Two Batteries?

[silent_1999]

I recently had some starter problems. I took the car to Autozone to check the battery and found out that the alternator isnt charging! Now, you may not see this odd, but I do. The reason is the alternator is only a month old, and the second one this year! The battery is new and checks out good, we now know the alternator is bad, my question is now that I'm running two amps (about 800-1000w/rms), and five neons, and EL string, do I need another battery so I can jam w/o keeping my car on? Futhermore is it ok to not put an isolator as long as the battery is close to the amps? Any experiance is helpful. Thanks!

[SeRiousZX2]

A second battery can't hurt. Placing an isolator is a neccessity when running 2 batteries. Usually it mounts up front close to the primary battery and alternator. Typically you want to stay withina 3-4 foot range from the alternator. Basicly, don't mount the isolator in the rear with the 2nd battery.

The 2nd battery can be as close to the amps as you want them.

I sell battery isolators. Just let me know if you need one in the "Just For Looks" section.

[silent_1999]

kewl, thanx

[JonsZX2SR]

If you want to use dual batteries, try the setup shown below. The relay will disconnect the secondary battery when the car is off, preventing current from flowing from the primary to secondary battery if the state of charge mismatches.

The switch allows you to disconnect the rear power circuit from the the rest of the car allowing you to run on isolated battery power for short times.

http://www.teamzx2.com/attachment.php?attachmentid=965&stc=1&d=1213313869

One characteristic of capacitors that is often overlooked is the output voltage of a capacitor decays with state of charge (unlike a battery.) This means you only use a fraction of the capacity of the capacitor and only for a short interval. Once the capacitor voltage decays to the (reduced) system voltage it stops providing additional current, then recharges (between peaks) when current demand falls. In the interim load on the primary system is about as bad as if the capacitor was not present.

http://www.teamzx2.com/attachment.php?attachmentid=977&stc=1&d=1213354294

From an industrial electrical power standpoint the correct way to use capacitors is to select them to operate at many times DC system bus voltage and use a high current bidirectional DC-to-DC converter to maintain bus voltage over a wide range of capacitor charge.

This approach is complex, expensive and beyond the scope of most automotive audio enthusiasts. It is, however, the same principal used to charge DC capacitors using the switching supply inside the audio amplifier.

A more effective way to increase stored energy would be to add individually additional capacitors to the + and - DC power supplies in each amp. That way the existing switching supplies would do most of the work and each amp would store reserve current.

the drawback is that without an electronics background to design such a setup, you could risk blowing up the switching power supply inside the amp if you did not limit peak turn on current.

[silent_1999]

Thanks for the info. I'm gonna try it out. Do I need an extra box to contain the battery, or can i just have the terminals covered?

[JonsZX2SR]

I'm 97% sure that your problem is that the alternator can't respond fast enough to peak current demands form the audio system. Just increasing the steady state output of the alternator isn't going to fix the problem.

I've used the two battery solution and it does reduce the dimming problem, but you still might see some flicker on huge bass peaks. What it does is supply most of the current for peaks from the capacitors and battery in the rear of the car. Instead of the primary battery and electrical system seeing 100-200 A peaks, they might see 15-20 A peaks.

In between the peak current demands, the rear battery will try to recharge. this might increase constant current demand along the supply cable from 15-20A to 30-40A. However, this demand is mostly constant, and the alternator, especially an upgrded unit should have no probelm with constant output.

What you might also want to try is reducing the supply cable until the rear batter starts becoming discharged, then go one size larger. The increased cable resistance will form an RC filter and smooth peaks seen at the front of the car.

There are even more complex solutions where a control circuit can monitor and disconnect the rear circuit when the car is idling or at low speed, detect rear battery charge and send a warning, and reconnect the rear battery at highway speed to recharge the rear battery.

These are beyond the scope of the typical hobbiest...

[silent_1999]

I'm 97% sure that your problem is that the alternator can't respond fast enough to peak current demands form the audio system. Just increasing the steady state output of the alternator isn't going to fix the problem.

I've used the two battery solution and it does reduce the dimming problem, but you still might see some flicker on huge bass peaks. What it does is supply most of the current for peaks from the capacitors and battery in the rear of the car. Instead of the primary battery and electrical system seeing 100-200 A peaks, they might see 15-20 A peaks.

In between the peak current demands, the rear battery will try to recharge. this might increase constant current demand along the supply cable from 15-20A to 30-40A. However, this demand is mostly constant, and the alternator, especially an upgrded unit should have no probelm with constant output.

What you might also want to try is reducing the supply cable until the rear batter starts becoming discharged, then go one size larger. The increased cable resistance will form an RC filter and smooth peaks seen at the front of the car.

There are even more complex solutions where a control circuit can monitor and disconnect the rear circuit when the car is idling or at low speed, detect rear battery charge and send a warning, and reconnect the rear battery at highway speed to recharge the rear battery.

These are beyond the scope of the typical hobbiest...

This is what I did, I added ground to the altenator, and the engine on the right side. Then I charged the battery fully. replaced the alt (that one was bad). So far so good. I had it bumping only for about 15 min with the car off and made sure to drive around about 10 after to charge the battery. Is a capacitor really neccisary, as I see no lights diming. BTW, now that I think about it I dont see lights diming, because the guages are ElecroLuminicent, and the headlights are HID, both have balasts. I never really know if I'm putting a large load on the elecrical system.