Leisure Battery next to regular battery?

[Madragonn]

Hi,

I use my stereo amongst other powered items a lot in my mk1 55s punto, constantly running my battery down. I am wondering how hard it would be to mount a second battery in the engine bay or if its worth routing cables to the boot, or if anyone has any info on this.

I am thinking of using a beefy 24v 70a relay wired to the ignition to split the charge only when my engine is running, as far as i know my alternator runs at 65a.

Thanks, Tom

 

[craigb244]

the 55 is a small engine so you could have a small battery to start the car and fit a bigger one that you can drain. that way you can start the car on the small one if the big one goes flat then once running switch the big one onto the circuit. it will be very simple to do.

btw that relay wont work you NEED 12volt relay. the voltage is nothing to do with what can be switched. its to do with the coil that does the switching.

 

[Madragonn]

btw that relay wont work you NEED 12volt relay. the voltage is nothing to do with what can be switched. its to do with the coil that does the switching.

Ahh, I just went for the "beefier the better" option because I was worried about the alternator kicking out about 15v.

edit: also does anyone have any idea on average how many amps a 55s would draw to start...

 

[volxstu]

Dunno about 30amps at a guess.
You will always lose power by having a battery in the front running amps in the back.
What sort of ICE are you running, things like neons ect are negligible.
Have you done TB3 and why would you add another battery into the system when the Original one is inadequate.
You wont really need a second battery until you ar running around 1500w RMS of additional equiptmentment.
Basically i think you are running before you have learnt to walk.
I would start with the following
1. The big three
2. Install O gauge power cablng.
3. Upgrade original battery to an optima yellow top (Higher AH)
4. Upgrade alternator.
All before you even consider a second battery (in the boot)

 

[Madragonn]

im just weighing up my options at the moment...

i can get a small battery for starting the car for next to nothing off a friend + a relay and wiring shouldent cost more than a 10er, this means id be able to run my original battery down to flat + still be able to start my car

or if i could get battery with a higher AH but im not sure how much id be paying for one.

also being a noob whats "the big three" ?

 

[craigb244]

im just weighing up my options at the moment...

i can get a small battery for starting the car for next to nothing off a friend + a relay and wiring shouldent cost more than a 10er, this means id be able to run my original battery down to flat + still be able to start my car

or if i could get battery with a higher AH but im not sure how much id be paying for one.

also being a noob whats "the big three" ?

The reason i replied to this is i was thinking of doing the same kinda thing on my turbo cento. putting a very small battery up front and the normal one in the back. this will let me have better weight distribution but also let me run my lights without the engine running for longer. I started the cento with a VERY small bike battery once and that was when i ran high compression n/a 1.2.

 

[Madragonn]

it just seems a cheaper way to run things off my car so i can run it to death and still start the car. if a bike battery or something small physical size wise would be enough to just run the car that would be ideal for mounting into the engine bay alongside the original battery.

i tend to have long breaks at college and sit nearby the car with music on for a good few hours and with summer comming would like a small fridge for beverages. A high capacity battery would do the job but the price of a small battery + charge relay i think its easier and failsafe.

 

[craigb244]

it just seems a cheaper way to run things off my car so i can run it to death and still start the car. if a bike battery or something small physical size wise would be enough to just run the car that would be ideal for mounting into the engine bay alongside the original battery.

i tend to have long breaks at college and sit nearby the car with music on for a good few hours and with summer comming would like a small fridge for beverages. A high capacity battery would do the job but the price of a small battery + charge relay i think its easier and failsafe.

the battery I used was from a non abs bmw GS 1100. i think its about 20Ah. this started the car without any bother.

what i would do in your case is this:
no need to over complicate things. you will need to have the power feed removed from the cars usual one and reconnected after the switch... otherwise the radio will draw from the little battery.

 

[volxstu]

Your are not taking into account that the alternator will not be able to charge the battery if it drops below 50% Charge.

 

[craigb244]

well i had to bump start my car 4 times while on holiday cos the lights drained the battery (TOATALY dead) left the car running for a few mins and the battery was charged enough to restart.

 

[volxstu]

Just because a car wont start that doesnt mean that the battery had gone below 50% and if it has then you will need to charge it otherwise your battery will keep going flat.
In your case i would be looking at why the battery is going flat. Are you using the lights without the Engine on , Is the battery getting old and in need of replacement.
I cant see why you need an auxiliary battery, the only reason us ICE people use them is to sustain a good voltage during music to keep the wattage of the amps up, not because we are abusing and negating to maintain our cars.
TB3 is the big three, upgrading the power delivery cables in the car to help maintain a higher voltage whilst using the car.

 

[craigb244]

no no no. we go campin and also i do bike sprinting which means campin over night in dark parts of wales. I usually put 2 of the spot lights on my car on. they last about 2 or so hours then they will suddenly go dim. there is then not enough power for even the fuel pump so the car then needs bump starting.

I now use the lights then run the car after a hour for 10mins to recharge... thats not something i want to do with the turbo so im going to have an aux battery just for the lights

 

[volxstu]

OK but for the op i would be looking to put a second decent sized battery split charged in the boot like so.

 

[Madragonn]

the battery needs to be over 50% for the alternator to charge it?

ive flattened it so the radio wouldent turn on and the interior light was dim,got a jump pack on it for literaly 30 seconds to start it on the drive to college about 15 mins it charged up using the alternator :S.

i guess a normal battery isnt ment for continious cycle's draning and chargin but it should last for a fair while.

 

[craigb244]

the battery needs to be over 50% for the alternator to charge it?

ive flattened it so the radio wouldent turn on and the interior light was dim,got a jump pack on it for literaly 30 seconds to start it on the drive to college about 15 mins it charged up using the alternator :S.

i guess a normal battery isnt ment for continious cycle's draning and chargin but it should last for a fair while.

the alternator usually needs a small amount of power to energize(create a magnetic field). this is not much tho just a few volts even the flattest of battery's should have enough.

 

[Madragonn]

makes sense. alltough i would be using the small battery for starting the car so that should have enough juice to get the alternator going.

ive also herd that alternators dont like charging batteries fully for long periods of time but as im not sure if the car will make it to its next MOT im not exactly concerned...

 

[volxstu]

Is nobody listening LOL. The alternator may be able to charge a flat battery enough to start it but leave it a couple of days and see what happens.

 

[Madragonn]

so it doesn't reach its optimum charge once its gone below 50% or ? quite confused

 

[volxstu]

Wahey we have got there, soory its probably my bad explanation skills. Once a battery has gone below a certain level the alternator cannot produce enough power needed to fully charge it. Trust me i know my battery now drops to 9 volts (rather than 14.4) as soon as i turn on the amp because the alternator cannot fully charge it.
If i were too charge the battery up with a better trickle charger then it will go back to almost full charge.

 

[Madragonn]

Ahh i get it now, guess specialised leisure batteries cope better when draining the battery.

I think my best option for my limited budget is to get a new possibly slightly beefier battery from costco.

also thinking about a circuit that cuts off power to the head unit when the battery level drops too low, could this be cheaply done ?