Current in a car battery

Thread Starter

Salgat

Joined Dec 23, 2006
221
I'm pretty sure that with Ohms law on my side I shouldn't have any worries, but for the circuit I'm using that normally uses a 9V in series with two AA batteries(12V total), should I have any concerns about replacing it with a car battery that is at 12V? Would a regulator probably be recommended? Mind you none of this is connected to a car:p
 

techroomt

Joined May 19, 2004
198
the 12vdc car battery will work, if, the circuit is only utilizing the 12vdc. the original had supply voltages available of 1.5vdc, 3vdc, 9vdc, 10.5vdc, and 12vdc.

no regulator should be required. the auto battery cells are just as loose on voltage range as flashlight cells.

the longer amp-hours of the car battery will last much longer then the flashlight cells.
 

Thread Starter

Salgat

Joined Dec 23, 2006
221
Ya that was my reasoning. He only used the 12V output of all the batteries in series. Since the AH is a lot higher, I reccomended a car battery(he is wants a high capacity battery), but for some reason he keeps saying that the AH means more current will output(which would violate ohms law). Thanks for your confirmation. By the way, do you know any other high capacity 12V batteries?
 

techroomt

Joined May 19, 2004
198
the childrens ride toys (jeeps,cars trucks, etc) have sealed lead acid (and others i imagine) 12 vdc batteries which have some pretty good punch.
 

SgtWookie

Joined Jul 17, 2007
22,210
Unless you're going to have a charger hooked up to the battery (thereby creating a true uninterruptible power supply) I suggest you look into "deep cycle" batteries. Normal automotive-type batteries don't last very long if you're going to drain them down without immediately recharging them. Marine batteries are designed for such usage.

If it's going to be used indoors, you should only use a SLA (sealed lead-acid) type battery, as otherwise the hydrogen and oxygen gasses (produced by charging/discharging) are highly flammable, indeed explosive.

Make sure you use a fuse! Should your wiring fail, a lead-acid battery is quite capable of melting heavy-gauge wires and causing fires.
 

Thread Starter

Salgat

Joined Dec 23, 2006
221
Well the use is for outdoors, he has an aluminem backpack with gear for paintball. His gun requires a battery for its trigger mechanism, and the reason for a high capacity battery is if he plays all day for example. He will be able to recharge every night if need be.
 

SgtWookie

Joined Jul 17, 2007
22,210
OK - SLA type would be much better than standard auto batteries. Little risk of an acid spill. One must always think about safety first.

Something else he might think about using is a bank of large electrolytic capacitors; they would be very lightweight in comparison to an SLA battery, and he could charge them up VERY quickly using a car battery. He would need to be careful to avoid excessive current in the charging wiring, however - simply connecting a bank of high-capacity caps to an auto battery would cause a very high initial current. Using a high-wattage 12v bulb, such as a headlamp (or several brake lights wired in parallel) in series with the charge ciruit would limit the peak current to a safe level, along with indicating that the charge was nearly complete when the light(s) extinguish.

It wouldn't be a bad idea to use high-current diodes to ensure the charge ckt was hooked up in correct polarity, and in case a single cap were shorted, it wouldn't cause all of the capacitors to discharge through it.
 

nanovate

Joined May 7, 2007
666
Where would I find a good charger for this(aka reliable site)?
Allelectronics has some good stuff at reasonable prices:

http://www.allelectronics.com/cgi-bin/item/BC-86/965/2_4_6_%22#34;SMART"#34;_BATTERY_CHARGER_MAINTAINER_.html
 
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