Charging two auxillary batteries

Gooday Geoff: if you search " charging camper battery " there is a lot on this forum & blogs
The redarce you have now would be good for your new 2nd car battery but you will need a different /better one for your camper , as I under stand it.
I dont think redarce sbi is the best one for your camper charging !!!!

cheers nick

Welcome Geoff!

You do need some way of electrically separating the two aux batteries when the engine isn't running, unless you plan on running them in parallel - paralleling is not a good idea if the batteries are some distance apart or have different characteristics. Probably the easiest way to separate them is to fit a second controller.

Cheers

John

Geoff

I am sure this is covered fully in the electrics article in ExplorOz
If not then have a read of Derek Bester's Site www.sidewinder.com.au
His articles are excellent

Personally I would change/rewire the Isolator to between the main and your (new) auillary battery, so when you are driving along you are charging the both.

Just remember that they will discharge together, if not isolated

Cheers
Bucky

Others will disagree but the fact is that if you use the correct cable you will have no voltage drop to the rear of the vehicle. i have two wet cell batteries under the bonnet and one battery at the rear of the vehicle no measurable voltage drop anwhere.
I have a mechanical isolater switch to seperate the starting battery only if required ,all batteries are wired in parallell ,i have 160watts solar panel on the roof running a 47 l bushman fridge set at minus 5 c constantly.
The longest i have left the vehicle without starting the engine and relying on the solar only to charge (note 5metres of cable from the panels to the rear battery and then approx 6metres of cable from the rear battery to the front batteries is three weeks no problems.
Of course i havent spent heaps on an electronic isolator and therefore there is nothing to break down.
I have had several electric isolators over many years all have given trouble after aperiod of time in my experience.Hope you have a good run with redarc gear i havent used that brand.

Hi Geoff,

how to charge a battery depends on a few things.

So the first questions are what is the purpose of the aux battery in the car?
How often will it be discharged, and how deeply?
What's the mounting spot like, under the bonnet, or in the boot?

Lowest operating temperature for good battery life, lowest cost/type of battery, lowest depth and frequency of discharge, lowest complexity of the setup, lowest cost of switch gear, best reliability, longevity of the battery are the interrelated factors.

Jot down these factors sorted according to your own personal preferences in descending order starting with the most important one.

Once you're done with this wish list, you can present it here in the forum and we can look at it and give you some ideas how to achieve this.

cheers, Peter

I have a 120 series Prado with a notoriously low output from the charging system, so a conventional isolator system that parallels batteries is no good. I have a second battery in the vehicle and tow an off-road Karavan with a 320ah battery pack.

I have had great success with this:

A Redarc SBI, but this doesn't parallel up the batteries. When it comes on it simply switches on a 12V supply to a dc-dc smart charger which properly charges the second battery in the vehicle, regardless of the Prado's output. There is also a load switching relay that makes the car fridge/freezer run off the second battery when the engine is off, and off the crank battery/alternator system when the engine is running.

The SBI also supplies 12V via heavy cables (6 gauge) to the Anderson plug at the back, which supplies another 12V dc-dc smart charger in the Karavan for its battery pack.

The two smart chargers run totally independently of each other and are programmed to suit their individual battery characteristics.

My smart chargers are RanOx, but you can't get them any more. Redarc make a couple of good ones, one of which has solar input as well.

There are quite a few differeing views on this particular issue, and some people are very strident on their position.

The truth is you can " get away" with a variety of different arrangements that may be less than technicaly ideal.

Firtsly, the most impotant issue is isolating the cranking battery so that it does not get flattenend when the other batteries get run down in camp.

Lots of people get carried away, with discussion about relativly monor issues and forget that this is the main finction of whatever battery isolation you are using.

with that in mind.

lots of people use and many manufactuers detail, the method of simply connecting the second and third batteries in parallel, using an anderson plug to connect the camper or portable battery box, that the third battery is in.

There are technical issues with that that make it less than ideal, but for thousands it is functional.

What is important in any multi battery situation is to supervise and maintain the batteries.

Most of us will be using some for of sealed battery so watering the batteries is less of an issue these days, but we do need to pay some attention to the individual batteries, by seperating them and charging them individually with a good modern charger and checking the voltages at rest after.

this way we will detect any failure in one battery that may drag another down.

the idea situation of course is to have some sort of seperate battery management for each additional battery.

