Do I (Does anyone?) Need A Second <span class="highlight">Battery</span> Isolator?

frank,
there are many possible answers to this question, some are ‘better’ than others and I say that in the nicest possible way.

The most likely battery to go flat first is the last in the chain which is in the caravan, because it's probably got the highest draining products to run, and IF it has a vehicle activated battery ‘isolator' between it (3rd battery) and the 2nd battery, it will ONLY recharge or connect to the second battery when the vehicle is running.

OR:

If the 'battery isolator' is a MANUAL SWITCH it will only equalize the 2nd & 3rd battery when the switch is set to connect the 2nd and 3rd battery in parallel together, even when the vehicle is not running it will equalize the two batteries (or it will keep them separated if required)

The two batteries, now in parallel, or only the 2nd battery will recharge ONLY when the vehicle is started after the Cranking battery is fully charged.
The benefits of a "larger" house battery system is they both will only partially discharge when connected together, whereby a single battery will discharge much further, greatly diminishing it's life span.


The use of 'quality' AGM Deep Cycle batteries will be very beneficial to your system because they charge deeper and much faster than wetcell batteries.

Mainey . . .

Could not get your link to work.

Not qualified in any way but my set up is along these lines
.
Cranking battery is connected through a Redarc to charge second battery in back of vehicle., when ignition is switched on.
Wiring for this second battery is then piggy backed through to Anderson plug at back of car and connects to van via Anderson plug.
The anderson plug on van connects to battery in van. Van battery will only be charged when iginition is on.

My understanding is that the 2 batteries charge after cranking battery has sufficient and not before.
I previously ran fridge in van via normal 7 pin plug but was not happy with result and if i forgot to disconnect 7 pin plug at a lengthy stop I stood the chance of flatening the cranking battery.

Now with the van battery charged through anderson plug I have the fridge connected to van battery to charge it while travelling.
Have used a "frige stop??" which turns off the current to fridge when van is stationery for around 3 minutes.
This way van battery will not go flat while stopped and 7 pin plug /anderson plug now is not connected.

Works well for me.

Pedro

Mainey,
I was told by experts that if the fridge is not opened it will not lose much in temperature.
This seems to be the case, and we had no problems during recent trip to SA.

If you had fridge running off the battery without battery being charged you stand a good chance of the battery being flattened.

The battery I have in van is a 40a AGM.

Pedro

Mainey and Peter,

Thanks for your responses.

The way my set-up is at the moment, the aux and the van batteries are in parallel via the Anderson plug and the fridge, when on 12v, runs off the van battery.

Because the two batteries are in parallel there's a good few hours capacity to run the fridge when parked, though if I figure that our "few minutes stop" is going to be over an hour I'll change to gas, then back to 12v when we get going again.

My main concern is when we're camped, when it's likely that the van battery will run down. I have a solar panel (fixed to the van) but they're always subject to weather, shade, orientation, etc, so cannot always keep up with demand.

Therefore it's quite possible for the van battery to be significantly discharged, while the vehicle aux battery is fully charged. It seems to me to be better in those circumstances to have a second isolator direct charge to the battery that needs it, the van battery.

The alternative would be to leave the car and van connected via the Anderson plug to parallel the batteries and share the load, but then requiring extended charging time to charge the two paralleled batteries.

But I prefer to have the van battery do its work running the camp, leaving the vehicle's aux battery always as a fully charged reserve just in case Murphy visits, which he often does! Then charge the van battery as needed.

As I said, I haven't seen or heard this discussed. Is there a technical reason why it's not done?

Frank