Before you ask why i need two batteries, one for back up on my shaved door handles, and for indoor car shows to run my lights and stuff. any help would be great. thanks

Brandon

 

It probably wouldn't be a good idea. I believe that would put 24 volts through your system rather than 12, which is not a good plan.

 

I thought if you run them in line with each other, the system stays 12 volts ??

-matt

 

There is a diffrence between series and parrallel. Parallel is the way it should be hooked up and you may want to put a battery isolator in (eBay $20 shipped) to keep both batteries well. I don't see you needing anything bigger than a lawnmower battery though, but a full size will be fine too with the isolator.

Parallel is negative to negative, positive to positive.

Series is one battery negative to the other battery's positive then positive to car positive and the opposite battery's negative to car ground.

It was hard to find a pic but this was the closest I can show for you to see, it shows subs but it is the same concept .http://www.the12volt.com/caraudio/boxcalcs.asp

The first picture with the subs applies to parrallel which is what you want. Series will put on a nice light show and a smile on the dealerships's face.

 

It is not a good idea to connect both batteries in parallel. The batteries will each develop different characteristics due to aging even if they are the same type. Thus one battery might tend to charge high and the other left relatively uncharged. The terminal volts vary by more than a volt sometimes, and the internal resistance of a lead acid battery is very very low, so large currents can flow between one battery and the next.
Usually when a second battery is installed it is used to power its own part of the vehicle circuit: the most common is to have a second battery powering a high power audio system so the audio can be used without the danger of a flat main battery and unable to start... such a system uses a charging diode, of the Schottky type (low forward voltage drop) to isolate the second battery from the first. Which is more than you wanted to know, I suppose...

 

You'll need an isolator like this one: http://www.surepower.com/isolator.html

Here's a PDF that talks about why you need one: http://www.surepower.com/pdf/ebr_int.pdf

 

Dont guys with lowriders do this with their hydrolics tho? You may have a point, but i dont think its that big of a deal, since its not really going to be under constant drain from something BIG like a huge amp or anything...

I dunno, just sounds a lil wierd. What you say somewhat makes sense (not fully understanding ) But i think he will be fine...

Let us know what happens if you try this out Euro

 

Lowriders do run up to 48v systems by running them in series/parallel but they also constantly charge/discharge them and typically get a poor lifespan out of them. It's an expensive hobby...

 

I think thats unnesecary because your alternator will still only recharge the same amount of voltage as it used to.....but then you're just splitting it between two different places. I suggest getting a Yellow Top Optima battery

 

If you wire them in parallel, it will stay at 12v but will up the amperage. If you wire them in series, it will put you at 24v and the amperage will stay the same. My friend wired in 2 batteries for his stereo and used a battery isolator. The amp he was using works best at 14.4 volts. The problem with that setup is it dropped him down to 12.5 since the alternator had to now charge 2 batteries. If he had a high performance alternator, that setup would probably work great. Speaking of alternators, does anyone make a high performance alternator for the max?

 

Backup for shaved door handles, installed properly, is an external hidden hood release. That gets you to the battery for a jump so you can get into your car in the case of a dead battery.

You can easily kill 2 batteries if you leave your lights on for a few hrs.
Thats not the back up solution.

 

In line is the only way if (parallel will bust it up to 24V). in line you will basically be increasing ur AMPS. all u need to check are ur equipment and if they take it.

 

Series will bump it up to 24 volts not parallel. Parallel will bump the amps up and maintain 12 volts.

 

Electronics 101

 

Do the extra battery and the isolater if you have a kickin system. Use the hood release option for backup.

 

I first was going to disagree but then gave it some thought and you are right, hooking direct in parallel even with an isolator would still allow current draw but only when the isolator is in connect mode I would assume. You would need some sort of diode I would say, easiest way would be to put a manual backup. But you could also rig an aftermarket solenoid attached to the lock rod on a separate mini circuit and on a battery on the isolator, the isolator would be wired to only allow the battery to be in the same circuit when in the run (not on) position. The trigger for that one solenoid can be hooked to the aux input.

 

Yes, that's a good idea.

ALT+ --------->|------+ve BATT1 -ve to gnd
ALT+ --------->|------+ve BATT2 -ve to gnd
this is the arrangement I was talking about, the >| is a Schottky diode with a typical spec. of 35A forward current with a forward voltage drop of 0.2V (ordinary diodes have a drop of 0.6V) Easily obtainable from semiconductor suppliers on the Net.

- and as you suggested, you could wire a relay to a suitable terminal so that, for instance, the second battery could be used in the AUX position only.
The function of the diodes is to allow the alt to charge both batteries, but not to allow either battery to discharge itself into the other. (Imagine going to an event. You use up your second battery on audio, it is flat. THEN you turn the key and you connect your fully charged main battery to it, with no current limiter. What do you think will happen? Smoke will happen! Sparks could fly, wires could melt.

