Range - Temperature

[TonyWilliams]

I see what I did wrong. I used the 4v charge cut off voltage of the MB as the voltage figure when I figured the power when I should have used the average voltage over the cycle which will be about 3.5v.
3.5v times 2900ma times 3696 cells = 37.514 kWh.

The published voltage range 4.2v to 2.5v, which is 3.35v average.

3.35v * 2900ma * 3696 cells = 35.9kWh

 

[sendler2112]

The published voltage range 4.2v to 2.5v,

Gladly, Mercedes has decided to stay well away from these values which result in a 600 cycle life of the cells to 80%. Running 4.05v to 3.6v shows tests of 3,000 cycles to 85% and the line is flattening out. Do you think we could actually see 6,000, 50% cycles, to 70% remaining capacity with careful use? Which is over 200,000 miles.

 

[TonyWilliams]

The published voltage range 4.2v to 2.5v,

Gladly, Mercedes has decided to stay well away from these values which result in a 600 cycle life of the cells to 80%. Running 4.05v to 3.6v shows tests of 3,000 cycles to 85% and the line is flattening out. Do you think we could actually see 6,000, 50% cycles, to 70% remaining capacity with careful use? Which is over 200,000 miles.

Huh? No, they won't "stay away" from those values. They will use them EXACTLY, as I spelled out several times.

You are the variation in the cycles. If you only charge to 60% and discharge to 40%, and repeat daily, you will get less "cycles" than the guy who charges to 4.15v (née 100%), and then discharges all the way to dead (2.5v, actually about 1%-3%).

Obviously, virtually everybody will fall in between those numbers.

The "28kWh" usable value appears to be 4v.

The "31-33kWh" usable value appears to be 4.1v to 4.15v.

Again, 4.2v is reserved as the threshold for regeneration.

I'm not giving you this data as merely conjecture. I observe the BMS data daily, including:

SOC%
Pack voltage
Min and maximum cell voltage
Minimum and maximum cell temperatures
KWh consumed
KWh regenerated / recharged

 

[sendler2112]

If you only charge to 60% and discharge to 40%, and repeat daily, you will get less "cycles" than the guy who charges to 4.15v, and then discharges all the way to dead (2.5v).

Sorry but this is definitely not true. The Panasonic charts show a 20% loss in capacity after only 300 cycles when charging to 4.2 and discharging all the way to 2.5. If Mercedes did this, the battery would lose 20% after only 35,000 miles. The next chart shows only 12% loss after 3,000 cycles when charging to 4.0v (as MB does) and discharging to 3.6v (60% remaining on the gauge?). This is 110,000 miles. And you could probably get that much again before you hit the 30% mark that designates a valid call for replacement. And the same chart shows that if you can keep to a 1C discharge, the loss of capacity is barely 8% after 3,000 cycles.
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This is well known that the last 10% on either end of a cycle is very,very hard on a Lithium cell. Especially on the bottom where the weakest parallel group will always be the same one to suffer the most. If you plan on keeping the car, or care about the next guy, charge up to the normal full mark at least once in a while so the cells can balance, and use what you need for each round trip and charge again.
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[sendler2112]

Not sure why Panasonic decided to run the 3,000 cycle test down to only 3.6v. The discharge graph doesn't look like the cells are really suffering until a rest voltage of 3.3v and when under a 2C load of 3.0v. 3.6v was leaving quite a bit of power on the table. I would expect a similarly long pack life down to these levels which results in many more miles.
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[TonyWilliams]

If you only charge to 60% and discharge to 40%, and repeat daily, you will get less "cycles" than the guy who charges to 4.15v, and then discharges all the way to dead (2.5v).

Sorry but this is definitely not true. The Panasonic charts show a 20% loss in capacity after only 300 cycles when charging to 4.2 and discharging all the way to 2.5. If Mercedes did this, the battery would lose 20% after only 35,000 miles.

I'm not sure what you think we are disagreeing on.

Of course, as I stated, Panasonic documents, and you post, the battery will suffer more if operated from 0% to 100% than from 40% to 60%.

Yes, according to the data, I suspect that 20% loss under those extreme circumstances is possible.

I already have 44.000 miles on one of my RAV4 EV's with exactly the same cells, and it has about 10-15% loss of capacity.

 

[heikospallek]

You are all quite the engineers here: Thanks for sharing your insights! Today, it is about 60F here in Pittsburgh and the car is 100% charged and the display tells me a range of 60 miles in E mode (in the past this turns out to be an accurate estimate when I drive very carefully avoiding quick accelerations). So far, I drove a total of about 1,200 miles. How does these numbers figure into your 35,000 miles versus 110,000 miles discussion? I did not do the math, but it looks like faster degrading than suggested by the calculations here. Or, do I miss something?

 

[sendler2112]

the car is 100% charged and the display tells me a range of 60 miles in E mode

Will you really only get 60 miles? You have to do a range test to really know.

 

[heikospallek]

the car is 100% charged and the display tells me a range of 60 miles in E mode

Will you really only get 60 miles? You have to do a range test to really know.

I did a few times driving down to 5-10 miles (in one case to 1 mile) and the estimate is accurate +/- 4 miles.

 

[sendler2112]

What does your average consumption show on the display? 2.0 miles/ kWh?

