litch
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Just a brain dump of things to take note of when designing your stereo system, no matter how powerful.
The Alternator
Understanding the Alternator's role is paramount to a solid power supply and thus a solid sound system - because it is _THE_ power supply.
People always tend to throw an extra battery in the boot, change the stock battery for a high performance model or add polyfarad capacitors to solve problems like amp cut-out, headlight dimming or poor sub performance but that's not addressing the actual issue, and more just re-enforcing the car's last resort to supply power.
Why?
An alternator will supply somewhere in the 13 - 15V range when the engine is running, and under load - it will continue to supply that voltage as far as it possibly can depending on engine RPM and the capacity of that specific alternator. Anywhere in that realm, of very little power draw right up to near its maximum limit - your whole car's electrics are being run off the alternator - even the battery is being charged (taking current) and not lending a single milliamp to the operation of the electrics.
But, as soon as you get near the alternator's maximum load, it will start to drop voltage, down, down, all the way to around the battery/batteries present - and that's when they they come into play.
The Battery
Like the alternator, the battery will also drop its voltage - but as soon as your start drawing current. This is not not a straight (linear) line, drawing 100A will not drop 10x the voltage as drawing 10A.
Also "Cranking Amps". Manufacturers go on to further define the maximum current draw depending on temperature (Cold Cranking Amps, Hot Cranking Amps) as the battery's ability to produce current (the chemical reaction is inherently dependant on the catalyst of heat) - but for the most part, you'll usually see CCA (Cold Cranking Amps) used which means that at some temperature (usually -18C) this is the current the battery can produce without dropping voltage below X, where X is usually somewhere around 7V to 10V depending on which manufacturer you talk to. That last part should immediately ring alarm bells as to the reliability of using the CCA rating (as its definition can differ so much between OEMs).
In any case, most modern cars will have a battery that can do several hundred CCA, but in terms of car audio we don't want the battery voltage to drop anywhere below about 12.0V (which usually means amp-cutout or those other issues I noted above).
So, choosing the battery (or batteries) is arguably just as important as picking the right alternator. If you've got a whopping 10KW system, it's going to want to pull somewhere around the 600-800Amps in peak requirements. No alternator is going to match that. Your basic high-output alternator is 170A-200A, so you've got to make up the 400-600Amp with multiple batteries that will handle that deficit without dropping voltage too far as to impact performance. Remember that the lower the voltage supplied to the Amp, the less power it can give to the speakers/subs.
Big3 and other wires
Provided you've spec'd out an alternator with one or more batteries are quite able to handle your loudest song with the high-beams on at night and the fan full cranked, then you should probably check your wiring at the same time.
Voltage drop is the killer of all audio systems and it caused by one (or both) of the following:
* Maximum supply current (Alt/Bat)
* Series resistance
We've already dealt with the top point in the sections above, but we need to address series resistance.
When dealing with low voltage (12V) and huge amounts of current (100A+) from very low resistive loads (Amps) the size of the wire interconnecting the circuit (Ground->Alt->Bat->Amps->Ground) and the terminals, plugs and everything in between plays a big role.
First rule: Each section of a circuit drop the voltage relative to its resistance over the total circuit resistance.
Second rule: The voltage drop across all sections equals the source/supply voltage. Thus, when you have 1 section (like when measuring the battery directly on each terminal) you see the source voltage (being the battery itself).
If you didn't get that, here's a simplified workout:
A 1200W Amp will draw 100A off 12V (Power = Volts x Amps).
At that point, pretending there is zero resistance elsewhere, it has a resistance of 0.12Ohms (R=V/I).
But, if we made the positive battery terminal have a poor connection which incurred a very small 0.01Ohm resistance. The total circuit resistance would be 0.13 Ohms. Thus the battery terminal would drop the voltage relative to it's resistance (0.01/0.13) which equates to about 1 volt. The amp would then be only left with 11V which would instantly take 200W off your amp's power capability (1000W).
So, in reference to the Big3 - Make sure you
* Clean all contacts/terminals
* Make sure all joins are solid
* Use 4AWG at the very least
And that includes:
* Alternator to chassis
* Alternator to battery
* Battery to Amps
* Other grounds/junctions you have
Farad Block Capacitors
They behave like a small battery, storing charge and discharging it to your audio amps when required. Though it's a bit of a double edged sword as once discharged, they too want power to recharge thus being in competition with your amps.
To quantify what these caps can do:
1 farad is equivalent to supplying 13Amps in a 1 second (@ 13V charge)
20 farad block can do 260A in 1 second.
Note that there are a few other metrics that come into play such as ESR and other resistances, but I won't get into that in too much detail, just know that a 20 Farad block won't supply 2,600A in 1 millisecond.
