Hello chaps,

So planning my next project of fitting an auxiliary battery and seen there are already a number documented on this fine site. Joe90's thread for example: http://www.fullfatrr.com/forum/topic26065.html is great.

Most people plumb into the 100a terminal in the boot and giving the whole car system additional capacity, which makes complete sense.

My plan is different. I want to have the second battery running an occasional 2000w inverter and some separate accessories which may from time to time drain the second battery low and I don't want that to impact on the front battery.

Naturally I want to charge the second battery so hoping that the 100a supply can do that and save me running a new cable from the front and connect it via a split charge voltage-sensing relay e.g.: http://www.12voltplanet.co.uk/voltage-sens...-140a.html

So my question really is this: once I connect that to the 100a terminal in the boot (which I need to draw charge from) do I need to isolate that (I think I need a diode for that?) so that the draw I take from the second battery is only from the second battery.

Second question is: if I have it isolated, is there a way I could un-isolate it to provide boost one day if the front were to run a bit low? Does the 100a existing cable support effectively a jump start from the rear battery?

So given all that, is there a magic box that can do all of this? It's usual for boats to have split charge diode systems to cross charge but not cross drain the starter and 'house' batteries. Maybe I need one of those.

Thanks in advance for any advice or thoughts on above. Cheers, Greg
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2011 Vogue SE 4.4 with lots of toys in Stornaway

...just found this:
The Enerdrive VSR has one more huge advantage in that it is Dual Sensing (bi directional), what this means is that if you have a battery charger, or solar power connected to your auxiliary battery, and that battery gets charged enough to hit the Enerdrive VSR's set points, then it will allow your charging source to back charge the cranking battery as well, making sure that it's kept fully charged too, but again, if the voltage drops below 12.8 volts, the Enerdrive VSR will again disconnect (isolate) the batteries...
http://www.ebay.co.uk/itm/Enerdrive-Voltag...1759086222 Cheers, Greg
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2011 Vogue SE 4.4 with lots of toys in Stornaway

I have a dual battery setup with a similar VSR. Connections are protected with a 100amp circuit breaker. Like a lot of us in Australia when out in the bush camping I use a 220w solar panel through a voltage controller to keep the second battery charged, mine is used to run a fridge freezer. I would not be happy to start the car from the second battery using the existing cable to the rear. It does not look meaty enough to me, it might be OK but why risk it. Just move the second battery to the front and use jumper cables in the unlikely case of the main failing to start the car. 2007 TDV8 VSE
2003 TD6 gone.
2002 P38a gone
1999 P38a gone
1997 p38a gone
1993 VSE gone
1992 VSE gone
1966 Series 2a with V8 conversion gone

I have a 100Ah AGM aux battery in the rear of my MY12, with a 140A VSR connected to the existing cable from the main battery that can be bypassed with a circuit breaker like Wayneg's but 200A rated.

Recently the quite new starting battery was found to be dead flat due to a combination of circumstances that included accidentally leaving the IIDtool fitted for 3 days so the circuit breaker was connected for about 15 minutes then the engine started using both batteries.

Graeme, I need a new second battery for my car - the two small, in line, rear batteries (2) were fitted in the rear floor by ULR Land Rover when the car was new in June 2012. There is a Redarc isolator also fitted.

What 100amp hr battery do you recommend that fits in the floor? Does the cover still fit?

cheers

Chris M 2017 Range Rover Vogue SE SDV8 (with e-diff)
2012 Range Rover Vogue TDV8 Luxury (SOLD)
2010 Land Rover Discovery 4 3.0 TDV6 HSE Stornoway Grey (SOLD)
2006 Land Rover Discovery 3 SE 2.7TDV6 Black, G4 Challenge Copy (gone)

I have an Oddessy Extreme pc1700 in mine. Fits in the rear with no problems.
GraemeS, Why a 200a circuit breaker, surely less offers better protection. 2007 TDV8 VSE
2003 TD6 gone.
2002 P38a gone
1999 P38a gone
1997 p38a gone
1993 VSE gone
1992 VSE gone
1966 Series 2a with V8 conversion gone

