Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26774
Yes Tim, I'm sure that would go down very well in the peace and quiet of the Le Mans camp site
5th Jun 2015 7:33 pm
DSL Keeper of the wheelie bin
Member Since: 11 May 2006
Location: Off again! :-)
Posts: 73085
No one will hear it over all the old folks' snoring.
5th Jun 2015 7:43 pm
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi Garath and as long as the batteries are fully charged, you can use the cig socket in the rear cargo area to keep the batteries topped up.
Do as Bodsy suggested and just take some fuses with you.
As for the batteries gassing and being dangerous, sorry but this is nothing but scotch mist.
For a starter, all types of lead acid batteries gas. Even the INCORRECTLY labelled “SEALED†batteries gas.
A battery labelled as “SEALED†means it won’t spill electrolyte, it will still gas.
Garath, using your alternator to top the batteries up ( via your cig socket ) means they will not gas, but using a DC/DC device means they have the potential to gas.
But even if they do gas, it is NOT dangerous and there are at least 2 dozen NEW makes of vehicles that have the cranking battery either in the cab or in an adjoining unsealed compartment and no one has any problems.2008 TDV8 RR Lux + 2009 D4 2.7
5th Jun 2015 8:58 pm
Gareth Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26774
As for the batteries gassing and being dangerous, sorry but this is nothing but scotch mist.
Nonsense.
This advice is suspect and you could easily end up gassed. I nearly did with a leisure battery in a caravan where the external venting was blocked and the charger did not switch off.Volvo XC60 - does all that the D4 should have done
Discovery HSE MY16 (good apart from the heating), now sold
Audi TT Roadster (wow)
MGB Roadster (owned since 1992)
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6th Jun 2015 5:52 am
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi jdhx and you would only get a good dose of rotten egg smell.
BTW, Garath was asking about using the power socket in the rear cargo area. This is powered from the alternator and unless the battery is stuffed in the first place, an alternator will not cook a battery.
As I already posted, if using a DC/DC device, which is nothing more than a glorified battery charger, then there is, as you found out, the potential of cooking a battery.
Battery chargers are renowned for cooking batteries, alternators are not.
Next, the only threat potential of having a battery cookout is if the battery is in a confined space, like in a cupboard, or small battery compartment.
If a battery or number of batteries are located in an open space like the cabin of a vehicle, or in a caravan, say under an open bed or seat, there is no danger created what so ever, while charging from an alternator.
Even when charging from a battery charger, if the batteries are in the same type of open area, all you risk is the smell if a battery is cooked out.2008 TDV8 RR Lux + 2009 D4 2.7
6th Jun 2015 7:31 am
tayaste
Member Since: 15 May 2013
Location: Chester
Posts: 7633
Tim, the ctek dc/dc mentioned above.The D250s. Can you explain a little more how this can cook the battery, only interested as I have one and had plans for it.
6th Jun 2015 7:35 am
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi tayaste, first a question for you.
How are you planning to set up and use the DC/DC device?2008 TDV8 RR Lux + 2009 D4 2.7
6th Jun 2015 9:47 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Afternoon Gareth,
Quite a spread of opinions on this thread! Whilst I don't indulge in those 'someone has said something wrong on the internet moments' but as there is safety involved it is probably worth looking into this yourself to make sense of the differing views. Lead Acid batteries may be full of chemical energy but treated with respect they are fine.
When you look into hydrogen gassing note if this is a phenomena of just some lead acid batteries or all of them; if 'sealed' means anything in the context of gassing and if gassing is more or less pronounced on the final stage of charging or not.
When considering placement, restraint and gassing in the context of standard mounting of a battery in a rear, front or cabin mounting location consider if the manufactures and regulators manage the issues with dedicated restraints, safety connections and hydrogen vents routed to the outside air. I'm sure you have noted the hydrogen vent to the wheel arch on the D4 battery already.
If considering connecting the battery direct to the vehicle DC system you are, in effect, adding a second battery in parallel to the main battery and vehicle charging system. If you connect to the perm live of the tow electrics consider the 2.5D wiring and the 30 amp fuse. If connecting to the switched tow electrics note the 2.5D wiring, the FET-controlled relay and its control configuration plus the 15 amp fuse. If you are considering the aux socket note the 2.5D wiring and that it shares a 20 amp fuse.
