28 replies to this topic

[sheepy89]

just a quick question if you were to put a 2nd battery in a car how would you keep it charged or is that not possible?

any help appreciated

sean

[rusty789]

Accumlative Chargers..

Let me just find a link to one.. I have one on the garage..

Edit: I can't find the link, but basically you put one 12v feed into this little box, and two out to each battery then it decideds which one to charge by comparing the two voltages..

I can't find it on maplin where I got mine from..

Edited by rusty789, 09 August 2010 - 09:46 PM.

[rusty789]

Found these two..

Link

The second one is more like what I have but I only paid £9 something..

[Sam Walters]

All a split charge relay system does is keep the batteries isolated from each other when the engine is not running.

I personally don`t think its worth the effort.

[sheepy89]

on the bottom one on that link it shows attaching it to the cars alternator + and - ports? where might these be (sorry probly a dumb question) and would that mean running wires from the back of the car to the front?

[david@skeggyminis]

his is what i use works great
http://cgi.ebay.co.u...=item2eaf15c896

[pbrain]

I normally use a pair of relays (1 small & 1 high power ~250A). i take the 'remote' from the head-unit to the first relay, with an ignition supply. Take the switched side of this to the high-power relay. The outputs of the high power relay go from alternator or existing battery to the second battery. Use the second battery to power head-unit & amps.
The benefit of this is:-
1, it won't drag the alternator on starting
2, the second battery charges when the ignition is one AND the headunit is on.
3, You can play music with engine off for as long as you like and will not affect main starter battery, no need to worry about flattened battery.

...alternatively, if you're going for a modest install (<500wRMS) then you can use a split diode (i have one which is not being used). This is a Lucas oil-cooled, twin diode. The centre tag is alternator in & 2 outputs, one for each battery. It's rated around 45A (i don't know if that's total or per diode) i couldn't find much info on it. Ideally mounted under the bonnet near the alternator with access to air-flow. If you're interested you can have for £20 via paypal (PM me) i only have one of these.

[sheepy89]

cheers everyone you have been very helpful.

just out of curiosity where would be the best place to put the 2nd battery?

[pbrain]

cheers everyone you have been very helpful.

just out of curiosity where would be the best place to put the 2nd battery?

i've removed the heater matrix and put a Red-top there & 4 Yellow tops behind the driver/passenger seats (not recommended for an everyday car!)
depends what you're installing. the easiest place is to put the second battery on top of the existing battery, using a DIY cradle. however, if you're planning on putting ICE in there, not good.
Instead of a large second battery, you could go for a bank of 12v alarm batteries and have these wired in parallel. the good thing about this, is you could have these fitted almost anywhere. ie. under the rear seats, in the side pockets. I would put 4 in each side pocket this should give roughly the same Ah as a large battery (8x 8Ah = 64Ah)

[sheepy89]

im sure i could make a housing for it in the boot on the opposite side to the fuel tank behind the side piece on the boot kit that way its out of the way. i shall have a think and see what i can come up with.

i only want the second battery anyway because i want to stick quite a few bits of electrical equipment in the car and dont want it diein on me lol. not quite sure what as yet mind but i keep having crazy ideas so always good to be prepared.

[david@skeggyminis]

hi you can get hold of a 12v battery from a disabilty scooter they are a small leisure battery and take up less room i use one to run my 12volt cool box all day at shows and does not drain the car battery at all also you could use a house alarm battery

[sheepy89]

ahh thats not a bad idea using a smaller battery. im sure if its not enough i could always just get another one and wire them together

[danrock101]

wouldn't it be easier just to fit a bigger/better battery?

[haggz]

upgraded my battery to ford transit one. not sure its cranking power but think its about 700 amp. re-routed battery lead from underneath to internal using hi-flex lead. my mate assured me if its good enough for a volvo bus it is okay for a mini. made new battery tray which was welded to floor by o/s rear shocker. bolt welded on to take earth lead and amp earth. amp is 1000w and when car is running battery charges ok even with lights are on. im sure multimeter read 14.38 volts. posted picture if it helps.

[pbrain]

wouldn't it be easier just to fit a bigger/better battery?

the benefit of a second battery with controlled charge/isolation is you can use the second battery for audio, fridge, alarm etc while the engine is off, then not having to worry about returning to the car with a flat starter battery.
Also useful if for some reason you do have a flat starter battery, flick the relay on and you've got a built in booster pack!