Printer Friendly Forum Posts - Dual battery setup

Ok I'm new to the forum and to car audio in general but I have some questions about a dual battery setup and any help would be appreciated. If I have two batteries one under the hood and one in the trunk and I have them hooked up like this: Alternator hooked up normally to the front battery and then a 4awg wire from the front and rear batteries' positive terminals to a distribution block which has wires going to all of my amplifiers. Then the total current drain from the distribution block is divided up equally on each wire correct? Will this setup result in the batteries draining each other as I have read in some places? I am looking to go with 2 yellow tops for my battery selection and I read some places that even they need to be vented is this true?

Any help would be appreciated.

do it like this, get a split charge relay kit, its a basic thing you need when installing two batteries. now when its connected you're amps will run off the battery in your trunk. this just allows both batteries to be charged properly. Buy a kit, smack it onto the batteries. Now you gotta look at the alternator and see if its cut out to produce enough for two batteries. dats all for now!

-------------
6* Rockford T2's
6* POWER AMPs
BLACK CORRADO
BAANNGGIINN

Nope. I disagree completely. Use NO isolators at all, and simply wire the two batteries in parallel. An additional battery is only going to be MAYBE two or four more amps required for charging, BUT the batteries must be the same age, capacity and type... if you are buying one with any type of isolator, then forget the isolation altogether, and plunk that cash on a second identical battery.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Ok but if I use this isn't it the same as using an isolator? if so then won't I have to have the total power that is used by the audio system go thru it?... what I'm trying to avoid is running anything larger than a 4 awg wire from my front battery because there simply is no way a larger wire would fit without me taking out half of the items under the hood to have a good place to drill. I'm trying to not only set this up for the system I will have but to be a little flexible in the future If I had the wiring as I mentioned earlier what are the con's to that? I'm not someone who plays their system very much without the car running I know I will need a bigger alt so I'm not expecting the dual batteries to solve all of my problems....

Ok wait I've read more about these while writing this post... so is this how it works... I connect the wire to the + on the front battery to the split charger then it to the rear battery and then the rear to the audio I can have it(rear battery) isolated from the other one... but won't I eventually have to have this set to be connected so that the alt will charge both so I'd either have to have the wire on this thing capable of handling my entire audio system or connect it, while the engine is running, with my audio system set to a low volume to recharge the rear battery???? confused cause I know that a DC flow only goes in one direction and that electrons actual flow is neg to pos but everything is always in conventional flow so it confuses me lol I'm very confused lol.

the connection I'm talking about is like this at the bottom of this page...

https://www.bcae1.com/battiso.htm

if I do this the current draw from the distribution block with be half from the front and half from the rear correct? I REALLY want an answer to that question =-) I also see some posts of people saying even if you have two of the same battery that unless they are from the same batch that the will slowly drain each other when you have the car turned off is this correct?

I was in the mindset of getting two yellow tops do you have any other suggestions haemphyst? I'm open to suggestions but I don't see where you really have to have an Isolator unless you'll be running your tunes all the time without running the car and for the isolator setups I have to have full power for my system going thru it which if I had something really power hungry wouldn't be possible because the power wire I'd need to run would be to big.

1: Forget the "split-charger"

2: You STILL have to have that large a wire, because your ALTERNATOR should be big enough to make any amount of power you might need. You are upgrading your alternator, right? You are correct. Dual batteries will NOT sove your problems... It won't "solve" any of them.

3: You are correct, the diagram at the bottom is the one you want to use. You can modify as you would like, just be certain your power cables are fused at both ends, and the batteries are paralleled...

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

S0 whatever my total amp current draw is that write going from the front battery to the distribution block has to be rated to handle that draw? what about the wire from the rear battery? Is it then only suppling power when the main one isn't? how is it getting it's charge lol confused again? I know I'm very close to understanding it but I just can't get over the hump lol.

here are the reasons I want a dual setup...

