Second battery.

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

Hi amts, and you are correct in that DC/DC devices charge at a lower current than an alternator can, but they also charge at a MUCH lower voltage than an alternator can.

Because of all the glossy but deliberately misleading advertising surrounding DC/DC devices, most people think because the adverts say a DC/DC device charges at a higher voltage, that this is the case for the whole charge cycle.

The reality is that this misunderstanding could not be further from the facts.

DC/DC devices ( and battery chargers ) are only able to charge a given battery at their highest voltage level when the battery is near fully charged, say from around 80% SoC or higher. And this depends on the size of the battery and the current rating of the charging device.

When charging a low battery, for the major part of the charge cycle, both DC/DC devices and battery chargers ( solar regulators ), charge at a much lower voltage than what the average LOW VOLTAGE operating alternator will charge at.

This is something that is very simple to demonstrate, even if you do not have a DC/DC device.

DC/DC devices are just battery chargers with an inverting input stage, but otherwise their output acts similar to that of a battery charger.

To this end, if you have a battery charger, next time you have a battery in a low state of charge and you are going to use the charger to charge it, first measure the voltage at the battery’s terminals before you connect the charger.

Then with the charger connected and turned on, measure the voltage at the battery’s terminals when the charger indicates it is in the BULK mode.

You need to make sure the charger is in BULK mode because some battery chargers analyse the battery’s SoC before they actually state charging the battery.

While a charger is analysing the battery, the terminal voltage will most likely be no higher than your first voltage measurement.

Once the battery charger is in BULK mode you can see voltages as little as half a volt higher than the battery’s original low voltage level.

As the battery charges, the terminal voltage will rise and eventually, the terminal voltage will reach the battery charger’s selected maximum charging voltage. This will only occur in the final stage of the charge cycle.

NOTE, this is a total contradiction of what most people think happens and what the DC/DC device sellers don’t want you to know.

It just does not look so good for their products when you know exactly how they REALLY work.

[dBC Member Find all posts View Profile Close dBC]

I believe the issue is the low charging voltage of the 150 series Prado. The solution is either to boost the charging voltage by either installing an AOC or DC/DC charger.

Spare a thought for those of us with a 2.8L 150 series where only one of those two options is available; there is no diode booster solution for us. In addition, I don't even see your initial 20 minutes of higher voltage. Here's a pic of my 25A DC/DC and alternator doing their stuff at first start-up after an overnight camp. The cranking battery (Blue trace) is pretty much fully charged at a resting voltage of 12.6V. The camping battery (Pink trace) is at about 50% SOC... a resting voltage of just under 12.1V with 0 amps (Yellow trace) being drawn.

8:02:30: fridge comes on, camping current (Yellow) drops to about -5A, camping voltage (Pink) drops to 11.8V
8:06:45: engine cranks, cranking voltage (Blue) drops to 11,7V, jumps to 13.6V and settles at 13.5V courtesy of the alternator
8:07:00 DC/DC charger starts jamming 24A (Yellow) into the camping battery
8:07:15 DC/DC voltage (Pink) exceeds alternator voltage (Blue) 13.8V Vs 13.5V

At this bulk stage, the DC/DC's sole mission is to jam 25A into the camping battery, and it will generate whatever voltage (up to a pre-set ~15V) is required to do that. Just 15 seconds into charging a 50% SOC camping battery, it needed a higher voltage than the alternator had on offer to achieve that. If I switched it across to charge from the alternator at that stage, less than 25A would have been going into the camping battery. The alternator's big-amp advantage would have been all over in 15 seconds!

After about 15 minutes (not shown), the DC/DC voltage passed 14V and kept climbing... whatever it takes to keep pumping in 25A (25A nominal... 24A measured). Had I been charging with the alternator, it would have been putting in much lower currents, thanks to the piddly alternator voltage.

It's extremely rare that I see 13.85V out of my alternator. I suspect if had an Optima+VSR solution in my rig, it may well charge it but I'd expect a very short life time out of the battery, just as you found Jimmy with your 3L prior to your AOC purchase... possibly worse given the alternator voltages I see.

[Guest Close Guest]

Hi amts, and you are correct in that DC/DC devices charge at a lower current than an alternator can, but they also charge at a MUCH lower voltage than an alternator can.

Thanks for clarifying. I recall now that when I first used my 240VAC charger, I put a meter on it and it wasn't charging at 14.4V as advertised. I asked the retailer and was told that was normal behaviour. Eventually, the charge voltage did go up to 14.4V.

