if you get two batteries without an isolator do you have to have the same battery in front and back or the same brand? I thought I heard that using two different types was not good, any help on this? I never play with my car off. Just wanted to say that before someone told me I needed an isolator, I decided to go with parallel.
The batteries need to be the same, and even then, parallel wiring batteries is not good for a daily application. The reason:
Each battery has a very small amount of resistance, and the resistance is not exactly equal on both batteries. If it were, no current would flow and everything would be fine. But what actually happens, each battery will essentially see the other as a very small load, and current will constantly flow from one battery to the other, and back again until the batteries are drained.
Parallel wiring of batteries is done often in higher class competition cars, but those people disconnect their stuff when they're not using it, eliminating the problem.
A battery isolator (diode based, not a relay), will allow you to run two batteries and each will not be able to "see" the other, so current is unable to flow between them. Current can flow from alternator to battery 1 and from alt to battery 2, but not back and forth between the batteries. With this type of system, the audio system could completely drain the back battery, and the front battery would remain full (the type of front battery and anything else connected to the cars electrical has no effect on the audio system, and vice versa)
anyone know someplace online I can order one for a reasonable price rated at 300 amp? there is a stinger one at car domain for 140 but its 200 amp, and then I dont know if I can use 2 runs of 0 gauge to it.
^^^Like I said in the other thread, it's just not practical to use an isolater.
The 240amp isolater costs $140. You can get a stinger 200amp relay for $55. You can wire two relays together to handle 500amps of current if you want.
The only reason I would reccomend an isolater is if you wanted to play your system with the car off. In which case you would want your front batt separated from the rear so you could drain your rear battery with your system and still start the car fine.
Nate, you will not have a problem with the batts draining each other while the car is on, the draining only takes place while the car is off. The relay acts as a switch that connects the batts while the car is on, and disconnects the batteries while the car is off. Thus it eliminates the possiblity of the batts draining each other.
^^^Like I said in the other thread, it's just not practical to use an isolater.
The 240amp isolater costs $140. You can get a stinger 200amp relay for $55. You can wire two relays together to handle 500amps of current if you want.
The only reason I would reccomend an isolater is if you wanted to play your system with the car off. In which case you would want your front batt separated from the rear so you could drain your rear battery with your system and still start the car fine.
Nate, you will not have a problem with the batts draining each other while the car is on, the draining only takes place while the car is off. The relay acts as a switch that connects the batts while the car is on, and disconnects the batteries while the car is off. Thus it eliminates the possiblity of the batts draining each other.
" Like I said in the other thread, it's just not practical to use an isolater. "
Of course it is.
" The only reason I would reccomend an isolater is if you wanted to play your system with the car off. In which case you would want your front batt separated from the rear so you could drain your rear battery with your system and still start the car fine. "
You could do that with the relay also. The relay is inherently flawed in it's design. It acts as a switch, connecting the two batteries when activated. You would need to wire the relay to activate when the ignition is turned on. Now, lets say the battery in the back is completely drained or close to it. What happens if you turn the ignition on without starting the engine? The batteries are connected and a large amount of current will flow from the front battery to the rear, possibly creating a situation where each battery is partially drained, neither having enough voltage to crank the starter. This problem could be avoided if the relay were activated using a manual switch, but then you would have to always remember to turn the switch on and off.
Bottom line: The isolator is the best way to run dual batteries.
But why would you want to? If you wanted to play music with the car off, you would be using an isolater instead of a relay.
"What happens if you........neither having enough voltage to crank the starter."
That's true, but why would you just turn on the ignition and not start the car? It all goes back to my point; if you want to play music with the car off, use an isolater.
I think a lot of this discussion could be resolved if Nate told us whether or not he was going to play the system with the car off.
Other than the isolaters ability to isolate the rear batt(s) when then car is off(or with the ignition turned on....but the car not running), I don't see what benefit the isolator would be to him.
The relay would be cheaper and take care of the differing internal voltages between the batteries problem.
anyways I was thinking I would probably get that 200 amp isolator, but where exactly does that go? (back battery, front...?)
Because if it goes in back then I think I will probably get that and have a seperate run of 0 gauge back to each of two batteries and use two seperate isolators. That plus a nice sized alt should suffice for a pretty good charging system, no?
In that case the relay would work for you, but if you ever did drain the rear battery, you would have to remember not to turn the ignition on without starting the engine..... like I said it's just not an ideal situation. But it would work.
