Dual batteries???!

madeofmilo · Post by **madeofmilo** » Sat Jan 15, 2005 4:08 pm

Hey guys,
I just put an xbox and tv in my car. It's awesome but drains my battery incrediably fast.
My battery at the moment is located in the boot (don't ask me why!) so there is a spare spot up the front.
Is it possible to have two car batteries connected in parraell? And have them both being charged as the car is running. And have both batteries for stereo/xbox when car is still.

Cheers Dave

C Fernance · Post by **C Fernance** » Sat Jan 15, 2005 4:50 pm

Try some 4wd accessory mobs. A lot of 4wd's run a second battery for winches, etc. It can be setup to charge your main battery first when your driving the car, then once it has a full charge it starts charging the second battery and so on.

Junkers · Post by **Junkers** » Sat Jan 15, 2005 10:28 pm

parallel = no, voltage would stay the same but amperage would double, unless there is a consistent draw something is going to blow, may have to make it's own personal power setup either that or get a big f off battery

ProZac · Post by **ProZac** » Sun Jan 16, 2005 9:56 am

The devices are still going to draw as much current as they need, parallel should be okay i think. Go to a car audio shop and ask someone there.

sigmaproject · Post by **sigmaproject** » Sun Jan 16, 2005 9:56 am

I had a Land Rover with duel batteries. Had a switch to selected either battery or to both at once. I used the duel battery position to start the motor and then would manually select either battery to charge them. But you can buy an electronicly controlled switch that controls the battery charging for you.

bazeng · Post by **bazeng** » Sun Jan 16, 2005 10:02 am

yes u can do it

parallel is fine..
make sure the batteries are the same size / CCA etc etc..

otherwise they will be constantly draining / charging each other..

i've had this done in my car (mazda 626) with a huge sound system..
basically all it willl allow you to do is have the system on for longer periods of time when the engine isn't on..

when the engine is running, u'll be using the alternator's power anyway so battery power is irrelevant.. unless your alternator isn't charging fast enough to keep up with the usage..

madeofmilo · Post by **madeofmilo** » Sun Jan 16, 2005 11:46 am

thanks mate, so dual batteries can work for big sound systems...my problem is my xbox and tv. My inveter has this function where it won't turn on unless the battery has plently of charge. And my battery will be perfect but the inveter wont turn on unless the car is running. I hope dual batteries will solve this problem and also allow me to listen to my stereo for more than 30 mins etc etc.

P.S bazeng....can I get the ride in your car sometime soon? :D

Dave

Junkers · Post by **Junkers** » Sun Jan 16, 2005 12:33 pm

bah woops sorry to put you wrong there ( realises power sockets have 10 amps

)

Paradoxx · Post by **Paradoxx** » Sun Jan 16, 2005 5:53 pm

The current rating is different to the current you will actually draw. If you have 20 batteries in parallel it will be fine, rather heavy, but it will power your shizzel for months. It basically means that whatever current you draw from them will be divided equally between the batteries, so effectively you will drain them in twice the amount of time as you would one. You can set it up a few ways if you wat to be tricky...

1: Simplest... connect another battery in parallel, simply use 2 4AWG cables to connect the two batteries together, + to +, - to -.

2: Tricky dicky... you can set up a couple of relays and a switch to select between the batteries. You can have battery 1, 2, 1+2 or none (ie off). This will allow you to use one battery and save the other, or use both batteries working the same as setup 1, or even switch them off altogether. 4WD accessory shops sell these kits but if you know someone who has a bit of knowledge about jippers (electricity) then get them to do it for a six pack.

Batteries are designed to be charged and discharged at a certain rate, so be carefull about discharging them rapidly as you can cause damage to the battery (ie collapsed cell) or it can even explode. Yes i have seen this happen. Also remember your alternator should provide all the jippers your car needs when its running to dont exceed the limitations of that... or you will need a bigger alt!

Steve.

Post by **Alspos** » Mon Jan 17, 2005 7:50 am

You may have to adjust your inverter somehow, it should run down to about 11.5 volts. We have a pile we use for some cameras here at work. You shouldn't need to have your car running.
4WD shops have an automatic switch to isolate batteries from each other so they both charge, one runs stuff, the other can start the car. Bit pricey though from hearing the 4wders at work talking.

SpidersWeb · Post by **SpidersWeb** » Mon Jan 17, 2005 11:09 am

StazzyBabyYeah wrote:parallel = no, voltage would stay the same but amperage would double, unless there is a consistent draw something is going to blow, may have to make it's own personal power setup either that or get a big f off battery

Just wanted to quickly set this one straight.

The amperage can not double, if neither the resistance nor voltage changes. In parallel the voltage does not change, and we haven't touched the car electronics - so neither has the resistance.

The resistance of the charging batteries does change, but since this is controlled by the alternator anyway, all that really happens here is the charge is split between the batteries. Running two batteries in parallel does not double the current output at all. The advantage here is that the load is split between batteries, so they only need to provide half the current each, thereby increasing the time they can run at that load level OR they can provide double the amperes, but only IF the resistance of the draining load is halved also.

Anyway this is how jump starting works. You are just hooking two batteries in parallel. With that said, Im confident a little home made relay circuit, with some big fat ass relays, and a voltage cut off for accessories (to ensure SOME charge remains), could make for a reliable dual battery seutp.

Just my 2c (or rather, $50)

Paradoxx · Post by **Paradoxx** » Mon Jan 17, 2005 8:57 pm

Do you have flybuys?

SpidersWeb · Post by **SpidersWeb** » Mon Jan 17, 2005 9:00 pm

No :(

Paradoxx · Post by **Paradoxx** » Mon Jan 17, 2005 9:05 pm

Does that include GST?

Alan · Post by **Alan** » Tue Jan 18, 2005 7:26 pm

If the inverter wont start without the engine running even thoght the batteries are fully charged it sounds more like the input voltage that the inverter needs to start rather than the capacity of the battery.

A good battery should give a reading of something a little over 12Volts.
With the engine running and the alternator outputting a charge you should see a measurement of 13.5-14 volts across the battery.

Fitting a dual battery wont change any of these values. It will only increase the time you can deliver current into a given load.

If the voltage is too low to trigger the inverter, maybe it can be adjusted?

Austarion

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