Dual battery setup for 2.8 1GD

[120D4D]

O.k. Surprisingly I saw 12.25v this morning, it rose to 13.95-14.00 within 15 seconds and stayed there for the minute before I had to head-off.

The only accessories hanging of this battery are brake controller, driving light harness, DC-DC charger.

(DC-DC starts on Bulk but moves through to Float mode within 60 seconds and I saw no voltage fluctuation during this time at all, probably because the Optima Aux was already reading 13.05v before starting it, so no real current draw needed.)

I will report again in a week.

[drivesafe]

Hi again Michael, and the fact that you have done some long distance driving will make the measurements more interesting.

If you can take a measurement in the morning and then after a week or so of town driving, take another measurement and see what you get.

I have a new range of isolators and the offer to test one in your vehicle is still on if you want to see if it makes a difference.

[120D4D]

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.

Sorry I missed this and will do in the morning. That said in the past I recall checking and seeing around 12.4(ish) in the cranker which I thought seemed low.

A disclaimer in the meantime - on the weekend I did a run from Melb to Adel (over 2 days) so would sunday's 4 odd hours at highway speeds impact the answer Tim?

[dBC]

Some further tests suggests that crossover point for me is about 70% SOC, at least for my SMF Calcium/Calcium Marine battery. 70% and above the 25A charger pumps more amps into the camping battery than the alternator can, below 70% the alternator wins out. With the battery at 70% SOC as indicated by the open-circuit voltage after 24 hours isolation compared to the manufacturer's chart, and the charger disabled (output fuse pulled), jumper leads from the cranking battery (13.61V with engine running) to the camping battery were only putting in about 18A at 13.5V (a 0.11V drop across the jump leads) and the current was dropping fairly rapidly as the camping battery climbed towards 13.61V. Meanwhile the charger is happy to pump 25A in all the way up to 15.2V.

You could probably do better with a better choice of battery, but my 2.8L charging voltage is really not up to the job of getting that last 30% into that battery type in a timely fashion. If you regularly discharge well below the 70% mark, than the alternator may still win out overall.

[dBC]

Must say I've been impressed with its functionality, and the insights it can give. Was about $65 delivered from the US, came in 2 weeks. http://www.progressiverc.com/powerlog-6s.html

Thanks. At that price it seems a very useful piece of kit for this sort of analysis. I'll be ordering one and posting some proper graphs, but in the meantime, a while back I had a crack at describing how my charger behaves just by observing the two cabin voltmeters after a shallow-ish discharge (~18 hr overnight stop with fridge and lights) here: http://www.pradopoint.com/showthread...l=1#post553712

The interesting thing for me is how quickly the camping battery voltage exceeds the cranking battery/alternator voltage.... typically just a few minutes, maybe 5 mins max. What that's telling me is that when the camping battery gets to that (unknown*) level of charge, its impedance has come up enough that the only way you can continue to pump 25A into it, is to have the voltage higher than 13.6V. If the alternator were feeding it directly, it could dump massive amounts of amps in and get it to that level of charge much sooner, maybe 1 or 2 minutes instead of 5 but then what? Because the alternator can't increase it's voltage to overcome the increasing battery impedance the current starts dropping away... clearly less than 25A, but how much less I don't know.

For recovering from shallow discharges, I think the VSR solution leaps out of the blocks and jumps ahead by a few minutes, but then hits a wall (limited by 13.6V). I have noticed when recharging after deeper discharges, the camping battery gets stuck on 13.4V for quite a bit longer (limited by the 25A) and that's where the VSR solution really gets well ahead.

(*) it's unknown because you can't deduce anything from the voltage while you're still pumping amps in. But we do know it was a long way from full, by the fact that the charger continued to pump 25 amps in for a long time after that.

[drivesafe]

So then it may be a DC to DC.

It certainly looks more like the way you may have to go.

Yes I did mean that

[LeadWings]

Is the low state of charge (2-3Ahr/hr) due to lithium batteries maintaining a near constant voltage while it is being discharged?

