D4's charging / battery problem

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Originally Posted by Ferret

To clarify, there is two batteries. And whether the reported SOC is correct or not, if the alterator is not putting out any current then the entire power to run the vehicle is coming from the battery and the alternator is more off than on.

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Hi Fettet and again, the graph just does not show enough info.


SoC is a guesstimate, and when the alternator is charging, where is the charge going.


You vehicle will be drawing somewhere around 40 amps ( day time ) to 50+ ( night time ) then there are two or more batteries drawing charge.


But at the end of the day, the amount of energy available comes down to what is actually in the batteries.


All cranking batteries are high current charging batteries, and so are batteries like Opima and Odyssey batteries.


These batteries will tolerate very high currents and this means that even short bursts while driving, will quickly recharge these types of batteries and yes, not likely to be to 100%.


The graph is nice to look at but tells you nothing about what is actually in your batteries.


The only way to get an accurate indication of what’s available, is to actually use the battery capacity and see what you end up with.


A few months back, after few charge/discharge cycles, to see what was available, using a 4 amp load applied to a DT90’s ACCESSORIES output, I discharged the cranking battery down to 12.02v and the Optima down to 11.53v.


After letting the batteries settle overnight, I then went for a 33 minute drive. I deliberately drove for as close to 30 minutes because my RR, and D3s have a 30 minute charge cycle before they settle on a “Cruise” voltage.


On getting back from the drive, I let the batteries settle for two hours and then carried out another 4 amp discharge cycle.


With both batteries discharged down to the same levels, I had drawn 45.6Ah from the two batteries.


A few minutes after the start of the discharge cycle, the the cranking battery was at 12.67v and the auxiliary battery was at 12.64v.


If your were to use an SoC table, the two batteries were THEORETICALLY well over 95%. They were actually around 75 to 80%


That is just too much of an error margin.

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Originally Posted by Stuart02

By "down" do you mean toward or away from the LED? I can't remember offhand which is for normal v winch but if you put the battery in for winch backup it might be set wrong? I'm guessing you had someone else do the traxide install?

Running a medium fridge and a few light strips for a couple of days should be nothing to the yellow top. My 2010 Sport does that after nothing but 4km commutes for months at a time (do you think SWMBO will catch a train?!?) and just a couple of hours drive to camp.

I do leave the tail gate up while around camp.

I consider the traxide the single most important upgrade for these cars both for going bush and city life. I don't know how the Toorak tractors survive, tbh. First time I had the footy on the car radio I drained the battery to warning level.

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https://uploads.tapatalk-cdn.com/201...781366b456.jpg

Like this - that’s in the “down” position? The way it was installed in the current vehicle and at a guess the previous vehicle with winch. Used the same guy to install both times.

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Originally Posted by drivesafe

SoC is a guesstimate, and when the alternator is charging, where is the charge going

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The graph shows battery current and alternator current, so it does indicate where the charge is going. The difference between the values is going to vehicle systems, lights, etc. The BMS controls how much is available to go to the battery so needs to know alternator output and current going to/from battery, which can be displayed.

Ferret‘s experience is similar to mine. We may not have all the technical details exactly correct but I think it’s clear that the charging regime of a D4 does not promote “full” or “approaching full” batteries whether you have a dual setup or not. It does a good job if you’ve run the batteries down to a low SoC by subsequently getting the batteries up to a reasonable level quickly but you don’t get full even when driving all day.

I agree the accuracy of displayed SoC figures coming from the BMS via diagnostic tool can be questioned especially when there’s a dual battery setup, ie how the BMS calculates SoC is unknown. But the relative performance seems to be realistic.

I have charged overnight for a whole week and had the BMS SoC reading (via iiD) up at high 90s and occasionally 100%, as you’d expect. But daily commuting without overnight charging it tends to sit at 80-85% for good condition new’ish batteries and sometimes, especially with repeated short drives, it’s left as low as 70% before increasing the alternator output enough so that there’s any going to the battery. This also makes sense given that, as you’ve said, the last 20% of capacity is controlled by the battery, which takes longer and won’t happen with shorter drives. And then when I’ve been camping the SoC indicates lower figures generally in line with what I’d expect for my overnight usage.

