Dual battery setup for 2.8 1GD

[drivesafe]

C'mon guys, make love not war!

An interesting idea DBC but perhaps open to too many variables?

As you've dropped me in this I guess I would fit the bill, having a 2.8L and an Optima aux battery and a DC/DC device - I dont have an isolator or couple metres of 6B&S on lugs but I'd be happy to run your test if anyone cares to lend the VSR and cable.

I guess I already know the result and must admit I dont want to go for a multi-hour drive to run the test!

Suggest with a simple isolator we would find the Optima pulls lots of Amps and takes on the bulk of charge very quickly then slows off thereafter. Nothing that hasnt already been pointed out by drivesafe and LeighW in the past...

That said I would be geniunely interested in the result - if the test can be arrange in such a way that I can run it around town on short-ish trips as this is my daily drive.
Suggest this would favour the isolator option somewhat though.

Hi Michael, I might just take you up on that offer, but in the meantime, try measuring your CRANKING battery voltage in the morning, before you start your motor.

NOTE, the table I posted up is idea for this sort of testing, as the cranking battery in almost every modern vehicle will have a constant load on it, all be it a VERY small load, but it makes the voltages compered to the table, pretty accurate.

[dBC]

I didn’t forget, as I already have people testing my gear in new Toyotas, and they are seeing different voltage readings to yours.

What is your gear, and what voltages are they seeing? Mine starts high-ish (13.6V) and after about 20 mins or so drops down to about 13.3V.

So which OPEN CIRCUIT voltage chart do you recommend people use?

The one for their battery, from the manufacturer. But remember, I'm only talking about using it for a one-shot experiment by some willing volunteer with a recent install. Then we'll know for sure if the alternator voltage is adequate for getting that battery type to 100% charge.

[drivesafe]

I didn’t forget, as I already have people testing my gear in new Toyotas, and they are seeing different voltage readings to yours.

Once again, the table I posted up is generic, in that all 12v lead acid batteries behave the in a similar manor once a load of the size I suggested, is connected to the battery being tested.

The same is NOT the case when carrying out a OPEN CIRCUIT voltage test on a 12v lead acid battery.

You have to have a copy of that battery’s specific OPEN CIRCUIT chart or you will get incorrect info, and the differences are quite large.

For instance, most AGM have a fully charge OPEN CIRCUIT voltage of 12.8 to 12.9v, while Optima Yellowtops have a fully charged OPEN CIRCUIT voltage reading of 13.1v, and many wet cell batteries will have readings between 12.7 to 12.75v.

So which OPEN CIRCUIT voltage chart do you recommend people use?

Once again, in RV situations, using OPEN CIRCUIT readings are a waste of time.

[120D4D]

Well, here's a simple test for someone with a 2.8L Prado, a VSR and an Optima battery:

. partially discharge your camping battery
. go for a nice long drive
. the instant you stop, rush to the engine compartment and isolate the camping battery
. leave it that way for at least 24 hours
. report the voltage at the battery terminals
. if it's reading 13.1V we know it's fully charged

This guy: http://www.pradopoint.com/showthread...l=1#post556058 claims that's what he sees when he tries that experiment with his DC/DC charger. If the VSR connected to a 2.8L Prado alternator can do the same then we're done here.

C'mon guys, make love not war!

An interesting idea DBC but perhaps open to too many variables?

As you've dropped me in this I guess I would fit the bill, having a 2.8L and an Optima aux battery and a DC/DC device - I dont have an isolator or couple metres of 6B&S on lugs but I'd be happy to run your test if anyone cares to lend the VSR and cable.

I guess I already know the result and must admit I dont want to go for a multi-hour drive to run the test!

Suggest with a simple isolator we would find the Optima pulls lots of Amps and takes on the bulk of charge very quickly then slows off thereafter. Nothing that hasnt already been pointed out by drivesafe and LeighW in the past...

That said I would be geniunely interested in the result - if the test can be arrange in such a way that I can run it around town on short-ish trips as this is my daily drive.
Suggest this would favour the isolator option somewhat though.

[dBC]

So what you are suggesting is that everybody should disconnect their batteries and leave them for 24 hours and then do an OPEN CIRCUIT voltage test.

Not at all, I'm suggesting someone do that experiment just once, with a new battery. Then we'll know for sure whether a 2.8L Prado can fully charge such a battery. Oh, and you forgot to answer this part:

So where do you suggest a 2.8L driver gets 13.65V?

[drivesafe]

So what you are suggesting is that everybody should disconnect their batteries and leave them for 24 hours and then do an OPEN CIRCUIT voltage test.

I can see how helpful that sort of testing is while you are off on a trip.

As I posted, OPEN CIRCUIT voltage testing is useless in RV situations and the table I posted up is both relevant and still in use today.

And before you make comments like “Technology moves on, so should you” you might actually try learning about the technology you quite obviously haven’t got a clue about.

Instead of telling everybody they have to waste 24 hours just to get an idea of their battery’s SoC, they could simply use the table I posted up or the many hundreds of similar tables, and with just a small load of about 5% of the battery’s capacity, connected to the battery, and they could get a accurate indication of the battery’s SoC in a couple of minutes.

Furthermore, OPEN CIRCUIT voltage readings are only accurate if you know, in advance of taking the measurement, that the battery is OK.

Common occurrence when taking OPEN CIRCUIT voltage readings to get an indication that the battery is fully charged, yet it will go flat with in minutes of applying even a small load to the battery.

