hi there . im wanting to fit a back up battery in the boot and still use the old one to. any ideas on the wireing needed?? any help welcome thanks!!!!
hi there . im wanting to fit a back up battery in the boot and still use the old one to. any ideas on the wireing needed?? any help welcome thanks!!!!
Just run both in parrallel. Ie link the 12v together with a decent gauge cable, and earth the second battery in the boot. Make sure the earth is as big as the live. Use 4 AWG cable minumum.
No don't run in parallel. You need to have a split charge relay in place between the front and the rear battery.
like so
I have such relay if you need it.
You need one of these http://www.m-99.co.uk/Electrical/12v...g_kit_-_c.html
No, run it in parrallel.Originally Posted by blue boy
No don't run in parallel. You need to have a split charge relay in place between the front and the rear battery.
like so
I have such relay if you need it.
Why do you recomend ot run it in parrallel? and not use a split charging setup
Basically, in an audio system, you want as much voltage as possible. Any electrical component will pull off the highest voltage source first (ie the alternator) and use the battery as a secondary supply if needed.
If you run a split charge system (like the one listed above), when the battery is charged, you are isolated from the alternator, while listening to your stereo, so your going to float around 12v, and keep dropping, while pulling more current. When the battery is below usable power, your going to need to engage the split charging relay while driving, to charge it back up, but the problem is you can't play your stereo loud while charging, as from the diagram above, you can see there is only a 10a fuse between the relay and the secondard battery. The moment you play any bass, this fuse will pop (as the stereo system is going to be purely wired to the secondary battery, but it will pull off the higher voltage source, the alternator). Not only that, if the fuse wasnt even there, the relay would probably pack up under the current anyway.
You could buy (long time ago) very heavy duty split charging relays, quite large, about 2.5" diameter, coil shaped with two larger terminals, to handle over 100a, so you can play the stereo system while in split charging mode....These were designed for high output car audio systems, but guess what, these relays are so innefficient due to the fact that they have to handle the current and heat, they lose about 2v across them whilst charging, so its catch 22, your back down to 12v at the amplifiers, even though the charging circuit is floating around 14v.
So basically, always pull of the alternator for best power, and surge response, fit the highest power alternator you can, and use 2 batteries in parrallel for extended capacity if required. Or best case, don't even run two, and just run a decent dry cell/Optima battery up front.
Ive built various competition cars from 158db right up to a European winner at 168.0Db, 2 subs only. All parallel wired, reserve deep cycle batteries..no split charge in sight.
I think Dave610 has got it wrong in terms of the functionality of the split charge relay.
Yes, the 2 batteries should be connected in parallel - positive to positive, but the split charge relay should be present between them.
The relay's job is to isolate the 2 batteries when the ignition is switched OFF. Switch the ignition ON, the relay kicks in and connects the alternator and the primary battery to the secondary battery. When the engine is on, both batteries are being charged and the stereo system is running off the alternator, so you will get the full voltage the alternator puts out (approx 14.4Volts).
The 2 batteries should be isolated when the engine is off so to stop the batteries acting as a load on one another, and hence draining the primary battery. Unless the 2 batteries are identical, they will act as a load on each other. Thats why you should never mix different capacity batteries in any electrical device.
In terms of buying heavy duty relays, you still can - Stinger do a 200amp one for around £75. This will perform the job I've described above - ie, isolate the batteries with ignition off, but being a high amperage one, you can connect thicker gauge wires so your system pulls power nicely from the Alternator and primary battery too.
I have this relay setup in my car, with a yellow top optima in the boot. I'm running in the region of 2700W RMS without any problems at all. The secondary battery shows a healthy 14.4 V on the volt meter with the engine on. Switch the engine off, the secondary battery is diconnected from the primary battery, and I can play my stereo off the Yellow top until its completely flat, but still start the car without a hitch.
Your Optima won't act as a load on your primary battery, when both are fully charged, in fact it will top it up.
If you want to sit in a carpark, and play your stereo till its flat, while pulling low voltage and lots of current then so be it. If you want max power, and minimal load, run it direct, with or without the engine running.
