soocom1

OK..
First:


I went to auto school way back in the day and I seem to remember a huge lesion in batteries.
That being if one puts in a higher power battery like a yellow top Optima or SVR or the like, that one has to match the cables and alternator to the battery.
Otherwise you have batteries that die on you.


My school days were back in the late 1980's so this is an old concept at least for me.


Larger cables (remember the Monster cable audio fad?) a higher output alternator needs to match the battery.
This because
1: The battery wont charge properly with a lower amp alternator,.
2: A larger battery without the proper size alternator will burn out the diodes.
3: It puts a heavy strain on the system, not so much the power output, but the power draw can actually cause a mismatch to the system and kill it.




Now things may have changed, but I seem to remember that matching the cables to the battery is Justas important down to the starter and the relay. Even the size of the relay can affect the charge.


Thoughts? Input?

aj2494

I don't see why that would be true. The only reason to ever upgrade your wiring is if you need to support a higher current. Car batteries all run at the same voltage and therefore the same current. Just because a battery has higher capacity or CCA doesn't mean that it puts more strain on your wiring.

In short, a better battery doesn't change how the circuit behaves, but it's more reliable. Now if you put a bigger alternator on there, that's a whole different ballgame since it's actually increasing the current in the main power wires.

Theoretically, the battery shouldn't see any capacity change when the car is running. With the alternator spinning, it's powering the car electronics, not the battery. The battery is a reserve in case the alternator can't meet the draw requirements on the system, AKA when the car is off or when the bass hits in a big system. This is why guys that don't know what they're doing throw a really high powered system in a car and then their headlights dim every time the bass hits. They didn't upgrade the alternator and their battery isn't built to support that much of an instantaneous draw, so the next step is to increase the reserve capacity (more batteries) and upgrade the alternator.

Long story short, V=IR, cable size is dependent on I, and a battery doesn't change any of those things.

Tsaani97xj

The statement all batteries run at the same voltage therefor the same current is absolutely incorrect. Current is the amp rating. I like to think of it like voltage is horsepower and current is torque. Regardless of this a higher current battery wont hurt your system unless your alternator doesnt put out enough current to charge the battery efficiently. You want to match the battery, cabling and alternator to your needs.

Fred/N0AZZ

If you install a higher amp alt. you will need larger wires than stock like a 135 or 150 amp alt. The stock wiring was only good for like a 100 amps or less a fellow on here sells a larger set of wires for the XJ's with large amps 5-90 is his screen name.


You can install any size battery you wish as long as the alt is in good shape to charge it. I have all 3 in mine because of extra electrical power needed for winch, lights, etc.

soocom1

That's where I seem to remember the issue with the diodes.
If the battery was too large, the pull of power from the battery out of the alternator would kill the diodes.

aj2494

Um... car batteries all put out ~12V. All car electronics are designed for a 12V system, so running anything besides that would fry equipment. Resistance of components doesn't ever change without heat, and if car batteries all put out 12V, current cannot change just because you swap in a different brand battery with different CCA or capacity.

soocom1

Resistance can change with age and corrosion.


But that's besides the point.


The issue is the draw on the alternator.
Sorta like trying to suck a milkshake through a thin straw.


Too narrow a straw and the amount of juice your pulling (sucking through) is greatly diminished, vs. that of a larger diameter straw.


The issue I remember was that the diodes of a smaller amp alternator would fry from the battery draw. That in turn would kill the battery itself and shorten its life as a result.

aj2494

Well yeah, but I'm just talking about having one battery in the car and then swapping it out for another. The system should behave the same.

I'll admit here that I don't know much about alternator diodes, besides the obvious fact that they only allow current in the intended direction. But your battery is essentially a giant capacitor. It doesn't physically draw power, it stores it. Simply put, if there's no power going into a battery, it's not sitting there trying to let the magic smoke out of whatever it's attached to. Car batteries can be hooked up in a circuit without an alternator and behave just fine. Alternators don't always put out their maximum output too. It depends on RPM for the most part, and if a lower output alternator would be damaged by a good battery like an Optima, your stock alternator would be damaged by your stock battery at idle. Do you get what I'm saying here?

soocom1

Ok.
So let me clarify where I am coming from and going with this:


Our XJ needs a new battery BADLY! (Obvious reasons, being Pep boys special, older style, etc.) Plus good old fashioned age.