As far as there being "no detectable voltage drop" in the post above......Um sorry there will be voltage drop, perhaps not under the circumstances that you measured it.
In fact unless you are running stonking great 25mm2 pluss battery cable all the way to the battery in your camper, there will be heaps of it at times.

But as long as the voltage drop is not excessive, it will do little more than slow down charging at times of the highest charge current....it can be argued that this is not a bad thing in some situations.
As the batteries fill with charge the charge current will taper off and the voltage drop with it.

In fact the voltage drop that will be present in lighter but still adequate cable will sequence the charge between the second and third battery ( for good or bad).
Given a similar state of discharge, the battery closest to the alternator will get a larger portion of the charge untill its voltage rises and the third battery will then get a larger share.
Most people never discuss or consider the above..but its there.


As far as the whole dissimilar batteries argument......the problems with dissimilar batteries are greatest when batteries are permanently and closely coupled, such as in paralell battery banks where one or more batteries are used in place of one larger battery.

When we have batteries in different locations, seperated by significant distances of wire and with differing loads and states of charge, they will always even if completly identical charge at differeing rates.

But as long as the batteries are in good health sooner or later given enough charge time they will all reach the same charge point dictated by the nominated charging voltage.

remember, possibly the most common reason for battery failure in campers is repeatedly not providig sufficient charge to stop the battery being hammered into its lower limit day after day..

cheers

cheers

Thank you to you all for your replies. I think Bantam hit it on the head and has got me thinking. I have read about the DC - DC chargers, they are the way to go but are expensive. Hard when on a budget. What do you guys think if I go the easy and cheap way of just getting another isolator ( SBI or whatever ) to look after each battery? I will explain my setup in more detail. The batteries are both Duel Purpose Marine Batteries, I was advised to get these instead of deep cycle because I don't get to go out often and these would handle infequent use better than the deep cycle which he said would need to be cycled often. The camper has a 120 AH and car is only 65AH. Later when I join the ranks of the Grey Nomads, I can fit a 90 AH of the same size which is a deep cycle type. It was a bit of a job getting the N50 size battery under the bonnet, Nissan obviously didn't think people would want to put another battery in their car! At this stage the new battery is installed under the bonnet ( but not connected ) and the rest is unchanged ( 6 B&S cable from starter battery to SBI, 6 B&S running through chassis to an Anderson plug at rear of car. I have used the body for the earth at the plug. ). I have enough 4 B&S cable here to wire up the car auxiliary. I don't have a winch, but I may think of getting one later. I hope this has explained things a bit better. Thanks again, Guys.
Geoff

Hi Geoff,

I fitted a auxillary battery to my 100 series cruiser and also installed a auxillary battery into my camper trailer as well, the starting battery is isolated by a 150amp Projecta Isolator.

From the isolator the wireing goes into a 4 way 225amp marine switch inside the car within easy reach and view. It allows me to control where i want the charge being sent to(ie, the aux car battery or aux camper battery at seperate times or both at the same time) I can also have it switched off all together . This setup also allows me to isolate power going to the back of the car while doing normal driving without the trailer on.

Both the wireing to the aux car battery and aux trailer battery are 50amp twin core with the black protective covering protected by a 40amp waterproof inline glass fuse.

The aux car battery is charged only by the car alternator while the aux trailer battery is charged through a 20amp projecta DC-DC charger as well as being hooked up to a 16amp projecta AC-DC charger for powered sights whilst the car is seperated from the trailer, this way i can have the trailer at 100% charge nearly all the time.

Have had tis setup now for nearly 12months and have not had any drama's as yet, the trailer battery usually is running LED strip lighting in the tent and outside to the tailgate and a 1000w inverter also wired to double power points inside the tent and to the tailgate, and sometimes runs the fridge.

The aux car battery usually runs the fridge for most of the holiday and the kids dvd players :-), and the uhf.

The car aux battery is a Ac Delco 95ah deep cycle and the trailer aux battery is a Allrounder 105ah deep cycle, very pleased so far with both batteries.

Cheers, Jack.

Geoff,

Plenty of info mentioned.
I have a Pirahna isolator between the main battery and the 100AH AGM in the rear of the vehicle. The camper came with a couple of diodes between the auxilliary battery in the rear of the vehicle and the battery in the camper. Not very sophisticated but works OK.