Help Adding 2nd Batt

[MegaHurtz 10+ year member]

The purpose of adding the second battery, as I see it, is to provide a second reserve capacity that can be drained without touching the first and causing the car to not start. You can also wire them in series to get additional reserve capacity and choose not to use an isolator, but I see the first method as being more preferable. I may have been a bit discriminating by saying that both batteries will kill each other, they may not, but there is a chance of it happening, and it's a risk that has to be taken... why take risks?

 

[knukonceptz 10+ year member]

Using a second battery for the sole purpose of just audio is pointless UNLESS your ONLY objective is to listen to the stereo with the car off. Take two batteries in parallel (I think series would be a mistake in a 12V application) and you have double the capacity for the whole car and system, the Isolated/Solenoid would only offer the same capacity as one single battery. Double the capacity will provided a more consistant/solid voltage output in the 12V range (it acts as an added buffer during peaks of bass notes)

So if you want the best solution for large voltage spikes - skip the isolator, if you just want to sit in a parking lot and not have to think about your car statring an isolator is fine - However, the second battery without an isolator ALSO gives you double the Ah rating (if both Batts are equal) so you have double the play time with car off......

 

[justinschmiidt 10+ year member]

whats the difference between building up your stock alt and adding a second batt.?

 

[knukonceptz 10+ year member]

Well the ALT powers everything - it operates at 14V, your entire car does while running. A higher output Alternator will make more amperage at the 14V level. Adding a second battery will add reserve capacity at the 12V level and act as an added buffer while the car is running in the 14V level, but it mainly will make it harder for spikes to reak the 12V barrier. If you have a decent sized stock ALT (110A+) you will probably not need to upgrade for most applications.

Adding a second or 3rd battery (without Isolator) can work as well as upgrading your stock ALT. Even if you have a 90A ALT and three batteries - you could run trouble free forever. The main point is that you do not operate your system and every accessory on your car at full tilt every second the car is on. During this lapse in time the ALT can over come the excess draw and recharge the batteries.

As I mentioned before a fun test with jumper cables - you'll have to check back previous posts, but all you need is a voltmeter a friend with a car and jumper cables to see the results.........

 

[justinschmiidt 10+ year member]

well i have like a 90 amp stock alt in the car im speaking about., thinking about adding another batt in the trunk with the yellow top under the hood. no isolaters and itll be just as good as a alt upgrade?

buying a 1981 monte carlo this week or so, anyone know what they got in the alt department stock?

 

[knukonceptz 10+ year member]

I ran 5 batteries (one under hood - 4 aux in hatch) for over a year on a 90A alt, total system draw was 380A I later added an external regulator to turn up the juice to 15V during shows. Never had a problem with voltage and worked out great when I locked my keys in the car with lights on, two hours later the car started right up.....

81 Monte is probably going to need an upgrade, but you can do almost anything with older cars

 

[iamamp3pimp 5,000+ posts]

The front and rear batteries need to be isolated. This can be done with a number of ways. The way that I recommend is to use an RV solenoid. There are other isolators, some of which can lose up to a full volt across the terminals, RV solenoids are supposed to be very efficient, or so I am told. There is a connection on the isolator for a wire that would become hot when the car is running (the isolator is essentially a high amperage SPST relay). Car turns on, coil energizes, current flows throughout the system, rear battery charges. The reason that you have to use an isolator is that the batteries will not be perfectly equal. When wired in parallel, they will attempt to level themselves off, resulting eventually in both of them being drained. The way to work around this, is to buy 2 identical batteries at the same time, but it doesn't sound like this is what you are going to do. Definitely fuse both batteries 18" from the positive terminal, this is not a should do, this is a MUST do.

they dont NEED to be isolated.

 

[XaznKewLguyX 10+ year member]

Let me get this straight. soo.. to add a 2nd battery

-instead of the power wire running from under the hood bat to my amps, I would just need to run it to the 2nd bat in the trunk

-fuse both ends of the power connecting the batteries

-ground the bat in the trunk to chassis (or would it be better to run it back to the bat under the hood neg post?)

-then run a power wire from the bat in my trunk to my amps?

Sounds too easy. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

 

[knukonceptz 10+ year member]

Just ground to chassis and that is it, very easy indeed since all the work is already done if you have a working system to begin with

 

[jluv 10+ year member]

Adding a second battery will add reserve capacity at the 12V level and act as an added buffer while the car is running in the 14V level, but it mainly will make it harder for spikes to reak the 12V barrier.

This is where I get confused. How does having an extra 12 volt battery keep the voltage from dropping down to 12 when the alternator is pegged during big bass notes?

It seems like once the alternator maxes out, and the system taps into the battery for power, it's at 12 volts, no matter how many batteries you have. Is that not the case?

 

[iamamp3pimp 5,000+ posts]

that is the case.....the second batt helps keep it at a 12.6 v level for much longer, as opposed to dipping even farther. also adds more current to the amps, and allows for more current to be released from them, resulting in a cooler running system as well.

 

[MegaHurtz 10+ year member]

Personally what I would do would be to buy an 8v and a 6v golf cart battery, wire the pair in series, and hook that up to your system. The amount of power and reserve you will get out of them will be amazing. I have a pair of batteries like that, when I go to show and shines sometimes, I take them and use them to run my car all day, they do a great job, and they literally run my car all day... like 10 hours.

 

[knukonceptz 10+ year member]

Whats the Ah rating on those two batteries - getting a similarly sized or larger 12V battery would yeild the same "play" time without requiring a recharge.

Ah = Ampere Hour - A unit of measure for a battery's electrical storage capacity, obtained by multiplying the current in amperes by the time in hours of discharge

 

[iamamp3pimp 5,000+ posts]

hes geting 14v though.....thats they key

 

[knukonceptz 10+ year member]

Yes, but there is not much benfit to the added voltage at this point. At a show, you most likely have the car open and trunk/hatch as well, so it not like your going for SPL, now you have two small batteries to haul around. If all your doing is connecting the audio system get the TurboStart 16V - its one battery and would power everything just as well. There is nothing wrong with what he is doing, but it can be easily done several other ways.