[GEEEXL Member Find all posts View Profile Close GEEEXL]

good forum but peeps using it as a primary source of income are fatiguing

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

Hi Jimmy and sorry mate, you are misinterpreting what you are reading.

The people at Optima are trying to tell you your problem is not whether the voltage goes over 13.85v, but the fact that you are not driving long enough to recharge the battery even if the voltage is above 13.85v.

As I have already posted, and Optima’s E-mail confirms what I have been trying to tell you, your issue is not caused by the battery or your alternator, it is solely caused by your driving habits.

Now to your supposed solutions, of which, neither will resolve your issue.

Even if you raised the voltage to 14.7v, because of YOUR SHORT DRIVE TIMES, you are still going to have an undercharged battery at the end of your drive.

.

I am interested to know why you think my email to Optima talked about driving times as I simply asked them
"I have a question regarding the d34M bluetop. In regards to the charging voltage it states that for an alternator charge it is recommended to be at voltages between 13.65 and 15v. If the charging voltage is below 13.65 will the battery still charge effectively? If it does still charge it at the lower voltage will it reduce its lifespan?"

And their exact reply was "lower than 13.65 is not ideal. it will reduce its life span."

So as you have said, and I agree that short driving times is not an ideal scenario for battery longevity, wouldn't a short drive at above 13.65 be better for the battery than a short drive below 13.65 given the information provided by the people who make the battery?

I do however stand corrected on my previous points, misread 13.65 as 13.85.

Anyway there is no use going on with this. Drivesafe has his opinion and I have mine and it's up to the other readers of this to read the points we have made and come to their own conclusion.
Agree to disagree?

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

Jimmy you still don’t understand what is being presented to you by both myself and the E-mail from Optima, and you do not know battery terminology.

From your post about what Optima E-mailed, where they stated if your battery is NEVER charged with a voltage at or above 13.85, then their battery will be damaged.

In your own posts your have specifically stated that the during the drive home, your alternator voltage was above 13.85v.

And as the battery is going to be continually charged each time you drive while at home. You stated that your battery was only “STORED” overnight!

As such and based on your post that your alternator went over 13.85v on the way home, then it is likely to go to those voltages each time you start your motor, and this means your Optima is regularly get charged at or above 13.85v and that means it will NOT be damaged.

Next, when a battery is referred to as being “STORED” it means the battery is not in use for long periods of time, like if it was taken from a vehicle and left in a garage for weeks or months at a time or if it is in a caravan that is not used for weeks or months at a time.

In these types of situations, the battery is deemed as being STORED.

The fact that your vehicle is your everyday drive, then the Optima is not being STORED because it is being charged everyday.

Also, my posts are not based on opinions, they are based on facts, and it’s these facts that I and Optima have presented to you that you misunderstand.

[dBC Member Find all posts View Profile Close dBC]

wouldn't a short drive at above 13.65 be better for the battery than a short drive below 13.65 given the information provided by the people who make the battery?

Probably a rhetorical question, but I think the answer is YES, although I doubt there's any magical cliff at 13.65V. I suspect Optima have their own version of the graph on p14 of this datasheet: http://www.odysseybattery.com/docume...M-002_1214.pdf. The numbers will be different because of the different battery design, but the basic principle remains the same. When pressed, all deep cycle battery manufacturers will tell you that a lower charging voltage will shorten the life of the battery if it's being used in deep cycling applications. In choosing 13.65 I suspect Optima have looked at their test results and chosen a number high enough to give a reasonable battery life, but low enough to not exclude themselves from various markets, but there's no doubt in my mind that the higher the charging voltage the longer the battery will live. This mob points out that sulfation occurs at any SOC less than 100%: http://support.rollsbattery.com/supp...tery-sulfation. Getting that last 10% in at 13.4V could well take forever, while at 14.5-15V it's easy and fast. Be wary of anyone quoting you hard and fast cut-off values like "sulfation can only occur below x%". There are very few cliffs in any of this stuff... it's all a spectrum, and the further you are on the good side of the spectrum, the longer your battery will last.

