Malm, 2011 i-MiEV, Portugal

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acmotor
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Post by acmotor »

Ah sorry Kurt, it was me68 who had measured 17.5kWh from the wall on a recharge.
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Post by offgridQLD »

"My recharging kWh is 8% less on a warm day 30 deg and 12% less on a cold day 10 deg at 78,549km.
This is based on 16.5kWh that I would charge when new."

Interesting that matches the general idea of what I'm finding in different ambient temps. In fact temperature plays a bigger role in usable capacity than I would have guessed befor owning the Imiev.

Take this last two weeks for example the weather on the Sunshine coast has been all over the place with big swings.

Last time I drove back on my regular 105km trip it was about 3C overnight and 14C in the day with a mean temp of around 8C took the freeway. Arrived home with out of the norm (low) 22% SOC (two bars)

One week later (today) the weather was 28C (about 18C min) and about 30C in my shed where I was charging. Same 105km trip. Arrived home with 5 bars on the meter.

That's A massive difference. Usually my runs are very consistent. within a percent or two each time. Dash gauge bars always the same so you have to use canion % to pick the difference.

Though the massive swing in the weather(temperature) over just one week showed up very well in the two SOC reading over the same trip (wind was nothing both times and weight was the same) Sat on speed limit both trips.

Typically it's a slow drift in the usable capacity from summer to winter and then repeats the same over again.

Is it as simple as the cold batterys voltage will rise faster so when charging it will show 100% SOC befor it actually is (as in the imiev always finishes the charge at 4.15v regardless of how many whr it had recharged.

Kurt



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Post by acmotor »

4.105V Isn't it ?
Yes to the voltage at end of charge being the shutoff point and that the voltage is reached sooner at lower temperatures resulting in less kWh in pack.
So is the temperature at charge time more to do with the capacity than the temperature during discharge ?
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Post by Malm »

I would like to know your values of current battery capacity. Mine now at 35 Ah. With 4 years and 4 month and 81000 km. It was very interesting that Canion could show us that value.
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Post by offgridQLD »

Yes sorry 4.105v, I'm thinking that's how it would work. Charge a cold battery and discharge it as a warm battery would result in less usable capacity that charging a warm battery and discharging a cool battery. As you can only take out what you put in.

Overall once you have lived with the car over many charge/discharge cycles that you monitor. You get to know the trends and notice changes over time based more on average results rather than the extreams.Though it did feel good to turn up at home with similar soc % than the first day I did the trip over two years ago.

If I had a 10% reduction at 80k and 20% at 160k I could live with that.

Kurt
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Post by acmotor »

Malm wrote: I would like to know your values of current battery capacity. Mine now at 35 Ah. With 4 years and 4 month and 81000 km. It was very interesting that Canion could show us that value.


Maybe the best way to compare battery capacity is still kWh from the wall using a standard 10A charge.
That is the only number that is without question. Working with Ah is subject to max and min voltages and nominal voltages. After all, it is all about energy in kWh.

I am putting between 14.3 and 15.1 kWh in from the wall. If I had to say it would be around 35Ah of what I consider was 39Ah at new. Refer to my earlier reasoning. We never had the 50Ah that the battery data sheet suggested.
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Post by offgridQLD »

Acmotor, perhaps the temperature of the cells when being charged should be noted when you take kwh from the wall. This most likely is the reason for any variation over a short period.

I'm not a fan of Ah units for any accurate data collection.

I will do a recharge this week from 20% SOC (canion reading) and see what kwh number I come up with. Asuming adding 20% to the wall meater reading at 100%soc is how your getting your numbers in that example.

Kurt

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Post by Malm »

I believe kWh from the wall as the problem of in one car 0.0% SoC is 280 total voltage, and in another 320 total voltage. The both can take the same energy from wall but the first one as less battery capacity. So, I believe Ah is a more correct number to compare the I-MiEVs, but not perfect, for sure.

From the wall, I believe I can take something like 14,2 or 14,3 kWh, from 0,0% to full.
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Post by offgridQLD »

Like I have mentioned a few times the Imives battery monitoring system opinion is the only one that counts. The BMS has full control if it wants to call your battery bank 5kwh usable capacity then 5kwh it is.

If it wants to call 280v 0% SOC or 330v 0% SOC then so be it.

You just have to hope the BMS has got it correct. It's a big ask considering all the variables a battery can have and I'm sure there are times when it dosn't get it correct.

