Thread: Dual Battery System - Disco Series 2A

<div class='quotetop'>QUOTE</div><div class='quotemain'>the higher current will cause the joint to heat which will cause the resistance to increase[/b][/quote]

You mean any increased resistance will cause more heat. :wink:


I will have to have a look at mine. I have the battery in the back of the Disco but have the back battery earthed to the chasis.
The good news is my business is Infrared Thermography. This means look at industrial control panels for a living telling them where they have hot spots by using an infrared camera. I will plug in the fridge & drain down the battery then scan the earth while it is charging, maybe that is the problem I have been having.

BTW a bad connection will heat up no matter what the load. I have seen 24v PLC wires that carry less than 1 amp reach more than 100deg because of a bad connection. This is a good thing to remember when crimping wires in your car because 100 deg around carpet or plastic will cause a fire real quick.

Hi walker, I ‘ve answered some of your questions in the last post.

As for an alternator not charging a battery fully, well I don’t know where this myth started but it does appear on a regular basis and it is nothing more than a myth.

Providing the vehicles alternator, regulator and wiring are all in good nick, the vehicle’s electrical system is the perfect way to charge a battery or two or three if you what and all at the same time and they will charge to 100% with the only varying factor being the time that each battery takes to charge and if the second battery is a long way from the alternator ( in the rear of the vehicle or in a trailer or caravan ), depending on the size of the cable, will take even longer, but will still fully charge eventually.

As for the use of a voltage booster, to get them to work properly you need to install thick cable and if you fit thick cable in the first place, you don’t need the booster.

In my honest opinion, for the same cost of one of the many boosters that are on the market, you would be far far better off investing the money in an extra battery. You would save money while at the same time give yourself heaps more capacity, far more that the booster would give you.
Cheers

Mines a series1 so the 2nd battery is in front of the air cleaner. Uses a Pirannah battery isolator. They use a bank of big relays to join the 2 batteries together when the main battery is over 12.5 volts. Only trouble is they burn out relays if you give them a hard time, so can't say i would recommend them. Some of the electronic ones will trickle charge the 2nd battery if it's flat before full charging kicks in, only trouble with big flat deep cycle batteries they take to long to recharge. Hope this adds to the confusion!
Cheers
PeterN
97V8i

I will try to find the post of someone who seemed to know what they were talking about in relation to battery charging (or lack of it). I started the whole thread about it a month back when my optima carked it after only 12 months. I have the battery in the back but I also used a large cable from battery to battery & only had 0.1v voltage drop under load.

Part of the problem may be that the battery is only charging at 12.8v max which I was told is not enough voltage to charge the optima. Not sure why I am only getting this voltage but after testing 2 other V8 Disco they were all only getting similar voltages at the battery with the engine revving at 1500RPM.

Here is a post from the other forum. My problem is that when there is something technical that I don't understand I tend to believe what others tell me. I don't want to buy a booster if I dont have to but I don't want to be stuck without a fridge like I was the other weekend.

Sorry it a bit of a long read :

<div class='quotetop'>QUOTE</div><div class='quotemain'>The Exide is an AGM battery (Absorbed Glass Mat.) These should realy
not be mixed with other batteries but with the low output from a
vehicle alternator it was not the problem in your case. It was the
lack of sufficient voltage. Gel cells require 14V, AGM - 14.15 and
flooded batteries - 14.4 to fully charge them. I am not sure off hand
what the sealed lead acid batteries (the original fit) require but it
is less slightly less than 14.4V.

I have not metered my D2 alternator but my D1 alternato initialy
produced 14.3V and after 5-10 minutes of driving the temperature
compensation dropped the output to 13.4 to 12.6V. I susspect the D2
will be similar. From this you will see that you will not efectively
charge a deep cycle battery from your alternator. It takes very little
power to start a motor, the initial higher voltage from the alternator
is thus able to replace the lost charge after starting. Even so a
cranking battery is only charged to 60-70% under most conditions, this
is so that the simple cheap regulator will not overcharge your battery
under any condition. The marine electricians know which way is up,
they exchange the cheap regulators with smart regulators (about $800)
to fully charge boat house batteries - most auto electricians dont
have a clue when it comes to deep cycle batteries.

Tim Loveday's Arrid "Twin Charge Battery Charger" (available from
http://www.12volt.com.au/) is the way to go. I had one fitted to my
last caravan and it kept the battery fully charged without hooking up
to the mains. It will produce full battery charging voltage with only
10V input. At $300 it is also cheaper than the fancy ones that the
auto electricians love and push. You can get 3-5 itmes more useable
capacity from your battery than you can get if you only charge from
your alternator, or for most people it will mean that they destroy
batteries at a slower rate.[/b][/quote]

Hi walker, if your alternator is only producing 12.8v then there is something very wrong with your charging system.

That voltage level is so low that it wouldn’t charge ANY type of battery and the light coming from your headlights would be yellow.

I have not done much research into so called temperature compensated voltage regulators and my own Rangie runs at 14.25 to 14.3 at all times. Even when running 6 additional 55 watt driving lights, the system voltage never gets bellow 14.2 and usually runs at 14.25 with all the lights on.

Of the info relating to temperature compensated voltage regulators that I have come across, none have stated the compensated voltage level gets bellow 13.6 and this is still to low to charge a battery properly.

To charge any vehicle battery you will need at least 13.8 volt constantly or the battery will not fully charge.

I saw your pictures on your web site when you first posted them and if you are only getting a .1 volt drop at the rear battery while under load then you either have a problem with your wiring or you are taking your readings from the wrong place.

I have a small AGM fitted in the rear of the Rangie and have it connected to the front battery with 10 mm square twin cable about 6 metres long and after taking the rear battery down to 11 volts, when it is first connected back to the vehicles charge system, via the battery management system, the voltage at the rear battery rises from 11 volts to about 13.4 -13.5 in about 30 seconds and the over the next hour ( during continuos driving ) the voltage rises to 13.8 - 13.9.

After a few hours the rear battery runs at 14 + volts. This voltage varies as the fridge cuts in and out.

Because of all the conflicting info that is out there, in the next few weeks I am fitting a number of Data Loggers in different places throughout the Rangie and I intend to test a number of different types of batteries, cranking, deep cycle and AGM batteries, under different operating situations to satisfy my own quires and when I have the data I’ll post it on my web site.

One more point, the numbers just don’t stack up in favour of these voltage boosters, again, instead of spending $300 on a device that will at very best might give you about 10% additional storage capacity, why not spend about half that and just add another battery and give yourself at least 50% more storage capacity.

Cheers

I am not getting 12.8v at the alternator but at the main battery. I thought this was too low but after checking a few others the were all the same. Will recheck everything.

But if anyone else out there with a series11 Disco V8 could check what voltage they have at the battery while engine running at 1500RPM it would be helpful.

where is your web site?