Split charge systems

[jayw]

hi there,
i put a second battery in my boot just 2 days ago. it is pretty simple but as the other guys says depends on what for. i just wanted more power throughout the whole system especially for the sounds. i already have my boot amp earthed via a bolt thats attached to the rear seats in the boot. so basically i put my extra battery in the boot beside the amp and connected the battery positive to the positive feed on the amp that comes from the other battery. then the boot battery earth also to the seat bolt to earth through the body. now my sounds are better and when im starting the car the starter motor turns over much much quicker and engine starts much faster. also car has more power when you put the foot down at lower rpm. very basic setup which works very well. and cos they are inter-connected both get charged from the alternator. also on starting i checked the amp wire that runs from the engine battery to the amp and it never heated up at all. so no worries there.

cheers rossco

Having just backtracked the topic...

Rossco, you have no fuse between the 2nd battery & the amp, the cable that's running to the amp from the front is probably 10AWG (or at best 8AWG) as supplied in amp wiring kits which is insufficient to carry that sort of current under heavy load (i.e. when recharging weak batteries).

Not to mention the implications an accident raises, if that supply cable is damaged & grounded you've got instant fire or explosion (take your pick). You may have a fuse at the front battery, but that won't isolate the curren coming back up the cable from the rear.Then of course theres spilling battery acid everywhere.

At best you need to add more fuses for safety's sake.
Of course, without a relay you flatten both batteries at the same rate and constantly charge at 1/2 rate.

[thanuttiscotsman]

hi there,
not to worry! yes there is a fuse in the line between the engine battery and the amp! the amp cables i have are not standard ones!! they can handle alot of current.!! nearly as thick as my jump leads! and i have the battery positioned in the same direction as the one under the bonnet so the breather holes are front to rear. the car doesnt sway that way no matter how you drive it so it wont leak!!! all the road movement is really left to right with cornering. also im going to have her on a new dteel tray all bolted down!! all the connections are good so nothing to worry about!!
and as the car has 2 batterys when starting the engine etc it takes power equally from both so not flattening either of them. and they both get a healthy charge!! up to 40a/h. this is a common mod for people needing more power.

rossco

[Mike E (uk)]

So long as you have a fuse located next to each battery terminal you will be OK safety wise.

You wont charge at only 1/2 rate with 2 batteries in parallel, the alternator will simply pump out as many amps as it needs to get the output voltage to its regulated level.

The rear battery will have slightly less charge because of the voltage drop from front to rear of the car.

The problem with the long cable will be on starting, when you will loose a more significant voltage because of the very high current. It will still help though, like when you jump start a car with cheapo jump leads and they get a bit warm, but the car still starts OK.

off topic again,

" you are adding around 70-80kg to it every time you get in it lol! "

True, but the car may crash if I do not sit in it & do some steering.

An extra 15 to 20 kilos of battery is not really significant, but it is still unnecessary weight to haul around up all the hills.

None of Jay's slug food for me then. I'll have the steak...

Mike