Dual battery setup for 2.8 1GD

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

Hi again Hally, and I think you need to do a bit of research as to what constitutes a fully charged battery.

Leigh has covered the charging possibilities pretty well, but you need to know the difference between a fully charged battery and a charging voltage.

A fully charged battery will have a SETTLED voltage of 12.7v. It is irrelevant as too whether the CHARGING voltage is 13.5v or 14.7v.

If the battery is fully charged, it is fully charged!

The one point of leigh’s post that I will reiterate is that while a low charging voltage will take longer to charge the battery from the 80% - 90% level to a fully charged state, the fact that an alternator will get a low battery to that 80% - 90% level MUCH SOONER than a DC/DC device can, means the low ( or higher ) voltage at the final charge stage is of little consequence to the total charge cycle.

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

So I wonder if it might just be best, in the new 2.8 GD Prado (given that at this stage we don't have access to a voltage booster diode for that vehicle) to use a VSR to do most of the aux battery charging, and use solar when stopped, and then just connect to 240 volts in a camp ground or when at home (something like a cteck 240v charger) to do an occasional "full charge" condition and charge to both main and aux battery..perhaps?

My issue with most VSR's is that they seem to be set to isolate the start battery as soon as you shut down the car engine, when in fact you could probably use say 10-20% of the start battery charge before it needs to be isolated..I think?

Thoughts dear gents?

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

I use the Redarc SBI12 and it definitely doesn't isolate the batteries when the engine is stopped. It waits until the voltage drops to the specified level, allowing both batteries to be used for a while.

[Prone Member Find all posts View Profile Close Prone]

Hally,

Your DCDC charger does not start charging at 14.4V, it may only be 12.6V for instance if the battery is low and then gradually rise as the battery charges, it won't get to 14.4V till the battery reaches a SOC of around 80%. The alternator on the other hand will instantly go to around 14.4V then gradually taper down to 13.8V or there abouts as the engine bay warms.

While I agree with what you wrote I think the above highlighted needs a bit of a correction.

The alternator will only go to a voltage that it can reach with its maximum current and the load resistance characteristics. It will function much the same as a DCDC charger with a current rating the same as the alternator.

True, the voltage is likely to be higher than that which you describe for the DCDC device because it most likely has a higher current capability than the DCDC unit, but it is still a current limited supply. If it could supply an infinite current yes it would go instantly to 14.4V or whatever its maximum setpoint voltage is. (I note that you did state "to around 14.4V") As it is not an infinite current device the voltage will settle somewhere between its maximum setpoint voltage and the battery voltage as determined by the total circuit resistance.

If the batteries are very flat and there is appropriate sized cabling between them the alternator voltage would be very close to that of the battery determined by the batteries internal resistance at that state of charge.

Cheers
Prone

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

Thanks maulbeagle,
Can I just double check with folk then please, doesn't the SB112 isolate the main start battery when the main start battery hits 12.7 volts...(is that right?)...so does that mean that whilst the Sb112 doesn't isolate the start battery straight away when you turn off the engine (as I believe some VSRs do), it does however isolate the start battery pretty quickly after shutting down the engine, thus not allowing you to use some of its state of charge on say a fridge?....I really don't know, but I would have thought it would be slightly better if the start battery was isolated at a slightly lower voltage than 12.7v....no where near flat of course, but a bit lower than nearly fully charged?

Thoughts/comments please?

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

Yes 12.7V is the voltage at which the SBI12 isolates the batteries.
Mine seems to have a bit of tolerance though, I think I needs to drop a bit lower than that (around 12.5V from memory) before it actually isolates.
After a decent drive, my main battery seems to hold this voltage for a fair while. I can't say how long, maybe i'll check when I get home from work (a 25 minute drive).