I'm simplifying things a bit but when batteries are in parallel they settle at a common voltage and share the load. When you look at the wiring on the main battery you see 50.0D wiring and 400 amp fuse to cater for the initial 120 amps or so drawn when the ignition is switched on with more on cranking. If a second battery is on this circuit it will try to join in.
If the second battery is on a switched ignition or on an 'engine running' command it may avoid the start but will participate in all other power demands. If it can take a charge it will try to draw the amps it needs. When the BMS drops the alternator output to zero it will try to share the power demands. When the BMS ghosts the battery voltage it will now try to do this with an unexpected battery attached. When the BMS applies the learned discharge and charging rate of the battery it will have some new challenges. When the BMS deliberately decays the state of charge the vehicle will draw from both batteries. When the BMS triggers the high charge rate with overrun / energy recovery charging this will be dumped into both batteries. Consider the amperage in and out of the battery system in these modes.
I've deliberately not passed any opinion in the above, they are just things to consider. I did, of course, have them in mind when I offered my previous opinion.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi Robbie and while I agree, in principal, with everything you posted, the suggestion of Bodsy, to carry some fuses is for this very reason.
If the Gareth’s D4 decides to carry out a cranking battery test, it may very well blow the fuse for the rear power socket, but thats all it will do.
Having another battery in parallel ( positive circuit only ) with the cranking battery will have no effect on any of the test procedures.
Plus, as the wiring to the rear power socket is so thin, even if the voltage at the front of the vehicle drops to 12.2v during the test procedure, I doubt if the current draw, because of the voltage drop caused by the thin wiring, will get to the point where it will blow the fuse.
Again, because the voltage difference between the discharged cranking battery ( 12.2v at lowest point ) and the fully charged voltage level of the rear batteries ( 12.7v at best ) and the combination of the thin wire, the likelihood of getting much more than a few amps being drawn from the rear batteries is about all you would get, and as such, this is unlikely to blow any fuses.
But, Gareth, just be on the safe side, and carry some fuse replacements.
Robbie, this is a simple one to test.
Get a fully charged battery and another battery at 50% ( 12.0v ) and connect them with 4m of 1.5mm2 wire and measure the current draw through the wire.
You might be very surprised at how low it is!
The thin wire acts as a quasi voltage/current regulator.2008 TDV8 RR Lux + 2009 D4 2.7
6th Jun 2015 11:55 am
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Gareth, one point I did overlook, you will need to have a fuse fitted at the rear batteries.2008 TDV8 RR Lux + 2009 D4 2.7
6th Jun 2015 12:00 pm
tayaste
Member Since: 15 May 2013
Location: Chester
Posts: 7633
drivesafe wrote:
Hi tayaste, first a question for you.
How are you planning to set up and use the DC/DC device?
I've got the gear ready to install a regular dual battery setup, I was hoping to bring a small Anderson plug through to the boot to enable me to connect the d250s to allow me to charge a third (removable) battery for camping and stuff
6th Jun 2015 12:14 pm
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi tayaste, if you run 6B&S ( 13.5mm2 ) twin cable, or 16mm2 is what you probably have over there, you will have no trouble charging a battery faster straight off your alternator.
If your 3rd battery is a 100Ah battery and is in a low state, it could easily draw up to 40 amps during the initial charging at the beginning of your drive.
How long you drive for will then govern the final state of charge of the battery.
A 20 amp DC/DC device is great for topping up batteries on short drives, but if you are driving for four hours or more, no matter what the state of the battery when you start, at the end of the drive, it will be up around 95+% regardless of what method you use.
I have not once come across a D3 or D4 that got any real benefit from DC/DC devices over what the alternator can do, even when charging batteries in a camper trailer or caravan, while driving.2008 TDV8 RR Lux + 2009 D4 2.7
6th Jun 2015 12:29 pm
Trackman
Member Since: 16 Apr 2010
Location: Glasgow
Posts: 430
Also remember the D4 does not have a constant 13.8V to 14.5V supply.
Mine can sit 12.6V especially after a long run which is no use for charging a battery ....
6th Jun 2015 8:52 pm
drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
Hi Trackman and to be candid, all the people I have dealt with have my dual battery system fitted and because of the way it works, it resolves the problem of the operating voltage dropping before all the batteries are charged.
NOTE, this a fluke not a designed feature.2008 TDV8 RR Lux + 2009 D4 2.7
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