1. have less current coming from both batteries so that I don't have to run anything bigger than a 4 awg
2. make wiring easier to say put in some neon lighting and cooling fans, etc... in the trunk that would be controlled by a switch or the car's remote.

Yes I will be upgrading my alternator I'm sure the current 103 amp alternator would be very unhappy if I put all that other stuff on it's load. btw any suggestions on who to get one from?

thanks

If I had the same setup as before but ran another 4 awg wire from the rear battery to the alternator then wouldn't it all work out the way I want it to? as in the current draw for the audio system on the fuse block would be divided up from the wire to the rear and front battery and I would get flow from the alt to the batteries and then back.

I see where you're coming from in thinking that the current will be split in half, but it doesnt really work that way. Seeing that you'll be mainly using your audio system while the car is running, you havent taken the alternator's power supply into account. Generally the alternator will supply almost all the power to the amps, seeing that it usually gives 13.8v or so. This means that most of the current will still be going down that 4awg wire anyway. If you really dont want there to be too much stress on that wire, you could install a stiffening capacitor. This will pretty much have the same(if not better) effect on the audio system in that it will supply the extra current when the amps need it (pretty much when you hit a large bass note or so). Its also safer for the boot, and they usually have built in volt meters, so u can monitor any voltage drops in the system.

Mind you, the Pioneer company cars here in Australia run 4 500w RMS mono blocks and 2 4ch amps on 4awg. Personally, i think thats pushing it, but unless your running some pretty serious gear like that, i think you can get away with that power cable.

BTW,

BTW, shouldnt the wiring already be quite easy to set up coming from your boot, seeing that u already have a distribution block?

Here u go redrazor...this site explains it pretty well...

https://www.bcae1.com/charging.htm

So I would have to run a second line from the alt which also went to the second battery to achive what I want to do?

You can run that same line thats already connected from your first battery to your distribution block. It doesn't matter whether you run it from the alternator or the battery, because they're all connected. Whether you need to run a second line or not depends on how much current you need to draw.

well ok I'm still confused and don't understand why this wiring ( Alt to front and rear battery side posts, Then wire from front and rear battery top posts to distribution block wouldn't splt the amperage... ) even without using the side posts I thought with both batterys going to the amp this would be like a series/paralell connection. With the batteries being connected in paralell and the amp the series but I'm fouling something up here so I'll go reread bcae1, and some other things on current flow and how alternators work again and again and again untill I've got it down. Thanks for all of your input so far.

Another question then (while I'm reading) If I just have one battery and run two 4g wires from the battery to a distribution block then wouldn't each one carry half the current on them? comments on my previous post would be helpful too. Well back to reading.

It would make sense that if you had the room to install two or three 4-gauge wires through the firewall that you would also have the room to install one 2 or 1/0 gauge wire. If you're only purpose in using two batteries is to split amperage then you're on the wrong path. I didn't read everything that was written here in this thread, but you must know that amperage starts at the alternator and goes through the chain, to the first battery and then to the second. Two batteries in parallel is the same voltage as one but twice the amperage capacity. Having that extra capacity should be the only reason to use the second battery. It sounds like that is not your intended purpose.

So I would say, find a way to install the bigger wire.

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Thanks for your response stevdart. As for more than a 4g no not at anywhere accessible with out removing some things because I have only enough room at two different spots to run a 4g wire thru each. I could run it underneath the car and encase it in some piping. Since I've talked to my father about this that's all he wants to do now. Lol I really DON'T want to do that. I guess I'll if I want a 2g wire I’ll just have to make way and move things so I can get to a good drilling area in the firewall. I thought adding a second battery as show at the bottom of this page...

https://www.bcae1.com/battiso.htm

would give me the desired effect of having half of the current flow going thru each line to the distribution block but I guess I'm wrong here... some other people have even said they don't see how the battery would be charged with this setup... I guess I still do not fully understand how the electricity flows and works so I'm just going to read up on everything I can until I understand it... If I can use 2 4g to hold half of the total current being used by the distribution block then I will go with that... if not I will just go with 1 4g wire and change my setup accordingly so that it will not pull more than that wire could handle.

