Dual battery setup for 2.8 1GD

[JohnC80 Junior Member Find all posts View Profile Close JohnC80]

So why doesn't the input fuse of 30amp blow. The input is the line from the start battery (alternator) to the dc.

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

So why doesn't the input fuse of 30amp blow. The input is the line from the start battery (alternator) to the dc.

The blue line shows the current being drawn by the battery when connected to a VSR which is connected to the cranking battery, the initial inrush current is over 60 amps, then it tapers off as the battery charges and draws less current.

The orange graph shows the current being drawn by the battery when connected to a 20A DCDC charger, the battery wants to draw more current but the DCDC charger can only supply 18 amps, it is in current limiting mode, if it tried to supply 60+ amps it would burn out. The fuse on the charger only needs to be rated at 30 amps as the charger can never supply more then 18 amps. The charger will draw somewhere between 22amps and 25 amps with the supply voltage around 13.5V.

[Fred63 Advanced Member Find all posts View Profile Close Fred63]

So why doesn't the input fuse of 30amp blow. The input is the line from the start battery (alternator) to the dc.

How did you go with your install?
BTW i am using a 30 A fuse with a 25 A DCDC have not had a problem and the Battery has been fully discharged a few times in the last 2 years.

[InnerCityBoy Junior Member Find all posts View Profile Close InnerCityBoy]

... here is a comparison of of an alternator charging a Marine pro from 50% soc compared to a DCDC charger, alas might not be an option for the 2.8.

Great to see some hard facts Leigh. When you say it might not be an option for the 2.8, I'm assuming you were testing an alternator with a booster vs. the DC charger, is that right? Any thoughts on how different a 2.8 alternator profile might look, and whether adding voltage drop over a cable run (eg. to a trailer) would impact?

Am I right in thinking that the 'ultimate' charging set-up would have a voltage sensitive relay that passes the alternator directly to the battery when higher than 20 amps (to do the fast bulk-charge stage), then pass through the DC charger when it falls under 20 amps (to do the deep charge / trickle maintenance)?

My plan: I have a wet-cell DBS under the bonnet and an AGM in the camper trailer. I'm going to rely on the alternator to charge my DBS, if a solution comes along in the future to boost the alternator voltage I'll add that. For the camper AGM I'm going to install a DC charger to manage both 12v and solar charging. I'm reading that if I deeply discharge the AGM, direct alternator charging would actually give a faster recharge, but otherwise a DC charger is probably better. I also only have 8B&S wiring in my tug which might struggle to carry all of the available alternator amps anyway :|

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Yes the comparison was done using a boosted Prado alternator versus DCDC charger.

At this time I don't intend to look into a solution for the 2.8L model, I would suggest you look at the green mod for Nissan alternator that some Nissan owners are using for similar alternators that are fitted to the 2.8L.

It depends on how you use your system as to which charging method would be the best in the 2.8, from what I have seen you will need a DCDC charger in the trailer, in car it would depend on the battery and how you use the system.

If your going to deeply discharge the battery and the battery will accept high charge rates and you need to get as much charge in as possible in short driving periods then a VSR setup may replace the bulk charge quicker.

If your only going to discharge your battery to around 70% SOC then I believe a DCDC would be preferable.

A system such as a VSR, with Optima or Lead crystal battery would most likley still charge quicker to around the 80% - 90% than a DCDC charger even in the 2.8, the DCDC charger quicker from then on, the Lead crystal batteries look good but haven't been around long enough to see if they'll live upto the claims being made yet and the location of the battery would need to be considered as they don't appear to like high temperatures.

You can get a Ctek Smartpass setup but it is expensive, it incorporates a VSR and DCDC charger in a fully automatic system but very expensive. The benefits are doubt in my opinion, if you have the charge voltage you don't need the charger part, if you don't then the VSR part is not going to give value for money. A 40A charger would be a better option.

[JohnC80 Junior Member Find all posts View Profile Close JohnC80]

Thanks Leigh appreciate that. So the 2nd battery can draw whatever the alternator can produce. What amps can the 2.8 produce?


Hi Fred63, I have done the install in the camper trailer but not the car. Hopefully get to it in the next wk or so.

