Oh No Another Battery Question

Thanks Garry for the reply,
It may be that if we leave out the charger both the auxiliary battery and c/t battery will run, in my case, the 80 ltr Engel in the tow vehicle. I've replaced all the batteries and overhauled the alternator in the last six months so I guess I had some thing wrong with my system.
Thanks again
Cheers
Graham

Hi Graham,

Yes, I think that would be possible, having both the Aux and CT batteries effectively in parallel.

I would recommend 6B&S dual cable if you are looking to charge the CT battery from the tow vehicle when on the move. Without the CT 12V charger, you will need every volt you can get at the CT battery.

I expect that I will probably NOT connect tow and CT when camped. The Tow Aux will handle the car fridge, and I will leave the CT battery to handle just the CT needs.

If camped out for some days without travelling, then the portable Solar should charge both Tow Aux and CT batteries just fine.

All good fun, Isn't it?

Hi Captain,
Thanks for the reply I'll check out the voltage from my vehicle and take it from there.
Cheers
Graham

Captain,

Thanks for sharing your experience with this.

At this stage, I haven't gone the 12v Redarc route, but I WILL measure the voltage at the CT battery when charging.

What do you think would be the minimum acceptable charge voltage at the CT Battery?

Many are fitting booster diodes to current model vehicles to up
the charge voltage, these devices work very well with no reported
adverse affects and at a fraction of the price of DC DC charges well
worth a look.

Hi Leigh,

interesting point you're bringing up.
Just the other day I had a customer with a late model Prado with this diode boosted alternator.

He was a bit cautious about the unregulated high charging current this increased voltage would cause through a discharged auxiliary battery.
I told him this may or may not be a problem, depending on the size/length of wires involved.

Since the internal resistance of a discharged battery is 4 or 5 times higher, battery heating may become a problem under high charging current conditions.
And since higher battery temperatures decrease the gassing threshold, it'll start gassing at a lower charging voltage.

At 25 degrees, gassing starts at about 14.2V, but this threshold could be as low as 13.6V @ about 50 degrees.
Because the alternator happily pushes 50 amps and more through the battery at this voltage level, and electrolyte disappears at the rate of about 1 gram/Ah while in the gassing region, there's going to be some loss of electrolyte.

Counter measures are thinner and longer wires which restrict the max charging current somewhat.
And you only have to reduce the max current by 30% to achieve 50% less heating (I^2*R), which could be all it takes to keep outside the gassing region.

Aim for at least 20 milliOhm of wire resistance: for #6 wire, that's a length of 14m, for a distance of 7m between aux battery and alternator.

Going heavy and short in wire size in connection with a diode boosted alternator is a good recipe for a dead battery half way down the track.

Another trick to overcome the high charging current problem is, to simply install a second aux battery in parallel.
This helps in two ways: the high alternator current is split between the two batteries, and secondly the depth of discharge will be lower, thus the batteries have lower internal resistance which makes for less heating.

cheers, Peter

Hi Phil,
you're spot onto what I am running in the T-Van and tow vehicle, during the last six months I've replaced all batteries and overhauled the alternator. Probably the alternator was slowly dying and caused all the other problems, the T-Van battery was about six years old.
Having bought a expensive AGM battery for the van I did not want to kill it unnecessarily but I think you are right the 50 w solar panel and a little help from the anderson plug will keep it topped up.
Thanks for the reply and happy T-Van travelling.
Cheers
Graham

Gday Graham,
Out of interest I also bought a 130Ah SSB AGM - arrived last week. I've got a spot in the cool of my canopy for it (its my 3rd battery in the landcruiser). But it will be running the 2 engels, and I've installed a CTek D250S for a couple of reasons - firstly, its an isolator, secondly, it limits the charge current to 20amps so my alternator can't hit it with too many amps and kill the battery, and thirdly it takes the input from my folding solar panels.

The AGMs get killed in a few ways - too much heat; too many amps from an alternator and being chronically undercharged.

So by mounting your SSB AGM in the Tvan, it won't get too much heat, it is highly unikely to get too many amps because of the distance from the alternator, and if you charge it on a 3 way charger every month or two when its sitting at home you'll keep it in good shape. A major issue with the Tvan is that it has a voltmeter connected all the time. this voltmeter consumes a trickle of current but its enough to run the battery flat when its in storage. I've put in one of those kill switches in the main earth lead at the battery so when its in storage, there is no way the battery can be quietly discharged.

Cheers
Phil

Thanks for that Phil, I'll organise a kill switch for the battery but hopefully it doesn't sit around for too long.
Cheers
Graham