Dual battery setup for 2.8 1GD

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

But hey maybe its time to bring out the popcorn again as I'm an auto electrician and there is no way that an alternator can charge a battery to the same level as a dc can!!

Been covered many times but maybe you have a new theory so I'll bite, please provide your data to show exactly why the alternator can't charge to the same level as a DCDC charger can?

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

I'm an auto electrician and there is no way that an alternator can charge a battery to the same level as a dc can!!

Hi again John, and the reason I replied to your post is that, as stated above, you made it quite clear you were not interested in contributing to the thread.

As far as your claim that an alternator can not charge a battery to the same level as a DC/DC device can.

How did you arrive at that “advertising hype”

Would you like to explain, for InnerCityBoy’s benefit why an alternator can not charge a battery to the same level as a DC/DC device can.

If a battery is fully charged, it is fully charged, no matter how you do it, so I’d love to here your explanation as well.

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

So there you go, you now want to have another 4 or so pages of banter regarding what is better. As LeighW has said it has already been covered hence the reason why I stated that I was not interested in the banter. I have read this whole thread hence the popcorn and auto electrician comment. And yes if a battery is fully charged it doesn't matter how it was charged but clearly some have an issue with different set ups. I still believe that this is a thread for a 2.8 battery set up as you failed to point in the right direction. As I said earlier if admin wants I can start a new thread.

We have now had about 4 posts totally irrelevant to a 2.8 battery set up.

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

Back on topic.

Like so many other Prado owners have already done, I plan to have a dual battery system installed.

The vehicle is a new 150 GXL with the 2.8 GD engine.

I know what I want, i;e. a second battery in the engine bay, a 12v outlet in the back to run a Waeco CFX and an external Anderson plug to feed a caravan fridge while on the move.

Happy to pay a professional to install what ever is required

I understand there is still some debate in relation to the operation of the alternator in the new 2.8 GD but despite having read lots of posts on this topic I have failed to grasp a real understanding of what parts, e.g. Isolator - DC charger, monitor, flux capacitor, etc. are actually needed and why.

Answers on a postcard please. : - )

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

I still believe that this is a thread for a 2.8 battery set up as you failed to point in the right direction.

Hi again John, and as both Leigh and myself have now asked you to elaborate on your claim, but going on your last post, you either have no idea and/or still have no intentions of helping ICB, or anyone else, trying to sort out what to do.

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

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.

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

I understand there is still some debate in relation to the operation of the alternator in the new 2.8 GD but despite having read lots of posts on this topic I have failed to grasp a real understanding of what parts, e.g. Isolator - DC charger, monitor, flux capacitor, etc. are actually needed and why.

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

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

As a matter of interest I have been meaning to do this for a while, 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.

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

Hi again John, and as both Leigh and myself have now asked you to elaborate on your claim, but going on your last post, you either have no idea and/or still have no intentions of helping ICB, or anyone else, trying to sort out what to do.

Mate all you seriously want to do is discuss how a dc is no good. That is not helping anyone. In a previous page when someone talked about a dc you claimed that they must be auto electrician. That is why I put that statement in mate. Move on champ. I am the one asking questions about a 2.8 battery set up. You are only wishing to discuss dc vs what you promote. I have a dc. Will it work. Not sure but that is what I have and you my friend will not change my mind.

If you cant help me or others who have posted, don't waste your time in replying.

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

Thanks for that graph Leigh.

For many years now, I have been asking why, if these wonder devices are so good, that none of the sellers of these wonder devices supply graphs to show how these wonder devices work when compared to how an alternator charges.

NOW EVERYONE CAN SEE WHY THEY DON’T SUPPLY COMPARISON GRAPHS.

As that graph clearly shows, an alternator will do a much better job.

[Mild7 Junior Member Find all posts View Profile Close Mild7]

Fascinating. So..

I fixed the problem of my SBi12 not closing.. It was a bad connector on the brown wire. A wire installed by Redarc at the factory. Redarc wanted me to pay for an Autoelec to diagnose this.

Funny, everyone gives Redarc such high praise for their after sales service. I on the other hand found it to be rude, condescending and ultimately my question of where to send the unit to them (at my expense) for diagnosis was flat out ignored. Thanks redarc. If my small family owned business ignored customer enquiries, we wouldn't be in business very long at all.

Another question, if anyone can or will assist: Will a 20A de-de charger do a better job than an alternator supplying 13.6v - 13.9v to both starter and aux at the same time?? Say if the Aux was depleated after a few days at camp, and I wanted to charge the aux with a quick drive? Or doesn't it work that way?

Mike.

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

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.

Yes Redarc support is usually very good if you accept what they say happily, if you start asking to many questions or indicate their product is faulty their mode can change quickly.

[Mild7 Junior Member Find all posts View Profile Close Mild7]

Thank you Leigh.

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

Thanks for the graph LeighW....and l'm trying to understand exactly what it means.

so...This is what I think, but please correct me or explain further.

you have a Marine pro deep cycle battery at 50% state of charge.

the top line in the graph is the charging current being supplied to the battery which for about the first hour, the alternator charging current drops from just over 50 amps down to about 20 amps.

the lower line is the charge current from a dc dc charger, (not connected at the same time as the alternator) I'm guessing it's connected to the same marine pro deep cycle battery at 50% state of charge.


the dcdc charger puts out 20 amps constant over the first hour. I'm guessing the dcdc charger simply can't put out the same current as an alternator.

hence, over the first hour, provided the alternator is connected to the marine pro battery with sufficient capacity cable, it will put a lot more charge into the battery compared to the dcdc charger.

what I'm not sure about then, is what effect the charge voltage has....ie if the alternator is controlled by the ECU or whatever, then the alternator voltage is restricted, but the dcdc charger can charge at a higher voltage than the alternator in the new prado...so....whilst the alternator can charge at much higher currents in the initial phase, surely the dcdc charger charges with a higher voltage? But does that make any difference?

i'm not arguing, or trying to contradict anyone, please don't think that, I am just trying to add to the banter and increase my knowledge....because I also am on the verge of installing an auxiliary battery in a new 2.8 GD prado...and I just want something that is easy, dimple, works, and suits my particular setup.

i am leaning towards avoiding having an aux battery under the bonnet..I have seen and experienced guard cracking from an aux battery under the bonnet...so that leaves me with an aux battery in the rear (which will be set up permanently for touring), ..and if that's the case 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.....but I'm still thinking, still reading, still asking questions....and still very interested in this thread....thanks for the info...and I look forward to more explanation, discussion and options...

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

The top graph shows the Marine Pro being charged via the alternator with booster diode fitted via a VSR and 10mm2 cabling, if 6B&S cabling was installed the charging rate would have been higher.

A DCDC charger does not charge at 14.4V all the time, it has to limit its output current to 20 amps in the case of a 20 amp charger to protect itself from overloading. The charge voltage might be for instance 12.5V at the start of charging and this will rise to a maximum of around 14.4V@24C as the batteries SOC rises. When the battery termianl voltage gets to 14.4V the charger will revert to constant voltage charging.

You can see where the charger reaches 14.4V in the graph where the current starts to drop.

Batteries don't need high charge voltages to accept high charge currents, if the battery is low then high charge votages are not required you can see on the graph where the DCDC charger reached 14.4V and the curretn started falling it is only from around the 70% - 80% SOC point that the higher voltage becomes benifical, charging at 14V or 14.4V will fully charge the battery it will just take longer at the lower voltage.