Battery Use While Car is Running

[qtipextra 5,000+ posts]

Awesome reading. Lots of good info.

 

[knukonceptz 10+ year member]

For a daily system, a single good battery should provide more than enough reserve capacity. Adding a second battery shouldn't be necessary, as the alt should be the source of power for the car. Remember that the alt has to replace any energy drawn from the battery eventually so regularly exceeding the alt's capacity and relying on the battery to pick up the slack is a sure recipe to kill the battery and bun up the alt. Adding more batteries won't help this situation either as it doesn't diminish the amount of power that the alt has to replace and it also can make the situation worse because multiple batteries wired in parallel will draw more current while recharging than a single battery.

There are a lot of guys running some serious juice out there.Trust me, the amount of 1/0 that leaves our door daily is shocking. If you have 1/0 in your car there is a very good chance you exceed the stock ALT output. Adding a second battery in the rear will help voltage loss - why? Resistance. The site linked below will show at 200A with 20ft of 1/0 on a 12V DC system will have a .808V loss from the cable alone. You put a battery 24" from your amplifier - see what loss you get - .081V. And I am quite sure the rear battery will discharge - why - RESISTANCE. Electricity flows the easiest way it can, so the source with the lowest resistance will discharge first.

http://www.powerstream.com/Wire_Size.htm

Again, if you play NON STOP and you have an under rated Alternator, yes it is possible for your batteries to get weak. If abused it could kill the rectifier in the Alternator. See Post #37 These are very extreme possibilities and I only mention then because it "could" happen. A DVM would warn of an issue if checked weekly/

The real bottom line is that it isn't possible to simply say that if you have X amount of amp power and the alt is rated for Y then you need to add Z to the car to make sure that you don't have any electrical problems simply because every system, every car and every user is different and what works for one may not work at all for another.

And that is the truth.......

some of your high output alts actually put out less power at idle than a factory alt....

A very good point!

 

[Thnking 10+ year member]

show me an alt that can put out 500 amps of current on a whim..also an alt is not flip a switch and it does full power.

I already told you, if the alternator can't match the load, then its time to move to banks of batteries. With a 500 amp load someone should be looking for more than a single extra battery.

 

[Thnking 10+ year member]

As far as an alt providing 500A, no normal system draws that kind of current. For a pure comp system, the alt becomes largely irrelevant during the burp as the battery bank becomes the primary current supply.

I’m glad someone in here actually understands this

 

[Thnking 10+ year member]

The fact remains that a HO alternator can cover loads most people have.

Is it going to be a case by case situation, yes.

Does someone need a 2nd battery when an alternator can be bought to match the load, NO. Even if the load exceeds the alternators output, which it does often with high frequencies, BUT it doesn’t do it for any significant portion of time. Well beyond what’s measureable with any typical DMM.

A battery is a storage device, it parasitic in the system, and is rarely going to discharge (besides leakage) when the alternator is running.

You two can argue the opposite until you’re blue in the face, but science tells us other wise, and no battery discharges until the voltage dips below it’s nominal…

If you have any problems with this idea, you can go into a high school classroom and ask any physics teacher.

 

[danteBirosel 5,000+ posts]

So to sum this all up..

It is recommended to get a rear battery that matches the front, if running a High Out Alt?

For example, if im running a 15" BTL and feeding it my Orion 2500d at around ~2300-2500w. Then running my front stage comps with a Direct 500/2 @ 100w per channel, would i need a rear battery?

 

[Thnking 10+ year member]

You don't even need one which matches the front.

But you won’t need one if you buy a HO alternator rated around 200amps, and you only need one rated that high IF you actually use the full gain from your amp. If the amplifier isn’t at full output, than your current draw is much lower (remember an insignificant amount of difference in SPL is a large amount of power difference when talking about KW systems).

 

[Thnking 10+ year member]

I just wanted to point out that more than likely, unless you actually set you amp to output max power at your listening levels (more than likely people do this at ¾ HU volume which isn’t their listening level), your stock alt may be just fine.