How much smarts Mitsubishi have packed into the bms is a bit of a mistery until some one pulls one down and works out how it's all been set up to monitor and controll SOC and usable capacity.

When the bms tells me (via canion) that I'm at 20% SOC I call that empty. When it tells me I'm at 100% I call that full. When 100% to 20% becomes less usable kWh I call that capacity loss.

Not much point knowing you have more usable capacity in your battery if the BMS won't let you use it.

Perhaps dropping the bank out of the car and cycling a cell or the weekest cell would be the only true reading. But unless you had a new cell spec to compare to.

Kurt

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Post by Malm »

Not that I think is good idea to let it go under 20%. But I really count with the entire energy, to 0,0%. I like to know if when the last bar disappears (at 12% SoC), I have enough energy to do more 10 km. With Canion and the voltages, I know how far I am of being stopped.

One of this days I'm planning in doing a 18 km trip all in turtle. And with voltages on the cells all the trip over 3,5/3,6 V, what I think is very secure to their safety.

Just fill safe to know the real limits, not that I go under 20% SoC often, I avoid that too. That´s the wisest choice.
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Post by acmotor »

My understanding...

100% SOC on canion means all cells are at 4.105V. Nothing about actual capacity, just that whatever capacity is full.
This is called full and depending on age, use and temperature, will represent less than 16kWh. However, if one cell only has 1Ah capacity then the whole pack capacity will be less than 385Wh.

0% SOC on canion is when one cell or more reaches the lower voltage limit. Is it 2.5V ?
It is possible, in a pack with varying cell capacities, for the average voltage to be anywhere between 2.5V and 4.1V when 0% SOC based on any one cell reaching lower voltage limit.

The higher the average voltage at low or zero SOC then the more spread there is in cell Ah capacity.
On the other hand, the lower the average voltage the closer the cell capacities are. So a lower average is possibly better, but it is the overall kWh of the pack that matters.

The one low cell will be working harder and will age faster.   Nothing new there in the reality of battery packs.

I think we are in agreement not to stress the pack by regular low SOC use.

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Post by Malm »

Lower limit is 2,75 V one cell. At least in my i-MiEV.
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Post by offgridQLD »

"Lower limit is 2,75 V one cell. At least in my i-MiEV."

What determines when the Imievs BMS pulls the pin and shuts the car down.

Is it a low voltage limit? (2.75v on any one cell) or just when the BMS reads 0% SOC on its SOC metering. Even if the lowest cell voltage is still reasonably high.

I can say for sure the BMS doesn't always get it correct (as we see the little adjustments it makes when its going off track)

At some point in time (how often I don't know) The car comes up with a new capacity number for the bank. The logic behind how when and why is a mystery.

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Post by acmotor »

my understanding....
A cell is charged when it no longer takes current at the nominated maximum voltage for safety / longevity and chemistry. Conversely, it is discharged when it's voltage falls to a nominated minimum as determined for safety / longevity and chemistry.

It appears that 4.105V is the magic top number decided on by mitsi and 2.75V is the lower limit. (actually anything below 3V or so gives minimal extra capacity as the voltage falls off fairly quickly)

The SOC is just a measure of the kWh in to go from min to max V.
You need to know that first.
Once you have that number you are just counting kWh in and out.
So, for instance, 16kWh in to go from min to max V you now call 100% SOC and know the total capacity of the battery.

If you pull 8kWh out you now have 50% SOC. If you then put 4kWh back in you are now at 75% SOC and so on.

This process gets a little out after numerous cycles and needs to be recalibrated by going back to min V and doing a full charge. In practice mitsi have been able to recalibrate without going to min V, just to 20% or so. Probably because the voltage vs SOC is so well linked.

SOC can thus be recalibrated and allow for degradation of battery pack.
100% SOC will represent less and less kWh over time.
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Post by offgridQLD »

Sounds good to me.

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Post by Malm »

"Is it a low voltage limit? (2.75v on any one cell) or just when the BMS reads 0% SOC on its SOC metering." The car don't run anymore, when it happens one of those two things. SoC can be at 4%, but if the lowest cell is at 2,75 V, it stops. If the worst cell is at 3,5 V, but SoC is at 0,0%, the car stops.

I think acmotor get it all right. I agree in everything.
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Post by offgridQLD »

"SoC can be at 4%, but if the lowest cell is at 2,75 V, it stops. If the worst cell is at 3,5 V, but SoC is at 0,0%, the car stops."

