dual battery setup

bandikook

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lets say i have an optima and i want to run two because of lighting and other drains on the battery. If i just connect a postitive from battery A to battery B and same with a ground, will my alternature chargebattery B too. If not, how do you set up a duel battery setup.
 

hoeker

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the way he's talking about hooking it up will work fine with no isolator needed. an isolator is for instances like winching, the winch is hooked to it's own battery so the battery needed for the engine isn't run down winching the truck. the vehicle can then start and charge both batteries through the isolator.
either system works fine, it just depends on your needs. if you just want extra capacity for lights, and they won't be on when the truck isn't running, the way you described is fine. if you like to sit by the campfire with your radio on until you pass out, hook the radio up to the second battery and get an isolator.

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Kritter

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"if you like to sit by the campfire with your radio on until you pass out"

Glad I am not the only one who does that!

Kris
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hoeker

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not that i do that, just heard it happens sometimes. lol

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orvacian

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If you directly connect two batteries in parallel, they need to be EXACTLY the same. This means age, size, capacity and so on. If not they will discharge each other while they sit. A dual battery isolator will work but there is some voltage drop through it. The best thing is a big high current relay switched with the ignition but they can be a little pricey. What you actually want is a bigger alternator more then a second battery though. With constant draw items like lights or fans you are just prolonging the time it will take to discharge the battery.

Here's a example: Let's say you have a 70 amp alternator on your Ford Festiva prerunner. You are running 840 watts of KC Highlites and the Festiva uses 30 amps while running. 840 watts = 70amps + another 30 amps for the trophy Festiva equals a 30 amp DISCHARGE while driving. Your Optima is mabye a 30 amp hour capacity battery. This means your battery would die after 1 hour of driving! So you add another battery. You only get 1 extra hour of run time! And that's if both batteries were fully charged to begin with. What will most likely happen is your alternator will die from all the extra load.
The only good thing the extra battery would do is give you more run time with the car off.

On the other hand, if you get a 120 amp alternator you have an extra 20 amps available above what you need (100 amp draw) and you don't need another battery.
 

hoeker

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well done!

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Eric_M

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orvacian,
say i run a 120 amp alt. can i just hook it up and call it a done job, or are there anything i would need to do to keep it from cookin anything? so in other words, will i run into any consequences by runing the 120 amp alt. with out doing anything besides bolting it in and hookin it up?

thanks

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Kbach66

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So much for debuting my new Festiva prerunner at the next MDR race!! Nobody keeps secrets anymore!!
 

orvacian

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The output amperage rating of an alternator is the maximum amperage it can potentially supply. A way to think of it is that the alternator has a certain amount of amperage it can give at a time; the battery and electronics will take what they need from the alternator. The battery stores that amperage and the stuff connected to it takes that it needs. When the engine is running the electronics are actually running off of the alternators output, not the batteries stored amperage. It's a little more complicated then that but you get the idea. Most alternators have a built in regulator so it will not overcharge your battery. I have a 140 amp alt and Optima in my truck and it works beautiful. Some older cars have a external regulator but it does basically the same thing. The amount of amperage the battery will draw when charging is determined by the output voltage of the alternator. What the regulator does is regulate the output voltage of the alternator so it stays somewhere around 13-14 volts. 13.5v is pretty standard.

<P ID="edit"><FONT SIZE=-1>Edited by orvacian on 02/12/03 11:09 PM (server time).</FONT></P>
 

Eric_M

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that answered my question perfectly, but 1 more question..... will a higher out-put alt. just bolt right up and use the same wiring connections as a stock one? thanks!

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orvacian

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It depends. The stock wiring is thick enough for the stock alternators output. If you double the output amperage you would probably want to use a heavier gauge wire. For 120 amp alt you would want at least 4 awg wire. The mounting depends on what type of alternator you get. I got mine from a e-bay retailer and it was exactly the same size as stock, it bolted right up.
 

michael_loomis

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depends on the alternator you buy , but yes it "should" . its a good idea to increase the charging wire to 8 gauge also , as the factories mostly use 10 gauge , some ive seen small as 12.
 

ntsqd

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Cole Hersee makes a constant duty solenoid just for this purpose, separating batteries when the ign is off. You can't push starter current thru it, but it'll handle everything else.

My general practice when adding stuff to an existing wiring system that has two batteries is to wire all of the added loads the the second battery. One option I like for hard service vehicles with separated batteries is to wire a Ford starter solenoid to put the batteries in parallel for self jump starting. Pull the solenoid's power from the second battery.

I've seen that advice about the two batteries needing to be the same or they will see-saw discharge each other many, many times. While I think it is a good idea to match the batteries, I think the damage potential (no pun intended) to the batteries is commonly overstated. A case in point is my '79 Suburban. It came with the dual battery option. They are wired directly in parallel from the factory, no isolator. One original battery is listed on the option sheet as having nearly a 1/4 again more capacity than the other battery.

TS

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orvacian

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The issue is not if the batteries will be damaged, rather that they will discharge while sitting in your driveway. Then you would be late to work and get fired, you cant pay your morgage so you get evicted, your wife leaves you because you are broke, then you get this super bad athletes foot and your leg has to be amputated, then you are crawling across the street and get hit by a semi. See how if you wire two different batteries in parallel, it could kill you!?!

<P ID="edit"><FONT SIZE=-1>Edited by orvacian on 02/12/03 11:29 PM (server time).</FONT></P>
 

michael_loomis

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Thom , i 've always been told that without an isolator one battery could drain before the other and likewise charge faster/slower.

what is your opinion ? i've never seemed to have any really big issues but on yachts they ALL have isolators.
 

ntsqd

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Maybe they will some see-saw discharge, but my point is that GM didn't think it was enough of an issue to include some isolation method in the dual battery option, one that paired disimilar sized batteries from the factory. One can argue that they are too costly for GM to consider using one, but GM would also take into consideration customer complaints and the cost of warrentying dead batteries if it were a huge issue.

Hell, I got fired and I wasn't even late to work.

I don't argue that some form of isolation can be a good thing. I do argue that an isolator is not a must-have part for dual battery installs. I do not believe you absolutely need to have one.

Boats have isolators for battery BANKS which are usually comprised of several to many batteries in each bank wired in parallel.

TS

I used swerve around my halucinations, now I drive right thru them.
 

Kritter

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While on the battery topic...extensive research was done to find the life of a battery and the conclusion was that a battery will last 37 months...hence the 36 month warranty so to everybody coming up on the 36 month...kill it now! People were paid boocoo bucks to do this research!

Kris
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Tyson

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I got a question then. I've seen a race truck that runs a regular optimum battery and the cold cranking one. THose are not the same battery, but how would I go by wiring that up to my truck. I know I'd want a switch of some sort so that the harding working battery could always start the truck and use the other for driving. Make sense. . .or is it that late hour where nothing really makes any sense?

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