heata
Member
It sort of sounds like you are trying to reinvent the wheel. Not sure why a standard dual battery set up would not meet your needs?
Parallel Batteries
- Thread starter pointblank5
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pointblank5
Member
Thanks Tony,
I was thinking that they'd both be cranking batteries, just the one at the front would be able to handle a discharge every now and then (eg optima yellow?)
Also, if I did run the front battery right down, then couldnt I turn the key to ON for a minute or two before I start it, this would let some charge flow from the charged up rear battery to the front battery, thus reducing the current pulled from the rear battery by the starter motor...
please point out anything wrong/dodgy with this
cheers, James
pointblank5
Member
If i had to re wire the whole sound system to run off the aux battery... i'd just give up on the idea LOL
I'd much rather just run the battery cables and solenoid wire (which i'd have to do either way)
Being a pair of batteries connected by heavy cables, they'll simply dump power as hard as they can if given the opportunity. They will happily exceed the charge rate of the battery too - while they're designed to dump 500A for cranking, they're only supposed to be charged at the MOST at 1C - about 100A for a 100Ah battery - and even that's probably too high. Rushing in the power at that rate will likely cause very premature failure of the battery. It's much better for lead acid batteries to charge them at a more sedate pace - your 100Ah battery will last longer if charged at no more than 25A.
I think I see where you're going with this - but in reality you probably only have a couple of audio units connected to power. Moving the power to the aux battery is the way I'd go with it.
I think I see where you're going with this - but in reality you probably only have a couple of audio units connected to power. Moving the power to the aux battery is the way I'd go with it.
pointblank5
Member
Thanks Tony,
this thought did cross my mind, but then what happens differently in a normal dual batt setup when the solenoid closes and the aux starts to receive charge? i thought it would be the same...
Cheers, James
The aux battery only receives a charge when the alternator is running, and only after the primary battery has been charged up to a certain point.
The consideration there is exactly the same as you would think if you were putting together the item for a mission: get the important stuff catered for first (cranking battery) and everything else comes afterwards.
Some isolators will allow you to draw from the cranker with the ignition off, but they'll switch this off once the voltage falls below a certain level in order to guarantee power in the cranker.
The consideration there is exactly the same as you would think if you were putting together the item for a mission: get the important stuff catered for first (cranking battery) and everything else comes afterwards.
Some isolators will allow you to draw from the cranker with the ignition off, but they'll switch this off once the voltage falls below a certain level in order to guarantee power in the cranker.
4.8GU
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Ok just to make it more simple ask yourself this question.
How much do i want to spend?
Take into account that if you don't really need a dual battery setup for camping (running fridges and lights etc) then what is the point of having one.
With the setups being proposed you will have to factor in 3-400 or more dollars for a good battery. At least 120 dollars for a basic isolator. probably 50 bucks worth of cable and terminals etc. 50 bucks for some sort of tray/battery box depending how flash ya get.That is doing it yourself too so no labour and you are already at 600 odd dollars, and that is with a basic isolator which in my view would probably not be the best set up in your case (second battery a long way from first). Could easily push $800 for top quality gear and a better isolation set up.
If you just want to run ya stereo for a longer period of time get a top quality start/cyclic style of battery. Optima would probably suit best as they have quick charge times and can drain a bit more.
The charge time is key here as you could drain it down and simply start the car and go for a quick drive and it would be all good. A normal battery probably wont charge as quick and if you add two batteries into the equation it will take even longer.
A volt meter with alarm would be perfect or even one of those battery terminals that show the voltage would be all ya need to keep an eye on the main battery to make sure you didn't go so low as to not be able to start the car.
You could even carry simple jumper pack with ya in the back to make sure you could always get started if need be. These are cheap and don't take up much room.
Just some things to ponder.
BTW it would be ideal to work out the current/amp draw of the stereo system and that way you could get a much better idea of how long a certain battery is going to last while providing power to it.
How much do i want to spend?
Take into account that if you don't really need a dual battery setup for camping (running fridges and lights etc) then what is the point of having one.
With the setups being proposed you will have to factor in 3-400 or more dollars for a good battery. At least 120 dollars for a basic isolator. probably 50 bucks worth of cable and terminals etc. 50 bucks for some sort of tray/battery box depending how flash ya get.That is doing it yourself too so no labour and you are already at 600 odd dollars, and that is with a basic isolator which in my view would probably not be the best set up in your case (second battery a long way from first). Could easily push $800 for top quality gear and a better isolation set up.
If you just want to run ya stereo for a longer period of time get a top quality start/cyclic style of battery. Optima would probably suit best as they have quick charge times and can drain a bit more.
