Battery Q

[VooDoo]

can i use a motorcycle battery in a car?

moving my main battery (2SM) to the trunk... need the space for a CAI project i'm doing. but i'm thinking of adding a small battery in the engine compartment so that the starter doesn't have to draw power all the way from the trunk. i'm hoping a small battery (i.e. one for a motorcycle) would do.

thanks!

[[SMAN]]

I wouldn't recomend a motorcylce battery as usualy those don't put out as much power as normal car batteries, however, if your looking for a small batter, find the style that goes for the honda civic, those are smaller than normal size.

[VooDoo]

ok. i'll look into that.

another question... is it ok to wire the two positive poles (small battery in engine compartment and main battery in the trunk) in series?

[88 LE]

Originally posted by VooDoo
another question... is it ok to wire the two positive poles (small battery in engine compartment and main battery in the trunk) in series?

Its okay to wire the batteries together, but not in series. 2 batteries in series would give you 24V.

You want to wire the batteries in parallel. Wire the 2 positives together and same for the negative.

[[SMAN]]

You wil also need to get somethign to put inbetween them to prevent each battery from trying to charge itself off the other one, i forget what it's called though.

[2wickedtoyz]

just go to the part store and get the battery with the most cranking amps and you won't have a problem with starting also make sure you are running at least 4gauge wire from front to back.

[Phi]

Originally posted by [SMAN]
You wil also need to get somethign to put inbetween them to prevent each battery from trying to charge itself off the other one, i forget what it's called though.

I think you're thinking about an isolator. It's recommended but not necessary under the right conditions.

Is an isolator needed when paralleling batteries?

Connecting 12 volt lead acid batteries in parallel can be done, but you must be careful to minimize the danger of fire or battery explosion. Yes, manufacturers of diesel pickups connect batteries in parallel to provide the high starting currents required by diesels in cold weather, but the manufacturers take the lowest cost solution to the problem, and figure that the batteries will outlive the warranty period.

Batteries can be connected in parallel only if they are of identical age, capacity, and manufacturing lot, and only if they will always remain connected in parallel. If the batteries are ever cycled indepedantly, they should be replaced with another matched pair.

If a mismatched pair of batteries is connected in parallel and then allowed to sit, they will pass current back and forth in an effort to ballance charge. If one battery is weaker than the other, it will attempt to drain the stronger battery. Eventually, one battery will short and the other will then dump all remaing charge into the shorted cell - resulting in two dead batteries or worse, a fire or battery explosion.

To prevent charge swapping/discharging/fires/etc, some kind of isolator is recommended for batteries in parallel. There are two types of isolators:

Contactor or relay
solid state diode
Contactors

A quality, sealed, heavy duty contactor is reliable and simple to install. A contactor connects an auxiliary battery to the charging system when the engine is running, and disconnects the battery when the engine stops. This allows one battery to start the vehicle and run the automotive systems, and the auxiliary battery to power winches, stereo systems, lights, transmitting equipment, campers, etc. The contactor also allows the auxiliary battery to boost the primary battery if the battery is dead and will not start the vehicle. Be aware that most auxiliary contactors can not handle starting currents, and all starter relays and solenoids will burn up if used continuously as contactors.

Isolators

Isolators use high current diodes to split the charging current between two or more batteries. Vehicles with high capacity alternators must use very large diodes to prevent damaging the diodes when a discharged battery is recharged. The diodes introduce a voltage drop into the charging circuit of each battery that must be overcome by the alternator, which is not a big problem for most modern alternators. With a diode isolator, the voltage regulator must be carefully wired to prevent overcharging or undercharging the batteries. An isolator will not allow batteries to boost each other, but a jumper cable is better for that anyway. Isolators are much more expensive than contactors. Hellroaring Technologies has gained a popular following among the 4X4 crowd for their rugged isolator which has a very low voltage drop.

Source: http://dodgeram.org/tech/mods/electric/2nd_battery.htm

More info: http://bart.ccis.com/home/mnemeth/12volt/12volt.htm

If size is your main concern get a battery sized for Hondas or look into and Odessey http://www.odysseyfactory.com/default.htm. These things are stupid small. Truthfully, a single Deep cycling battery (ie. Optima) in your trunk is more than enough if you don't have any crazy audio.

[VooDoo]

wow. the project doesn't look as simple as i thought it would be.
looks like i'll just stick with one battery and move it up into to the trunk.

thanks for your thoughts, guys!

[Phi]

try and get a deep cycling battery. Not only for better performance, but safety reasons too. Sealed batteries are perfect for this kind of stuff. Let us know how it goes

[VooDoo]

i'm currently using a sealed maintenance free battery.
unfortunately Optima's don't get here to the PI. If ever they do, they cost an arm and a leg.

Here's the battery I'm using now... its one thats locally available here.


Size: N50/2SMF
Amp-Hr: 65
Res. Cap.: 111

btw, is it ok to use OAWG or 2AWG audio power cables? some friends were advising me against it saying it would be better to use the cables similar to those used in welding machines.

[88 LE]

Originally posted by VooDoo
btw, is it ok to use OAWG or 2AWG audio power cables? some friends were advising me against it saying it would be better to use the cables similar to those used in welding machines.

Either one will work.

Welding cable just has a different type of insulation on it.

[VooDoo]

but would a welding cable be safer to use?

which type of cable would i be better off using?

i don't want to burn my car right after the project. hehehehehe!

[Phi]

Here's more info on Odyessey batteries. Check out the tiny starter battery they have Model PC680MJT - Battery measures 3.11" wide x 7.27" long x 6.67" tall with the metal jacket and weighs 15.4 pounds.

http://www.odysseybatteries.com/auto.htm

[KILLACAMNY]

You can get a dry cell Stinger battery that has either 1000 cranking amps or 1700 cranking amps.

[Phi]

I think his objective is to get something small. That stinger battery is huge.