Thread: Dual Battery

Originally Posted by setsuna

Have seen a few setups using various controllers.

I have noted most controllers run the batteries in parallel for charging.
is there any issue with charging?? -- over charging, or undercharging using batteries of different sizes/types?

David.

Well, you could hardly run two 12V in series - could you

Have a look at index7 Tim is an Aulro member and knows a lot about batteries, controllers etc., as well as making the best one I know of. There is a good description of how the SC40/80 works.

There is no danger of overcharging if your alternator is working correctly, but with two batteries to be charged, you need to be doing enough Km's to keep them both up, as a properly designed controller will look after the main starting battery as a priority.

Cheers,

Lionel

Hi Dave, as Lionel pointed out, one of the main factors to getting batteries charged is drive time.

What size is your alternator?

Originally Posted by setsuna

I have noted most controllers run the batteries in parallel for charging.

Umm, do you know of another way?

well, I thought that the controller may 'switch' alternator input between the batteries.

I don't know the capacity of my alternator, it is a stock Disco1 300TDI.
I guess it is around 75Amps.

Projecta, Sidewinder or the SC Series. now that is the question.

they all seem to operate the same, but the SC unit has the additional runtime off the main battery before isolating, extending AUX runtime by 50%.

David

Hi setsuna, there’s a lot more to the benefits of the “SC” as compered to other isolators.

The SC40 and SC80 not only add around 50% additional capacity to your auxiliary battery but this same feature also means you don’t have to discharge your auxiliary battery any where near as low as you would with any other isolator and this has spin-off in itself.

Because your auxiliary battery is not taken as low, it will have a much longer operating life span.

Again, after free camping for a day or two, because your auxiliary battery’s load is shared with your cranking battery, your auxiliary battery is not going to be as low when you start driving so you will not have to drive anywhere as long to fully charge your battery as you would with any other isolator.

And there are other subtle benefits but this will give you an idea of the main advantages to fitting one of my SC40 and SC80 isolators.

Originally Posted by setsuna

well, I thought that the controller may 'switch' alternator input between the batteries.

I don't know the capacity of my alternator, it is a stock Disco1 300TDI.
I guess it is around 75Amps.

Projecta, Sidewinder or the SC Series. now that is the question.

they all seem to operate the same, but the SC unit has the additional runtime off the main battery before isolating, extending AUX runtime by 50%.

David

its a 100amp

Originally Posted by setsuna

Have seen a few setups using various controllers.

I have noted most controllers run the batteries in parallel for charging.

is there any issue with charging?? -- over charging, or undercharging using batteries of different sizes/types?

David.

It's never a good idea to mix batteries of different types as they have different characteristics. Generally speaking you have 3 different types of batteries you might use in your car/4WD. The older style lead acid comes in sealed and non sealed, sealed lead acid calcium and AGM type batterys such as Optima and Odyssey.
The older style lead acid battery charges at around 13.5 volts and is found in Series Landrovrers, Classic RR's and my early P38 RR. Calcium lead acid batterys are found in newer vehicles such as SWMBO's D2, and charge at 14+ volts. I dont know what your D1 has. Measuring the charge voltage will tell you which type it should have.
AGM (Absorbed Glass Matt) batterys are an evolutionary step ahead in 'Gell Cell' type battreys. They are still a lead acid battery but the 'acid' is held in paste form between the lead plates instead of a liquid in the case of other lead acid type batterys. I don't know of any car/4WD that these come in as standard, they are usually fitted aftermarket. They also charge at 14+ volts.
Whilst its OK to put a Calcium/AGM battery into a vehicle with a 13.5 volt charging system, you just might never get to 100% charge, you don't put a non-Calcium/AGM battery, ie older type battrey into a newer 14+ volt vehicle as the battery will be continually overcharged and will either fail or have a reduced life.
So to answer your original question. You can mix older style lead acid batterys with Calcium/AGM types if you have a 13.5 volt system but the system won't work efficiently as the voltage requirements of each battery are different. It won't blow up or anything, it's just inefficient. You can mix Calcium and AGM types as they have similiar voltage requirements, but you won't get the full benefit if you do it in a 13.5 volt system. Don't put conventional lead acid batterys in a modern car/4WD which has a 14+ volt system.
Hope some of this makes sense.

Deano

Hi DeanoH, but sorry mate, most of your post is incorrect.

You can put any type battery with any other type battery and you won’t have a problem.

And it makes no difference if it’s in a new or old vehicle.

Up until about 6 or 7 years ago, vehicles had constant operating voltage levels of anything between 13.5 to 14.4v, today they have variable voltage levels form 13.2 to 14.9 here is Oz and anything up to 15.5 in colder climates.

Furthermore new vehicles like D3s, D4s, L322 RRs and RRSs have high start-up voltages that remain high for a given period of anything from 10 to 30 minutes, after which time the constant operating voltage is applied and this will be anything down to 13.2v.

With the exception of Calcium/Calcium batteries, most other automotive batteries can, given enough time, be fully charge from as little as 13.2v and do so on a regular basis in many D3s both here and overseas.

As to Calcium/Calcium batteries being fully charged, it seems that the only way to fully charge these batteries is to use a much higher charge voltage BUT, this is only needed to get these batteries from 95-97% to 100% and not achieving a 100% charge state is of little relevance to the use and life span of these batteries.

So back to setsuna’s set, and any type battery with any other type battery will work fine.