 

[TonyWilliams]

You are all quite the engineers here: Thanks for sharing your insights! Today, it is about 60F here in Pittsburgh and the car is 100% charged and the display tells me a range of 60 miles in E mode (in the past this turns out to be an accurate estimate when I drive very carefully avoiding quick accelerations). So far, I drove a total of about 1,200 miles. How does these numbers figure into your 35,000 miles versus 110,000 miles discussion? I did not do the math, but it looks like faster degrading than suggested by the calculations here. Or, do I miss something?

In the EV community, we tend to refer to that "range" on your dash as the Guess-O-Meter, or "GOM".

The GOM reflects the economy of previous drives, plus temperature, and whatever else the programmers wanted to include to arrive at a guess as to how far you'll go.

The bad part is what you drove yesterday has no connection to what you'll do in the future. I'm not sure what you're referring to on the 35k to 100k miles issue. That doesn't apply to your issue.

Anyhoo, the bottom line is that we can't determine range or battery condition through the GOM. End of issue (at least for me). You guys are welcome to debate it.

Only Tesla uses a logical range figure that makes sense for determining both how much range and how much battery energy remains. Tesla uses "Rated Range" which is directly related to the amount of battery energy indexed to the EPA range.

Therefore, a full charge doesn't even need to show 100%, since it will show 265 miles. As the battery degrades over time, the fully charged car will show less rated range.

RANGE AUTONOMY FORMULA

Range autonomy in any thing that moves over land, through the sea, or in the air is always a product of autonomous stored energy (gasoline, diesel, jet fuel, nuclear “stuff”, rocket fuel, or electricity) multiplied by the consumption rate (economy) of that stored energy (miles per gallon, km per liter, tons per hour, or miles / km per kWh consumed).

So, the range of your Mercedes is always:

(Usable kWh stored) * (miles / km per kWh consumption rate) = (range in miles / km)

We know how much the battery holds from a "normal" charge; 28kWh

The only variable missing is what the predicted consumption rate will be to determine your future range.

 

[TonyWilliams]

Here is the thread from the RAV4 EV forum about the GOM:

http://www.myrav4ev.com/forum/viewtopic.php?f=7&t=825

 

[sendler2112]

tells me a range of 60 miles

Just look at the trip meters and tell us they say your average consumption is.

 

[heikospallek]

tells me a range of 60 miles

Just look at the trip meters and tell us they say your average consumption is.

I see "2.0 mpkWh"

 

[sendler2112]

I see "2.0 mpkWh"

Then your battery capacity is at least 100%. 2 miles x 30kWh =60 miles. Although there is conjecture that MB reports consumption including losses from the wall to wheels which would look more like 28kWh total. I talk to a guy on ecomodders that recently got a Nisan Leaf and he is occasionally able to get as high as 4 miles per kWh. His lifetime average is 122.9 MPGe.
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http://ecomodder.com/forum/showthread.php/nissan-leaf-30243.html
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Yours would be about 68 MPGe. If you could make your driving more efficient, you would have more range. See the driving tips at Ecomodders.com
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http://ecomodder.com/forum/EM-hypermiling-driving-tips-ecodriving.php
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[TonyWilliams]

tells me a range of 60 miles

Just look at the trip meters and tell us they say your average consumption is.

I see "2.0 mpkWh"

That is REALLY poor economy, and I saw somebody post 2.2 on another thread and show about 67-ish miles driven and 2% remaining.

Something is up. I'm not sure what that is, but that is very poor economy. The Rav4 EV weighs about the same 4000 pounds, with likely worse aerodynamics, and for me to get 2.0 - 2.2 miles per kWh would take some INSANE driving.

An almost 5000 pound Tesla Model S gets better than that.

There's a smoking gun on several of these cars, but I'll help you guys figure it out. You don't need any fancy driving to do better than 2 miles per kWh.

 

[heikospallek]

Something is up. I'm not sure what that is, but that is very poor economy. The Rav4 EV weighs about the same 4000 pounds, with likely worse aerodynamics, and for me to get 2.0 - 2.2 miles per kWh would take some INSANE driving.

While I am German and used to drive on the Autobahn, I am driving VERY economically and certainly have outgrown any youthful speeding behavior. So, I can say with certainty "It is not me!"

 

[sendler2112]

The other 62 mile ranger took his car to the dealer and the tech got 107 miles out of it.
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"I've had the "Battery Discharged" warning at somewhere below 70 before. But the dealer just said that a tech drove it home and back for a total of about 107 miles. I don't get it. Even if we drive conservatively, the state of charge meter is below 1/4 after about 60 miles. So everything we have indicates that we only get about 70'ish miles of range, but then they are able to get 107 (with the heater)."

 

[sendler2112]

What is the rest of the trip screen info? 2.0mpkWh and what else. Average speed? Elapsed time? 2 hours with the heater on costs you 10 miles
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The other owner with the range issue was showing 2.2 miles/ kWh and an average of 27mph which indicates a lot of stop and go. Every time you step on the brakes you are wasting energy unless you are very careful and think way ahead..

 

[sendler2112]

Here is another possibility to consider with the sub 0C overnight temps. You are only charging at work so the car is not plugged in overnight. I wonder what and when the battery heater is doing. See if you can take note of the battery percentage toward the end of the trip home when everything is warmed up and before you get out when you park the car. Versus what it says in the morning before you take off and during the first part of the trip before everything is warmed up. You could even reset the trip computer a few times each way to get an idea of the average consumption at different stages of the round trip. Set up a video camera of the dash so we can see what it says and when while you are driving?