Just about ran the battery out yesterday,barely made it home

So yesterday I had no plans other than to come straight home after work and usually after my 64 mile commute I have about 15-20 mile range left when I get home.
So at work I played around and took people for a ride and showed how quiet and how much torque this thing has.
Then on the freeway home with the AC on, I took it to it's max of 85 and then set the cruise control to 80mph. The speed limit is 75 and everyone here drives at 80-85.

Then my fiance called and wanted me to stop at the store and also her rental house to bring her stuff.
I did all that and after getting home I had 9 miles left. We had to go back to her house and the round trip is 8 miles. We took my car since I've always been able to regenerate and gain some miles in the city.

After getting to her house the range said 5 miles and I had a 4 mile drive to get back home.
There are a few charging stations along the way home so it really wasn't that big a deal but we were having friends over for dinner and didn't want to have to stop and charge for 20 minutes to get an extra few miles.

I easily made it home and had 2 miles to spare. When our friends came over I took them for a ride and got home with one mile left.
I wanted to see what would happen if I went to zero so we drove around my neighborhood a bunch or times with one mile remaining and I drove with the AC on and went at least a few miles.
So I think there's some kind of buffer built into the system that gives you a few extra miles.
When I pulled back into the garage I went 82 miles and used 19.8kWh.

Think of it this way. On an ICE vehicle, when the fuel gauge reads empty the vehicle doesn't just stop, there is always a reserve. Same thing for the FFE. My full charge budget is currently 65 miles, I should have no problem getting 20+ more miles by driving smart.

Our son (age 17) drove our car down to 0 recently. He was 2 miles from home and he just kept driving until he was home. So we know there's at least 2 mi of reserve. Personally I think that's where the other 3 kWh are - at the bottom as a reserve. Ford doesn't tell you it's there on purpose. No, I'm not going to test this theory. Someone else can do that!

Note: This is just a theory. Don't count on 3 kWh of reserve if you need it to get where you can plug in.

hcsharp said:

Personally I think that's where the other 3 kWh are - at the bottom as a reserve. Ford doesn't tell you it's there on purpose.

Click to expand...

There may be some small reserve beyond when the car reports "0 miles" of range, but it's nothing like 3 kWh's worth. Draining an additional 3 kWh beyond the known 19.5 kWh of normal usable charge would bring the battery dangerously close to an actual complete discharge, something that can permanently damage lithium-ion batteries. I don't think the FFE would ever let the battery get that low.

I suspect the "safety charge" for the FFE battery is about 10% of its total capacity (or, about 2.3 kWh). This is a minimum level of charge, which the car will never discharge below. This would be in line with industry practice to avoid "bricking" li-ion batteries through complete discharge. This safety charge of 2.3 kWh plus the normal usable charge of 19.5 kWh totals 21.8 kWh, which works out to about 95% of the total capacity of 23 kWh. This would also align with industry practice to avoid actually fully charging li-ion batteries (again, this also avoids damage, especially if the battery were then to be left in the fully-charged state for an extended period).

WattsUp said:

There may be some small reserve beyond when the car reports "0 miles" of range, but it's nothing like 3 kWh's worth. ...
I suspect the "safety charge" for the FFE battery is about 10% of its total capacity (or, about 2.3 kWh). This is a minimum level of charge, which the car will never discharge below.

Click to expand...

I assume you are speculating or do you know for sure? I can't find any definitive evidence on this (not saying you're wrong). Has anybody ever run their car until it actually stopped? And then reported how many kWh they used after hitting 0 miles? Obviously it won't let you discharge to an unsafe level, or a level that will be difficult to recover from if you plug it in.

WattsUp said:

This would be in line with industry practice to avoid "bricking" li-ion batteries through complete discharge. This safety charge of 2.3 kWh plus the normal usable charge of 19.5 kWh totals 21.8 kWh, which works out to about 95% of the total capacity of 23 kWh. This would also align with industry practice to avoid actually fully charging li-ion batteries (again, this also avoids damage, especially if the battery were then to be left in the fully-charged state for an extended period).

Click to expand...