From Toyota's point of view, they're not trying to recharge a deep cycle battery. They're merely trying to top back up a battery that under "normal" operations will never drop below 90% or so. Most battery manufacturers permit much lower charging voltages for their non deep cycle batteries. Optima for example specify a minimum charing voltage of just 13.2V for their non deep cycle models. That's why I'm not a fan of some VSR solutions that allow the cranking battery to participate in providing energy for the overnight camp, especially in the case of low alternator output voltages. I like my VSR to isolate at about 12.6V so that the cranking battery remains in the state Toyota are assuming it'll be in. If you let both batteries contribute to the overnight camp you've now got two deep cyclers (well one deep, and one deepish). Combine that with low charge voltages and you've now got two shortened battery lives.

And finally, a quote from Optima's website: https://www.optimabatteries.com/en-u...ng-agm-battery

"Alternators are NOT chargers. Don't rely on your alternator to do the work of a charger. If your battery is discharged to the point where it cannot start your vehicle, use a charger as soon as possible to make sure your battery gets fully charged. An alternator is meant to maintain a battery, not charge it."

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

Hi dBC and I know that from your months of tolling the internet for info to back your claims, that you now consider yourself an expert in this field.

Well I have been in this field for 40+ years and I do not consider myself an expert, because things are continually changing.

For example, cranking battery technology has advanced big heaps over the last 15 or so years, and cranking batteries are better and more robust than they have ever been.

But if you had any knowledge of how the RV industry used batteries only 15 years ago, you would know that for many decades, the RV industry used cranking batteries as both auxiliary and house batteries, as these were the only batteries readily available, until the advent of cheap deep cycle batteries and then AGMs.

Back then people didn’t need as much battery capacity as they do today, but they also had smaller alternators, so things sort of evened out.

So you actually have no idea how a cranking battery can be SAFELY used.

Most battery manufacturers permit much lower charging voltages for their non deep cycle batteries. Optima for example specify a minimum charing voltage of just 13.2V for their non deep cycle models. That's why I'm not a fan of some VSR solutions that allow the cranking battery to participate in providing energy for the overnight camp, especially in the case of low alternator output voltages. I like my VSR to isolate at about 12.6V so that the cranking battery remains in the state Toyota are assuming it'll be in. If you let both batteries contribute to the overnight camp you've now got two deep cyclers (well one deep, and one deepish). Combine that with low charge voltages and you've now got two shortened battery lives.

You were obviously having a go at my isolators, as they are the only isolators specifically designed to work that way. But the problem for your OPINION is that the facts are the opposite.

You already have one Toyota owner, who had a DC/DC device and now has one of my isolators fitted, and is now getting much better charging results for both the speed with which his auxiliary battery is charged and the higher settled voltage of his cranking battery.

And remember, his posts are not based on an unsubstantiated OPINION, Michael’s posts are based on REAL WORLD facts. And note, Michael’s results are similar to the feedback I have been getting from my customers for more than 20 years.

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

Not sure if this has been mentioned in any of the threads on dual battery systems for 150s with the 2.8D4D, but the Electrical Specifications in the Owner's manual states that the system has two charging rates; Quick Charge at 15A max, and Slow Charge at 5A max.

[dBC Member Find all posts View Profile Close dBC]

Hi, yes it failed prior to AOC installation.

So Jimmy, prior to your AOC install, how long did it take you to notice the damage done to your Optima by the low charging voltages? Often with longevity issues it can take a year or two before you notice your capacity is way down, and by then the damage is done and it's too late to do much about it. Given all the other variables, it's very difficult to compare charging strategies in terms of battery longevity. You really need to do a controlled lab experiment not unlike what Odyssey did with four samples of their batteries, and unfortunately it's a test to destruction. The results were pretty conclusive and good on them for publishing them. It's a shame more deep cycle manufacturers aren't so open with their testing data.

[dBC Member Find all posts View Profile Close dBC]

Not sure if this has been mentioned in any of the threads on dual battery systems for 150s with the 2.8D4D, but the Electrical Specifications in the Owner's manual states that the system has two charging rates; Quick Charge at 15A max, and Slow Charge at 5A max.

That is interesting, good find rpn, although I'm struggling to get my head around what it actually means. I believe some vehicle manufacturers use the battery ground strap as a small R shunt. By measuring the mV drop across that they know how much current is flowing into/out of the battery, but I see no sign of any of that on my 2.8L. Whatever it means it could well be a clue to the low alternator voltages some of us see. 120D4D sees voltages quite a lot higher than I do and we've both got 2.8L engines.

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

There is some question marks regarding the content of that document, table 7 shows three inrush currents ranges with a supposed charge voltage of 14.7V. If the battery is discharged to the same point and then charged at 14.7V how can you end up with three different inrush currents?