 

[audiolife 5,000+ posts]

a good deep cycle battery can cover a lot heavier load momentarily than an alt can also no alt guy wants to admit at around idle-low rpm that a high output alt really isn't much better than factory.your extra voltage allows things to work more efficiently(as long as you are at an rpm to take advantage of it) but it still doesn't provide you with a low voltage cushion the battery would provide which if you ask an amp company what the number 1 reason why amps fail is due to power falling off when the system is being used heavily (most cases when you are really thrashing on your stereo i bet it isnt when you are going 35+ mph anyway). sure you can get an alt to put out monster power at low rpm/idle but it will cost in more ways than one. EVEN if you get a ho alt you would be DUMB IMHO to not take advantage of what an extra battery can offer with the alt as it would give you the best of both worlds.

 

[qtipextra 5,000+ posts]

Does an extra battery in the rear have to be a deep cycle for best performance? Say you have a stock battery up front, and a good brand standard conventional type battery in the back (Diehard battery, 700 CCA). Would this help stabalize the same as a deep cycle?

Also, what specifications on a battery should you look for if you want a battery for the specific purpose of keeping voltage stable?

 

[knukonceptz 10+ year member]

Any battery used in the rear should be a sealed type battery, a wet vented battery will produce vapors that will make you sick.

So in physics class, when you were working with 12V batteries, were they operating at 14V? Thats an honest question.

I will be posting a video - hopefully tomorrow - my buddy has 8 batteries in his house powered by a 50A power supply running a 120A load - according to him it rarely gets in the 12V range. I am taking voltmeter, DC Inductance Meter (Clamp) and video. Will post that hopefully Sunday night

Then later this week, I will demonstrate what this does in a car with 1) stock battery and 2) added battery in rear using dual clamp meter, dual voltmeter. One of each meter in the front, and one in the rear along with dual video so it can be captured and then editied to play side by side. I have a third clamp meter to show ALT output as well

What I expect to find out of the second video - the rear battery will discharge at a higher rate then the front battery and keep voltage higher. Why do I expect this - DC resistance of the cabling at 18ft VS DC resistance of cabling at 2ft. All cable will be Kolossus and ran on the outside of the car. Batteries will be fully charged by a trickle charger before hand and between the two tests so that eveything is equal. Signal will come from a tone generator. All meters will be checked to verify readings match before test begins so that not a single question can be raised or suspect.

Vehicle is my POS DD that at one time was used for DB Drag, it has been gutted for the most part making it easy to do this with. Alt is a 90A Ford unit, and the amp will be a large Class AB amp (might as well use something that isnt efficient to show worse case IMHO)

My point - a HO Altenator is helpful- not everyone can get one for there car, not everyone can afford one, but there is no replacement for the reserve capacity of a Battery(ies) espically when mounted inches from the demand. And the additional batteries will serve no additional strain on a properly working charging system.

 

[audiolife 5,000+ posts]

deep cycles are generally used because they have alot greater reserve capacity. the more reserve you have the more potential the extra battery has to keep the voltage from falling off over a greater period of time. you also have batteries that burst well but fall off over time in use (less reserve) it all depends what the situation/system calls for. people will say "you dont need that" or offer their 2 cents in. the way i look at it is this. you spend $ on your system to do what you want. if it is powerful and has some expensive subs/amps and you like showing it off at all the worst thing the extra batt will do is HELP protect your gear. it helps in performance over a range as well. a battery with a low esr also helps as it charges and disperses power. what is more of a load to the alt? a wet cell lead acid battery or a much lower esr agm cell? we know that a high esr cap doent do too much so how will a battery with a really high esr help a great deal?why do serious people only use specific types of batteries for their systems? im not branding anything either so one cant say im persuading that route. if knu is doing this test if he could have him try it with an old school starter battery and maybe one of those batteries he used that is agm.

 

[knukonceptz 10+ year member]

Battery under the hood is an Interstate MT-35, the rear battery is a Genesis G26EP, specs listed on the link below

http://www.enersysreservepower.com/documents/EN-EP-RS-001_0506.pdf

Sitting in my garage right now at 12.83V for the past 3 months on a shelf.

 

[audiolife 5,000+ posts]

sweet would it be hard to talk you into testing it both ways? starter battery in back and in front?

 

[scooter924 10+ year member]

So would it matter if I kept my stock battery upfront and put my yellow top in back? I thought I read that it would cause problems if the batteries werent the same.