While it is industry practice to prevent the cells from reaching a low state of charge, and also to prevent them from being charged full, I don't think it is common to advertize a 23 kWh battery when only 19.5 is usable. What does Nissan do? That begs the question where is the other 3.5kWh? The Tesla Roadster has a 56kWh battery but only advertises a 53kWh battery because that's how much is usable. Ford was very conservative and I suspect they put most of the additional 3.5kWh un-stated reserve at the low discharge end of the pack. It's bad for longevity to charge full but also bad to discharge low even if it's still at a safe level, say 10 or 15%. In essence, they might be trying to prevent drivers from destroying their batteries by displaying 0 miles when there's 3kWh left. They still let you drive it below 0 to prevent an emergency.

Assuming they're not resorting to false advertizing (23 vs 19.5) we can't allocate any of the 3.5kWh at the top of the charge cycle. Ford was conservative and only charges up to about 85% of the chemical capacity of the cells. It never allows you to do a range-mode charge like Tesla which still only goes up to about 90 or 95% of chemical capacity.

All of this is speculation of course. Would be nice to get real answers from Ford engineers.

hcsharp said:

WattsUp said:

There may be some small reserve beyond when the car reports "0 miles" of range, but it's nothing like 3 kWh's worth. ...
I suspect the "safety charge" for the FFE battery is about 10% of its total capacity (or, about 2.3 kWh). This is a minimum level of charge, which the car will never discharge below.

Click to expand...

I assume you are speculating or do you know for sure?

Click to expand...

It is all speculation, based on educated guessing and things learned about other EVs, lithium-ion batteries, etc. But the math works out for the FFE as well...

The EPA sticker says the FFE can go 76 miles with an efficiency of 320 Wh/mi of "wall-to-wheels" energy. So, how much total energy is that?

76 miles * 320 Wh/mi = 24320 Wh

Since it is wall-to-wheels, that 320 Wh/mi figure includes the energy used to charge the car (per mile). We know li-ion charging is not 100% efficient; it is about 80% efficient. So, how much energy (can we conclude) must actually be stored on-board the car used to go 76 miles?

0.8 * 24320 Wh = ~19456 Wh

This is one thing that leads me to believe that that "usable capacity" of the FFE battery is indeed about ~19.5 kWh. Another is my own personal experience which has showed that an my FFE when empty (showing "0 miles") takes somewhere over 24 kWh to charge from the wall (which corroborates the above figure of 24320 Wh of wall-to-wheels energy).

I've also noticed that, if I drive along at an average energy usage (as reported by the car, representing the internal "battery-to-wheels" flow) of 256 Wh/mi, I can easily achieve the advertised 76 miles of range. It is no coincidence that 256 Wh/mi is about 80% of 320 Wh/mi. Again, just a reflection of the charging overhead, which again leads me to conclude that 19.5 kWh is the usable energy capacity of the FFE battery.

In any case, given that 19.5 kWh seems to be what the car can actually use, and given that we know that li-ion batteries are never fully discharged and (preferably) not fully charged, the FFE having something like a 10% buffer and only charging to about 90-95% capacity seems very plausible. I don't know if we can call it "false advertising" to state that the car has a 23 kWh battery (the car is also advertised as having 76 miles of range, which it easily achieves) but it would appear, based on empirical evidence alone, that the full capacity of 23 kWh simply isn't at our complete disposal. (But, neither would the total capacity of the battery in any EV.)

Now, I've heard stories of people driving a little further after their FFE has reported "0 miles", but I've also stories of people whose car shut off only seconds after "0 miles" appeared. I would be more willing to chalk that kind of discrepancy up to variations in the range prediction algorithm, perhaps not counting down to 0 miles at exactly the same rate in those different cases, rather than a "secret" reserve Ford hasn't told anyone about.

I agree, though, it would be nice to learn the exact technical details from Ford.

That all makes sense and the math works. Thx for the explanation. I'll have to abandon my theory. I guess my son was lucky to make it 2 miles after he got to 0. It still surprises me that Ford advertises a 23kWh battery when it's totally impossible to use that much. Tesla does not do that. Chevy (Volt) does not do that. I don't know what Nissan does.

Ford only has one charging mode. They don't have a special range mode for occasional long trips. In order to get the battery longevity they are experiencing, they can't be charging to more than about 85 - 90% on the high end and, like you estimated, only down to about 5 - 10% on the low end. Of course capacity is irrelevant because all we care about is how far it will go...

