Thread: TECHNICAL QUESTION REGARDING SECOND BATTERY.....

<span style="color:blue">here is my only worry........



if i have two baterries connected in parallel (as soon as the ignition is switched on), one is flat and the other is fully charged, will the full one be over charged as the alternator tries to charge the flat one......

or......


will the two batteries come to some sort of balance and charge up together.......?


are there any experts out there that have an understanding of all this....?





or would it just be easier to connect them up in parallel permanently and just know that my fridge etc will run for two nights instead of one.....?</span>

Hi Defenderzook, If you want to permanently connect the two batteries together in parallel, they have to be the the same type, size, age and preferably make, even then you will get some sort of battery equalising as there will be a difference in each battery’s voltage level.

Also, you will have to have pretty thick cable running between the two batteries because each time you start the vehicle you are going to be pulling heaps of current from both batteries.

Now the one thing that really goes against permanently paralleling starting batteries in the manor you are contemplating is that if one battery kicks the bucket, not only are not likely to know but in a very sort period of time, you will at best have a flat second battery and at worst, stuff the second battery.

In your situation, you would be better off fitting a dual battery charge controller with the main advantage being that it will ( if it’s any good ) protect your starting battery from being flattened while you are using power at your favourite camp site and the other advantage, particularly with types like mine, they are simply fit-and-forget. They do all the monitoring and switching automatically.

And to your question about connecting two batteries together while charging. Once the motor is running, it makes no difference what the state of charge is in either battery. As the highest voltage being applied to the system is now coming from the vehicles alternator, this is the controlling voltage.
So even if you had one fully charged battery, one flat battery and because of the size of your alternator, you could easily have a third battery that is say only half charged, and the alternator, with the help of your vehicle voltage regulator, would simply pump out current at a higher voltage than any of the batteries and this would, providing you drove long enough, eventually fully charge all the batteries.

Cheers and hope this helps.

By the way Defenderzook, our SC40’s and SC80’s have one major advantage over ALL other dual battery controllers that I’ve come across.

While most drop out as soon as the voltage starts to drop, ( shortly after the motor is turned off ) ours exploit the fact that your cranking battery has a huge surplus of stored power so both the SC40 and the SC80 tap into this power, which extends the operating time of you other battery, but at the same time they will still isolate the main battery when necessary, leaving it with more that enough power in it so you can start your vehicle when you need to.

Cheers again.

thanks guys....its actually starting to make sense......



and with my fender i have noticed that if the battery is weak(not fully flat)...
and has enough power to crank for only about 3-4 seconds it wont fire up...it will just crank itself dead.....there is still enough power for the ecu to think if the starter is not used (ie clutch started) and im off....provided i am parked on a hill....

how low will the sc40 or 80 allow the main battery to drop so as to prevent this.......

and....how long will the sc 40 take to charge up a large battery such as the standard fender one.....?
it sounds like a very clever little gadget.....

Quick question for you drivesafe on deep cycle batteries, in a dual battery setup if you aren't using the deep cycle battery regularly I have heard that you should fully discharge and recharge the deep cycle battery monthly :!: :!: Is this true :?: :?: If so what method or how is the best way to do this :?:

Matt.

Hi again Defenderzook, your electronics should keep functioning while the battery voltage is anything from 8 volts up, this doesn't mean that anything else will work.

The SC40 and SC80 will, if installed as per the directions that come with it, allow your auxiliary battery to charge at exactly the same rate as if the battery was connected directly to the alternator.

Hi Matbor, there is heaps of good info on the net about batteries but from all the info I have sorted through unnecessarily cycling a lead acid battery, no matter what type is, is not only a waste of time but is more than likely very detrimental to the battery.

If the battery is permanently fitted in the vehicle and connected to the vehicles charging system by one means or another, what you are far better off doing is doing nothing at all.

The battery will behave almost exactly like your cranking battery and retain the charge being applied to it each time you go for a drive. This virtually excises the battery.

If you want to try and increase the operating life of the battery, you could, about once a month, use a battery charger that can carry out an equalising charge. This may give your battery a small amount of extra charge capacity.

I personally work on the theory that if the system is set up correctly and you carry a bit more stored capacity than what you are likely to need, the dual battery system should be fit-and-forget as the vehicle’s own electrical system will do a pretty good job of looking after everything and instead of spending heaps to try and squeeze that extra 5% out of your battery, spend the savings on a bigger fridge or what ever and this way you will get a far better return for your hard earned money.

Cheers.

from what i have read on the net about deep cycle batteries the amount of life you get out of the battery is somewhat fixed tot he number of discharge and charge cycles it goes thru.

memory is a little hazy on it but it is about 300 cycles if you go down to 11.9 volt

the lower you let the voltage go the less cycles you get

how true is this mr drivesafe sir?

<span style="color:darkred">whilst on the subject of batteries.....


the product available called inox.......
does it work...?
and if it is so good....why isnt it used in the initial fill of the battery....?

if anyone has any info i would really like to know about this product......</span>