Whereas, when using my table, if the battery is stuffed, the voltage reading will be falling as you are taking the measurement, so again, no need to waste 24 hours when you are getting an almost instantaneous indication that the battery is stuffed.

Again, before you comment about some else’s knowledge , might pay you to get yourself up to date!

[dBC]

Geeze, steady petal... what's got up your nose? As I said above, I consider myself entirely neutral.... each have their benefits and disadvantages. I've always used VSRs when the alternator voltage permits.

The “FANCY” table, that you are trying to ridicule, is a simplified version of a table that has been provided in technical documents by battery manufacturers and other providers, for at least the last 30 to 40 years and is used to measure a battery’s SoC,

Technology moves on, so should you.

while the battery is in use, LIKE WHEN IT’S IN A MOTOR VEHILCE.
The fact that you used the OPEN CIRCUIT voltage as a charge reference clearly demonstrates that you have no genuine experience in this field.

Well, here's a simple test for someone with a 2.8L Prado, a VSR and an Optima battery:

. partially discharge your camping battery
. go for a nice long drive
. the instant you stop, rush to the engine compartment and isolate the camping battery
. leave it that way for at least 24 hours
. report the voltage at the battery terminals
. if it's reading 13.1V we know it's fully charged

This guy: http://www.pradopoint.com/showthread...l=1#post556058 claims that's what he sees when he tries that experiment with his DC/DC charger. If the VSR connected to a 2.8L Prado alternator can do the same then we're done here.

neglected to mention that the same battery manufacturer specifically states that you can fully charge their batteries with a voltage of 13.65v.

So where do you suggest a 2.8L driver gets 13.65V? I rarely see that voltage when the engine is running, and that's with dedicated wires running from the cranking battery to a voltmeter that draws about 7.5mA so there is pretty much zero voltage drop down that wire. And also confirmed with a precision recently calibrated voltmeter on the battery terminals. You can see here: http://www.pradopoint.com/showthread...l=1#post554331 that the 13.4V displayed in my icon to the left is at best 13.5V.

[drivesafe]

You'll need to decide for yourself whether you believe that fancy colour graphic in the middle of that page, or the battery manufacturer's data quoted on the page after.

Hi dBC it is obvious, from your statements, that you have very little experience in this field.

The “FANCY” table, that you are trying to ridicule, is a simplified version of a table that has been provided in technical documents by battery manufacturers and other providers, for at least the last 30 to 40 years and is used to measure a battery’s SoC, while the battery is in use, LIKE WHEN IT’S IN A MOTOR VEHILCE.

The fact that you used the OPEN CIRCUIT voltage as a charge reference clearly demonstrates that you have no genuine experience in this field.

But whats worse is that while you were using to wrong voltage reference from Optima’s web site to back your claims, you at the same time, very conveniently neglected to mention that the same battery manufacturer specifically states that you can fully charge their batteries with a voltage of 13.65v.

OOPS, you couldn’t post that info up as it would completely destroy your claim that you needed a higher voltage than the alternator can produce, to fully charge a battery.

[drivesafe]

And the big 4WD companies and auto elecs wouldn't be telling you that because they make more money out of the Dc/Dc charger, would they?

And also that most of them do not know the first thing about Dual Battery Systems and they are easily sucked in by the grossly exaggerated advertising hype.

[dBC]

Well, people appear to have done both and report success so you probably won't go too far wrong either way. The debate comes down to how quickly the 2.8L alternator will charge your battery Vs a DC/DC charger and that's pretty hard to quantify. It also depends on the type of battery, and how deep a discharge cycle it typically sees.

I consider myself fairly neutral on the technology. I've run VSRs in cars with a descent alternator output voltage (Disco-II and a V6 120 series Prado) and I switched to a DC/DC charger for the 2.8L because of the low alternator voltage.... 13.4-13.6V is what I usually see out of the alternator. If you do deep discharges, and you need to do a partial recharge quickly, then VSRs are probably the way to go. If you do fairly shallow discharges and you're more interested in getting the battery back up to 100% in a timely manner, then DC/DC chargers are the way to go. Some report never seeing their camping battery fully charged with just an alternator (http://www.pradopoint.com/showthread...y-Guide/page42). You'll need to decide for yourself whether you believe that fancy colour graphic in the middle of that page, or the battery manufacturer's data quoted on the page after.

[Kalgoorlieprado]

I don't think there's agreement on that, especially with the 2.8L engine and it's fairly low voltage alternator setting (and no diode solution to boost it), and it's difficult to do a direct comparison in order to get actual data.

Hmmm Im at a loss!

[REN470]

And the big 4WD companies and auto elecs wouldn't be telling you that because they make more money out of the Dc/Dc charger, would they?

[AussieAndy]

All the big 4wd companies and most auto electricians (at least around my area) recommend the use of some sort of DC/DC charger, so can they really be wrong. Both ways will get the job done, just one costs more, is better for your battery and is recommended by many.

[dBC]

I don't think there's agreement on that, especially with the 2.8L engine and it's fairly low voltage alternator setting (and no diode solution to boost it), and it's difficult to do a direct comparison in order to get actual data.

[Kalgoorlieprado]

So.. After reading all of this im still confused.. Which is the best option for a dual battery set up?!

Just want it mainly to run a Engel in the rear when Im doing weekenders, and some LED lighting..