Upgrading Your Charging System
This is a popular topic and many people think there are simple answers. The answers may be simple but the solutions are often very expensive. Some of the problems and solutions will be covered on this page.
This is the most common complaint for those who have installed high-power sound systems in their vehicles. This problem can sometimes be overcome by installing an alternator rated for higher current but this isn't always the case. Some alternators have a slight regulator lag and, even though the alternator can produce the required current, it doesn't react quickly enough to prevent short-term dimming. This can vary between various alternators, even if they're rated for the same current. In some instances, the owner of a vehicle will install multiple alternators. The OEM alternator will power the vehicle's electronics and charge the OEM battery. One or more alternators will power the amplifiers and charge auxiliary batteries. Since the amplifiers aren't drawing current from the OEM system, the lights cannot dim.
If you replace incandescent headlamps (standard and halogen headlamps) with HID headlamps, the headlamps won't likely dim. HID lamps have a ballast that acts like a regulator. This regulator will keep the voltage/current constant and will therefore prevent dimming.
In some instances, you may be able to use a voltage regulator for incandescent headlamps. This is safer if you only do it for the low beams OR the high beams. This will prevent the loss of light if the regulator fails. A regulator like the Accuvolt can keep the voltage constant. In the near future, LED headlamps will be available. These will be easier to regulate because LEDs don't need the full voltage of the charging system.
As was stated on the charging system basics page, the alternator supplies all of the power to all of the electrical accessories (amplifiers, lights, power windows, power seats...) as long as the engine is running (unless the current demand exceeds the capacity of the alternator).
Many people want to know when they should replace their alternator. The short answer is... when it fails. If you just want the battery to remain charged and your present alternator is keeping it charged, it's doing its job. If you want a system to be as close to perfect as possible and money is no object, replace your alternator when you install the amplifiers.
Multiple alternators was previously mentioned. It's very difficult to install multiple alternators on many of the newer cars because there simply isn't any available space. For older vehicles and trucks, there are more options. You can buy brackets for multiple alternators. THIS is one example.
Extra batteries are great if you want to listen to your system with the engine off. While the alternator is charging, the extra batteries will only draw current which could otherwise be going to your amplifiers. For proof, all you have to do is measure the voltage while the engine is running. It should be approximately 13.5-14.4 volts DC. Then turn the engine off and measure the battery voltage again. Now it'll be around 12-12.5 volts. Whenever the voltage at the battery is near 14 volts, there is current flowing into the battery. The only time that the battery supplies current with the engine running is when the current capacity of the alternator has been exceeded. When that happens and the batteries are the source of power, the voltage supplied by the batteries will be significantly less than the voltage of an alternator that's capable of supplying the required current.
One Farad (and larger) Capacitors:
Large, one Farad, capacitors only help to maintain the charging voltage for a tiny fraction of a second under high current demand situations. They won't really solve your current supply problems if your alternator can't keep up.
Capacitors DO NOT increase the charging system's voltage.
Battery isolators only prevent draining your starting battery when listening to your system with the engine off. Most of the time they will actually rob power from your system. Diode type isolators will usually have a small voltage drop across the diodes (approximately .4 - .7 volts). Some of the newer diode-type isolators use FETs either in parallel or in place of the diodes. The FETs will eliminate most or all of the voltage drop in that type of isolator. Solenoid type isolators don't have as much voltage loss as the diode based isolators but the solenoid coil does pull current. Some coils may pull as much as 3 amps of current. Now 3 amps of current isn't much but if you're using 2 solenoids and you're already having trouble with a weak alternator, it'll just add to your problem.
This is something that most everyone does but in most cases, it's useless and sometimes dangerous. The '3' are the wires/cable/straps that make various connections. One is from the battery to the body of the vehicle. Another is the wire between the battery and the alternator. The third is the ground between the engine block and the firewall. The connection between the battery and the body and the connection between the engine block and the firewall can be done without any problem. The one from the alternator to the positive battery terminal can cause some safety issues. In some vehicles, there are over-current protection devices in the battery-alternator line. In older systems, the device was a fusible link. A fusible link is a short length of wire that's smaller than the wire it protects. When too much current flows, the wire burns open. For most wire, this would be dangerous but fusible links have a fire-resistant silicone insulation that contains the molten copper. In other vehicles, the protection device is a fuse in the fuse box under the hood. If these are bypassed and there is an alternator failure that causes a direct short to ground, there could be an electrical fire.