Do i need a battery isolator IF.......?

[BassAddictJ 5,000+ posts]

i plan on adding a battery in the back for the stereo. The extra battery will be connected directly to the alternator with 2 runs of 1/0 (1 pos 1 dedicated neg). The extra battery will not be connected to the chasis, only to the alternator (pos post and neg post).

Should i still get an isolator so that the alty will not charge the stock battery when it's fully charged?

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[mokedaddy 5,000+ posts]

First of all a battery isolator is only for batteries run in parallel. If coming straight off the alternator an isolator will do nothing accept cause a voltage drop.

Also it is better to run the negative to your front battery than ground at the alternator since the battery is the actual ground of the vehicle.

 

[helotaxi 5,000+ posts]

The alt won't charge the battery once it's fully charged, isolator or not. Very rare that an isolator is needed really.

 

[helotaxi 5,000+ posts]

First of all a battery isolator is only for batteries run in parallel. If coming straight off the alternator an isolator will do nothing accept cause a voltage drop.
Also it is better to run the negative to your front battery than ground at the alternator since the battery is the actual ground of the vehicle.

Actually with the car running, the alt case is the point of zero potential. It should be connected to the battery negative with a heavy gauge wire making them electrically the same.

 

[bonesninja 5,000+ posts]

i'm with helo...only time you should really need an isolator is if you play your system for extended periods of time with the vehicle not run ning and don't want to run the risk of draining your starting battery

 

[Chevyaudio 5,000+ posts]

The alt won't charge the battery once it's fully charged, isolator or not. Very rare that an isolator is needed really.

exactly...and it doesn't mater where your 2nd battery is connected really. The electrical system of your car is a loop. Connecting the 2nd battery to the car's main battery is the same as connecting the battery directly to the alternator. This is also true with the ground. The Alts ground is usually just the bracket that connects it to the engine block which in turn is connected the the chassis of the vehicle.

Long story short...no you do not need an isolator.

 

[mokedaddy 5,000+ posts]

Actually with the car running, the alt case is the point of zero potential. It should be connected to the battery negative with a heavy gauge wire making them electrically the same.

learn something new everyday.

 

[BassAddictJ 5,000+ posts]

Actually with the car running, the alt case is the point of zero potential. It should be connected to the battery negative with a heavy gauge wire making them electrically the same.

yah...that's pretty much what scottiej told meh.

doing 1/0 (1 pos 1 neg)

and having the extra battery (d3100 //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif ) not connected to the stock battery will prevent it from the 2 batteries from draining off each other when the car's off they're connected.

 

[helotaxi 5,000+ posts]

and having the extra battery (d3100 //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif ) not connected to the stock battery will prevent it from the 2 batteries from draining off each other when the car's off they're connected.

No it won't. They're still connected even if you don't wire them directly to each other. As was mentioned above, your car is one big parallel circuit. If it's wired to the alt, so is the other battery.

 

[azeroth123 10+ year member]

Yeah thats where the isolator comes in, if your goal is to have the separate battery for use when the engine is off for relatively longer periods of time. Attaching the rear bat directly to the alt does not bypass the other battery like you are thinking, they are still directly connected in parallel as if you connected straight to the starter batter itself...

 

[Bigrick31 10+ year member]

No matter what point in your electrical system you connect the second battery it is still electricly connected to the second battery. whatever you do just make sure not to connect your first battery in series with your second batters thus raising the voltage of the two batterys to 24volts.