redrazor wrote:

well ok I'm still confused and don't understand why this wiring ( Alt to front and rear battery side posts, Then wire from front and rear battery top posts to distribution block wouldn't splt the amperage... )

Let me correct something in what i said - it does split the amperage in half, but only when the car is off. Both batteries will be providing the usual 12v or so. When the car is running, thought, thats a different story. The alternator will be providing about 13.8v, and will hence be providing all the power to the amplifiers while charging the (both)batteries at the same time. The only time power will be drawn from any of the batteries is when the power draw from the amplifier is exceeding what can be supplied by the alternator. This will cause a voltage drop in the system and current will be drawn equally from both batteries.

redrazor wrote:

Another question then (while I'm reading) If I just have one battery and run two 4g wires from the battery to a distribution block then wouldn't each one carry half the current on them? comments on my previous post would be helpful too. Well back to reading.

Yes , 2 x 4g wires will double the cross-sectional area of the cable carrying current. This will exactly halve the max resistance of the wire from the battery to the amplifiers, thus doubling the maximum current flow.

I = V/R

If R is halved, I is doubled.

chuckstasy -

Thank you for your help. These are all things I read and knew or should have known I just couldn't put most of them together until a little while ago. Your posts have just reassured me of the facts. I'm still a little sketchy on why the dual battery setup of having 2 cables coming from the Alternator with 1 going to each battery and then to the distribution block wouldn't cut current it in half but it's a moot point as I will go with the dual 4g setup from one battery. As for the dual battery setup I will continue to read about the dual setup and electricity flow as well because I like to understand why something is thee way it is instead of just saying ok it's that way and go on. I'll make sure to upgrade my alternator, grounding wires and properly fuse everything and be as safe as possible.

I may be a stubborn SOB when trying to learn things sometimes but I usually don't give up until I get it correct.

Thanks again for everyone’s help.

What about just hooking the 2 battiers up like on a diesel truck!?! They come stock with 2 battiers.

Someone sell me on why not to use an isolator with two batteries.

-------------
Top Secret, I can tell you but then my wife will kill me.

forbidden wrote:

Someone sell me on why not to use an isolator with two batteries.

Here's my argument, Rob... Right or wrong, it's RIGHT...

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

That is quite convincing.

-------------
Nik
Jeeputer Progress
[|||||||||||-] 90%
Check it out.

haemphyst -

Thank You for the link to these previous posts. It's very helpful.

forbidden wrote:

Someone sell me on why not to use an isolator with two batteries.

There is no simple answer.. it depends on what you're trying to accomplish. As noted, Ford uses dual batteries in parallel in some of their diesel trucks.. Porsche did also in some 911-912 model years.. I've even seen it done on ag tractors. They've determined that one battery wouldn't be enough, so they did two in parallel.. no isolator.

On the other hand, isolators are widely used in situations where power is being used while the engine is off.. so the starting battery isn't drained. One common configuration I've seen is a starting battery, isolator, and 4 six volt deep cycle golf cart batteries wired in series parallel. While sitting with the engine off power is drawn from the 4x6v battery bank; once the engine is started the isolator connects everything together and charges the battery bank.

Hope this is helpful..

Jim

This is what I was hoping to see, two possible and logical answers to the same question. It depends on the use of the system entirely. Both methods are correct. The last vehicle I did was basically the same thing. One primary starting battery + isolator + 3 gel-cells. The next one I am doing has no isolator so that both batteries may be used in the system.

-------------
Top Secret, I can tell you but then my wife will kill me.

forbidden wrote:

This is what I was hoping to see, two possible and logical answers to the same question. It depends on the use of the system entirely. Both methods are correct. The last vehicle I did was basically the same thing. One primary starting battery + isolator + 3 gel-cells. The next one I am doing has no isolator so that both batteries may be used in the system.

Hope springs eternal.. eh?..

Jim