Dual battery setup for 2.8 1GD

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

Thanks Michael, and I have just read it.

Cheers, Tim.

[dBC Member Find all posts View Profile Close dBC]

I had a chance to do some more experiments with the logger. If you're the sort of camper who manages to run the engine each day for at least a short duration, either as you put the boat in, duck to the shops, or just start the engine to give the battery a bit of a tickle while other campers aren't watching, I was curious to see how a charger would compare with a VSR during that initial couple of minutes of charging. Before each experiment I got the camping battery to roughly the same SOC, a little over 60% by rough estimate. One experiment started with the camping battery at 12.23V and the other at 12.24V, each after an hour's rest with a very light load on (just a few tens of mAs).

I simulated a VSR with a set of jumper leads. The good news is I finally captured some semi-decent voltages out of my alternator.... 13.8V for an extended period. The bad news is I lost a good 0.4V across the jumper leads at peak current (34.54A) although that settled down to about 0.2V drop as the current dropped away. A well-installed heavy duty VSR setup can probably do quite a bit better than that, so my simulation is at best rough. I also fat-fingered my initial connecting of the leads, so you'll see it drops to 0A for 1 second as I get a better purchase. The logger was set to take 4 samples per second, and the interruption took exactly 1 second (4 readings).

The first two graphs show the first few minutes of charging with each (don't be deceived by the different scales on each). The third compares the energy pumped into the battery over the first two minutes (I shifted them on the timebase so that they both counted the start of current flowing as 0:00:00).

[dBC Member Find all posts View Profile Close dBC]

For those playing at home, last 7 days cranking battery voltage before being started in the morning:
12.25
12.23
12.30
12.43
12.36
12.32

DC charger disconnected after second day but made no real difference...

If you've ruled out any significant current draw overnight, have you tried putting the battery on a 3-stage charger? If the highest voltage it's ever seen is ~13.8V from the alternator, it might just be in need of a good absorption charge, followed by a good float charge.

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

Hi Michael, for now, can you hold off with charging either battery just yet and please keep monitoring your cranking battery voltage.

To be able to see if there is a real advantage to the way my isolator might work in your Pardo, can you leave your batteries in the state they are in from just driving.

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

Hi Michael, for now, can you hold off with charging either battery just yet and please keep monitoring your cranking battery voltage.

To be able to see if there is a real advantage to the way my isolator might work in your Pardo, can you leave your batteries in the state they are in from just driving.

Will do, I don't have an AC charger handy anyway!

Reference photo Tim:

[LeadWings Member Find all posts View Profile Close LeadWings]

I was working on the car on the weekend so I thought I would post a photo of the second battery spot for the new 2.8 L diesel, as I don't think I have seen one posted yet (?).

I don't know what was there for the old 3L diesels, but as far as I can tell (and others have commented) the factory installed battery tray looks the same design to the starter battery tray.

I couldn't be arsed removing the starting battery, but you can see it is the same spot welded tray, and the 2nd battery spot has the tie-down etc built in.

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

I was working on the car on the weekend so I thought I would post a photo of the second battery spot for the new 2.8 L diesel, as I don't think I have seen one posted yet (?).

I don't know what was there for the old 3L diesels, but as far as I can tell (and others have commented) the factory installed battery tray looks the same design to the starter battery tray.

I couldn't be arsed removing the starting battery, but you can see it is the same spot welded tray, and the 2nd battery spot has the tie-down etc built in.

[ATTACH=CONFIG]24354[/ATTACH][ATTACH=CONFIG]24355[/ATTACH]

This could be a long story...that has been covered many times in the past in various posts...so I'll keep it as short as I can, and hopefully still useful for you and those new to the 2.8 Prado.

In Europe the Prado comes with two start batteries (something to do with cold climate cranking etc). In Australia we have only the one battery standard, and what appears to be an ideal spot for a second battery...but putting a heavier AGM type battery there can be problematic.

I had a 3L Prado (and now have a 2.8 GD Prado) and the difference around the vacant "second battery" location between the two models is that the older 3L prado had an aircon pipe that would have to be moved if you put in a second battery ...(ever so carefully else it could fracture costing lost of money to repair).. whereas the newer Prado has the aircon pipe already located away from contact with a second battery should someone choose to install one ..as you can see in your second image the aircon pipe passes beside and battery tray area...so the location in your second photo is just begging for a second battery to be placed there...and some people have already done so.