You could of course do it the simple way. Install a 110AH battery in the rear connected to the protected 100A cable at the rear fuseboard. Connect the battery earth locally through a manual means of isolation and fit an isolator to the vehicle battery earth. I have this arrangement and never had a problem. If you wish to run a load on the second battery such that it might discharge it simply isolate the vehicle battery manually first. You then always have the vehicle battery to start the car whatever the condition of the second rear battery.
For what it's worth I wouldn't be inclined to try and start the car with the rear battery only, the circuit to the rear fusboard is only rated at 100A. The cable might be ok for the duration but I doubt the fusible link would be. Even if the link survived the process it could well be partially degraded such that it might blow well below it's normal rating in the future. In such cases it would prudent to carry a spare fusible link.

Chris, I had to cut out a section of the plastic bracket to fit a Remco RM-12DC (the deep cycle version, not dual purpose). I'll track down some pictures that I took at the time.

My CB is 200A to ensure that it doesn't prematurely trip although a 100A should suffice. It's not protecting the cable, it was only the least expensive battery switch. If the cable shorts to earth then the fusible link will disconnect the main battery and the VSR will disconnect the aux battery even before the fusible link blows when the sense voltage drops below the cut-out point.

Leaving the 2 batteries connected for 15 minutes allows significant charge transfer so that starting will not be drawing all its current via the rear cable. Furthermore, cables and fuses are rated for continual current draw but for short periods, as occurs when starting a modern engine that starts in a couple of seconds, cables and fuses can safely carry several times their rated capacity.

this is a mod I'd really like to do on my Mercedes , the previous model had a split double battery set up , my model has just the one and its doesn't like being left for more than a week without being used , the year model after mine went back to the twin setup so Mercedes clearly realised the car needed the extra that another battery brings , so I think I will have a read and see if I can adapt what you guys have done to it
simon

Thanks Graeme! 2017 Range Rover Vogue SE SDV8 (with e-diff)
2012 Range Rover Vogue TDV8 Luxury (SOLD)
2010 Land Rover Discovery 4 3.0 TDV6 HSE Stornoway Grey (SOLD)
2006 Land Rover Discovery 3 SE 2.7TDV6 Black, G4 Challenge Copy (gone)

The only picture that I can find...

Click image to enlarge

Thanks for the pic Graeme, looks nice.

So it seems most (especially the Australians!) have a fridge or other connected to the second battery. If your fridge or other ran ran ran until it drained the battery, would the starter battery get drained too?

This is the same as a caravan set up, no? Like this: http://www.altecautomotive.co.uk/caravantr...-666-p.asp

. Cheers, Greg
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2011 Vogue SE 4.4 with lots of toys in Stornaway

The voltage sensitive relay only connects the aux battery whilst the main battery voltage is high enough then disconnects at a slightly lower voltage that in practice occurs within a short while after the ignition is switched off.
Your referenced item uses the same principle although better to have the VSR connected to a high current supply to ensure that the VSR stays connected rather than drop out shortly after connecting due to voltage drop in the supply wire.

Ok thanks Graeme. Just trying to get up to speed on this stuff...

My worry is that the second battery could be 'abused' a bit, running an inverter or accessories and in some circumstances that will run the second battery below what is ideal.

And so I don't want that in any way to impact on the starter battery.

Presumable your set up runs a fridge or CB radio and does the VSR protect the starter battery from drain?

Second question - how do you isolate the draw so that those accessories only draw from the aux battery?

. Cheers, Greg
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2011 Vogue SE 4.4 with lots of toys in Stornaway

The VSR effectively isolates the 2nd battery once the engine is turned off. I have rewired the accessory plug in the rear loadspace directly to the second battery so I plug my fridge into that socket. When I am set up camping I connect up a solar panel via Anderson plugs to keep the 2nd battery charged. I have never had the 2nd battery go flat.
bembo449.. I too have a Merc, a Sl500 which will run the battery flat if left for 2 weeks or so. I have rigged up a small 18w solar panel in my garage window, connected to the car it seems more than enough to keep the battery fully charged. 2007 TDV8 VSE
2003 TD6 gone.
2002 P38a gone
1999 P38a gone
1997 p38a gone
1993 VSE gone
1992 VSE gone
1966 Series 2a with V8 conversion gone