 

If anything you will burn up the alternator, becuase it maybe running at 12 volts, but the alt. is having to charge twice as much. get what im saying? i was going to do this but i talked to the car customization plus here in town and he told me a way to hook up with the isolator and a circuit breaker. so you set the breaker in the wire going to the second battery then you break the circuit so then you can run off the back battery so then you can start your car still. so then you start it back up and then you switcht he circuit breaker back and it recharges both batterys. but if anything get a more powerfull alternator such as a 250-300 amp alternator. and run 0 gauge wire for all power wires to your starter and what not. i upgraded to 4 gauge with everything and i noticed brighter headlights, my system hit harder, and my lights barely dimmed. hope this helps.

 

Borrowing from research/reading/experience with DC systems in boats, maybe the way to go is a battery combiner. It's a little different than the isolator already posted. It's basically a voltage-sensing relay (VSR). The batteries are isolated from each other (so one can't drain the other), unless there is a charging voltage coming from the alternator. When there is a charge voltage, it then electronically allows current to pass to both batteries in parallel. When the charging voltage is no longer present, the combiner isolates the batteries again. It's an elegantly simple solution. Googling it quickly, here's another description:

"Combiner A combiner is an electrical apparatus used to permit two battery (banks) to be charged "intelligently." The combiner relies on the fact that the voltage across a charging battery will rise as the battery charge increases. When the charging voltage is great enough, the combiner electrically connects both batteries in parallel to permit them both to become charged. When the batteries are not being charged the combiner electrically isolates the two banks. Using a combiner in place of the isolator that is original equipment in the GMC permits the electrical isolation (keeps the engine battery from becoming discharged) when you use the coach 12V electrical AND allows both batteries to be charged when charging voltage is present. This can simplify the electrical system if you want to permit charging of the engine battery from the coach charger."

The combiner I put in for my boat was like $50-100 and was rated to 50amps.

 

That 'combiner' you are talking about, is exactly what my circuit does, posted earlier. Except the diodes cost about $5 each so you could save a lot of money if you wire it yourself. The diodes need heatsinks, not too big.
There's been an awful lot of nonsense spoken about this, on this thread!

 

Cuz I'm a noob my post was nonsense, or were you referring to someone else?

For anybody that still has an open mind about a solution...

http://www.yandina.com/c100Info.htm

$60, includes wiring, no need for heat sink, no user-effort. Hook it up and you're done. Like I said the first time, "simple".

 

No, those people who suggested putting the batteries in series, or so on. But as for the guy who just wanted backup for his door locks, he could just use a small LiOn rechargable battery, with a charging diode from the main car power line, and perhaps add a small solar panel in the rear window to keep it topped up when the car is parked for a long time. Quite cheap - if you know what you're doing.

 

euro max looks ill//

 

I agree completely, I design 12 & 24VDC fire alarm & security systems and I deal with wiring batteries in parallel & series everyday.

Parallel will take 2 12V 24Ah batteries and make 12V 44Amphours,
Series will take 2 12V 24Ah Batteries and make 24V 24Ah

You don't want 24VDC there isn't anything that will run on that, and you would have to step it back down to 12V, and with the same amphours, your batteries will drain just as fast.

Also before you hook up 2 batteries in parallel, check the amphours of the batteries, add them and make sure your alternator can charge them and still have enough amps to run the car's electrical system. ( I have no idea how much it takes)

 

I new a guy with a low rider, and he had 6 batteries in his truck, at the time I wasn't sure if the were wired for higher voltage or higher amps, but I do know he charged them with an external plug in charger in his garage, and they were not connected to the car's electrical system at all.

 

Actually that way of setting it up is flawed as well. Although it'll work just fine as long as you don't drain the auxilary battery too much, if you run the aux. battery for a period of time that it drains it past say %80 then you're going to overheat your alternator. Alternators aren't designed to charge batteries, they're designed to provide power to a car while it's running and to keep the battery maintained. In short, you'll use way more power from a battery if you run a large stereo system and/or lights for an hour or two than you will starting the car. So when you close the breaker and charge the battery it's doing the same thing you were trying to avoid: charging to an extent beyond it's designed capability. And the battery itself becomes overheated if you charge it too fast as well. This is why most home battery chargers take 4-6 hours to fully charge a battery; to prevent overheating the battery or the charging device. And yes while jump starting a car essentially does the same thing, lets the alternator charge a dead battery, it's still not a healthy thing for either of them, and certainly not something you'd want to do every day. So if you went this route, I'd be sure that you start your car every now and then to keep the battery at least most of the way charged, or if you have a deep cycle that's designed for rapid withdrawal and recharge then use a charger (not the alternator) to charge it back up when you're finished using it for extended periods of time.