Member Since: 09 Jan 2011
Location: Chilterns
Posts: 4130
Second Starter Battery
Has anybody fitted a second battery for Winter Starting (Back up) purposes rather than the usual Yellow Top for camping etc. Could you then link it to Main Starter battery and charge both in a Duel charge fashion?
You could also charge two batteries with your split charge solution and then have a isolator for the one you'd want to use as a backup to wire up with the main in case you need it or http://www.traxide.com.au/complete-diy-dua...e-battery/.
However, I'd wonder where you'd put a second one after the troubles I had finding a suitable spot for just one D4
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9th Feb 2017 5:54 pm
DSL Keeper of the wheelie bin
Member Since: 11 May 2006
Location: Off again! :-)
Posts: 72771
My aux battery is connected to the crank one by a solenoid, so when the solenoid sees the crank battery (ignition on) it links the two. Thus always starting with 2 batts.
The D4 has limited space as the aux battery box is full of other stuff! Its a bit of a job to move that out to make the space. I know its something Bodsy has done.Mark.
2006, D3 SE Auto - gone but not forgotten.
2014 BMW 530d M Sport Tourer.
1977 Triumph Spitfire 1500
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9th Feb 2017 7:32 pm
Gazellio
Member Since: 09 Jan 2011
Location: Chilterns
Posts: 4130
nessie wrote:
Haven't done so, but the same principles apply.
You could also charge two batteries with your split charge solution and then have a isolator for the one you'd want to use as a backup to wire up with the main in case you need it or http://www.traxide.com.au/complete-diy-dua...e-battery/.
However, I'd wonder where you'd put a second one after the troubles I had finding a suitable spot for just one
So you need an isolator between the two. How is the (starting) connection made is there an isolator switch and what about charging the 2nd battery?
9th Feb 2017 7:36 pm
Gazellio
Member Since: 09 Jan 2011
Location: Chilterns
Posts: 4130
OK so now I am the expert...
If car batteries are connected in parallel, the more-charged one will always be trying to jump-start the less-charged one. So, although you could simply wire a second car battery in parallel with the first, there are better and safer ways to implement a two-battery system.
Battery Isolators
One excellent way to implement a two-battery system is with a battery isolator. These devices range from less than $50 to several hundred dollars, depending on the sophistication and features. Ideally, the job of a battery isolator is to combine the power of the two batteries for everything from powering devices to starting the car, while making sure that a fault in one battery can't kill the system. In essence, it becomes a redundant array of batteries—all the benefits of a backup battery, with none of the drawbacks. And depending on whether starting power or device power is more important to you, an isolator can make sure that devices deplete only the secondary battery, always leaving the primary battery charged to start the car.
In practice, the isolator uses a bit of the power itself ( diode isolators will drop alternator output by about 1 volt, have large heat sinks, and are somewhat inefficient). It's not that easy to keep two different batteries fully charged, united in power, but divided in risk. Isolators come in several kinds, from simple switches that flip from one battery to another, to complex microelectronic circuits that actively monitor the charge levels on both batteries, charge them appropriately using alternator power, and use both of them to power devices and start the vehicle.
Because of the large currents needed to charge a battery, any second battery setup will need to run thick (4-gauge or so) wires from the alternator/front battery back to the second battery, unless the second battery is also being mounted near the engine. Exactly how to do this will be in the installation instructions that come with the battery isolator.
Dual-Output Alternators
If you want a very simple isolated system, you may be able to achieve it with a dual-output alternator. These are designed to charge two separate batteries independently. You can install your second battery to be charged by the secondary output of the alternator, and wire most of your devices to this second battery. When the engine is running, the vehicle will power the devices. When the engine is off, the second battery will power the devices, leaving the primary starting battery untouched and always charged and ready to start the car.
Conventional Versus Deep-Cycle Batteries
In "Upgrade Your Car Battery" [Hack #6] I discussed the two basic types of car batteries. In RVs, the usual approach is to have both kinds of batteries, each doing what they do best. A conventional, high-cranking-amps, lead-acid battery is connected to the ignition, lights, and basic car electronics. A second, big, deep-cycle battery (or several) is charged by the engine as well, but when the engine is off these batteries power devices such as refrigerators, TVs, computers, and so on.
