[Trypt]

Just after some info and opinions on a non isolated dual battery system. much like on those diesel jack-a-poos

im not running a fridge or anything but if i was going to id put a manual isolator in.

Main reason im thinking of doing this is i want to fit a winch and ive got the second battery so i may aswell use it.

[shep]

Just fit a bigger single battery.

[Trypt]

i have a 450cca main atm and the other is 450 aswell. would 900 amps be worth the effort?
and would it be a good idea to run a bigger cable from alt aswell?

[Trypt]

i have a 450cca main atm and the other is 450 aswell. would 900 amps be worth the effort?
and would it be a good idea to run a bigger cable from alt aswell?

[Scales]

its NOT 900 AMPS.

its 900 cca. which is how many amps it can deliver in a 30 second window while maintaining a total level of at least 7 volts or so from memory. This is measured at 0 degrees btw.


Bigger cable from alternator wont do anything without upping the amperage. Think of the cable as a water pipe, if the source/flow of the water is still the same (amps from the alternator), changing the diameter of the pipe wont let any more water through... one reason i laugh my ass off at kids with their massive power cables going to stereo amplifiers that draw fuckall!


All you will gain in this particular instance is 1 of 2 things:

you will either be able to supply more current to the winch, therefore it will seem faster/more powerfull (if one battery and current alternator was not sufficiently doing this)
OR
You will be able to winch for a longer period of time (if the current battery/alt were able to provide enough power in the 1st place)


I think you will probably fall into a little of both, might seem a touch quicker and you may get an extra few seconds out of a pull.... is it worth it???? only way to find out is buy a winch, try it a few times with one battery and then rig in a 2nd one if you dont think its up to the job

your charging times will take longer as you have more storage to fill up. but your electrics shouldn't suffer any other detrimental effects.

[shep]

If you have the battery's then it should only cost around $40 to isolate it properly.

viewtopic.php?f=5&t=4891&hilit=Second+battery+in+a+Sierra

[Trypt]

Thanks.
I should have mentioned I'll be doing a alternator upgrade as well. Either 85 amp Magna or a falcon
If i mount the 2nd batt on the passenger side near the firewall what size cable should I run and should I earth it to the car or back to the main batt?

[Scales]

Earth to body, my 2ndary is earthed to the engine, just cant be assed moving it.

I used welding cable.

[Trypt]

ok thank you very much

[got_bar_work]

If it for winching 35mm2 min
I earth mine to the motor
Shorter root lenght to get back to alternator
Go to jay car and get 2big ass fuses for each end of the cable and one for the winch
They sell 500a ones which should be good
Also up ur wire to alt if changing it and put a fuse on that aswell

[jdk81]

Be careful with the earth cables.
Unless you have drastically changed how your earth cables run, I would suggest either earth to the other battery, or engine.
If you intend to start the car off your 2nd battery only, then you need thick cable which will pass enough current (without too much loss) to start the car.

Remember the factory earth between body and battery is light guage cable.
There is poor earth between the chassis and body. Many have to add their own earth cable to fix fuel tank sender issues etc.
The earth between engine and battery is thick cable.
High current passes from cranking and the alt generating.
This is why when adding a winch etc you should run the earth all the way to the terminals.

[fordem]

Scales wrote:

Bigger cable from alternator wont do anything without upping the amperage. Think of the cable as a water pipe, if the source/flow of the water is still the same (amps from the alternator), changing the diameter of the pipe wont let any more water through... one reason i laugh my ass off at kids with their massive power cables going to stereo amplifiers that draw fuckall!

Better wipe the smile off your face - the kids apparently know something you don't, even if they don't know the reason why - a larger cable gives them more power, so the bass hits harder.

You're quite right the current doesn't change, but the voltage drop across the cable is reduced, and since the available ouput power varies with the square of the voltage at the amplifier end of the cable, more available voltage means more available power.

A larger cable from the alternator will have exactly the same result - more voltage available at the load, so more power - even though the current remains the same.

[Trypt]

Would HD jumper lead be ok for cables. i have a spare set in the shed

[Scales]

depends on core dia.

my gut says yes, but my cautious side say check.

[Trypt]

so because im pretty crap at maths what diameter is 35mm2 cable

[shep]

Trypt wrote:

so because im pretty crap at maths what diameter is 35mm2 cable

Proper wire isn't measured by the thickness of the insulation. The stuff I used in the link I posted Is from memory 24mm2