The charge time is key here as you could drain it down and simply start the car and go for a quick drive and it would be all good. A normal battery probably wont charge as quick and if you add two batteries into the equation it will take even longer.
A volt meter with alarm would be perfect or even one of those battery terminals that show the voltage would be all ya need to keep an eye on the main battery to make sure you didn't go so low as to not be able to start the car.
You could even carry simple jumper pack with ya in the back to make sure you could always get started if need be. These are cheap and don't take up much room.
Just some things to ponder.
BTW it would be ideal to work out the current/amp draw of the stereo system and that way you could get a much better idea of how long a certain battery is going to last while providing power to it.
Can I just add to 4.8GU's post ... if you're going to get a jumper pack, make absolutely sure that it can deliver (not just say it can) over 500A. I would look at the "1200A" units or better. As discovered by an esteemed member of this forum (Krankin), the little 4-banger diesels can haul a bit over 500A to turn the engine over.
pointblank5
Member
well I thank you guys very much for all the info you have given!!
I think this ones just gonna go into the good old too hard basket!
I might go with 4.8GU's suggestion... upgrade my battery. I could just throw my old battery in the tray when camping with some jumper leads instead of buying a jumpstart pack.
Just a question on batteries themselves...
I have an AC delco 730cca 90ah battery in my nav, I have looked at the optima website, and the one that would physically fit is an 830cca 66ah deep cycle/cranking battery.
Am i missing something here? looking at the amp-hour ratings, the one i already have would last longer.
Maybe the optima can actually use more of its "amp hours" so to speak and still be able to start the car??
anyone understand what im on about LOL
Cheers, James
I think this ones just gonna go into the good old too hard basket!
I might go with 4.8GU's suggestion... upgrade my battery. I could just throw my old battery in the tray when camping with some jumper leads instead of buying a jumpstart pack.
Just a question on batteries themselves...
I have an AC delco 730cca 90ah battery in my nav, I have looked at the optima website, and the one that would physically fit is an 830cca 66ah deep cycle/cranking battery.
Am i missing something here? looking at the amp-hour ratings, the one i already have would last longer.
Maybe the optima can actually use more of its "amp hours" so to speak and still be able to start the car??
anyone understand what im on about LOL
Cheers, James
The Optima batteries are supposed to be better (my information on those might be biased by someone's profits though, so don't take that as gospel just yet).
A higher CCA just means the battery can dump more power - the RC value shows how long the battery will last (usually measured over a 20 hour period because lead acid batteries are slow to react/respond). Your 730CCA battery is more than capable of turning the engine over and happens to be 50% larger in capacity than the Optima - so if I was making a choice, I'd choose the one you had already.
I'd still look at one of those jumper packs. Could be useful for you, might allow you to help jump start another vehicle without risking your own car's computer etc - in the end, a good investment.
A higher CCA just means the battery can dump more power - the RC value shows how long the battery will last (usually measured over a 20 hour period because lead acid batteries are slow to react/respond). Your 730CCA battery is more than capable of turning the engine over and happens to be 50% larger in capacity than the Optima - so if I was making a choice, I'd choose the one you had already.
I'd still look at one of those jumper packs. Could be useful for you, might allow you to help jump start another vehicle without risking your own car's computer etc - in the end, a good investment.
pointblank5
Member
ok cheers for that info mate.
Just one thing i dont quite understand... in a normal dual batt setup, when the starter is fully charged, and the isolator closes to start charging the aux batt, wouldnt it get that big rush of current from the starter battery and exceed the charge rate of the aux batt? or does this have something to do with the alternator voltage being applied to both batteries...
and also i gather that its ok to have two dissimilar batteries in parrallel when theyre being charged by the alternator, but shouldnt be left in parrallel when the engine is off... is this right?
cheers, im learning alot here thanks!
James
Just one thing i dont quite understand... in a normal dual batt setup, when the starter is fully charged, and the isolator closes to start charging the aux batt, wouldnt it get that big rush of current from the starter battery and exceed the charge rate of the aux batt? or does this have something to do with the alternator voltage being applied to both batteries...
and also i gather that its ok to have two dissimilar batteries in parrallel when theyre being charged by the alternator, but shouldnt be left in parrallel when the engine is off... is this right?
cheers, im learning alot here thanks!
James
terryc
Member
Yes,
Nope, unless both batteries are hopelessly flat, the flatter one will be getting the larger charge and the fuller one the lessor. The problem starts when the alternator is expected to run the light show and recharge two really flat batteries, then the alternator may overload. Also alternator output is usually rev related.
