All about Caps,Batts and Alternators
All about Caps,Batts and Alternators
I clipped this from this article Forum at CarSound.com
A BATTERY WON'T MAKE YOUR LIGHTS STOP DIMMING. Repeat that aloud several times. It may make them dim LESS, but even with an ideal battery (a 13.0V ideal voltage source with infinite current capability) they'll still dim.
Your charging system approximates a perfect voltage source. Your alternator takes a finite amount of time to respond to a load increase by increasing its field current. It also has a finite maximum output current, after which its output voltage starts dropping quickly.
Your alternator is putting out approximately 14.4V to charge your battery, which is sitting at approximately 12.8-13V. So current is flowing into the battery, causing a chemical reaction (charging). When drawing current, the alternator output voltage drops. This causes the regulator to increase the field current to get the voltage back up. While this is happening, your system voltage dips.
Here is where capacitors come in. A standard stiffening cap has a very low ESR (less than 5 milliohms, hopefully), and a suitably low ESL. It also has a stored charge (depending upon the size of the capacitor in farads) at a potential of 14.4V or whatever the charging system voltage was before the transient
When the car's loads (as a whole, everything from the coil to the lights to your amps) pulls the voltage down from 14.4V, current starts flowing out of the cap, supplying the circuit, and keeping the voltage up until it is depleted to the level of the alternator/battery.
If we can keep the voltage up long enough to let the alternator keep up, the lights won't dim (because the system voltage will stay reasonably level).
Once we exhaust the supply from the alternator and any caps we might have, we start on the battery. The bigger the battery's plates, the more current we can draw before the voltage starts dropping (keep in mind this has nothing to do with the voltage rating or the Ah rating of the battery). However, a bigger battery draws much more current when charging, thus loading the alternator further and causing our lights to dim sooner.
With enough capacitors, you can completely prevent your car's lights from dimming, regardless of your system. This becomes impractical very quickly due to the current required to recharge the capacitors after they're depleted and the cost of the components.
Thus, after a certain point, you just need a bigger alternator. HO alternators don't tend to put out much more power at idle to prevent stalling the engine. So for a very serious system count on a HO alternator and a high-idle system. But IMO, you need in excess of 4000W of amplification to warrant this.
Batteries. They're great for starting your engine. I recommend replacing your battery every three or four years with a high-quality replacement, not larger than you need. Preferably a very high quality battery such as an Optima Red Top (Yellow Top if you do more than 15-30 minutes of engine-off listening at a time). This keeps the charging current at a minimum, and makes sure you can start your car in the morning.
A good battery will have a minimum ESR. However, it takes a battery a good amount of time to go from charging to supplying power, even the best ones. So they're not the device you want to use to smooth out your electrical system.
A BATTERY WON'T MAKE YOUR LIGHTS STOP DIMMING. Repeat that aloud several times. It may make them dim LESS, but even with an ideal battery (a 13.0V ideal voltage source with infinite current capability) they'll still dim.
Your charging system approximates a perfect voltage source. Your alternator takes a finite amount of time to respond to a load increase by increasing its field current. It also has a finite maximum output current, after which its output voltage starts dropping quickly.
Your alternator is putting out approximately 14.4V to charge your battery, which is sitting at approximately 12.8-13V. So current is flowing into the battery, causing a chemical reaction (charging). When drawing current, the alternator output voltage drops. This causes the regulator to increase the field current to get the voltage back up. While this is happening, your system voltage dips.
Here is where capacitors come in. A standard stiffening cap has a very low ESR (less than 5 milliohms, hopefully), and a suitably low ESL. It also has a stored charge (depending upon the size of the capacitor in farads) at a potential of 14.4V or whatever the charging system voltage was before the transient
When the car's loads (as a whole, everything from the coil to the lights to your amps) pulls the voltage down from 14.4V, current starts flowing out of the cap, supplying the circuit, and keeping the voltage up until it is depleted to the level of the alternator/battery.
If we can keep the voltage up long enough to let the alternator keep up, the lights won't dim (because the system voltage will stay reasonably level).
Once we exhaust the supply from the alternator and any caps we might have, we start on the battery. The bigger the battery's plates, the more current we can draw before the voltage starts dropping (keep in mind this has nothing to do with the voltage rating or the Ah rating of the battery). However, a bigger battery draws much more current when charging, thus loading the alternator further and causing our lights to dim sooner.
With enough capacitors, you can completely prevent your car's lights from dimming, regardless of your system. This becomes impractical very quickly due to the current required to recharge the capacitors after they're depleted and the cost of the components.
Thus, after a certain point, you just need a bigger alternator. HO alternators don't tend to put out much more power at idle to prevent stalling the engine. So for a very serious system count on a HO alternator and a high-idle system. But IMO, you need in excess of 4000W of amplification to warrant this.
Batteries. They're great for starting your engine. I recommend replacing your battery every three or four years with a high-quality replacement, not larger than you need. Preferably a very high quality battery such as an Optima Red Top (Yellow Top if you do more than 15-30 minutes of engine-off listening at a time). This keeps the charging current at a minimum, and makes sure you can start your car in the morning.
A good battery will have a minimum ESR. However, it takes a battery a good amount of time to go from charging to supplying power, even the best ones. So they're not the device you want to use to smooth out your electrical system.
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Derek, that post is about 100% fact with 1 small part left out/not addressed. The 4000W system on a stock alternator is fine for an alternator with a cooling fan. Alternators without cooling fans (like our civics) get very hot.. as they ehat up their potential output drops substantially. When I have the day off Thursday I'm gonna attack the forums and all the "Experts I can find and pool together as much info as possible...I'll Post all my findings back here.
Cheers
Mohawk
Cheers
Mohawk
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