So I think the SoC readout is accurate enough to assess what the BMS is doing in an overall and relative sense. It seems that the system just wants the battery to be between 70 and 85% and is not interested in anything else. I wish it was programmed to periodically charge the battery up to full or at least close. And I also wish it didn’t wake up all the ECUs when you open any door, why not just the drivers door, even that would be a big help when camping.

Scott

Imo something to be aware of is that anything but a professional multimeter will read anywhere up to 0.15v wrong at 12v. Between my cheap meter and my mates Fluke, on a cold day there was 0.2v difference. I thought I had a bung meter until I read its specs on accuracy.

I've also noticed that even a 0.3amp draw E.g door open is enough to pull an aging battery (e.g 3 years old) down 0.1-0.15v. Presumably this is an issue of surface charge depletion as recovery is very fast.

I believe all this can all add up to give quite eroneous readings at 12v unless you really know what your doing.

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Originally Posted by LRD414

So I think the SoC readout is accurate enough to assess what the BMS is doing in an overall and relative sense. It seems that the system just wants the battery to be between 70 and 85% and is not interested in anything else. I wish it was programmed to periodically charge the battery up to full or at least close. And I also wish it didn’t wake up all the ECUs when you open any door, why not just the drivers door, even that would be a big help when camping.

Scott

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Hi Scott, and again, while the vehicle’s BMS has access to a large number of factors, to be able to come up with an SoC reading, this does not give a real idea of what’s going on.


The only way to know if the vehicle is even attempting to charge batteries, primarily the cranking battery, is to have a voltage reading.


In each of the ALTERNATOR spikes in Ferrets graph, I’ll lay money that the voltage goes to 14.7v every time. At this voltage level, the batteries will be taking heaps of charge.


And as posted, short of doing a controlled discharge test, there is no way of knowing just how accurate, or inaccurate those SoC readings are.

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Originally Posted by drivesafe

In each of the ALTERNATOR spikes in Ferrets graph, I’ll lay money that the voltage goes to 14.7v every time. At this voltage level, the batteries will be taking heaps of charge.

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Yes it does go to 14.7v, you can see the battery voltage increase and you can see the battery draws ~50+ amps before rapidly falling from those peaks even when the voltage is held at 14.7v But all that (the alternator spikes) only happens because you are braking or coasting. That is, the battery is being charged only because of opportunistic reasons related to traffic flow or road layout.

What happens when you are not city driving, instead driving along flat deserted country roads where little to no braking / coasting is required? - Your battery is depleted to some lower state of charge. It doesn't matter if you can measure SOC accurately or not - if your not charging because there is little need to brake / coast your net SOC is most likely falling.

Anyway, I'll send you the data and you can paw over it.

Quote:

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Originally Posted by Ferret

What happens when you are not city driving, instead driving along flat deserted country roads where little to no braking / coasting is required? - Your battery is depleted to some lower state of charge. It doesn't matter if you can measure SOC accurately or not - if your not charging because there is little need to brake / coast your net SOC is most likely falling.

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This is where the voltage readings are needed.


Your alternator can operate down to 12.7v and not draw on your batteries.


It’s only if the voltage drops below 12,7v that the cranking battery will start to compensate for the lack of alternator power.


BTW, your use of the brakes has no effect on the alternator voltage rising.


As you have stated, when coasting the voltage rises.


When coasting, the accelerator peddle is not being pressed, as is also the case when braking.


If the accelerator peddle is not pressed, then the kinetic energy of the vehicle is used to power the alternator at high voltage ( 14.7v ).

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Originally Posted by drivesafe

This is where the voltage readings are needed.

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What relevant voltage reading are you not seeing on that chart.

Hi Ferret, that is nothing more than a line on a page, it gives no actual voltage reading, just a line on a page.

Here you are Drivesafe

Attachment 155851

That was after a warning to start the car. I had 2 Optimas i circuit + the cranking battery. Were the Optimas taking 50A each?

You should see what having a DC2DC charger does to the charging circuit when the batteries are down a bit. Current cycles between 50A & 200A continuously. I have now added a remote control to enable me to disconnect the 12V from the D4 to the DC2DC until the D4 batteries are charged up a bit.

When somebody figures how the D4 BMS works, please let us into the secrets.