Dual Battery Set up

[Koopa]

Hi guys.. I am also looking at installing a dual battery system in a T5. I am looking at some different setup and before I found this thread, I was leaning towards the following;

1. 100amp deep cycle connected to main battey through a diode battery iscolator. This will charge the Aux battery when the engine is running, and iscolate the main battery when it is not. Also looking at a model which has a manual override incase I need to crank off the Aux battery.
2. Off the Aux battery have
- 1000w inverter with two double socket power point wired in the van
-12v bus to power lights, fans etc.

3. Down the track..Install a battery charger for Aux battery when external power is available or for use with Solar panels.

This thread talks about installing a battery charger to be able to charge the Aux battery off the main. My understanding is that if you directly hook up the aux battery to the main, then this should charge the aux battery ( with an iscolator for the above mentioned reasons).

I'm not too electrically savvy but am I missing something here? Do you actually need a battery charger atall( except for when external/ Solar power is available)?

Cheers

[Transporter]

If you install 2 batteries in parallel, just connected with the wires and nothing else, you will put quite a load on the alternator, if both batteries would be flat and when you will use your second battery the current will flow from the starting battery and you probably won't start one day. Also, the connecting wires would have to be quite thick at least the same as the battery cables that are in the vehicle now.

The 12V to 12V charger has advantage that you don't have to run the starting cables from your main battery, you only need cables that are for 50A current. I used 150A cable from the battery positive to the 12V to 12V charger under the front bench seat, so I can use the AUX battery in emergency for the start up. The 12to12 charger also allows to charge batteries with different chemistry and it's usually 3 stage charger, much better suited in long term.

[Syncrotek]

Back in the day, aux. battery charging isolators were diodes only, most diodes introduce
a voltage loss to the connection, meaning the battery being charged through the diode(s)
will not rise to sufficient voltage to maintain the correct charge, which will lead to reduced
battery life and low capacity for use. Aux. battery charging isolators of today are more
sophisticated and (mostly) will not have voltage loss. So make sure you don't use the diode
type.
The alternators on the T5 are rated at 120 amps, (may vary on some models) so can cope with
the charging of 2 or 3 batteries without problems,... but... and this is the thing to consider...
when you discharge the aux. battery(ies) by use of accessories, it might be 3/4 discharged
when you start driving home, and due to the action of the alternator's regulator the aux. battery
will take perhaps more than the drive home to recharge, so this is the reason for the 240v
battery charger, when back home switch that charger on until the battery is fully charged,
ready for the next use.
There is a whole lot more that can be considered for auxiliary batteries, i.e. solar and other
charging systems, seperate switching, etc.

[Transporter]

The alternators on the T5 are rated at 120 amps, (may vary on some models)

...140A in 5 cylinder models. I'm not sure of the long term impact on the alternator health if someone would just connect another battery in parallel. It could work with the new batteries but once the batteries would get older, I don't know, I wouldn't do it.

[SnowMotion]

In my research before installing I was advised that unless the batteries are identical in battery capacity issues would develop from the imbalance of the charging through traditional isolation charges. I believe the van batter is 60ah and the Aux is 100ah so this would mean that the Aux battery would not be charged fully. It was also discovered that the Alternator is controlled by the CAN Bus system and the output is variable so the charging capacity is not linear. This is where an independent charger that actually boost the charge it receives works in advantage.
The solar panel is an easy and effective option.

[Kuzzo]

Hi guys, I know this thread is a few years old now, but hoping there are still some watchers? Maybe I should open a new thread?

So, I have an 09 T5 transporter and looking to fit a second battery. I notice that under the passenger seat there seems to be provision (space) where a battery might be fitted. Though unsure if there is electrical provision there.

Was wondering if in fact this space is for a dual battery and if the electricals located under there are prewired for second battery?

My transporter is a workhorse and I have 18V cordless equipment which I charge using Makita 12V charger plugged in to the electrical system. Also have usual other stuff, ie. dash cam, phone chargers etc etc. Trouble is, all these bits and bobs can drain the battery overnight and I get into a vehicle that hasn't enuff power to start the engine. So, thought if I pop an extra battery in that can at least power my Makita charger, it will help me.

Any thoughts/feedback?

Cheers
Stephen

[Transporter]

The 12V to 12V charger works the best and it's the easiest to wire up.

There is 12V with ignition "on" under the seat, that you need to switch your second battery charging, but you need to run 12V positive from the engine bay, placing the fuse in line as close to the battery positive. By using 12/12 charging you don't need a heavy gauge wire to the charger that should be connected as close to the second battery as possible.

I will take the pictures of my set up in the afternoon and poste them here.

[Kuzzo]

Thanks Transporter, really appreciate the advice. Looking forward the the pics put up.

I just ordered a CTek D250S to get me started. I should be able to mount that directly in the cavity under the bench seat where the second battery will go. What size fuse would you suggest I place at the primary battery?

[Transporter]

What size fuse would you suggest I place at the primary battery?

30A fuse should do.

[Transporter]

Ok. Here ismy set up with Projecta 12V charger, 1000W inverter and 75Ah SLA gell battery.





100A Fuse for the inverter +12V. Bolted to the bench seat base from the inside.


Just in case you wander if 75Ah battery has a big enough capacity? You have to consider what you're going to run of the inverter. I was running a laser printer, laptop, sometimes even 25A power supply when updating the software in customer's car, with quite short trips. The battery was always able to fully recharge.
The lengths of your trips are crucial for the second battery proper charging, use too big battery, drive short trips and the battery will always be undercharged and have a shorter life.



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