They state:

"The message to be taken from this graph is clear – in deep cycling applications it is important to have the charge voltage set at 14.4 – 15.0V. A nominal setting of 14.7V is a good choice, as shown by the test results." now that's a good one, if you have a 100Ah battery is unlikely your going to purchase a charger that can supply the inrush current at 14.7V.

Then:

"Standard internal combustion engine alternators with an output voltage of 14.2V can also charge these batteries. The inrush current does not need to be limited under constant voltage charge. However, because the typical alternator voltage is only 14.2V instead of 14.7V, the charge times will be longer than those shown in Table 5."

Pardon, they have just stated if you charge these batteries at less than 14.7V you'll severely impact their life but now you can also charge then with a standard alternator, well which is it? If you can charge it at 14.2V you can also charge it no doubt at 13.8V it will just take longer again.

The statement:

"An example of the second type of automatic charger would bring the battery up to 14.7V, then switches to a float (trickle) voltage of 13.6V; it will stay at that level indefinitely. The second type of automatic charger is preferred, because the first type of charger will undercharge the battery."

This implies that the 13.6V float charge will bring the battery up to a fully charged state which is what happens with most chargers. The life cycle versus charge voltage all seems to be revolving around the absorption time, higher charge voltage shorter absorption time. It would be interesting to see the same chart given a charge time of 48 hours for instance.

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

That is interesting, good find rpn, although I'm struggling to get my head around what it actually means. I believe some vehicle manufacturers use the battery ground strap as a small R shunt. By measuring the mV drop across that they know how much current is flowing into/out of the battery, but I see no sign of any of that on my 2.8L. Whatever it means it could well be a clue to the low alternator voltages some of us see. 120D4D sees voltages quite a lot higher than I do and we've both got 2.8L engines.

They measure the current with a hall device, or a shunt in the battery terminal, trying to measure the resistance of the earth strap would be unreliable any slight variation in the strap or connections would have a sever impact.

From what others have posted there is no hall device or shunt but as I haven't looked at one personally can't say, but when I had a quick look at the schematics I didn't see any monitoring device shown.

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

So Jimmy, prior to your AOC install, how long did it take you to notice the damage done to your Optima by the low charging voltages? Often with longevity issues it can take a year or two before you notice your capacity is way down, and by then the damage is done and it's too late to do much about it. Given all the other variables, it's very difficult to compare charging strategies in terms of battery longevity. You really need to do a controlled lab experiment not unlike what Odyssey did with four samples of their batteries, and unfortunately it's a test to destruction. The results were pretty conclusive and good on them for publishing them. It's a shame more deep cycle manufacturers aren't so open with their testing data.

Hi dBC,
The first time I could truly say that I knew the battery was kaput was last month when I remember going out to the car in the morning and seeing the aux battery at 12.1 volts. That time I just assumed I had left something on, but I drove it around all day and got back home and overnight again it dropped to 12.1. The confirmed moment of kaput-ness it when I put it on a CTEK and it wouldn't accept any charge at all.
Looking back I was up in Darwin in January and noticed that the resting voltage was about 12.4 volts. I just assumed that it was due to the heat/humidity. I also noticed late last year I'd be packing the car for a day trip and have the fridge running with the car off for about 2-3 hours before we would leave and the voltage would drop to 12.3 or so volts over a couple of hours with the fridge running. I put this down to the fact that my fridge is a little power hungry and I was cooling it down from the 35 degrees plus it was in the NT.
In hindsight those two things were indicators of the batteries demise. I purchased an AOC and new battery on the same day, I know its no comparison but I wasn't buying another optima.

[dBC Member Find all posts View Profile Close dBC]

They measure the current with a hall device, or a shunt in the battery terminal

Thanks for the clarification. Yes, I can see neither of them on mine, at least not near the battery. From memory, my battery connections look just like my old 120 Petrol. Two fat red wires.... one going into the very nearby fuse box and the other heading down low out of sight... presumably to the starter motor. One fat black wire heading down out of sight, with a short skinnier one running straight over to the body right near the battery. I guess a hall effect sensor could be located in the fuse box on the red wire.

But I take my DC/DC input straight off the cranking battery +ve terminal and I connect my air compressor straight onto the cranking battery terminals. Both of those draw some serious amps, and they're clearly being sourced by the alternator because there's no voltage sag on the cranking battery when they're doing their stuff. I'm having trouble reconciling that with the Owner's Manual statement that rpn found.