[Tremelune]

I was reading up on Teslas, and it seems that the batteries last the longest when they are kept near 50%. Essentially, a good working range is 30-80%, and only charging to 100% right before long trips helps promote battery longevity.

I know the battery packs aren't the same, but they're both essentially a huge bank of standard lithium rechargeables, right? Does this charge range hold true for our cars as well?

Teslas have the ability to charge to a preset level, so you can set it to (say) 60%, and it'll stop when it reaches that mark, and just stay there for days. The ForTwo has no such limiter, so I'm wondering how much effort I should put into timing my charge to unplug it.


Ultimately, in life, this doesn't matter...but I like to optimize occasionally inconsequential elements of my existence for fun and profit...

 

[MB DNA]

. . so I'm wondering how much effort I should put into timing my charge to unplug it.

Ultimately, in life, this doesn't matter...but I like to optimize occasionally inconsequential elements of my existence for fun and profit...

Tesla and smart, apples and oranges.

Four years of ED ownership - just plug and play . . .

 

[lebikerboy]

My son drives his ED 50 km's to work every weekday.
Therefore he charges every two days to 100% capacity.
So far, so good. I charge our Leaf whenever it gets down to
around 30% and usually disconnect at around 90%.

My buddy charges his Tesla Model S to the same parameters

mentioned earlier. I tell him to just get over it...

 

[Yinzer]

The lithium cells used in Teslas and the Smart ED are not the same format. The smart used 93 large prismatic 50AH cells custom made to MB's specs, in series. The Tesla uses thousands of little commercially available 18650 cells (bit bigger than "AA") in parallel - then series. The chemistry is a bit different too (NCA for Tesla, NMC for Smart and other EVs). But all lithium-based chemistries have the same behavior to greater or lesser degrees so should be cared for the same way. Try to keep the car at a mid-SOC level as much as is practicable.

The trouble is, with the Smarts ED's rather dinky battery, it is hard to start off on many driving errands with much less than 100% SOC - especially in cold weather. So I use the timer on my EVSE to delay charging so it get charged to 100% no sooner than a few hours before driving the car.

And if the car is left outside in very cold weather (<-20C) it needs to be plugged in - and that means that it will get unavoidably charged to 100 percent.

 

[sokoloff]

But haven't we determined that the battery doesn't actually ever charge to 100% even when the state of charge tells us it is? That's kind of a safety factor built in when it's left on the charger for an extended period, isn't it?

Len
2014 EV Coupe 17,500 miles
2014 EV Cabriolet 9,500 miles

 

[Yinzer]

There is a quick way to check that. The charge discharge curve of NMC cells will be pretty flat at 3.6 to 3.8 volts between 10 percent and 99 percent SOC, but spiking to 4.2 or 4.3 volts when hitting 100 percent - this is the point where charging switches to a constant-voltage top-off/taper the current mode to keep any individual cells from over-volting. The mechanical analogy is the cells behave like filing a bottle with a narrow neck. The ammeter on my EVSE indicates that this is what the Smart's charger seems to be is doing.

I'll run the battery pack diagnostics with charging just finished. If right at end-of-charge, it shows cell voltages of 4.2 or 4.3 volts per cell, then it is charging the cells to 100 percent.

 

[sokoloff]

Just did a battery check today and this was one of the readings:

SOC : 100.0 %, realSOC: 99.0 %

Looks like when it reads 100%, it is darn near 100% or am I misinterpreting something?.

Len
2014 EV Coupe 17,500 miles
2014 EV Cabriolet 9,500 miles

 

[Yinzer]

What were the cell voltages?

Just now, with charging just having shut off, mine stated SOC = 100% realSOC = 94.1% and the average cell voltage was 4.170. While I don't know what the "real SOC" indication is supposed to mean, 4.2 volts is pretty much 100 percent full for any kind of lithium-cobalt-metalA-metalB type battery chemistry, as well as lithium-polymer chemistry.

 

[sokoloff]

My 4.175 vs. a full charge of 4.2 comes out to 99% which pretty much matches what the state of charge numbers indicate.

From this mornings test:

Individual Cell Statistics:
-----------------------------------------
CV mean : 4175 mV, dV= 26 mV, s= 2.78 mV
CV min : 4151 mV, # 6
CV max : 4177 mV, # 3

Len
2014 EV Coupe 17,500 miles
2014 EV Cabriolet 9,500 miles

 

[Yinzer]

My 4.175 vs. a full charge of 4.2 comes out to 99% which pretty much matches what the state of charge numbers indicate.

Except that that would not explain my results.

I have messed with lithium cells a lot with my semi home-built 2 wheel EV's and as I wrote, the no-load voltage/SOC relationship is far from linear - especially at the top - it is analogous to a bottle with a very narrow long neck. The last 0.1 volt represents going from 99.95% to 100%

 

[Tony Margulis]

I've wondered the same thing, which is why I purposely use slow mode on the level 1 charger overnight. So if/when it does hit 100% SOC it's close to me waking up and going to work. I also am wondering if the 453 has a built in buffer that the 451 doesn't. According to the EPA, the 453 motor is a hair more efficient, the batteries are the exact same size, but the 453 is rated at 10 miles less range.

 

[Yinzer]

According to the EPA, the 453 motor is a hair more efficient, the batteries are the exact same size, but the 453 is rated at 10 miles less range.

That is becasue the EPA changed to a more conservative test method. In Europe, the 453 is rated as getting a little better better range per charge.

 

[jimsokoloff]

According to the EPA, the 453 motor is a hair more efficient, the batteries are the exact same size, but the 453 is rated at 10 miles less range.

I believe the 453 batteries are slightly larger than the 451's (55 Ah vs 52Ah and 96 cells vs 93 cells).

 

[Tony Margulis]

According to the EPA, the 453 motor is a hair more efficient, the batteries are the exact same size, but the 453 is rated at 10 miles less range.

I believe the 453 batteries are slightly larger than the 451's (55 Ah vs 52Ah and 96 cells vs 93 cells).

Wouldn't the 453 get better mileage then?

 

[jimsokoloff]

Better range, yes, of course. I was responding to correct the claim that it had a battery of the exact same size.

 

[Yinzer]

Wouldn't the 453 get better mileage then?

Yes. And most reports are that it does get better range.

 

[SMART-GUY]

Just did a battery check today and this was one of the readings:

SOC : 100.0 %, realSOC: 99.0 %

Looks like when it reads 100%, it is darn near 100% or am I misinterpreting something?.

Len
2014 EV Coupe 17,500 miles
2014 EV Cabriolet 9,500 miles

Hello,
Witch software use to check battery status?
Thanks

 

[sokoloff]

This is what I use - Battery Health Check Tool for smart Electric Drive (model 451)

Full disclosure - my son builds them.

Len

 

[jimsokoloff]

Indeed. I make and sell them for people who don't want to build it themselves or find a local electronics hobbyist to build it for them.

If I'm guessing correctly that you're in Romania, you might prefer to buy it from a seller in the EU rather than waiting for it to arrive from the US. Both units are using the same software.

 

[SMART-GUY]

Indeed. I make and sell them for people who don't want to build it themselves or find a local electronics hobbyist to build it for them.

If I'm guessing correctly that you're in Romania, you might prefer to buy it from a seller in the EU rather than waiting for it to arrive from the US. Both units are using the same software.

Thanks,
I will order one.