However, the issue with the 3L prado with placing a second battery under the bonnet (especially if the battery was anything much larger than a small factory cranking battery) was that some folk ended up with the weight of the battery and movement of the second battery causing the inside of the wheel arch to crack, the call it the inner guard..which proved to be a tricky repair for some. Some people didn't even know they had cracked the guard until it was highlighted on this forum...and the crack would continue to grow.

I think the Prado was designed to handle two smaller "factory" sized start batteries on smooth bitumen roads in Japan, but if you put in an AGM or deep cycle type battery and then use the car off road you run the risk of cracking the inner guard. It looks like they have beefed up the inner guard area somewhat in the new 2.8GD Prado, but I decided not to take the chance of cracking metal with a second battery under the bonnet in my new Prado, and I have placed my large AGM in the rear cargo area...and I promised my mechanic/diesel fitter that I wouldn't put a heavy AGM battery under the bonnet (as he had seen and heard of too many cracked guards.)

...its a shame, as its potentially a useful location under the bonnet begging for a second battery. Some folk have installed a second battery in that area, and if you do, it seems useful to add some strength and support... so some people use a propriety or custom metal battery tray with an additional brace that goes from the battery hold down clamp to the front upper cross member...which stops the battery rocking back and forth and moving about which contributes to the flexing and fracturing of the metal under the battery in the wheel arch area.

...anyway...that's my understanding...there are a few options and a few opinions.

Out of interest, a few of us with 3L prados actually swapped the factory start battery and placed in on the driver side, and placed an AGM or larger deep cycle battery in the spot where the factory battery was...that way you didn't have to move the aircon pipe etc very much...just a CM or so very carfully....and Derek at ABR Sidewinder even produced a second battery wiring harness/kit for that very purpose. I've decided not to move my start battery this time, I've preferred to try and keep things where they belong else mechanics who don't know your car get confused when they work under the bonnet...I have a 33kg Deep cycle AGM battery in the rear cargo area incorporated in a custom drawer system I have made..and it works a treat. Food for thought anyway...and sorry my reply wasn't as short as it should have been.

[dBC Member Find all posts View Profile Close dBC]

Inspired by the lack of huge amps in my earlier jumper lead experiment (posted above) I got to wondering whether I could knock something up (that was safer than jumper leads) in order to take it for a drive and see how the alternator would go at charging the camping battery. A quick rumble in the parts bin got me there with: a 40A in-line blade fuse, 1m of 6mm cable, a 70A relay and a switch for controlling the relay. Not exactly suitable for high charging currents, but given the biggest I saw with the jumper leads was 35A it was worth a shot. Unsurprisingly, I've introduced a bigger voltage drop than with the jumper leads... almost 0.3V at 15A, but otherwise the pattern was very similar as with the jumper leads: an initial in-rush of about 35A dropping down to about 15A in less than a minute. What was unknown with the earlier jumper lead experiment is what happens after two minutes, because that was as long as I was prepared to stand there holding unfused jumper leads. With the new set-up and the need to head down south, I was all set to log how well the alternator could do at charging the camping battery.

I'd previously captured a similar charge cycle but with the DC/DC charger, which I've included below for comparison. In both cases the camping battery started the charge cycle from as similar state as I could manage. One was reading 12.22V and the other 12.21V, each after an hour's rest with about 20mA being drawn during the hour. The graphs pretty much speak for themselves. The current into the camping battery during the alternator charge continues to decay away. You can see that the voltage drop (the gap between the pink line and the blue line - caused by my inadequate wiring) reduces as the current drops away. There's no doubt that a properly installed heavy duty VSR will come close to eliminating that drop, but the best you could hope for is that the pink line would sit on top of the blue line giving you an extra 0.3V, which will bring the current up a bit, but nowhere near the 24A being supplied by the charger during that time - as indicated by the pink voltage line in the DC/DC charger plot - it pretty much instantly gets well into the 14Vs in order to maintain the 24A, something you'll never see out of a 2.8L alternator/regulator (unless someone's come up with a tweak?).

The final graph compares the AHs pumped into the battery under each charging method. While it doesn't look too alarming displayed like that, rotate it 90 degrees and you get a feel for how much better the charger is. For example it takes the alternator twice as long to pump in 10AH (1h5m Vs 27m). Both approaches were still adding charge as I arrived at each of my destinations and shut down. It's tempting to equate that decaying current as a sign the battery is getting full, and that's generally true when the voltage is high enough but in this case the battery is a long way from full. The decaying current is really indicating you don't have enough voltage to charge the battery quickly (not helped by the voltage drop in my wiring, but primarily due to the alternator voltage setting).