Now given that both myself and the other half (who owns the beast) wants to play a little bit with it, foundational thought here (meaning that I am trying to build up ahead rather than play catch up) one of the first "play" items is a larger battery.


Now I am fully aware that a battery of any nature (in the same voltage class that is) will operate much the same is not really the point.


The current draw of all electrical items including the battery means that there is a steady and exponential increase of such items as current draw, actual voltage use, amperage, wattage, etc.


When I was in school, the aspect taught (and remember this is in the days when auto sound systems drew HUGE power lots) was that the draw on the alternator was specific to the total use by all items + a given percentage. This is to allow for heavy pulls and draws on the current.


(Ergo why the Monster cable point I made.)


The problem came in that many in the early days of large car audio systems discovered was that they would install huge batteries into their car thinking that the extra capacity of the battery would mean higher volume. What was discovered was that the batteries (which actually do have a current draw on the alternator, hence why its there) that the larger the cells and more numerous the cells, the heavier the draw from the alternator.
This in turn would over use the circuits in the alternator, killing the diodes and ergo, draining the battery in the process.


For those who remember, in the early 1980's the large stereo systems installed would typically drain the power of the factory battery whilst killing the alternator.


Then some got the brilliant idea to replace the 450 and 550 CCA batteries with the large 750 CCA batteries from trucks.
(84 IROC anyone?) This in turn would start wiping out the alternators and someone got the idea to start selling the alternator upgrade kits.


Anyone remember the early MTX recommendations?


Rockford Fosgate told everyone that their amps HAD to have a minimum 110 Amp alternators in order to work.


When the budget crowd showed up on scene (early boom boxes and bazooka tubes) the owners of these monsters thought that by simply putting in the larger battery was enough.


The whole of the process started all over again.




So because we are wanting to eventually get such play items like a winch, a better sound system, lights, etc, the base foundation of that is a larger battery, larger cables and larger alternator.


When reading on the forum about the Optima batteries and the problems some have with them, some of the posts made me remember that the alternator needed to be matched with the battery. This is why I think some of them are burning up the Optimas faster than others.




IMO

Fred/N0AZZ

Just buy the largest battery with most CCA's that will fit into your battery box and have hood clearance PERIOD!


Any size alt will charge it if driven enough and if not discharged heavily (requires longer charge time) if it has been.


When you upgrade to a larger alt and ONLY THEN will you need larger wiring for everything, The End...

aj2494

This. It doesn't matter what your battery's CCA is, a smaller alternator just charges it slower. Your battery does not draw more amps because it's an Optima, and the current between the alternator and battery is 100% dependent on your alternator's output.

Tsaani97xj

My point was voltage is not current. A larger battery to start with will not affect anything until your load changes with extra toys. At that point your alternator may not be able to keep up and this will drain your battery. The excessive cycling and deep drain of the battery will kill the battery and overwork the alternator. As I said and others have it all has to fit/work together. If you are stock now just put the big battery in. You wont hurt anything until you make other changes.

WJBill

What he said, with a larger battery it will lose fewer amps when starting your car and so the alternator will have to put few amps back in and be able to work less. The reason diodes get fried is if you over work your alternator with too many electrical accessories or run the alternator in an open circuit (running your car with the neg. or pos. cable removed).

autosurgeon

Well as a current Automotive Instructor may I suggest go to www.cdxetextbook.com and do some reading your remembered information is a mess.

Wiggleworm

Do like Fred said and put the biggest battery you can fit in there. When you have the money or start your upgrades get ahold of 5-90 to upgrade your wiring here http://www.kelleyswip.com/electric.html then you can grab a 136 amp alternator from a Durango/Dakota to help with all your addons.