Which of these indicate 80% charge?

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Lambtron

Well-known member
Joined
May 25, 2015
Messages
93
Location
North Las Vegas, Nevada
80% of new single cell voltage? (4.2V)
80% of available cell voltage?
80% new pack voltage?
80% of available pack voltage?
80% of new pack KWh?
80% of available KWh?
80% of Gids new or available?
 
I believe that it's 80% of available cell voltage. Nissan reserves a few percent at the top of the state of charge. That means that 80% indicated is probably more like 75% actual.
 
SageBrush said:
Lambtron said:
as
Which ..
80% of available KWh when done right.

Lots of SoC meters are highly inaccurate because they only read voltage.

Thanks! That does seem to make more sense. In a way earlier post somebody had mentioned that it was 80% of the cel voltage, but even with perfect cels @ 4.2v the cel v drops to 3.36 v at 80% voltage times 96 pairs. 332.56V. This would be way below, more like 35% on leafspy. I need to stop this late night mathematical masturbation.
 
The drop in cell voltage is not linear or proportional as the cell energy is depleted. This is particularly true of Li-x cells.

Google 'Lithium ion cell voltage discharge curve' to see examples.
 
I'm curious where you are getting all these readings from (LeafSpy?), because I have run into a similar problem in reporting SoC from my (recently installed) OVMS module.
I am forced to use GIDs as a reference to report battery SoC (requirement of whoever wrote the Leaf OVMS module), but it's only accurate at high SoCs; for example, an 83% charge (10 bars) yields a very accurate SoC (based on GIDs)...but as you deplete the pack, it becomes much less accurate to the point that it is several percent off below 50% or so. There are measurements like "new car" SoC and "nominal" SoC, but things like "new pack KWh" and "available KWh" change as the pack degrades. Conversely, Dala's CAN-bridge mod seems to report an accurate SOC (in the dash) over the entire range. The question is: how does it do it given the non-linearity of these other voltage/GID based measurements?
 
Lambtron said:
80% of new single cell voltage? (4.2V)
80% of available cell voltage?
80% new pack voltage?
80% of available pack voltage?
80% of new pack KWh?
80% of available KWh?
80% of Gids new or available?

80% of available kwh is probably the closest but Gen 2 BMS started playing head games which means even LEAF Spy is not accurate since it gets all its information from the BMS.

Voltage? Not even close. Voltage drop is very gradual at higher SOC and accelerates rapidly at low SOC.
 
When charging, after the 3rd blue light starts blinking and the fuel gauge hits 9 to 10 bars.
 
Since OP seemed interested in the nitty gritty, here is some of it:

A battery takes on ("charges") or releases ("discharges") Amps. Amps are due to the flow of ions, measured in columbs. As ions flow they are subjected to an electric field gradient called voltage. So the total energy involved (minus losses) in filling or discharging a battery is the total Amps integrated over the voltage.

Imagine a discharge graph where the Y axis is voltage and the X axis is Amp hours. The area under the curve (AUC) is the total work capacity (energy) of the battery. The *average* voltage can be found over the discharge curve, and that is referred to as 'nominal battery voltage.'

If we know the total Amp hours that can be discharged from a full battery and the average (nominal) voltage, we can use Ohm's law to calculate the energy:

A*hrs * Volt = Watt*hrs

This is why a simple voltage reading is a crappy way to estimate energy: it ignores the drop in voltage as current is drawn. And while better, an average voltage between what is present now and when the cell is discharged is also not accurate because the voltage. drop is not proportional.
 
Don't forget the effects of temperature, etc on the battery performance. I'd say any SOC reading is simply an estimate and the only folks who know its accuracy would be the engineers who designed the system and wrote the code. There is simply no way that a battery's capacity can be measured in the same paradigm as a gas tank - there are way more variables involved and some of them can't be know. Eg, a battery will have a different 'capacity' when discharged at 0.1C then when it is discharged at 2C. How does a SOC algorithm account for that?
 
Lambtron said:
80% of new single cell voltage? (4.2V)
80% of available cell voltage?
80% new pack voltage?
80% of available pack voltage?
80% of new pack KWh?
80% of available KWh?
80% of Gids new or available?

80% of Nissan's definition of "100%" voltage for the battery's chemistry (user-allowed voltage), which is probably somewhat less than the cells' rated maximum, which itself would be an arbitrary value representing a compromise between storage, safety, and longevity.
 
Nubo said:
Lambtron said:
80% of new single cell voltage? (4.2V)
80% of available cell voltage?
80% new pack voltage?
80% of available pack voltage?
80% of new pack KWh?
80% of available KWh?
80% of Gids new or available?