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

So I wonder if it might just be best, in the new 2.8 GD Prado (given that at this stage we don't have access to a voltage booster diode for that vehicle) to use a VSR to do most of the aux battery charging, and use solar when stopped, and then just connect to 240 volts in a camp ground or when at home (something like a cteck 240v charger) to do an occasional "full charge" condition and charge to both main and aux battery..perhaps?

My issue with most VSR's is that they seem to be set to isolate the start battery as soon as you shut down the car engine, when in fact you could probably use say 10-20% of the start battery charge before it needs to be isolated..I think?

Thoughts dear gents?

One of drivesafe's isolators will allow you to do just that.

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

While I agree with what you wrote I think the above highlighted needs a bit of a correction.

The alternator will only go to a voltage that it can reach with its maximum current and the load resistance characteristics. It will function much the same as a DCDC charger with a current rating the same as the alternator.

True, the voltage is likely to be higher than that which you describe for the DCDC device because it most likely has a higher current capability than the DCDC unit, but it is still a current limited supply. If it could supply an infinite current yes it would go instantly to 14.4V or whatever its maximum setpoint voltage is. (I note that you did state "to around 14.4V") As it is not an infinite current device the voltage will settle somewhere between its maximum setpoint voltage and the battery voltage as determined by the total circuit resistance.

If the batteries are very flat and there is appropriate sized cabling between them the alternator voltage would be very close to that of the battery determined by the batteries internal resistance at that state of charge.

Cheers
Prone

An alternator acts as a constant voltage source, it will maintain its "float" voltage till such time that it is unable to, ie overloaded, note the rated voltage at maximum output will be lower than the designed float voltage ie around 13.5V. Interestingly if overloaded the alternators current output tends to rise quicker than the voltage drops due to the negative temperature coefficients of the rectifiers and windings.

The prado's alternator has sufficient reserve current to force a 100Ah battery that has been discharged to around 50% SOC to its float voltage with seconds of starting the car, if you have more than one aux it will take a little longer depending on how you have configured your wiring.

In my setup I have a 100Ah aux in car, and two 100Ah batteries in the Vista, within 30 seconds or so of starting the car the cranking battery is at 14.5V, all batteries are interconnected with a double run of 6B&S cable, the Vista's batteries are in parallel configuration.

A typical battery will draw around 60 amps when first connected, this will drop to around 40 amps after 10 minutes or so and be around 30 amps after 25 minutes.

The Prado alternator has a reserve capacity of around 70 amps with all accessories turned off.

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

LeighW - yes, kind of got a week out of battery used my solar to top up when needed.

As for Drivesafe I can see after looking back at all your posts you have never had a good thing to say about dc-dc's and most threads you reply to is related to this which you then hijack to babel on about how a relay and booster diode work better (which funny enough you and LeighW sell). I can now understand why you would start to become negitive towards my post when I mentioned I had a dc-dc and worked great.

Once again after looking back at previous threads I have noticed that both Drivesafe and LeighW have always pushed towards an isolator and diode booster that they sell.
Mods I would like to no if this is within the rules.
Thanks Dan

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

LeighW - yes got a week out of battery used my solar to top up when needed.

As for Drivesafe I can see after looking back at all your posts you have never had a good thing to say about dc-dc's and most threads you reply to is related to this which you then hijack to babel on about how a relay and booster diode work better (which funny enough you and LeighW sell). I can now understand why you would start to become negitive towards my post when I mentioned I had a dc-dc and worked great.

Once again after looking back at previous threads I have noticed that both Drivesafe and LeighW have always pushed towards an isolator and diode booster that they sell.
Mods I would like to no if this is within the rules.
Thanks Dan

Take a breath Hally, the comments about charging using the various systems are based on plain science. They are facts a DC-DC can only at best charge at it's rated capacity and this will always be less than the alternator powering it both due to efficiency losses and the fact that you lose current when you increase voltage and even more so if the DC-DC is rated at 20 amps, end of story.

By the way I run a booster diode and my mate runs a DC-DC. Over the past 5 years camping together he has to run his Prado a lot more often and longer to keep his battery charged when we are running the same size fridge, so real life experience confirms the science.