I was able to go about a mile after the "charge depleted" message came on before losing power. That was uphill, though. From what I can tell by retracing my steps over the same route and looking at the trip meter, there was something less than 1kWh left. On flat terrain I'm guessing that I could have gone maybe 3 miles. Here's the story:

http://www.myfocuselectric.com/forum/viewtopic.php?f=8&t=927

12v battery was fine, so lights, gauges, power steering, brake booster, etc still worked.

We drove it till it lost acceleration (coasted in next to our garage) and went about 1-2 miles past 0. We did it just so we understood its limits and what would happen exactly. Feels like it just goes into neutral.

The GPS is funny. The circles of range shrink and shrink until zero and then they disappear. lol.

I wouldn't recommend planning on going past 0. I get the SSN the moment I hit it, and the accelerator stops working completely about 15 seconds afterwards. It's happened 4 times now, and each time, I supposedly had more range than I needed...

I wanted to know if zero was really zero so after my wife brought the car home from a trip with about 7 miles on it, we drove it around to deplete the battery fully. We got the "battery depleted" message and then continued to drive around my neighborhood. I don't think we drove more than another mile on nearly flat ground before it just wouldn't go any further.

Accelerator would not work. All instrumentation still worked, lights stayed on, etc. Power steering went out but could still manage to steer. Ended up pushing the car home, about 100 yards and then it charged up like normal.

I did this with only about having the car for 2 weeks, have had it for 3-1/2 weeks so far. Haven't had any problems charging or any loss of battery capacity that I can tell. At least now I believe that zero is close enough to empty to believe it.

Focused_Driver said:

All instrumentation still worked, lights stayed on, etc.

Click to expand...

All those things are powered by the 12V battery.

In the FFE, depleting the high-voltage battery is sorta like having an empty gas tank. The rest of the car still works. You just can't drive it anywhere.

I did a similar experiment myself; but mine was to see what the available battery capacity is. Ford likely pads the charge and the depletion to prolong battery life. I've had mine for 12.5 months and using the trip meter and running the battery down to 1% and 1 mile to go, I had consumed 17.8 kWh and drove for 84.5 miles. While sitting in the garage with the car on while collecting my data, the depleted battery warning popped on and showed 0 miles and 0% battery. I had gunned the motor just before pulling into the garage to see if all the power was still there, and it was. Wh/mile showed 211.

I drove with no heater but most of those miles were late evening, lights on, and in hilly terrain. Also, for grins, the guess-o-meter reported 92 miles the next morning for the range. Also driving temp was in the 60-70 range.

davideos said:

I did a similar experiment myself; but mine was to see what the available battery capacity is. Ford likely pads the charge and the depletion to prolong battery life. I've had mine for 12.5 months and using the trip meter and running the battery down to 1% and 1 mile to go, I had consumed 17.8 kWh and drove for 84.5 miles.

Click to expand...

Interesting. Thanks for sharing! I think this is the first report of some capacity degradation for FFE. Did you do a similar experiment when the car was new, for comparison? If not, then I'll assume your car when new had 19.8 kWh usable like mine did. Was it still at 17.8 kWh when it hit 0%? Then your car's capacity is down just about 10%. Or using 19.5 that is often quoted around here, you're down 9%. How many miles do you have on your FFE?

Also driving temp was in the 60-70 range.

Click to expand...

I know from experience that colder temps cause temporary decrease in available capacity, as opposed to capacity degradation from aging/use. I think 60F isn't cold enough to be a factor but I'll defer to those on this forum who know a lot more about Li battery behavior.

I'm approaching 10k miles on my vehicle but will have to wait til April or May for weather warm enough to do my next capacity check.

I didn't do any analysis when it was new. I have just over 10k miles now. However, I think the range is about the same...which is why I was driving conservatively to get the most distance possible; I did do that when it was new.

I do believe the percentage of battery remaining on the eco screen is non linear. Not sure if it is hard programmed or somewhat adaptive, but as the battery drains from 100% to 50%, for each 10% down, an additional 1.6kwhs is consumed per the trip-odometer. After 50% or so, that amount increases such that 17.8kwhs are shown consumed when the battery gets to zero.

I'm curious if anyone else has done a measurement in this way and what expended power on the trip-odometer reads as the battery on the eco screen depleats. It could just be that it is either wrong like the guess-o-meter for range, or the power consumption on the trip-odometer doesn't account for other power used...or even more likely, battery recharge losses when regerative braking is engaged.