80% of Nissan's definition of "100%" voltage for the battery's chemistry (user-allowed voltage), which is probably somewhat less than the cells' rated maximum, which itself would be an arbitrary value representing a compromise between storage, safety, and longevity.

That's what I told them, but everybody wants to complicate it with coloumb counting. BMS programming for smaller EVs like bikes is also based on voltage. Nissan's LBC/BMS also tries to keep track of AH in/out, but AFAIK charging regulation is based on voltage.
 
I more than understand the Ohm's Law part of this. I guess the part that is puzzling is that all of the manufacturers while speaking the merits of 80% never discuss 80% of what. It's kind of like when sales commercials talk of 50% off but never discuss "Off what" Retail? wholesale? some arbitrary made up number? This number would help in determining whether beyond a certain point of battery loss, charge limiting has no benefit.
 
I seem to recall, when I drove a 24 kilowatt-hour Leaf, that an 80% charge would yield pretty much 80% of the available range of a 100% charge. I don't drive enough now to confirm that the same holds true for a 40 kilowatt-hour Leaf.
 
LeftieBiker said:
I seem to recall, when I drove a 24 kilowatt-hour Leaf, that an 80% charge would yield pretty much 80% of the available range of a 100% charge. I don't drive enough now to confirm that the same holds true for a 40 kilowatt-hour Leaf.

That is right, which is NOT 80% of maximum voltage.
Meaning if Max voltage is 400 volts, 50% of range is NOT 200 volts

Even if you realize that 'empty' is about 250 volts so the drop from 'full' to 'empty' is 150 Volts
50% range is NOT 400 - (150*0.5) = 325 volts

80% 'charge' means 80% of maximum usable energy when the battery is fully charged.
 
There is nothing magic about 80%, it is just an easily recognizable difference from 100% full. It is enough different that you aren't confused about whether you are at 100.

Assume you were an average customer without all the technical knowledge and the CAN buss tools of Laefspy, etc,, then what would you do--use the "fuel" gauge just like charging your phone. The gauge displays on the dash from "0 to 1" in 12 steps, 80% of Full would be 9.6 bars, so between 9 and 10 bars. That just happens to be about when the 3 Blue charging lamps transition from 2 to 3 lights, and is more useful because you can't see the fuel gauge while charging.

Can you do your daily commute with only charging to that level? Can you get 2 days of driving with that, or even more days? If so there is no need to charge to "1" everyday, and research has shown that a pack will suffer less capacity fade with a lower charging practice.
AC1775H.png
 
What I'm saying is that the BMS uses cell voltage to get to the 80% of capacity zone. I didn't mean that it goes for 80% of maximum cell voltage, just that it uses voltage to know when it's hit that target. If the original post put it the first way and I agreed with that, it was the drugs talking - I'm still hospitalized.
 
FWIW, ran my 11 bar 30Kwh down this morning to VLBW from 81% indicated and 84% per LS. 18.6 KWh /Drove 53 miles (3.68 m/kwh) used 14.48 KWh. Ending avg. cel v was 3.48, pack v was 326v. 8 gids, Pack temp 113* Percentages definitely not based on cell voltages.
 
SageBrush said:
LeftieBiker said:
I seem to recall, when I drove a 24 kilowatt-hour Leaf, that an 80% charge would yield pretty much 80% of the available range of a 100% charge. I don't drive enough now to confirm that the same holds true for a 40 kilowatt-hour Leaf.

That is right, which is NOT 80% of maximum voltage.
Meaning if Max voltage is 400 volts, 50% of range is NOT 200 volts...

I don't think anyone means to say the correlation between SOC and voltage is linear, just that there is a correlation which can be used. My wording may have implied it, but if so I was being careless about not defining my assumptions. I meant "the voltage level that corresponds to 80% SOC".
 
Nubo said:
SageBrush said:
LeftieBiker said:
I seem to recall, when I drove a 24 kilowatt-hour Leaf, that an 80% charge would yield pretty much 80% of the available range of a 100% charge. I don't drive enough now to confirm that the same holds true for a 40 kilowatt-hour Leaf.

That is right, which is NOT 80% of maximum voltage.
Meaning if Max voltage is 400 volts, 50% of range is NOT 200 volts...

I don't think anyone means to say the correlation between SOC and voltage is linear, just that there is a correlation which can be used. My wording may have implied it, but if so I was being careless about not defining my assumptions. I meant "the voltage level that corresponds to 80% SOC".
As mentioned above, the voltage discharge curve is affected by load, temperature, hysteresis and no doubt other variables I am unaware of. These variables are more noise than the change in voltage in the middle of the discharge curve. This is why SoC meters based on voltage stink, and coloumb counters are needed.
 
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