So with the 3.5v and 0% SOC example the car has made a conservative estimation of the capacity.I often see avarage cell. Voltage vs % SOC variations.

For example I might have 30 logged Canion screen shots where the SOC at the endof the trip is 21% but the cell voltage (avarage) varies a lot.I think this is where I notice the bms SOC (or new usable capacity) errors/variatios the most.

Kurt


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Post by g4qber »

http://www.greencarreports.com/news/109 ... y-capacity

Malm how often do you dc fast charge?

Seems that balancing cells and slow charging is important for maximising range.
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Post by acmotor »

Is there a canion equivalent with cell voltage monitoring for the model s ?

Having worked with numerous string battery packs and experiencing various balancing techniques, I would say that the imiev BMS is exceptional ! Balancing appears to be live during all recharging so the top balance is not that critical other than to calibrate the SOC ( energy ) meter. ( along with the minimum voltage as the 0% point )

It stands to reason that charging up and down but not visiting the min and max limits means the bean counter (SOC meter) will eventually be out. Temperature and rate being factors but even those are catered for in the BMS as much as possible.

Interesting that Mitsubishi limits the DC fast charge to 80% and tesla allows 98%.

I wonder if this is solely a temperature thing if charging from empty ?
Given the good cell balance, wouldn't it be practical to charge from 20% to 100% (98%) ?
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Post by Malm »

Rarely do it.
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Post by offgridQLD »

"Ah sorry Kurt, it was me68 who had measured 17.5kWh from the wall on a recharge. "

Acmotor,
        I Just went back through my Data. Last year I did a test run just once (curiosity got the better of me) Down to turtle onset. I then recharged the car from 8.5% SOC back to 100% on the 10A charger.

15.76kwh in from wall + 8.5% = 17.09kwh from the wall.

Today I'm doing the same test again but this time from 22% SOC back to 100% and will post the results when it's finished charging.




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Post by offgridQLD »

Results from today's charge. 12.7kwh + 22% = 15.49kwh

As you can see this is why I don't trust this method. Sometimes it results in 15.5kw others 17kw its all over the place.


There is no way I have 9% less capacity. If that was the case I would be arriving at my regular 105km trip on turtle every time.

The reality is I see very little difference at all from new just a few % drop in the middle of winter. last night I arrived home from the 105km trip with 4 bars remaining (exactly the same result as the first time I did the drip years ago.

The only way to know the true capacity is to pull the cell out and charge it to a set voltage and discharge it to set voltage.

I'm finding the KWh from wall + canion SOC % is to inconsistent and doesn't reflect the real world results.

Unless my meter is totally useless (inconsistent)






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Post by offgridQLD »

Did another capacity test today using Acmotors method ac in + canion % soc remaining I got 16.57KWH

Again 2 days ago I got 15.49kwh today 16.57kwh and not long ago 17.5kwh

I cant trust this method.

Acmotor,
          what kind of AC energy meter are you using? The charger is power factor corrected isn't it? My meter always reads the same number while its charging so to me the meter seems consistent.

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Post by acmotor »

Arlec power meter PC222 from Bunnings.
Ningbo power meter PM001-A form Red Dot
Both agree within 1% of true RMS amp and volt meters
Both display frequency and power factor as well as A,V,W and kWh
Both suggest imiev pf is .97 to .98

My energy 'add up' is kWh from the wall plus energy meter bars (at 1kWh ea.) not canion % SOC
That is where your calc varies from mine. I am not convinced of the % SOC that canion shows even though it gets it generally from the imiev. If canion shows 8.5% at turtle then so what, it is not accessible.
If the energy meter shows zero bars then I am happy to take it that the battery is flat. I don't go there anyway.
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Post by offgridQLD »

No I could drive my car at 130kph down the freeway in turtle it's just a light on the dash that comes on when the car is at 8.5% SOC. The energy is usable not even any power restriction. the voltage is still high even under load . I have never taken the car to the point where it shuts down. 0% SOC.

Bars on the dash gauge is no better than canion as they both are representing the same thing. They come and go at a set % value on canion like clockwork. It's a concreat rule

For example 22%(canion) is always 2bars (every imiev in the world will follow this rule)
8.5% is always turtle and so on you can note it for your self and watch it repeat like clockwork.




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