I did my last test back in Oct; I didn't note the temp but I'm going to guess 50ish.
There was a distinct non-linearity at both top and bottom.
1500 mi on the car.

Charge Used-kWh
Level%
99 0.0
95 0.4
90 1.1
85 1.9
80 2.8
75 3.9
70 4.8
65 5.8
60 6.7
55 7.7
50 8.7
45 9.8
40 11.1
35 12.3
30 13.3
25 14.0
20
15 15.7
10 16.5
5 17.3
3 17.5

GladeStorm,
Thanks for sharing your data. It looks like you are right on par with me. That first 10% for me is usually 1.5kwh to 1.6kwh, but the other day, it was about 1.0. I think that sometimes the car doesn't quite get the battery to the peak. 50% of the time, when I leave my house in the morning, the regenerative braking doesn't work for the first mile. My first 1/4mi is all downhill. I believe this is because it doesn't want to charge when the battery is full. However, in the long run, as you have shown, it is just for that first 10% and not after.
I think this is the best way for us to determine the state of our batteries...provided that Ford didn't program the car to compensate for degredation by taking back some of the margins.
Thanks again.

I posted these numbers in September, noting the same nonlinear behavior of the percentage displayed at the higher end:
(Outside temps were comfortable, 70s I believe.)
At 90% remaining, I used 1.5 kWh.
At 75% remaining, I used 4.1 kWh.
At 50% remaining, I used 9.4 kWh.
At 25% remaining, I used 14.7 kWh.
I plugged in at 19% remaining, at which point I used 16 kWh.
Projected usable capacity according to those numbers went up from 15 to 16.4 to 18.8 to 19.4 to 19.7 kWh as I drove.

On the other trip when I actually went down to 0%, I didn't log the interval numbers like this but I saw the same basic pattern with relatively rapid drop from 100% down to ~75% using just over 4 kWh, followed by more steady decrease of about 2kWh for every 10%, all the way to zero having used 19.8 kWh. Rather than drive around til it hit 0 and risk having to push, I pulled up to a charger with 2% remaining and turned the heater on high to use the final 2%, which didn't take long.

I trust the trip meter numbers more than the percentage. I see it like my phone/tablet percentage, which do kind of the reverse in that they hang out near 100% for a long time, but drop like a rock from 15% to 0. In my FFE I believe 100% and 0%, and take everything in between as a ballpark estimate at best. It's still more useful than the blue battery graphic, but I'd like it to be truly accurate.

You know, it would be great if Ford did program the car to allow some access to the battery's unused margins over time. Since rate of capacity loss decreases over time, the benefit of keeping those margins decreases too. Of course you'd want to keep a minimum charge reserve but the high end margin would be less necessary in an already aged battery. I would think Ford would brag about a feature like this so I doubt it's the case.

I agree, it's prudent to have some periodic measure of battery capacity particularly for those of us who aren't leasing.

dmem,
Thanks for the data. I'll have to check again in summer to see if the 20 degrees makes a difference. At least I have a baseline now.

I agree that the percentage might not be that accurate. Who knows what it is based on...probably battery voltage, which isn't very linear at all. I'm also wondering about the trip-odometer too as power consumed does roll backwards during regen. Does it take into account the efficiency of the charging circuit and the retention of the battery?

Anyway, I'll keep my eye on it. Thanks again for the data.

davideos said:

I agree that the percentage might not be that accurate. Who knows what it is based on...probably battery voltage, which isn't very linear at all. I'm also wondering about the trip-odometer too as power consumed does roll backwards during regen. Does it take into account the efficiency of the charging circuit and the retention of the battery?

Click to expand...

The trip meter does "register" regen energy. One way to watch this in action is to perform a long, steady, efficient brake (e.g., as if trying to achieve a 100% brake score) from a significant speed. You should be able to observe the total kWh used click backwards a little bit (due to regen, you just "un-used" some of the trip energy).

Even when you reset the trip meter mid-trip, so that it reads 0.0 kWh, and then do some regen immediately after, it will not start clicking forwards again until all the "negative" energy has been consumed. Unfortunately, the trip meter will never display the negative kWh energy that has been registered, but it is accounted for internally in its computations.

Your other question about whether the trip meter takes charging and battery efficiency into account is a good one.