Dual Redundant Batteries?

[Nd4SpdSe]

Once my swap is done, im gonna upgrade my stock battery to a Optima Red Top, but while im a it, i wanna run a 2nd one in the trunk. Not just for the extra run time while my car isnt running, but also for redundancy for my car alarm. How would o go about doing this, or is it possible?

[BumpNGlow]

it sounds like you want an isolator b/t the batteries. That way you will always be able to start the car regardless how long you have the stuff in your car on. You are going to have to re-route all the power wires back to the secondary batteries, but it's worth it.<p>http://www.eatel.net/~amptech/elecdisc/battiso.htm

[lakersfan1]

You don't need like a whole second $100 Optima just for your alarm backup battery. They make little 12 volt batteries specifically for car alarms. About 4"x2"x3" cube. I've seen them with little battery isolators built in to prevent overcharging, too. I've seen then bundles with the isolator for $35 or someting. I want to say that was on PartsExpress.com<p>I bought one without an isolator at a local Frys Electronics for $15.<p>[ July 22, 2003: Message edited by: lakersfan1 ]</p>

[Nd4SpdSe]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by BumpNGlow:
it sounds like you want an isolator b/t the batteries. That way you will always be able to start the car regardless how long you have the stuff in your car on. You are going to have to re-route all the power wires back to the secondary batteries, but it's worth it.<hr></blockquote><p>I have a 4 guage wire going to the the trunk, would that be enough?<p>I something about switches in that link. Ideally, i would like both batteries functioning as one large one, so if the main battery goes, i can automatically still start the car or still have a functionning alarm with my second one. Especially since my boss told me stories about people drilling holes on batteries from the underside, waiting until the acid drains out and break into the car, the alarm not working due to the dead battery.<p>Also, i only get between 45min to 1.5h with my whole system running, including the carpc, all on the stock battery. When i first installed the carpc, i used to get almost 2hours, but i think the battery age is starting to show. So ideally, i would like to be able to watch at least 1 whole movie, even 2, with the whole system running. <p>The A/C inverter cuts out at about 10.5v, and i've let it and was still able to start my car, so an unknowingly completely dead battery is almost impossible. But man, i was waiting for a friend, and was watching tv. I barely finished a simpsons episode before the a/c inverter starting freaking out (it squeels when the voltage gets close to cut-off)

[lakersfan1]

If you put two batteries of the same exact make, and are both the same age, you can get away with just hooking them inline.<p>Otherwise, you'll need an isolator.

[bulldog131775]

what you want instead of an isolater is a relay because it is far easier to hook up and its easier on the alternator i can sell you one if you need one. I sell stinger relays and thats what I use in my car with 2 dry cell batteries

[Nd4SpdSe]

How does that work? Relays work as switches right? That means the bettery will function only when i select it, no?

[BumpNGlow]

Ok, this is all from the page I sent you earlier:
Solenoid/Relay Based Isolators
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Solenoid Based Isolators:
This type of isolator uses large high current relays to control the flow of current. The diagram below shows two solenoids. Solenoid A determines whether the second battery is connected to the rest of the charging system or not. Solenoid B connects the second battery to the distribution block. The second solenoid allows a complete disconnect from the amplifiers for safety. The diodes connected in parallel to the solenoid's coils are used to protect switch A and switch B from inductive kickback when the solenoid's coils are de-energized. The advantage of the solenoid based isolator is that there is virtually no voltage loss across the contacts. The main disadvantage is that the reliability isn't quite as good as the diode based isolator. <hr></blockquote><p>and Diode Based Isolators:
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Diode Based Isolator:
This type of isolator is basically two very high current diodes in a heat sink. The diode based isolator has the advantage of long life and trouble free operation but many of the diode based isolators cause a .4 to .6 volt loss which means that the batteries will not charge to as high a voltage as when they are connected directly to the alternator. The diagram below shows the connection for the diode based isolator. Some diode type isolators have a fourth terminal which controls the current flow through the device.<hr></blockquote><p>I really think the Solenoid Isolator is the only way to go for you.