Incidentally your battery is not 'lasting a week' if it is being topped up by solar.

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

I'm not sure about 'lasting a week'
All I said was there for a week !
This is the first time I have run a dc-dc out of my last 5 4wds I've had duals in, and I think the relays are fine in particular vehicles but with technology comes change. As for my fridge i could run it for avg 2 days with out any top ups to keep it onthe safe side

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

Hi again Hally and your response is the typical reply owners of DC/DC devices make, when it is pointed out that they could have achieve the same or better results it they had not wasted their money on such devices.

Also, I do supply DC/DC devices, just not these toys.

But I only offer them to people who have a situation where they are going to get a genuine benefit from using a high current DC/DC device, like when needing to charge and maintain large banks of batteries in a caravan or motor home, or if they want to fit lithium batteries.

Furthermore, I have not promoted my brand on this site, even though there is a number of member on here, who have my products in their Toyotas, and I was asked by a number of them, to post on this site, to counter the B/S surrounding the use of DC/DC devices.

As I have already posted, I have never stated that a DC/DC device could not fully charge batteries, but when I see people like yourself, making claims that do not reflect reality, I will correct that misinformation.

If you care to do some research, you will find that my systems offer the FASTES RECHARGE times over any other type of dual battery system available and do so in a much kinder way for all the batteries in one of my system.

So yes I do argue when people post up replies based on nothing more than the grossly misleading advertising hype used to sell most DC/DC devices.

Also as I don’t mislead people about my products can and cant do, so why should I have to sit back and watch as unsuspecting people get continually bombarded with grossly misleading advertising hype, by the owners of DC/DC devices, who usually have no idea how they own systems really perform.

Like it or lump it, in the vast majority of dual battery setups, DC/DC device, at best will do no better than what a correctly set up direct alternator charge setup will do, and in many cases, a DC/DC device will actually take long to recharge batteries than what an alternator can do by itself.

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

Please folk, stay on track...I guess this is what maulbeagle meant by "grab the popcorn" because the "discussion' that follows can get seemingly excited...there are varying opinions and set ups, and the discussion can get quite passionate which is great. There are many options available for batteries and dual batteries and triple battery setups, and there is a place it seems, for each of the varying devices depending on teh set up, what you need, what car you have etc..

I guess the issue for me is that the new edition Prado has a comparatively lower alternator output voltage.

In our previous prado we installed a voltage booster diode, and a VSR and it was a great set up, and worked well, however we want to do something different this time with our aux battery set up.

1. I don't think I want to put an auxiliary battery under the bonnet in the engine bay this time if I can help it. (I want to be able to swap my auxiliary battery easily between vehicles etc, and I also don't want to risk a cracked inner guard (despite the beefed up guards n teh new Prado) and I think I also don't want the extra weight up front (given I will already have a bull bar and a winch)

2. I want to run a Waeco 50l fridge in the rear and I also want to use solar panels when camped. I am also considering if I have a system that has an MPPT solar charge controller, then I will run full solar panel voltage directly to a red anderson plug to maximize the input from my solar panels.

So, the options are a VSR or a DCDC set up...and there seems there are pluses and minuses for different set ups.

I like simplicity, I like portability (to be able to remove the system from my car in about 5 years time perhaps, and I want something that works well and doesn't allow my batteries to discharge too far or overcharge.

The voltage boosting diode with a VSR worked well in our previous Prado, but one of these simple and easily installed and effective devices is not yet (if ever) available due to the design of the new Prado alternator set up...I think.

So its through discussions like this that I can get ideas and suggestions and soon I will have to make a decision for my set up.

So please keep the discussion flowing folks, I like hearing about personal experiences that folk are having with the new 2.8 GD Prado, and also I have enjoyed reading about the booster diode, and DC DC chargers, and reviewing the products, but when the time comes to purchase the gear I feel you need to speak directly to folk who work in that area and have them look at my setup..because there is only so much info you can discuss and relay on a forum.

