AW: [DML] grounding equipment to battery?

["Elvis Nocita" <elvisnocita@xxxx>]

Hi Kayo,

you seem to be very familiar with Hifi and stuff, but do you really know a
cap is ?

Why should it soak up all the current that the alternator generates ?
Once it is loaded it doesn't need any current anymore as long as it is not
discharged by something. You need it (if needed at all ?) only to keep the
voltage stabilized when an extreme kickbass needs to be powered. imagine the
wire from the amp to the battery as a resistor and an inductivity. when very
fast a high current is needed, first the inductance will slow down the
current rise.
(I am not sure if you will really sense that.) But even worse, the extreme
high
current needed produces a voltage loss over the wire, so the amp won't see
the
whole 12V or better 13.8V produced by the generator or stored in the
battery.
If you have 0.1 Ohm wire resistance (pretty much, but may happen with bad
contacts)
and you need about 30A for that bass, then you will have a voltage loss of
3V which
will be missing for the amp to produce that correct signal for your speaker.
Now
in this case, the cap (placed directly next to the amp) will provide the
current
needed.
If the signal lasts longer, than the cap will be discharged to the same
voltage that
the amp would see without the cap ! There is no such thing like you
described !

But what also happens is, that every voltage ripple produced by the
alternator or fan motors or whatever, will push and pull current through the
amp wire because there will be a voltage difference between cap and battery
! This current can produce even more distortions
if ground connection is wrong !

So you're right to say - forget that stuff in a Delorean as long as you
wanna keep
your ability to hear. It is not necessarry at all.

To find the best spot for the ground connection - look where the radio is
connected !
I guess it's the ground screw at the fire wall. But for a high power radio
you will
have to replace the original ground and +12V wire to the radio with let's
say 1.5...2.5mm² wires. But in most cases it is simply - try it out ! There
are only two or three spots
to connect the ground and they are all located next to each in the
electronic compartment.

For regular cars you normally hook the ground up as short as possible to the
chassis.
That's how I fixed several noisy stereo systems in cars which all made hear
you the alternator and therefore the engine rev through the speakers.

I also think in 90% of all cases the filters they sell for the
cinch-signal-wires are not needed at all when having a good and correct
ground connection (connect +12V directly to the battery and make sure it is
a real good connection !).

Gold contacts ? look nice cost a lot and only prevent corrosion. From
resistance issues - gold is worse than silver or copper ! It simply looks
nicer and somebody makes more money...

And before changing the alternator - clean all the contacts first, replace
nuts and washers and don't forget the carbon brushes in the alternator -
cost about 5 bucks and one hour of work to replace them when worn (probably
after 50k miles or so, mine after 35k miles !)and give your alternator the
chance to work properly. A "better" alternator won't solve your connection
problems !

My two cents on car hifi...

Elvis & 6548



> Just another of my two cents and not to flame Martin's suggestion, there are
> a few things to know about "caps" or better known as "stiffening capacitors"
> in the auto hi-fi business. ?

[very long quote trimmed by moderator]