Amts, I think you mean "Is the low rate of charge (2-3Ahr/hr) due to lithium batteries maintaining a near constant voltage while it is being charged?" My answer would be I would say not - maintaining a constant voltage when charging would only help you, as opposed to the voltage going up when charging which would give a lower dV between the source and the battery.

The amps to the battery will be a complicated function of the battery voltage, the alternator voltage (also may be a function of amps the alternator is trying to put out, but I suspect the Prado has an alternator capable of 100A so would be negligible in my case) and the voltage drop between the two (also a function of charge current). Lithiums are pretty good at soaking up charge, and these batteries could be charged at up to say 50A no problem.

Looking at the plots the battery terminals were at about 13.2V before charge, that then rose to 13.4V on charge on the trip out and 13.1V rising to 13.3V on charge on the way back. The Prado was putting out 13.7 to 13.8V, so that is only 0.3V to 0.4V difference to push the current along and into the battery. If the Prado could be coaxed to putting out 14.2V, then the greater difference in voltage would result in more amps being pushed to the battery. Maybe double, maybe more. I would not want more than 14.2V to 14.4V, as the higher voltages could overcharge and damage the Lithiums.

Pity is my old tug (VW Passat) put out 14.2V, and I ran a test when towing, but I had not set the logger up properly and it did not record the file. Would have been interesting to see what that setup resulted in.

If anyone in Perth has an older Prado (or any other car) with a boost diode so it outs out 14.2V or above and an Anderson on the hitch we could run a quick test to compare!

Is the low state of charge (2-3Ahr/hr) due to lithium batteries maintaining a near constant voltage while it is being discharged?

[LeadWings]

Hiya Drivesafe, I'm pretty up with Lithium stuff too - the battery has a BMS and low voltage cut-out. And I have a different meter I use to measure AHr in and out when in use.

But to me the take out for this thread is that for my setup the Prado only delivered 2-3 Amps into a near fully charged battery, and then on the way home with a battery that was at least 40% discharged (ie had taken 40 A Hr out of a 100 A Hr battery) it still only delivered 2-3 Amps. So it will not do for my requirements (and for most other peoples if they are set up the same - the reason for posting the data).

So my first step will be check for voltage drops in the chain from the Prado battery to the trailer battery and eliminate if possible. But I expect that may only get me up to say 8A or 10A at best - which will not be enough. So then it may be a DC to DC.

[LeadWings]

What a nifty little logger. I want one!

Must say I've been impressed with its functionality, and the insights it can give. Was about $65 delivered from the US, came in 2 weeks. http://www.progressiverc.com/powerlog-6s.html

[dBC]

Drivesafe, what charging voltages are your 2.8L Toyota customers seeing?

[drivesafe]

Hi Leadwings, I have been working with lithium batteries for about 5 years now and there are so many recommendations on how they should be charged and maintained.

Unlike lead acid batteries, where you should give them a good charge to get them to a fully charge state before you put them in storage, many of the lithium battery manufacturers recommend that their batteries are not charge to 100% if they are to be stored for any length of time.

You would need to contact your battery’s manufacturer, not the supplier, but the manufacturer, to get exact details relating to your specific brand and type.

Anyway, while in use, you can cycle them from 20% to either 95% or 100% depending on your charging setup.

If you are getting 13.8v at the battery, when it is near fully charged, then your battery should be in the 95% to 100% range, and you can drive all day long and not harm your battery while the voltage is at 13.8v but no higher.

Storage, and again, you need the specific specs for your battery, but 13.8v charging voltage before storing should be ideal.

Now to the catch with lithiums, which you are probably aware of. The terminal voltage is no indication of the capacity, and as you posted, you had a terminal voltage of 13.2v after charging. I think you will find that the battery was still fully charged.

If you want to find out how well charged your battery is, after a trip, you can only get this sort of info with a lithium battery if you install a full battery monitoring system, and that can get expensive!

Or for your own piece of mind, you can carryout a constant current load test.

You simply get something like a 21w 12v globe and apply it to the battery and see how long the battery powers the globe.

