Simultaneous charging dis-similar batterys..

If they do then i'm in deep $h1t, my batteries couldn't be more dis-similar.

Cranking battery is a 870CCA Calsium/calsium and Aux is a 60AH Fulriver AGM Deepcycle battery.

Baz.

A deep cycle prefers a 3 stage charger BUT it will still handle just about anything you can throw at it..

If after driving for a couple of hours the voltage out of the aux batt is 12.8V plus then thats just about fully charged and the beers will be nice and cold........so you can sit back, relax and forget about the batts !!!!!!

"what options to safely charge a dual system??"

Use a "smart" battery Isolator. One that will only swap over to the auxiliary battery after the primary (starting) is fully charged.
This will happen is a very short time, if the primary is in good condition and hasn't been drained down.

This is the big difference between a "simple" solenoid installation and a "smart" Isolator.

The simple solenoid will just link the batteries together. If one battery is below par or faulty, it will "drag" the other one down to it's level, possibly shortening the life of a battery in otherwise good condition.

The smart Isolator will keep the two batteries electrically separated and they will charge and discharge independent of each other, thus having no impact of the other battery's operation or lifespan.

4WDTV......Baa!!!

I watched that segment to Signman.

The issues they raise are potentially real but I think they overplayed the issues.

It is more likely in practise that the batteries lifetime will be reduced and that because of the imprecise nature of these things that the user may not even realise a problem, because at the end of the day the charging system is still mainly a short term constant voltage which drops on alternator heat up.

Robin Miller

My rig has 3 batteries on board. Two of them are permanently hooked together in parrallel (both Supercharge 760cca starter type).

The 3rd is a 120a/h Fullriver and that receives it's charge via an Arrid Twin Charge (20amp).

It all seems to work pretty well thus far. The only improvement I could make would be to charge the Fullriver via the 15amp 3 stage (240 volt) charger (which I also have permenantly mounted and hardwired), via an inverter. This would ensure the Fullriver does not get overcharged I guess, but I think the Arrid does a pretty good job anyway.

Cheers

Roachie

I also seen that segment in the Tv show , and i am now a little concerned, my Aux battery is a Marine calcium battery ( different to cranking battery) then the Battery in the caravan is a deep cycle battery that is charged when hooked to the car via the aux power point of the 7 pin trailer cable.......

will keep an eye on things a little closer now

Boc

With my head in the sand Dave, I "charge on" with fingers crossed - the new conveyance came with one of these Surepower thingies installed by ARB [ http://www.surepower.com/separator.html ] - 2 crankers are paralleled in the Cruiser and the aux is a calcium cranker of some sort (the 9000 Warn is wired to that) - might find out one day if the whole setup is happy that way :-o).

Car Alternators put out a fixed voltage - ANY battery connected to it will draw whatever current it needs at it's state of charge.

If any of your batteries doesn't overcharge when it's the only battery connected to the Alternator, then how on earth can it overcharge if you connect an extra battery in parallel with.

Car Alternators DO NOT SENSE THE STATE OF CHARGE OF BATTERIES CONNECTED TO THEM.

Well I didn't see the show in question, but from the description posted here, they seem to have way overstated the issue.
I'd hazard a guess that over 90% of vehicle dual battery systems use dissimilar batteries. How come so many people get years of good service from their system?
As Mike DID has said, the amount of current a battery draws in charging is determined by the battery, not the alternator. They are pretty dumb devices (as are most isolators). As a battery charges, it's internal resistance increases. With the increase in resistance it draws less current, until when fully charged it's resistance is such that it draws no current at all.

In a standard set up, with the aux running a fridge overnight, when you start the engine the next day, the aux will have a lower internal resistance the the starter. If you don't have a voltage sensing isolator, the aux will draw more current than the starter initially. This is generally only an issue if you do multiple short runs with a run down aux. In this case, you could flatten the starter by repeated starting before it can get a decent charge.

There is very little chance that (as someone said above), the discharged aux will draw current from the starter and flatten the starter. With an isolator (even a simple solenoid), the two batteries are only connected when the engine is running. It is very unlikely that the aux will draw so much current that it will take all the alternator can give, and then take current from the starter as well until it is flat.

I've run dissimilar batteries for years. Currently the original Hilux starter, with up to 3 AGMs (one in Hilux, 2 in CT). All AGMs are in parallel when CT is connected. Isolation is via a simple solenoid. Had the current set up for close to 3 years. Next time (probably not till next vehicle) I will use a voltage sensing isolator (Redarc for example) as additional protection, but in the meantime my system (and thousands of others like it) work just fine. If I was going to stuff my starter through overcharging, I think it would have happened long ago.
I suspect this segment was sponsored by someone trying to sell something. As we all know, sex sells. But fear probably does as well.

I use a solenoid set up but only connect the aux batt for charging when it requires it by a flick of a switch. I monitor with a voltmeter (purchased from Derek who posts here very regularly) to monitor both batteries. I did this after stuffing one of my batteries following my dual setup, even though every1 seems to think this could not happen. Maybe the 4WDTV show is right????

can anyone explain to me how a battery which to my understanding is no more than a storage device can "draw"current
as far as i know the alternators function was to replenish the charge being consumed by starting and accessory requirements of the vehicle???

cheers

one option which I went for is a sterling power products battery to battery smart charger. I am no expert, but it should avoid such issues ( or so I am told )
Gil

Hi Signman

Just use Kirchoff's Laws/Thevenin's Theorum:

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Kirchoffs First law.
The total current flowing towards a junction is equal to the total current flowing away from that junction. i.e the algebraic sum of the currents flowing towards a junction is zero


Kirchoff's Second Law
In a closed circuit the algebraic sum of the products of the current and the resistance of each part of the circuit is equal to the resultant e.m.f in the circuit.

Thevenin's Theorem.
This theorem is used to determine the voltage / current flow across / through two points say A and B in a complicated circuit which includes and number of sources and loads. The theorem states

The current through a resistance R connected across any two points A and B of an active network ( a network containing one or more sources of e.m.f. ) is obtained by dividing the p.d. between A and B with R disconnected , by ( R + r ) where r is the resistance of the network measure between A and B with R disconnected and the sources of e.m.f replaced by their internal resistance.

Consider a general network containing voltage and current sources. The network can be replaced by a single source of e.m.f (E) with and internal resistance r. E being the e.m.f. across A- B with the load disconnected and r being the total resistance of the circuit measured across A-B with the load disconnected and the e.m.f. sources replaced by their internal resistances.

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Happy days
George

It's called a 'joke' Mike - perhaps you should stick to promoting guns to Scouts????????

Happy days

George

All this battery theory gives me a headache. I prefer to keep it simple.

The way I think:
Toyota designed an alternator to charge wet cell cranking batteries. So I only use identical wet cell cranking batteries for 1st, 2nd or (rarely) 3rd batteries.

I don't use wet cell deep-cycle batteries - the battery companies know that alternators won't charge them fully, so they only put 6/12 warranty on them.

I don't use AGM and gel batteries because they cost a fortune, and I don't flatten my batteries. Most days I drive my vehicle, so it recharges, and all I'm running is a fridge and fluoros.

As for 4wdTV saying a car alternator can overcharge a cranking battery...................hehehehe

Both my batteries died with in 2 months of each other not long after I bought my GQ, One was a wet cell cranking battery the auxillary was some kind of sealed battery.

My auto electrician said that you'll shorten the life of BOTH your batteries if they are not the same type for the reasons stated before about charging rates etc.

Now I have an N70 wet cell cranker and a wet cell marine battery with some deep cycling capability as the auxillary.