Existing duel battery setup right for my Kimberly trip

Thanks Mainey,

I thought it was a cranking battery. Should I just set it up with a standalone AGM that just gets charged from the solar panel?

Do you know how large a AGM I should go for if I only have a 120watt solar panel to recharge it?

Cheers
Matt

Bill,

Yes its in the engine bay and looks like the Century N70ZZ fits the cradle perfectly.

I was just researching and it seems that AGM battery should not be run in parallel to a crank battery, so was thinking to leave my existing setup and just add a separate AGM in the back of the car just to run the freezer. Not sure how well this would work with only being charged from the 120 watt solar.

cheers
Matt

No batteries should be connected in parallel except when charging.
It may be acceptable when discharging, but usually you want them isolated so that you always have your cranking battery.

Being in the engine bay, the battery(s) does not have to be sealed. (If in cabins or boots and not in a vented enclosure, batteries must be sealed - ie, AGM, and I think Gel-Cels, but not wet-cells.)
Wet cells are more forgiving than AGMs, though otherwise AGMs are a far superior battery.
But I would consider a low-voltage cutout. I often use the MW728 "Battery Protector" as sold by ARD-Sidewinder (~$20). (That can also be tricked...)


An ignition or accessories controlled isolator is better than none - unless you forget to turn the key off.

Whether Ign or Acc depends...
If you want to parallel them for cranking, use Ign power.
If you want them isolated for cranking but paralleled with Ign or Acc, then use Acc.

My preference has always been to power the isolator (solenoid/relay) from the alternator's (regulator's) charge lamp circuit. Most are able to power relays/solenoids up to one Amp & maybe more. (Though newer ones may handle >1A when earthing charge & other lights, they may not be able to supply much +12V current and may thus not be able to turn on "big" relays.)

I often use a typical Japanese 60 Ohm (250mA) automotive relay. If I need a hefty relay/solenoid/contactor capable of hundreds of Amps, I'll energise that from the "first" solenoid.

If you can find the chargeLamp circuit (aka L or D+) from the alternator, then it's probably easier wiring that anyhow, and it is fully automated - it only connects the batteries when the vehicle is charging.


Normally such battery interconnections have a fuse at each battery end in case the interconnect cable shorts to chassis etc. But if it is physically secure, it may not be needed - until an accident or some +12V short!
I use circuit breakers as my 2nd battery powers a fridge and I haven't yet set up a blown-fuse indicator.... I was using 30A blade fuses... Now it's 50A CBs.


Just some FYI on parallel batteries:
If batteries are to be left connected in parallel, they should be matched which means same battery, same batch, same condition, same temperature, and matched +ve & -ve inter-connections with the power taken off diagonally ie, -ve off one, +ve off the other.
The more you deviate from such conditions, the faster the batteries will fail.
Also the further you discharge them, the faster they will fail.

Matt,

No problem having different types of batteries (ie AGM & wet cell cranker) when separated by a good quality "isolator". The isolator should keep the two batteries separated from each other (otherwise it is a piece of crap) so that a drained auxiliary battery will not affect the starter battery.

If you add another AGM battery in the back, I would consider using something like a Sidewinder Flyer to house it. The Flyer has it's own built-in isolator and is also charged by the vehicle alternator when on the move.

I run a Flyer as my auxiliary containing a 100Ah AGM and also a 75Ah Thumper (also an AGM style), both of which can be charged by the alternator. (They have separate charge circuits.)
I also use an 80 watt solar panel when at camp, but this is usually connected to the Thumper which is removed from the vehicle to power the fridge, also placed in the tent or camper annex.

There is no reason why you could not connect your solar panel to your auxiliary when stationary.


Bill.

Chippunk,

regarding parrallel batteries, you advocate making sure the connections cover both batteries. Fine with this but I have only connected like this for charging (either alternator or charger) and not bothered for loads, where it is easier for me to just connect different things directly to one battery or another while the batteries are parrallelled.

My thought was the draw was not really high enough for there to be any real problem. The main fridge is connected to one battery and the lights, second fridge and everything else to the other. There is a short, well heeled parrallel connection between them that I would have thought would equalize them well enough.

any thoughts.

Yep - any difference is a difference.
Even Optima point out what impact a small parasitic load has on storage life - a weeks to months instead of 1-2 years. (Not that I recall the metrics even though I'll have them somewhere, but Optima IMO make some fairly fascinating claims.)

See rpc.com.au...deepcycle_faq for the oft recommended diagonal connection - and that's for adjacent matched batteries.


The main thing to remember with permanently paralleled batteries is that when one fails, so does the other.
Putting it differently, one takes the other one down (with it) - ie, double the basic failure rate (ignoring other mutually induced failures).

As to what is acceptable....
I used to think 3 years from a wet cranking battery was good, but I have been doubling that despite abuse - ie several flattenings.
But I know people that have had Optima's fail within 3 months to 1 year, and they still buy Optima.

RPC are talking about solar system. I assume in regular if not constant use. For the amount I use the batteries I think the long term affect would be negligible. They are ony parallelled when beng used, otherwise I turn the parallel.

RPC spruke the problems of parallel batteries and that it should be avoided and have have just one. I would like to see them carry around a 280 ah battery. To avoid this problem I suppose they would be suggesting batteries in series. Then they are only useful when they are in series. I use mine indepenantly and in parallel.

What parasitic load are you referring to? Does having batteries connected in parallel create some type of ongoing minor conflict that can drain the batteries differently to if they were not connected. If you think this is the case I am going to do an experiment. Leaving them sit 30 days one way and then 30 days the other to see what happens. Would this be long enough to get a meaningful result, do you think.

What is your question?
I was commenting on your R2F4 and of "non-diagonal" load connection - ie, discharge imbalance.
The RPC info was merely one for the load balance - whether charged via solar or alternator is no major difference, and battery behavioural aspects are the same.

The parasitic loads are any small connected load though I was also referring to their leakage current (self discharge) which increases as the battery discharges.


Yes - connecting batteries in parallel causes a mutual damage scenario ito one brings the other down. If both are ok, then no problem. If one is faulty, then both become faulty (and "faultier").

Don't waste your time repeating tests that others have done. You could have 2 paralleled batteries sit happily for months (or years if AGM) or 2 matched AGM fail within weeks....

Just rediscover what others know....
Maybe start with jgdarden.com/batteryfaq/ - Car and Deep Cycle Battery Frequently Asked Questions (FAQ) 2010 - eg 10. WHAT CAUSES MY BATTERY TO DRAIN OVERNIGHT?.


But if you only parallel batteries whilst charging there is no problem (whether matched or unmatched).
If you parallel them whilst discharging, it is not as bad a problem as when unused.
The above assume adequate (full) charging of both batteries between discharges; that both are in good condition (no collapsed cell or discharged battery draining the other when not charging); and that loads are much greater than self-discharge currents.

I was sent this photo recently, it's a very nice setup in a compact space
It clearly shows the batteries wired in series, then paralleled to deliver a massive 44O Amp Hours

Image Could Not Be FoundMaîneÿ . . .

Thanks that sounds exactly what I am after. Now to work out which AGM to get....my head feels like its going to explode after all this research. There is so many opinions on Duel Battery setup out there!

If anyone has any tips of a good value AGM 100-120ah in Perth please let me know?

Cheers
Matt

Matt,
another major benefit of being an ExplorOz member is we can use the Member to Member private contact system.

Look at the "send member" button, the information you seek can be asked, answered and even purchased - and all in private.

Maîneÿ . . .

I would love to join mainey, but too many expenses at the moment getting better set up. You can email me at sleeveATdykstraDOTidDOTau