Dual battery setup for 2.8 1GD

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

Excellent, thanks LeighW


...but I guess the very reason why we have this thread, is because we can't use a voltage booster diode in the 2.8 GD prado...so, if the graph compared the output of the 2.8GD alternator would it be much different to the graphs you supplied?

For or me, I guess if you don't want the aux battery under the bonnet, the realistic option is a DCDC charger...?

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

I am thinking of a dcdc charger...because I can do a longer run of suitable capacity red and black cable, to a dcdc charger...but I would like to have a dcdc charger that also has a solar input option as well for my panels.....

If you get the 40amp dcdc it is solar ready
Also take into account how you use your aux if under heavy use the 20amp may be to slow to charge to full again

[Guest Close Guest]

LeighW,
Can you explain further what happens at the 10:35 mark when both lines converge and are closely following each other. What is the SOC of the battery at that point from the 2 charging methods?

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

LeighW,
Can you explain further what happens at the 10:35 mark when both lines converge and are closely following each other. What is the SOC of the battery at that point from the 2 charging methods?

Yes please and then same at 11.28 they both seam to dip down to min amps?

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

Thanks. This helps a lot.

A basic dual battery setup consists of an isolator and an auxillary battery, the aux generally supplies power to the accessories, the isolator disconnects the auxillary battery from the cranking battery when the motor is not running to prevent the accessories flattening the cranking battery.

A VSR type isolator can be used if the alternator can provide a reasonable charge rate to recharge the aux in acceptable time frame, if your alternator is putting out a reasonable charge voltage and adequate cabling is provided a VSR setup will charge much faster than a 20A DCDC charger providing the battery will accept the charge.

A DCDC charger which also acts as an isolator comes into its own when a suitable charge voltage is not available from the alternator.

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

Hi Puddock, and with a bit more time given to this thread, this thread will most likely resolve yours and ICBs quires.

Yes indeed. We non electrical types are lucky and thankful to have access to people who know what they are talking about when it comes to this stuff. I am going to wait to see what eventuates re the 2.8 alternator before deciding what to buy.

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

The DCDC charger can only charge the aux, the alternator will put more back
in to the aux than a DCDC charger would with a quick drive, it will take a 20A charger
two hours to replace about 18 amp hours into the battery.

That is only 45% efficient.

Is that because the 20 Amp charger is not supplying about 20 Amps or is there a lot of heat somewhere?

Just a bit confused??

S.

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

Sorry off day, it will replace with 18Ah in an hour.

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

LeighW,
Can you explain further what happens at the 10:35 mark when both lines converge and are closely following each other. What is the SOC of the battery at that point from the 2 charging methods?

Sorry guys, I plotted the DCDC charger over the alternator data and makes it confusing as
it gives the impression that both fully charged the battery in the same time frame and of course
this is not the case.

I'll expand the data for the DCDC charger later and post up the graph.

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

Sorry guys, I plotted the DCDC charger over the alternator data and makes it confusing as
it gives the impression that both fully charged the battery in the same time frame and of course
this is not the case.

I'll expand the data for the DCDC charger later and post up the graph.

Perhaps add a voltage trace for both.

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

I have updated the graph above so that the data plotted is over the same time frame, sorry it is sideways but that the system insists on showing it that way

Points of interest, at 10:38 or thereabouts the alternator had replaced approximately 30Ah and the battery was around the 80% SOC, the DC charger 18.5Ah and around 68.5% SOC.

At around 11:00 the alternator had replace approximatley 40 Ah ie the battery was around the 90% the DCDC charger was around the 30Ah and 80% SOC.

At 11:30 the alternator current was around 2 - 3 amps, for all practical purposes the battery fully charged, the charge current for the DCDC charger was still around 15A,
it would take about another 30 minutes for the DCDC to finish charging the battery.

Voltage plot of aux being charged by alternator, unfortunately there were drops outs in the wireless monitor and as was more interested in the amp side I wasn't worried about the drop outs. Didn't plot the DCDC charge for the same reason, it would be similar to the aux being charged by the alternator just over a longer period till around 80% SOC then steady at 14.4V

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

Excellent, thanks LeighW


...but I guess the very reason why we have this thread, is because we can't use a voltage booster diode in the 2.8 GD prado...so, if the graph compared the output of the 2.8GD alternator would it be much different to the graphs you supplied?

For or me, I guess if you don't want the aux battery under the bonnet, the realistic option is a DCDC charger...?

The charge rate would slow down more quickly as the battery charges.

[Guest Close Guest]

Just a reminder people.. We all know anything to do with Dual batteries has a long history of turning argumentative and bombing off topic quickly.. So lets all play nice and remember the title.. Overall there is some excellent information posted, and good debate, but keep it civil.

You are all welcome to start a new thread if you wish to go off topic, as you are also welcome to use the little report post button for any posts you feel are 1: Argumentative / 2: Trolling / 3: Off topic. It will then be looked at at a moderator level.

Thanks all.

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

Hi LeighW, just a question regarding your graph.

By my uneducated guess it looks like the alternator starts around 50amp. Most 20 amp dc chargers have an input fuse of 30amp. Why doesn't this fuse blow if the alternator is putting 50amp to the 2nd battery?

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

Hi John, an alternator connected directly to the battery ( via a VSR type isolator ) can provide what ever current the battery can draw, up to the available output current limit of the alternator, which can be 100+ amps in some cases.

Whereas DC/DC devices are current limited by their very nature and as such, can only supply what the DC/DC device is rated at.

So a 20 amp DC/DC device can only supply 20 amps to the battery, no matter how many amps are available from the alternator.

This is the very reason an alternator, in the vast majority of dual battery setups, can charge a battery quicker than a DC/DC device can, and the deep the discharged state of the battery when you start your drive, the quicker an alternator will charge the battery over what a DC/DC device can do.

there is a lot more to it but this is the basics.

BTW, the reason for the 30 amp fuse on a 20 amp DC/DC device is because they are very inefficient at what they do and actually need to draw far more than 20 amps from an alternator, to supply the battery with just 20 amps.