I'm not sure how big a discharge I'd need to do before the alternator's big-amp advantage kicked in for an extended period, but deeper than I'm prepared to go for the purposes of experimentation, and deeper than I ever go when camping. The car pretty much gets used every day when I'm camping, and I think this test shows I'd need to use it quite a bit longer if I were trying to replenish the battery from the alternator. At any rate, my 6mm experiment wiring wouldn't be up to the job so I suspect this is about as much comparison as I can contribute. A fairly simple test for anyone with a VSR setup in a 2.8L would be to put a clamp ammeter around the feed to the camping battery after you've started up. Unless you've got a very depleted battery, or you've found a way to tweak more volts out of the alternator, I think you'll be lucky to see more than about 15A going in, except maybe for the first minute.

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

Well only two days into testing the new Traxide SC80 set-up and I've seen 12.60V this morning!

Just prior to the change I was seeing between 12.35 - 12.40 in the morning so the early signs are good. - This is my daily drive so driving patterns are the same.

I will continue to run this set-up and report back regularly with what the SC80 is doing, I'll start watching the Aux next week also.

[robby4675 Lurker Find all posts View Profile Close robby4675]

Hey guys,

First time poster so please go easy. I am racking my brain trying to work out which dual battery system I want to put in my 2015 2.8 1GD prado.
I've been looking at the Redarc BCDC1220. I wan't to be able to be self sufficient for four nights, running 2 engels, lights, etc. The plan is for a big trip from Perth to Broome with a four night stay in Karijini. I know I probably need to incorporate a solar panel. Will be more than likely towing a camper trailer so getting the Prado fitted out in the next few months.

Any recommendations would be really appreciated.

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

If your looking at four nights without solar then your going to need a lot of battery capacity. If you allow around 2Ah draw for one of the engels running as a fridge and 4Ah for one as a freezer that's 144Ah per 24 hour period!

You don't say when your travelling, Broome and Karijini (absolutely marvelous place) can get very hot, so power consumption may be higher.

I would suggest your going to need at 300Ah of batteries and around 300W of solar to keep things going allowing for slightly overcast etc.

There is a generator area at Karijini but some of the generators can be rather noisy I would personally try to avoid that if possible.

[Bobcrusader Member Find all posts View Profile Close Bobcrusader]

Robby - some camper trailers have 1 or 2 batteries, so the trailer might determine how much you need to do to the Prado. The BCDC 1220 (Ignition Control version) is a good option and can pair with a regulated solar panel (or 1225 with unregulated panel).

[404pug Avid PP Poster! Find all posts View Profile Close 404pug]

I have a Marine Pro 720 installed on the rhs of my 2.8. I was just away for 8 days, staying 2 nights in each and not running the car in between. I have super heavy [2awg?] cables to and from the starting battery. It is controlled by a VSR. After the car has run for a while it appears to settle into a charge rate of about 12.5 -12.6 volts. This appeared to keep both the 2nd battery in the car and the deep cycle AGM in the trailer charged. The 2nd battery in the car runs the 40 l Engel fridge and the camper battery just a few lights. I have a 20 amp DCDC charger sitting in the shed and carried it with me in case I needed to change one of the set ups but didn't need to do so. it may take a longer trip to see if there are issues. Thoughts?

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

I have a Marine Pro 720 installed on the rhs of my 2.8. I was just away for 8 days, staying 2 nights in each and not running the car in between. I have super heavy [2awg?] cables to and from the starting battery. It is controlled by a VSR. After the car has run for a while it appears to settle into a charge rate of about 12.5 -12.6 volts. This appeared to keep both the 2nd battery in the car and the deep cycle AGM in the trailer charged. The 2nd battery in the car runs the 40 l Engel fridge and the camper battery just a few lights. I have a 20 amp DCDC charger sitting in the shed and carried it with me in case I needed to change one of the set ups but didn't need to do so. it may take a longer trip to see if there are issues. Thoughts?

Do you mean charging at 13.5 - 13.6v?

I'm in the middle of testing Drivesafe's Isolator and started recording my thoughts to post up which I should get to tomorrow hopefully.

robby4675 I've found a VSR/Isolator does work on the 1GD and would certainly take this path if setting up a dual battery again from scratch with my Optima. Suggest you consider Traxide's new SC80 isolator for its flexibility - shoot Drivesafe a PM if you want to know more about it.

[robby4675 Lurker Find all posts View Profile Close robby4675]

Thanks guys i'll look into the Traxide. Is the factory battery a throw away item?