Nissan 370Z Forum - View Single Post

90 ST · 12-24-2010, 11:51 AM

1.Replace the ground strap (cable) between the battery and the car chassis (body) with a 0-gauge cable. This will help correct any voltage loss caused by high resistance in the stock cable. Replace the stock charging cable between the battery and the alternator with a 0-gauge cable from the Memphis Connection line.

2.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. Since it is difficult to provide some type of current demand chart for “X” amplifier(s), we must approximate when deciding whether or not to upgrade an alternator. As a basic guideline, most stock vehicle alternators range from around 60 amps (Honda Civic) up to 200 (ambulance or other emergency vehicle). Considering more Hondas are driven daily than ambulances, you can see the problem beginning. 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 (15amp demand), and the wipers are on because it’s raining, so the wipers are on also (15amp demand), then you have just consumed 45 of the available 60 amps from your alternator. Now you turn on the stereo (6 15” subs powered by an 1100 watt high-current, Class A/B amplifier with 50% efficiency). The amplifier, which is playing into a 1ohm load, will require about 80-90 amps continuous for really loud playback levels and much more on peaks. So, you can see the problem. Also remember that the ambulance mentioned earlier probably only has an AM/FM radio, with no external amps. It does have lots and lots of lights, a really loud siren, and some really powerful communications equipment. All of these items need plenty of current! 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.

3.More voltage: Some 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 (all Memphis Class D models incorporate under/over voltage protection). Since most amplifier power supplies 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 (13.6 volts for example) 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.

4.Capacitors: Stiffening capacitors are always a good addition. Anything that will supplement the peak voltage demand is good for high power amplifiers. 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. In fact, some early uses of ‘stiffening capacitors’ were for noise filtering, with little thought given to other benefits. We recommend using the Memphis Connection 17-1FCAP and/or 17-1FCAPM from the Memphis Connection line.

5.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 trend as of late with SPL only vehicles is large battery banks that are not even connected to the vehicle’s alternator. These battery banks, often 16volts, are charged from an external source. So in this case, the alternator capability is not relevant.

6.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). Nothing like losing voltage near the source (alternator). 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! Ohms law teaches us that current demand increases as the voltage decreases, putting the amp(s) at risk of premature failure. 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. Remember that one weak battery in a bank of batteries that do not isolate the main battery will prevent the vehicle from starting.

Right from Memphis

12-24-2010, 11:51 AM	#17 (permalink)
90 ST A True Z Fanatic Join Date: May 2010 Location: Calgary Posts: 1,861 Drives: 90 and 15 GMC Sierra Rep Power: 421	1.Replace the ground strap (cable) between the battery and the car chassis (body) with a 0-gauge cable. This will help correct any voltage loss caused by high resistance in the stock cable. Replace the stock charging cable between the battery and the alternator with a 0-gauge cable from the Memphis Connection line. 2.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. Since it is difficult to provide some type of current demand chart for “X” amplifier(s), we must approximate when deciding whether or not to upgrade an alternator. As a basic guideline, most stock vehicle alternators range from around 60 amps (Honda Civic) up to 200 (ambulance or other emergency vehicle). Considering more Hondas are driven daily than ambulances, you can see the problem beginning. 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 (15amp demand), and the wipers are on because it’s raining, so the wipers are on also (15amp demand), then you have just consumed 45 of the available 60 amps from your alternator. Now you turn on the stereo (6 15” subs powered by an 1100 watt high-current, Class A/B amplifier with 50% efficiency). The amplifier, which is playing into a 1ohm load, will require about 80-90 amps continuous for really loud playback levels and much more on peaks. So, you can see the problem. Also remember that the ambulance mentioned earlier probably only has an AM/FM radio, with no external amps. It does have lots and lots of lights, a really loud siren, and some really powerful communications equipment. All of these items need plenty of current! 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. 3.More voltage: Some 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 (all Memphis Class D models incorporate under/over voltage protection). Since most amplifier power supplies 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 (13.6 volts for example) 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. 4.Capacitors: Stiffening capacitors are always a good addition. Anything that will supplement the peak voltage demand is good for high power amplifiers. 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. In fact, some early uses of ‘stiffening capacitors’ were for noise filtering, with little thought given to other benefits. We recommend using the Memphis Connection 17-1FCAP and/or 17-1FCAPM from the Memphis Connection line. 5.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 trend as of late with SPL only vehicles is large battery banks that are not even connected to the vehicle’s alternator. These battery banks, often 16volts, are charged from an external source. So in this case, the alternator capability is not relevant. 6.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). Nothing like losing voltage near the source (alternator). 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! Ohms law teaches us that current demand increases as the voltage decreases, putting the amp(s) at risk of premature failure. 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. Remember that one weak battery in a bank of batteries that do not isolate the main battery will prevent the vehicle from starting. Right from Memphis Last edited by 90 ST; 12-24-2010 at 11:54 AM.