Here are a some suggestions to improve the existing charging system of your vehicle when installing a higher powered stereo set-up. Although they may not be a cure-all, these are preventive measures to consider taking at the inception of your system design.

• Current Path - Replace the ground strap (cable) between the battery and the car chassis (body) with a 4-gauge cable. This will help correct any voltage loss caused by high resistance in the stock cable. It is also a good idea to replace the stock charging cable between the battery and the alternator with a 4-gauge cable

• Alternators - There is no substitute for a large supply of current. Batteries and capacitors don’t produce anything; they are merely a storage medium. Once a vehicle is running, the alternator picks up the bulk of the electrical demand. Check with the vehicle manufacturer concerning the stock alternator ratings.Most stock vehicle alternators range from around 60 amps (Honda Civic) up to 200 (ambulance or other emergency vehicle). Let’s say you have a 60-amp alternator, and that you are driving in mid July with the A/C on (15 amp demand from the blower motor). Your headlights are on because it’s dark outside (15 amp demand), and the wipers are on because it’s raining, so the wipers are on also (15 amp demand), then you have just consumed 45 of the available 60 amps from your alternator. Now you turn on your stereo system. Lets say you have four 12 inch Rockford woofers hooked up to a Rockford T10001bd. The amplifier, which is playing into a 1 ohm load, will require about 80 amps continuous for really loud playback levels and much more on peaks. So, you can see the problem. A final consideration is that alternators have hot and cold ratings. In other words, the current capability varies with temperature. The higher number is the cold rating, and the lower number is the hot rating (typically 20-30 amps less).

• More voltage - Some after market alternators are available with variable voltage output. This can be a good thing or bad thing. Most amplifiers can handle upwards of 16 volts on the power supply input. Since many amplifier power supplies today are regulated, the output improvements with higher voltages are minimal. However, higher supply voltage helps to keep current demand under control. Furthermore, current demand (that which is placed on your alternator) increases as voltage drops (remember that only alternators provide a continuous source of current and voltage). This becomes a serious problem as you add more and more high power amplifiers driving low impedance loads. Finally, do not mistake a good voltage measurement at the amplifiers as an indication that the charging system is OK. Only a load test will indicate whether the alternator is charging properly.

• Stiffening capacitors - Stiffeniing Capacitors (also called Power Caps) are used to help out your charging system in handing big signal bursts (or peaks) from larger amplifiers. A Power Capacitor is somewhat like a battery in the sense that it can store current. But unlike a battery, it can charge and discharge extremely fast. When used in a 12V audio system, it acts like an extra reservoir of power. These are one of the lesser expensive upgrades to aid your existing charging system. Most people don’t realize that capacitors also filter some of the ripple (noise-A/C that gets past the rectifying diodes inside the alternator) from your charging system.For more information and installation diagrams on stiffening caps, check out our section on power caps.

• Multiple Batteries - Great for parking lot listening, and just something else for the alternator to have to deal with once the vehicle is running. While large SPL systems do benefit from multiple batteries, there is still no substitute for a powerful alternator. One recent trend in competition circles with SPL only vehicles is large battery banks that are not even connected to the vehicle’s alternator. These battery banks, often 16 volts, are charged from an external source. So in this case, the alternator capability doesn't matter.

• Isolating Multiple Batteries - Dual battery isolators utilize large diodes to isolate each battery. This is great if one battery goes down, the isolator will still allow the vehicle to start from the stronger battery. The problem lies in the voltage loss of the diodes in the isolator (as much as 1.5volt drop across the isolator input and battery connections in some cases). Combine this with a typical loss of .5 volts in a 12-20 foot run of 4 gauge cable (from front to back in the average vehicle), and you could lose as much as 2 volts! A drop in voltage means an increase in current demand. This could result in shorter life for your amp. The best method of isolating the main vehicle battery from the secondary batteries is with a large solenoid. This should be wired to connect the main and secondary batteries ONLY when the vehicle is running. This helps preserve the main battery for starting the vehicle. If nothing is done to isolate the main battery from additional batteries, one weak battery in a bank of batteries will prevent the vehicle from starting.