NOTE, this is something you should only do if your battery has it’s own BMS. Otherwise you are going to have to setup a means of disconnecting the battery when it’s voltage drops to 12.0v, which only occurs at the end of the discharge cycle. Other wise, you can damage a lithium battery with a single over discharge cycle.

[dBC]

What a nifty little logger. I want one!

[LeadWings]

New 2.8L Diesel and Lithium Trailer Battery

I have a confession, I have a lithium battery in my camper trailer. I have also just bought a new 2.8L Diesel Prado, and ran a charging test on the weekend and thought I would post some info on how it went.


I am hoping this does not turn this thread into a "Lithium vs Lead Acid" war, similar as tends to happen with alternator charging vs DC-DC convertor posts. So here goes.


Lithium batteries have very different charging requirements and methods than lead acids. For a 4 cell/12 V setup, the optimum charging setup is throw heaps of amps at the battery as long as it does not go over the voltage set point, say 3.55V per cell or 14.2V for a 4 cell pack is about optimum, then hold 14.2 volts and taper the current till the battery is full. So when I got the Prado, and put a battery meter in the dash, I noted that it tends to hold 13.8V. That is about 3.45 V per cell - which is around 95% full. So I figured this could be good - if the Prado can quickly charge the battery to 13.8V, then I won't need a DC-DC or similar.



Some background on my setup - 2.8L Diesel Prado, with VSR and 6 AWG/B&S twin wire to an Anderson on the tow hitch. Camper trailer has smaller wire (too hard to change) I am guessing 8 or 10 AWG 3m back to the battery. Battery is a 100 A Hr 4 cell LiFePO4 Winston lithium pack made up from some cells from an electric car that got tired. Currently don't have a second battery fitted to the Prado.


Camper trailer (Trak Shak) has 2 fridges, both 35L Waecos and some LED strip lights.



So I was going away for a 3 day weekend, and I thought a perfect trip to do some measuring. Measuring was done with a PowerLog 6S connected directly to the battery in the camper trailer set to log every 30 seconds.




I connected the battery around 9am Sat morning to run the fridges and get them cold. We set off around 12ish, and the drive was around 1 1/2 hours. We then set up and ran the fridges for rest of Sat, Sunday, and Monday. Packed up and connected the trailer to the Prado again around 10am Monday and drove it about 50m, it then sat for around 2 hours before the 1 1/2 hour drive home. Then turned the fridges off etc and disconnected the battery. Was a fairly cool weekend, say 15C in day and 5C at night, so fridges were not working too hard.


Attached are a voltage plot, a AHr plot and a current plot. I also watched the volt meter on the dash when driving, and it did go down occasionally to say 13.4V but generally stayed around 13.8V.


Firstly the voltage plot - you can see the voltage is hovering around 13.2V before I connected the Prado to leave. Don't know why this was so low, as the battery was charged a few days before. You can then see that the voltage goes up to around 13.4V while being towed. Then while the trailer is sitting there for the weekend the voltage drops from around 13.25V to 13.1V (bumps are due to voltage sag as the fridges cycling on and off. Then the jumps up to 13.3V as the trailer is towed home.




Amp-Hr plot - Fridges use around 5 AHr getting cold, recover around 3 AHr while towing to site, then use around 40 AHr over the weekend, then recover around 3 - 4 AHr on the drive home.



Last but not least the current plot. Fridges suck around 2A when on, so you can see the 2A spikes for one fridge, then 4 A if they are both on simultaneously. You can clearly see the negative current when the battery is being charged by the Prado on the way there and the way home - around 2 to 3A, and impacted as the fridges cycle on and off. Odd spikes to 5A, but they look short.




It looks like as it is set up I would only get 2-3 AHr per hour of driving, which is no where near enough for sustainable use on an extended trip of driving every day for say 3-4 hours - we would be using 20-30 AHr per day, and getting at best 8-12 AHr back. So would need mains/solar supplement.


So my conclusion? I would like it if the system voltage could be adjusted up, to say 14.2V but it looks like the simple diode type fix isn't available for this model (yet - here's hoping).


So I think I will bite the bullet and install 6 AWG/B&S wiring in the trailer if I can, measure again and will probably have to get a DC-DC converter.