how would i go about setting up a dual battery system in my van?
basically i have a band. and we all have laptops/cell phones/ handheld systems etc that we will probably be bringing with us when we are on tour.
i want to add an extra battery to run extra cigarette lighters to each row of seats in the back of the van.
im guessing ill probably have to run multiple wires from the battery to be able to handle the amount of power i want to use for each one. since ill probably using converters to be able to plug the laptops and chargers in. but i could be wrong about needing extra wires lol.
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After you find a suitable location for another battery, you need a way to have them connected while the engine is running, and separate when it is not. The closer the 2 batteries are to each other and to the alternator, and the gauge of the wires used will determine the charging performance to a point. The voltage regulator in engine computer is the weak link.
The easiest way of combining and separating the batteries is with a continuous duty solenoid sold at NAPA. When it sees 12 volts from your ignition key or other switched 12 volts source, it combines the batteries, and disconnects them with the engine off.
Everything you need to power you laptops and chargers must be wired directly to the second battery. The inverter you buy should be close to the second battery over fat cables. Use regular extension cords to extend AC power.
Laptops use more battery power than you imagine. Mine pulls 3.0 to 7.5 amps depending on the task. Lets say it draws 5 amps per hour on average. The average size group 27 battery contains 100 amp hours of battery. If you want your battery to have any kind of lifespan, you should not deplete it more than 50%.
So you really have 50 amp hours of usable battery, and 1 laptop can deplete this in 10 hours. Inverters are also only 90% efficient or so, so you just lost another hour. The DC to DC 12 volt car adapters are better.
Some electronics do not like the modified sine wave from a MSW inverter but this does not seem to affect laptops. Pure sine wave inverters produce nice clean power, for 300 to 500% more $$.
Also keep in mind the vehicle's charging system is designed to top off a slightly depleted starting battery, not charge a heavily depleted deep cycles or dual purpose batteries. To replace 50 amp hours into the battery would take 4 to 8 hours of highway driving to bring it up to full charge. Upgrading the alternator wont help much, because the voltage is controlled by the PCM, and it drops the voltage to low too quickly so as to not overcharge the single stock starting battery.
That is the correct solenoid, although I've seen them rated for higher continuous duty amperage.
Usually you mount them on the firewall. You find a fuse from your panel which only has 12 volts when the key is on the on position and run a wire from that to the hot(+) terminal. The - can just be grounded to the firewall.
From the auxillery battery to the ciggy plugs, 12/2 awg wire should be plenty. But the ones furthest away from the battery might be better off with 10/2 awg.
The inverter, if over 400 watts will most likely come with it's own 6 awg wire with alligator terminals for a battery. One laptop draws upto 100 watts. The other various chargers you mentioned draw up to 10 watts and probably much less.
Flooded Lead acid batteries are not safe for interior use. They off gas during charging and during heavy discharging. AGM batteries like LIFELINE only off gas if they are overcharged, and are much safer than regular flooded wet cell batteries, but the 2 different types of batteries should not be paralleled/ combined, as they have different charging rates and acceptance rates. Do not consider gel batteries for this use. They are very finicky about charging currents, and one overcharge can ruin them.
Optima batteries are AGM, and have less capacity than other brands of AGM for the same price and footprint.
The inverter will be fused, but each other ciggy plug should be fused closest to the battery as well. A fuse block makes it much easier than wiring an inline fuse holder on each circuit.
Most items that use ciggy plugs have their own fuse inside the ciggy plug, but that only protects the wiring and device after the plug. The wires leading to the plug from the battery if shorted can cause a fire, and need to be fused.
If you put a flooded battery inside, it should be in a sealed battery box, vented to outside. I think a couple companies make such a thing.
If you go with an AGM battery, replace the one under the hood with the same exact one as well, and put the interior one in a box to protect the terminals from being shorted.
An AGM battery and a regular flooded wet cell battery should not be paralleled.
A flooded wet cell starting battery and a flooded wet cell deep cycle battery can be combined during charging, but should not be left in parallel when sitting unused or when discharging relatively slowly over any length of time.
Basically they charge and discharge at different rates. The stronger battery will always be undercharged and the last to be discharged. It works, but it's like the chain theory. It's only as strong as the weakest link.
Ideally, any batteries that are ever charged or discharged together should be the same brand, model and age. It is not an ideal world and mixing battery types will work, but one will always get overcharged and use lots of water, and the other will always be undercharged. The weak battery will always reduce the lifespan of the stronger.
Batteries come in different configurations for different purposes. Starting batteries are designed to deliver a high burst of current, quickly. They are not designed to be slowly discharged over hours as are deep cycles. Deep cycle batteries can be used for starting batteries, but must be sized much larger to deliver the same cold cranking amps. In fact, true deep cycle batteries will not list a CCA rating. Only dual purpose or Starting batteries will.
My point is that you do not want a starting battery powering your appliances. If you do not plan on ever powering these appliances with the engine off, then you do not need a second battery.
If you so plan on powering items with the engine off, you need a dual purpose/ rv/ trolling/marine battery, or even better, a true deep cycle battery. A starting battery will not last, longevity or per charge wise, under deep cycle use. True deep cycle batteries are hard to find, and almost never available in auto parts stores. They are more commonly found in Marine stores, RV stores or RE( renewable energy) stores. A true deep cycle battery will last longer in deep cycle use than a dual purpose battery, but costs more.
In general, The heavier a battery, the better.
The gasses that escape batteries are hydrogen or hydrogen sulfide gas. They are lighter than air. They need to be vented from the top of the box, to a point no lower unless forced ventilation is used.
Any thing going through the floor should not allow any air to flow around it. A hole in your exhaust system could kill you under the right(wrong) circumstances through CO poisioning.
I keep my batteries under the floor, behind the driver's seat. My access panel is sealed, and the 2awg wires leading through the floor are insulated from chafing and sealed with caulk.
Last edited by landyacht318; 10-06-2009 at 11:52 PM..