Rule of thumb: If you play long deep notes, don't use one. If you prefer songs with punchy short drum kicks, maybe it'll help but in both cases, perhaps look elsewhere for the solution (Alt/Bat/Wires)
The Alternator
Understanding the Alternator's role is paramount to a solid power supply and thus a solid sound system - because it is _THE_ power supply.
People always tend to throw an extra battery in the boot, change the stock battery for a high performance model or add polyfarad capacitors to solve problems like amp cut-out, headlight dimming or poor sub performance but that's not addressing the actual issue, and more just re-enforcing the car's last resort to supply power.
Why?
An alternator will supply somewhere in the 13 - 15V range when the engine is running, and under load - it will continue to supply that voltage as far as it possibly can depending on engine RPM and the capacity of that specific alternator. Anywhere in that realm, of very little power draw right up to near its maximum limit - your whole car's electrics are being run off the alternator - even the battery is being charged (taking current) and not lending a single milliamp to the operation of the electrics.
But, as soon as you get near the alternator's maximum load, it will start to drop voltage, down, down, all the way to around the battery/batteries present - and that's when they they come into play.
The Battery
Like the alternator, the battery will also drop its voltage - but as soon as your start drawing current. This is not not a straight (linear) line, drawing 100A will not drop 10x the voltage as drawing 10A.
Also "Cranking Amps". Manufacturers go on to further define the maximum current draw depending on temperature (Cold Cranking Amps, Hot Cranking Amps) as the battery's ability to produce current (the chemical reaction is inherently dependant on the catalyst of heat) - but for the most part, you'll usually see CCA (Cold Cranking Amps) used which means that at some temperature (usually -18C) this is the current the battery can produce without dropping voltage below X, where X is usually somewhere around 7V to 10V depending on which manufacturer you talk to. That last part should immediately ring alarm bells as to the reliability of using the CCA rating (as its definition can differ so much between OEMs).
In any case, most modern cars will have a battery that can do several hundred CCA, but in terms of car audio we don't want the battery voltage to drop anywhere below about 12.0V (which usually means amp-cutout or those other issues I noted above).
So, choosing the battery (or batteries) is arguably just as important as picking the right alternator. If you've got a whopping 10KW system, it's going to want to pull somewhere around the 600-800Amps in peak requirements. No alternator is going to match that. Your basic high-output alternator is 170A-200A, so you've got to make up the 400-600Amp with multiple batteries that will handle that deficit without dropping voltage too far as to impact performance. Remember that the lower the voltage supplied to the Amp, the less power it can give to the speakers/subs.
Big3 and other wires
Provided you've spec'd out an alternator with one or more batteries are quite able to handle your loudest song with the high-beams on at night and the fan full cranked, then you should probably check your wiring at the same time.
Voltage drop is the killer of all audio systems and it caused by one (or both) of the following:
* Maximum supply current (Alt/Bat)
* Series resistance
We've already dealt with the top point in the sections above, but we need to address series resistance.
When dealing with low voltage (12V) and huge amounts of current (100A+) from very low resistive loads (Amps) the size of the wire interconnecting the circuit (Ground->Alt->Bat->Amps->Ground) and the terminals, plugs and everything in between plays a big role.
First rule: Each section of a circuit drop the voltage relative to its resistance over the total circuit resistance.
Second rule: The voltage drop across all sections equals the source/supply voltage. Thus, when you have 1 section (like when measuring the battery directly on each terminal) you see the source voltage (being the battery itself).
If you didn't get that, here's a simplified workout:
A 1200W Amp will draw 100A off 12V (Power = Volts x Amps).
At that point, pretending there is zero resistance elsewhere, it has a resistance of 0.12Ohms (R=V/I).
But, if we made the positive battery terminal have a poor connection which incurred a very small 0.01Ohm resistance. The total circuit resistance would be 0.13 Ohms. Thus the battery terminal would drop the voltage relative to it's resistance (0.01/0.13) which equates to about 1 volt. The amp would then be only left with 11V which would instantly take 200W off your amp's power capability (1000W).
So, in reference to the Big3 - Make sure you
* Clean all contacts/terminals
* Make sure all joins are solid
* Use 4AWG at the very least
And that includes:
* Alternator to chassis
* Alternator to battery
* Battery to Amps
* Other grounds/junctions you have
Farad Block Capacitors
They behave like a small battery, storing charge and discharging it to your audio amps when required. Though it's a bit of a double edged sword as once discharged, they too want power to recharge thus being in competition with your amps.
To quantify what these caps can do:
1 farad is equivalent to supplying 13Amps in a 1 second (@ 13V charge)
20 farad block can do 260A in 1 second.
Note that there are a few other metrics that come into play such as ESR and other resistances, but I won't get into that in too much detail, just know that a 20 Farad block won't supply 2,600A in 1 millisecond.
Rule of thumb: If you play long deep notes, don't use one. If you prefer songs with punchy short drum kicks, maybe it'll help but in both cases, perhaps look elsewhere for the solution (Alt/Bat/Wires)