[120D4D Avid PP Poster! Find all posts View Profile Close 120D4D]

Another idea might be to use Redarc's 'ultimate dual battery set-up' wiring diagram to have both options available.

Any brand of DC-DC and isolator would work of course...

[ATTACH=CONFIG]22343[/ATTACH]

Leigh - I take it this would allow the bulk charge off the alternator and higher volatage of the DCDC?

.. Am I right in thinking that the 'ultimate' charging set-up would have a voltage sensitive relay that passes the alternator directly to the battery when higher than 20 amps (to do the fast bulk-charge stage), then pass through the DC charger when it falls under 20 amps (to do the deep charge / trickle maintenance)? ..

Hi ICB, I made just that point earlier!

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

The battery can draw whatever it wants up to the reserve capacity of the alternator.

Talking caravans etc:

Look honestly the "Ulimate" setups are a waste of money IMO, if you have sufficient charge
voltage for the VSR to be effective and suitable cabling is installed the DCDC is only going
to charge faster from around the 80% up point in a caravan for example.

If you don't have the voltage to start with then the VSR part isn't going to do much,
basically the best your going to get 50% operation out of both parts, there the Ulimate
in that the seller is making Ultimate profit!

If your alternator is or can be made to put out a suitable charge voltage at the battery then
go the VSR setup, if not then a DCDC charger is the way to go but I would only consider a 40A
or greater if the battery/s can handle it.

In car:

If the volts are there VSR for sure, cheaper will give very good performance, much better
than a 20A charger. A 40A charger should give similar performance to a VSR setup but the
costs will be greater, only comparable if charging one battery and no load connected to battery.

Charger may derate if under bonnet so may need to be located outside the engine bay and if it
doesn't have a remote temperature sensor then you could get issues with charge voltages.

[InnerCityBoy Junior Member Find all posts View Profile Close InnerCityBoy]

Hi ICB, I made just that point earlier!

So you did ... it just took me a little longer to catch up

[InnerCityBoy Junior Member Find all posts View Profile Close InnerCityBoy]

Talking caravans etc:

Thanks as always for your detailed insights Leigh.

Just to annoy with yet one more question ... my AGM (and I think most AGMs) states a 'maximum' charge of 36.4 amps and 14.6v, and a 'regular' charge rate of 13 amps. A DC charger AGM profile will keep the amps and voltage within this range; on the other hand if charging of an alternator direct that is pumping out 50+ amps, does this have the possibility of damaging the battery?

Or maybe I've totally misread the specs ... which is entirely possible: http://www.superstart.com.au/Product...8/Default.aspx

[Hally Senior Member Find all posts View Profile Close Hally]

Isn't it true that the slower your charge a lead acid battery the better for it and the more life you will get from that battery? Not sure on the specs for the optima

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

There used to be a lot of debate about charge currents, the DCDC battery manufactures
used to argue that slower was better, then 40 chargers came along and surprise, surprise
they dropped the argument...

Most AGM's don't mind high charge rates when the battery is discharged, it
is only as the battery reaches a high state of charge that the current becomes
an issue, if you put a 40A charger on a AGM it will aslo pump 40 amps into the
battery, in either a VSR or DCDC charger by the time the battery gets to 80%
SOC the amps will be falling to safe levels.

Dual batteries systems are a compromise, I have never heard anyone say
they are unhappy with their system because the batteries charge to fast!

[Fred63 Advanced Member Find all posts View Profile Close Fred63]

Dual batteries systems are a compromise, I have never heard anyone say
they are unhappy with their system because the batteries charge to fast!

Exactly, they are a compromise.
Workout what you need then decide based on that.
Both Systems will do the job.
Which is better? go back to what and how you will be using the system.

[stevehastings Junior Member Find all posts View Profile Close stevehastings]

I just got installed a redarc bcdc and a optima yellow top ran my fridge well last weekend. Will see how it goes this weekend running fridge's one in camper trailer and one in prado

[brogers Advanced Member Find all posts View Profile Close brogers]

I just got installed a redarc bcdc and a optima yellow top ran my fridge well last weekend. Will see how it goes this weekend running fridge's one in camper trailer and one in prado

Hello steve,

what was the model of the charger you installed, and what was the model of yellow top optima...please