So drivesafe, can I ask you please, in the new 2.8 GD Prado, given that the alternator output voltage is a little lower, do you suggest using a VSR from the start battery to charge an auxliary battery located in the rear cargo area, or would a DC DC charger be a better way to go? ..and LeighW mentioned that you have an isolator (VSR) that might allow me to isolate the main start battery when its voltage drops a little further than some other isolators. Can I get some info on your isolators please?

And LeighW, I know I have asked before, but is it correct that we may not see an alternator voltage boosting diode for the new 2.8 Prado. The voltage boosting diode still amazes me, and some folk I tell can't believe it works till I show them..simple yet effective at boosting alternator output voltage... I still don't know how it does it, I know exactly what a normal diode does, but how this changes alternator voltage is interesting electronics...I wonder who initially discovered this.

Anyway, I look forward to more passionate and informative discussion good folk.

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

I also don't have a bias on any system, I don't need to sell my product to make a living, the statement was made a DCDC charger will always charge faster that is clearly not the case.

If I'm asked for advice I give what I feel is appropriate for the setup concerned and how they intend to use it, as members of this site know, if I feel a DCDC charger would be the best option I tell them so. If you really need a DCDC charger I would suggest a 40A unit to give similar recharge times to an alternator for one aux if your choosen battery can handle the current.

It is intersting that most of the DCDC charger manufactures still market VSR's if they were ethical and believed DCDC chargers are the only way to go then they should stop selling the VSR's?

I had a lot of respect for Redarc once but over the past couple of years most of that has disappeared, once they would give unbiased advice, these days they are only interested in pushing their premium product. As an aside to this, if anyone is thinking of buying their DCDC/solar unit think again, their glossy states:

"Solar input voltage range 9-28V (suitable for 12V panels only)"

when you buy the unit and read the user manual it has minium turn on voltage for solar is 17.5V, people are having problems with the units not firing up when connected to solar panels, Redarc's response has apparently been "their units are designed to work with their panels" and apparently refusing to refund.

I also read recently of someone who ordered a Redarc BMS in their camper, apparently after a lot of messing around they found out the unit was faulty, it was repalced with another which was also faulty, and then another which worked for awhile then also went faulty. Redarc was very appolgetic and replaced the units, still three faulty units in a row doesn't say much for their quality control.


brodgers,

I need to visit Toyota within the next few days, I'll see if a service manual is available for the 2.8ltr whilst I'm there.

Cheers

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

Hi bloger and first off, as yet, I have not had one of my isolators fitted to a new Pardo and like Leigh, I have not been promoting them for use in the new Pardo until I can get feedback on whether they will operate as required.

To that end, I have a customer who has just ordered one of my isolators for his new Pardo and even after I explained I had no knowledge of wether they will work or whether there may be problems, he still requested one of my isolators because of the way they work as compared to anything else available.

So I have made arrangements with him, where I am supplying an isolator, on the basis that should it not work as designed, he will be fully refunded.

But while, as I stated above, I have not had any working experience with the new alternator setup on Toyotas, as I have only had one “new” vehicle where my isolators would not work ( Ford Rangers, BEFORE Ford changed their alternator operating system in their latest version ), so I am quite confident my isolators will work as designed, with the new Toyota alternator system.

One more benefit of my isolators, based on what you are planning to do. All other isolators must be located as close as practicable, to the cranking battery, otherwise, in low voltage situations, they will continually oscillate on and off.

Because my isolators are designed for a different type of operation, they can actually be fitted elsewhere in the vehicle, or even in a camper trailer or caravan, and will still work as designed.

So in your case, you could fit one of my isolators with your auxiliary battery, thus simplifying the whole setup and installation.

This would also make it easier for you, in 5 years time, to remove the system to use in your next vehicle.