Pushing more than your alternator can take with an extra battery/cap?

[UnderFire 10+ year member]

don't add a second battery/batcap, that alternator won't cut it..

Not true, my truck comes with a 60a alternator stock, and by using secondary batteries, people who use them for off-roading run like 8 lights, winches and compressors constantly, with very low voltage drops. Everything else you said is very true, it's not the system that matters, it's how you use it.

 

[BnGRacing 10+ year member]

I understand batteries dont replace a HO alt but thats not an option. At least not for this car. Not worth getting an alt that will rival the cost of all my equipment combined. I just want to know if adding the 2nd battery will let me reliably run around 1000-1200rms. Prob more around 1000.
Also, wont I need to relay isolator? I thought just hooking up two different sized batteries drain one of them super fast.

Your system will perform WORSE with an additional battery.

A battery needs a constant 13v @ 7A to maintain their charge. If you're adding a 2nd battery, you're effectively asking the alternator to charge TWO batteries and power your system. It would be the same as using an amp that was 10% less efficient. Batteries are a load on the system.

 

[Moofs 10+ year member]

pshtttt, I might just not upgrade further with this car. I'll just save for my next setup or something.

So just to double check, a batcap wouldnt be better being it chargers so much quicker?

 

[TheUnderFighter 10+ year member]

You really should be fine with a good battery under the hood and a big 3 upgrade... that should be more than enough man. It varies from car to car, but I'd be surprised if that didn't cut it.

 

[RAM_Designs 5,000+ posts]

A battery needs a constant 13v @ 7A to maintain their charge.

Where did you get this bit of info from? First of all, not every battery will be the same. Secondly, if the batt's capacity and voltage drops that quickly, how in the world are we able to start out cars in the morning after they have been sitting for 12+ hours?

 

[martiandancer31 10+ year member]

wtf is going on in this thread? lulz

 

[i2ain2thunder 10+ year member]

I understand batteries dont replace a HO alt but thats not an option. At least not for this car. Not worth getting an alt that will rival the cost of all my equipment combined. I just want to know if adding the 2nd battery will let me reliably run around 1000-1200rms. Prob more around 1000.
Also, wont I need to relay isolator? I thought just hooking up two different sized batteries drain one of them super fast.

If their resting voltage matches there really shouldn't be a problem.

 

[907tacokid 10+ year member]

i have been running 2300rms through my truck (toyota tacoma stock 80amp alt) with just the big 3 and stock batterie, running a volt meter so i can tell when i turn it up to loud and makes the batterie drop volt. now im getting a batterie to put in back so i can turn it up just a little more and not have to worrie about having my batterie not start my truck. i would get a new alt but the cheapest one is over 500 bucks for my truck. so sadly its not really in the picture at this time. all my wiring is 0g.

 

[Moofs 10+ year member]

a lot of conflicting responses. but it seems that if I stay in the 1000-1200 rms range adding at 2nd battery should do the trick.

 

[bubbagumper6 5,000+ posts]

i have been running 2300rms through my truck (toyota tacoma stock 80amp alt) with just the big 3 and stock batterie, running a volt meter so i can tell when i turn it up to loud and makes the batterie drop volt. now im getting a batterie to put in back so i can turn it up just a little more and not have to worrie about having my batterie not start my truck. i would get a new alt but the cheapest one is over 500 bucks for my truck. so sadly its not really in the picture at this time. all my wiring is 0g.

I'm skeptical. What amp?

 

[BnGRacing 10+ year member]

Where did you get this bit of info from? First of all, not every battery will be the same. Secondly, if the batt's capacity and voltage drops that quickly, how in the world are we able to start out cars in the morning after they have been sitting for 12+ hours?

When the engine in your car is running, the battery under the hood is drawing around 7A of current.

When the engine in your car is running, the alternator's output will be 14.4v (about) and the battery will be 12.6v. Current flows from high to low. Likewise, when you start your car in the morning your battery is at 12.6v. Turn on your headlights before your crank the engine. Start the car and you'll notice your lights are a bit brighter. You're now running on a higher voltage plateau since the alternator is spinning.

The issue isn't a battery losing voltage or charge quickly, the issue is that batteries are at a lower voltage than a spinning alternator. Adding another battery that's below the alternator's voltage will be another load on the system. This is why good capacitors are not a load; they're at the same voltage.

 

[dipitydoo 10+ year member]

i agree with your last last statement, it is a matter of how its used. the off roading example works great, because you are not constantly offroading, using the winch, compressors, lights, etc, constantly. in a stereo system, constantly taxing a small alternator will not allow it to charge 2 batteries simultaneously. that's why its good to put your system in first, play it for a while, then decide on upgrades depending on what your goal is.

 

[bubbagumper6 5,000+ posts]

When the engine in your car is running, the battery under the hood is drawing around 7A of current.
When the engine in your car is running, the alternator's output will be 14.4v (about) and the battery will be 12.6v. Current flows from high to low. Likewise, when you start your car in the morning your battery is at 12.6v. Turn on your headlights before your crank the engine. Start the car and you'll notice your lights are a bit brighter. You're now running on a higher voltage plateau since the alternator is spinning.

The issue isn't a battery losing voltage or charge quickly, the issue is that batteries are at a lower voltage than a spinning alternator. Adding another battery that's below the alternator's voltage will be another load on the system. This is why good capacitors are not a load; they're at the same voltage.

They aren't a load when fully charged but the moment they begin discharging their voltage starts dropping, thus creating the load on the alternator. And just an FYI, there aren't any "good" automotive (audio) capacitors on the market, even if they are quality built they just aren't large enough to make any kind of impact with our large stereo systems. Do some reading brah -> Capacitors