There's never any risk of killing the starter battery by powering nonessential accessories, and if the deep-cycle battery goes dead, no harm is done—the engine can just charge it back up on the next drive, if it's long enough. However, keep in mind that the stock alternator isn't designed to charge batteries from a deep discharge on a regular basis, so you may want to upgrade it as well [Hack #9] .
This arrangement depends on a good battery isolation circuit, and the same system can be installed in any vehicle with room to put an extra battery.
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8069
There is a much easier and simpler way if it is just for emergency starting, once you have decided a safe place to position the second battery on a D4, I have a D3, simply connect both batteries together using a conventional starter solenoid operated with a switch inside the car, once the engine starts switch the solenoid off, keep the battery charged by putting the Ctek on it once a month or after it has been used.
Saves carrying jump leads and I have used it several times when I've been caught out both summer and winter, the battery I use was off a Peugeot diesel, nothing special.It can when others can't,
It will when others won't,
It goes where others don't.
9th Feb 2017 8:28 pm
DSL Keeper of the wheelie bin
Member Since: 11 May 2006
Location: Off again! :-)
Posts: 72771
anglefire wrote:
That's on your D3 Del - not the D4.
The D4 has limited space as the aux battery box is full of other stuff! Its a bit of a job to move that out to make the space. I know its something Bodsy has done.
Ah missed that. My brain is not in the game at the mo
9th Feb 2017 8:41 pm
Gazellio
Member Since: 09 Jan 2011
Location: Chilterns
Posts: 4130
I guess if its sitting there jump leads will also do the trick...
9th Feb 2017 8:55 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8069
That's what I started with, but so much easier and impressive to just press a concealed button, mine is hidden beside the right air vent and cannot be seen when the door is closed, very convenient especially when SWMBO is on the phone saying battery is flat, or you are on your way to a wedding with best bib and tucker on that's when they usually fail.
It only need one heavy cable to join the batteries together through solenoid +I've, earth goes to chassis, single wire goes to switch in cab, job done It can when others can't,
It will when others won't,
It goes where others don't.
9th Feb 2017 9:48 pm
gstuart
Member Since: 21 Oct 2016
Location: kent
Posts: 13597
this looks a really interesting thread
after my orginal battery going flat today and buying a new one
i've now also started to read up about these spilt charge systems
9th Feb 2017 9:50 pm
xcentric
Member Since: 01 Apr 2015
Location: Shropshire, UK
Posts: 1081
I have a D4 and fitted a 2nd battery in battery tray by moving stuff out of the way, not that hard. T-max split charge system, with controller on access panel in boot, next to the usb and 12v take off points. Pressing a button connects the 2 together for starting etc if one is low, otherwise isolated, and charging both when engine running etc. Wiring was straightforward, though it took time to get trim panels off and back on again, but basically fine.
9th Feb 2017 11:44 pm
gstuart
Member Since: 21 Oct 2016
Location: kent
Posts: 13597
xcentric
many thks for the info
will have a look into the T max systems
10th Feb 2017 4:41 am
gstuart
Member Since: 21 Oct 2016
Location: kent
Posts: 13597
xcentric wrote:
I have a D4 and fitted a 2nd battery in battery tray by moving stuff out of the way, not that hard. T-max split charge system, with controller on access panel in boot, next to the usb and 12v take off points. Pressing a button connects the 2 together for starting etc if one is low, otherwise isolated, and charging both when engine running etc. Wiring was straightforward, though it took time to get trim panels off and back on again, but basically fine.
interesting read
new battery coming today and also wondering about keeping my existing battery for now and using it as the aux when i set up the t max split system
bought the exide one, as it has good reviews on here
10th Feb 2017 9:25 am
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8069
It's to big to fit in the aux tray It can when others can't,
It will when others won't,
It goes where others don't.
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