The point with CCA batteries on the alternator is that it really takes a days driving for full charge Vs 30mins for a working charge(can start the car again).
Yes. The problems start when one of those batteries starts to break down. If they are in parallel, then the bad will drag/flatten the good one, which is what someone pointed out in a prior message.
My 2c is;
Keep your CCA under the bonnet. when it comes time to replace it, then get the biggest one you can shoehorn in, espcially if you have a winch/lots of cold weather starting.
I've never purchased brand CCA batteries. AFAIK, brand batteries last just as long/short.
If you want a second battery, then get a AmpHr rated one, isolator and then a 12V to 12V charger to properly charge it. Hint, 4PDT switch and you could reverse the flow to charge up the starter whilst you enjoy a leisurely morning tea/lunch.
Someone mentioned C/4, i.e. a totally flat (and fscked) battery could be charged up in four hours(actually 10% longer). This rate is achievable with MODERN AGM batteries, but you reduce the life by 2/3rd(from 1,500 cycles/5years{?} to 500 cycles/18 months.
The first point is that the slower discharges and charges give better life as do shallower discharges(bigger AmpHr for the load)
The AmpHr rating is actually C/20 and is reduced for higher rates. Recommended maximum depth of discharge is 50%.
Exactly what Terry said.
Terry pointed out a 12V-12V charger. This essentially takes power from a 12V battery and provides a finite amount of current to another 12V battery. They work, they are an alternative to my 12V->inverter->charger->auxbatt setup and they might cost less too, I haven't investigated them.
If you set things up smartly, you could spin the thing around so the aux battery can charge the starter if necessary - but that's a situation you should never get into. If you are winching, for example, you MUST have your engine running, vehicle in neutral, someone sitting in the cabin with their foot on the brake. We probably should go out and do a winching and take photos and make a thread showing people how it's supposed to be done in every detail, but that's a discussion for elsewhere!
The best bet - to make sure you get the most out of your battery systems - is to keep them isolated if you can, and if you MUST use them in parallel, make sure they're identical batteries and preferably from the same batch. Keep every cell's acid at the same specific gravity, don't top one battery up without the other, do equalising charges at the same time etc etc. This will keep them "in tune" with each other and minimise the back-and-forth draining effect.
Terry pointed out a 12V-12V charger. This essentially takes power from a 12V battery and provides a finite amount of current to another 12V battery. They work, they are an alternative to my 12V->inverter->charger->auxbatt setup and they might cost less too, I haven't investigated them.
If you set things up smartly, you could spin the thing around so the aux battery can charge the starter if necessary - but that's a situation you should never get into. If you are winching, for example, you MUST have your engine running, vehicle in neutral, someone sitting in the cabin with their foot on the brake. We probably should go out and do a winching and take photos and make a thread showing people how it's supposed to be done in every detail, but that's a discussion for elsewhere!
The best bet - to make sure you get the most out of your battery systems - is to keep them isolated if you can, and if you MUST use them in parallel, make sure they're identical batteries and preferably from the same batch. Keep every cell's acid at the same specific gravity, don't top one battery up without the other, do equalising charges at the same time etc etc. This will keep them "in tune" with each other and minimise the back-and-forth draining effect.
pointblank5
Member
thanks guys, the advice is much appreciated!
I think I am gonna go with a larger capacity starter batt. and volt gauge
The supercharge allrounder looks like it will suit my needs, while staying under 30kgs!
just out of interest... In a dual battery setup with a normal SLI batt, a deep cycle and an isolator... when the isolator kicks in these batteries are in parallel right? and this is OK or is it not ideal but acceptable? just trying to get my head around the do's and donts
thanks again, James
I think I am gonna go with a larger capacity starter batt. and volt gauge
The supercharge allrounder looks like it will suit my needs, while staying under 30kgs!
just out of interest... In a dual battery setup with a normal SLI batt, a deep cycle and an isolator... when the isolator kicks in these batteries are in parallel right? and this is OK or is it not ideal but acceptable? just trying to get my head around the do's and donts
thanks again, James
They are in parallel, but protected. A decent isolator will watch the voltage of the primary and feed power to the aux battery itself while it's safe to do so. You don't get a direct parallel connection like you would with jumper cables. It's also not a DC-DC charger kind of thing - but it's fair protection for the primary battery.
pointblank5
Member
Thanks again Tony,
If/when I do eventually hook up a second battery i think i will go with something like the redarc isolator various people have mentioned. I think i can make it work for me
Cheers!
If/when I do eventually hook up a second battery i think i will go with something like the redarc isolator various people have mentioned. I think i can make it work for me
Cheers!
