the battery.

The little blurb that came with the capacitor said to connect it to the positive, but then it said to connect the ground to the nearest ground we could (Specifically stating it should be grounded to the body in as short a distance as possible).

This seems counter intuitive to me -- we're trying to isolate the system. Why would we not want the capacitor to be connected to the same common ground running directly to the battery? Should we be grounding everything else to the body too? (ie: not use a wire directly from the battery)

He picked up a "55 amp noise suppressor" (that's what the packaging said) -- but when we got it out; it was clearly marked "35 amp" -- if he put two in parallel -- would this be ok for a 50 amp draw?

Thanks
Ol'dave.

 

[jassing]

I've always run the power lines directly to the battery -- IF your using a dedicated "accessories" battery; if you're using one battery for the whole car, I don't think you gain much by wiring all items directly to the battery.

Noise suppressors are not a 'fix' they're a band aide. Read reviews of amps (walmart, etc) and you'll see people really don't know what they're doing "I installed this amp; and got a high pitched wine [sic] when the engine is running" -- iow - they blame the amp for the noise.

Try to avoid noise - suppressors if you can; find the source, fix the source.. Just my $.01
BUT if you do use them, I would say using two in parallel could work; but (I'm not an electric engineer, nor do I pretend to be) I think when you do that; your total amps is not the two combined. if you install 2 35 amp suppressors, they will not support 70 amps; they'll actually only support something less. But I really have nothing to back that up; just a gut feeling.

 

[DarrenFishtrain]

so -- if we use a seperate battery for the audio; then go directly to the battery, otherwise, ground to the nearest point.. OK -- any idea why it makes a difference?

 

[corbintechboy]

I have a system in my car. I have 2 12s and a 1200 watt mono amp running at 1 ohm (bridged). A capacitor is not going to fix the problem. The problem is that a stock alternator only puts about about 120 amps max (at higher RPM). the capacitor stores voltage and supplies that voltage when there would otherwise be a drop in voltage caused by the sudden spike needed. So it is 12v storing 12v still limited by the amps.

The only true way to fix the problem is a high output alternator, as there is not a way to produce more amps then the car can produce other then the charging system. I actually have the same problem with dimming lights and I am having a very hard time finding an aftermarket alternator.

Without properly fixing the problem the unit will eventually take out the voltage regulator. The sudden drops will cause the regulator to have to work overtime to try and keep a even voltage in the vehicle. Even a second battery run in parallel won't fix the problem because it is still limited by what the charging system can supply.

Hope I was a help...

EDIT: To address your question, it has to do with resistance. Resistance causes heat in a electrical system and by keeping the ground as close as possible to the device, you keep the resistance as low as possible. I have actually seen ground wires start on fire (I used to be involved in bass competitions).

 

[jassing]

interesting -- because when I had a big booming stereo in my car -- deep base notes dulled the car (lights dimmed) -- but when I added a second battery and wired all stereo gear directly to that battery -- and added an isolator the dimming was gone, but had some clipping -- added dioes and a couple caps (military surplus -- I thin they were about 1 farad.) Clipping gone.

I don't think his question was so much about the caps as the grounding everything to the body.

 

[corbintechboy]

interesting -- because when I had a big booming stereo in my car -- deep base notes dulled the car (lights dimmed) -- but when I added a second battery and wired all stereo gear directly to that battery -- and added an isolator the dimming was gone, but had some clipping -- added dioes and a couple caps (military surplus -- I thin they were about 1 farad.) Clipping gone.

I don't think his question was so much about the caps as the grounding everything to the body.

That may very well work if you are running the latest Walmart system.

My amp draws 100 amps at full tilt. My charging system puts out 115 at about 2800RPM. There is no amount of any battery or anything that would fix me bumping at full tilt.

I run all Memphis stuff. This is not amateur grade stereo equipment. You will still be limited by anything you do by the amps you put out. You could add 50 batteries and if the charging system can not keep the system charged, eventually you are going to end up with batteries that are running in a deficit.

If my charging system were to fail, my system would kill my battery in about 34 seconds flat. 2 batteries would only slightly delay the inevitable. Capacitors are all limited and can only store what the charging system can produce in short bursts. Dimming may indeed slow, with a good system you are still over stressing the regulator and it will eventually fail. Nothing comes free....

 

[jassing]

still think that your answer is in search of a question... you are probably right -- let's just say that. still doesn't answer his question...

 

[kb2vxa]

For various technical reasons the proper location for the capacitor is between the + and - leads to the bass amp as close to it as possible. That little blurb assumes the vehicle body is the negative return, so very wrong since that drags in a load of crap from the electrical system. Maybe that's why radio installs go directly to the battery for power? (;->)
"This seems counter intuitive to me -- we're trying to isolate the system."
You called it, it is what it seems to be.

"He picked up a "55 amp noise suppressor" (that's what the packaging said) -- but when we got it out; it was clearly marked "35 amp" -- if he put two in parallel -- would this be ok for a 50 amp draw?"

You don't say whether it's a passive or active device, if passive two in parallel will double the current handling capacity. Frankly I hate that type, they don't do poop for noise suppression. Taking my best guess it's active, passive devices only have a positive feed through lead and much thinner ground lead, active devices have four leads, two + and - inputs and two + and - outputs all large diameter to handle the full current draw. That being the case it's unwise to parallel them being each unit has slightly different characteristics and one is likely to hog the current. First it blows, when it's gone the other gets all the juice and POOF, filters go bye bye.

"He picked up a "55 amp noise suppressor" (that's what the packaging said) -- but when we got it out; it was clearly marked "35 amp"..."

I'd take it back to the store and raise a little hell. Then I'd open the package of the next one and examine the contents after receiving credit for the return and before leaving the store. Never mind warranties, most states have "fit for merchantability" laws and the word lawyer softly spoken with a lowered gaze works wonders. Just lower your head and look up into his eyes, what you'll see looking back is priceless.

Looks like the kid has a great body weld tester there, just check the mirror periodically for a trail of nuts and bolts.