Whats the point of adding a second battery to an audio system (anyone would think to improve performance) if your going to run it at below nominal voltage.
What would make more power to the amplifiers. A standard battery in the front only, running off the alternator, at 14.4v, or the best super dooper battery in the world, in the boot, running at 12v and below and slowly dropping?
Yes, your Stinger relay will read 14.4 V, at the back of the car, but not once you start pulling the current through it.
I ran 12k rms like this, 4 optima Yellow tops, and a single leisure battery in the front. Charging at 15-16v. No problems, no voltage drops, no problems starting.
I ran 24k in the Golf, 18v charging system, 8 x 3000rms amplifiers. Two quad coil 15"s...Couldnt even use fuses let alone charging relays.
Last edited by DAVE610; 07-08-2007 at 12:31.
Who's suggesting running at 12V or below? Its pretty obvious you will get more power running off the alternator at 14+V as opposed to the battery at 12V.Your Optima won't act as a load on your primary battery, when both are fully charged, in fact it will top it up.
If you want to sit in a carpark, and play your stereo till its flat, while pulling low voltage and lots of current then so be it. If you want max power, and minimal load, run it direct, with or without the engine running.
Whats the point of adding a second battery to an audio system (anyone would think to improve performance) if your going to run it at below nominal voltage.
What would make more power to the amplifiers. A standard battery in the front only, running off the alternator, at 14.4v, or the best super dooper battery in the world, in the boot, running at 12v and below and slowly dropping?
Yes, your Stinger relay will read 14.4 V, at the back of the car, but not once you start pulling the current through it.
I ran 12k rms like this, 4 optima Yellow tops, and a single leisure battery in the front. Charging at 15-16v. No problems, no voltage drops, no problems starting.
I ran 24k in the Golf, 18v charging system, 8 x 3000rms amplifiers. Two quad coil 15"s...Couldnt even use fuses let alone charging relays.
The idea of the relay in an audio setup is to isolate the amp batteries from the main car battery when the engine is off to minimise the risk of drainage.
Not so that you can run the stereo at 12V with the engine off.
This is not the case when you are talking about leisure batteries where the setup is to isolate them whilst in use with the engine off (for running appliances like fridges and TVs in a caravan for example). The isolator in those cases stops the main battery running flat whilst the engine is off but the appliances are running.
See here for their use :
http://www.stingerelectronics.com/pr....asp?strID=340
If you're setting up a competition system with mulitple banks of batteries, then yes, the relay is not necessary because you have lots of reserve power from all the batteries. But if you're adding just a second battery which is not identical to the original battery, its best to isolate them with a relay, especially if the car doesn't get used much and sits on the driveway a couple of weeks without being started.
The second battery in an audio setup provides better power for the amps if you run the battery close to them in the boot. You'll get less voltage drop on shorter lengths of cables between the amps and battery than cables running the length of the car from the battery under the bonnet.
If you've set up 8x 3000rms amps in cars without any fuses, I'd be thinking twice about taking any advice from you in setting up high current electrical devices.
Are you teaching me to suck eggs?
You're running 14v and below. Batteries float around 12, overcharging to 14 initially just drops back to 12 pretty damn quick. You can drain a dry cell battery in one burp down to 9v.
You will get less voltage drop with shorter cables - Yes, but pretty academic seeing as you have a voltage drop as your not running off the alternator in the first place...
I *think* I know what Im doing, I did own the largest car audio specialist store in the UK, European distributor for Audiosystem, STEG, Soundstream etc..
SX stu.....
I bet ur sorry you asked ! lol
What do you want the second battery for?
If its for beefing up your amplifier power then NO relay
If its because you dont drive your car much and want extra starting power now and then or for camping usage etc then use a relay
Hope this helps
Dont leave both batteries connected together when alternator is not running (ie use split relay charging), both batteries will drain together and when this is done with none matched pairs of batteries can lead (from memeory) to situation where one battery drains into the other battery and typically the current flow when this happens is very high, it doesent do the batterys the greatest of good either,
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