[Schorschi]

In recent days I've been testing how little battery power I need to get to work.

For the roughly 20-mile trip, consisting of 15 miles of highway and 5 miles of urban roads, I use up about 22% charge (according to the SOC gauge), not using the AC or heater. The economy reading on the dash display shows me some 4.1 mi/kWh for that trip.

But: if I calculate based on distance covered vs. energy used (i.e. kWh) I get a completely different value.

My first year annual service check-up back in April reported a battery capacity of 50.2 Ah. That converts to about 17.3 kWh (P * t = U * I * t <=> P * t = 93 * 3.7V * 50.2 Ah = 17,273.82 Wh ~ 17.3 kWh; 93 is the number of battery cells, 3.7 V the voltage of each cell).

22% of 17.3 kWh is 3.8 kWh. Dividing that into the 20-mile distance I covered, I get 5.25 mi/kWh, quite a bit off from the displayed 4.1 mi/kWh.

If I calculate the reverse, i.e. take the displayed economy 4.1 mi/kWh and divide that into the distance covered, 20mi/4.1mi/kWh I get about 4.9 kWh used for the 20-mile trip, but that's about 28% of 17.3 kWh, my total battery capacity.

I understand that I don't have the full 17.3 kWh battery capacity available, since battery management doesn't charge to 100% and doesn't allow discharging to 0%. I don't know what the actual usable capacity is, but let's assume it would be 80% of my battery's capacity. 80% of 17.3 kWh is about 13.8 kWh.

If the SOC gauge's 100% were equivalent to 13.8 kWh, then my used 22% of that would be about 3 kWh. With the 20 miles covered, that would be equivalent to about 6.6 mi/kWh. So that figure is even more off from the displayed 4.1 mi/kWh.

Where am I off with my calculation?

 

[SuperSmartie]

There are a few explanations:

The miles/kWh display is a guessgauge, as is the SoC meter. But the latter is a bit closer to the truth.

The battery voltage is not always 3.7V. It's higher than that most of the time, closer to 4.0 to 4.2V. the 17.8kWh "nominal capacity" is as the name says only a paper value. Discharge capacity under moderate load is closer to 20kWh. And yes, you have all that available (I checked).

There are charging losses: The battery voltage is higher during charge than during discharge (due to internal resistance) and the charger has some losses.

Once you take all that into account, the dashboard miles/kWh comes somewhat close to kWh Energy from the wall per miles driven.

 

[Yinzer]

I experience the same thing, but more pronounced. I never see more than about 3.6 mi/kWh, yet I know that with careful driving, I can get 90 miles on a charge. The standard advertised capacity of the pack is 17.5 kWh, so there is really no need to mess with AH and the variable cell voltages with charging and discharge - since these already figure into that advertised capacity. In my case, this indicates a real efficiency of 5.1 mi/kWh or 6.4 mi/kWh under a more realistic assumed 80% usage.

I know from using a kill-a-watt to measure the consumption when I charge my motor scooter (which uses what I would assume to be less efficient - high internal resistance Chinese "GBS Brand" LiFePO4 cells) that charging efficiency is pretty high with lithium cells - certainly in the 90s percent. So, the factors mentioned by SS above still does not explain the discrepancy.

 

[SmartElectric]

The answer is easy. The SOC meter is non linear.

As I found out on a long trip:
Smart Electric Drive: Running on empty, cause' that's the way I roll

I typically see SOC drop rapidly from 100% to 80% and then it drops slower from 80-30% and the last 30% takes much longer to use up, all given the same driving (ie same wh/mi).

 

[Schorschi]

Today I went full throttle for a few hundred yards on the highway. Then stuck behind a truck going 55 mph all the way until my exit. I ended up at the same 78% charge left when I got to work. The economy gauge showed 4.4 mi/kWh this time. Before it was at 4.1 mi/kWh. So, yeah, totally useless gauge.

 

[MB DNA]

It's kind of like that old school barometer hanging on the wall, needle moves but who knows?

 

[Banjoguy]

Okay, so I am a complete newbie to electric cars. I firmly believe in them and I intend to lease ( I am told the only way to own one ) a Smart ED. ( to be honest I find it ironic that a 65 year old is contemplating anything that ends in ED....) but I have a question.

If I buy used ( and I have asked this before but did not get an answer to my question ) what do I look for? With gas engines I can see the condition of the engine and checkout the mileage. But what do you look for with electrics .... When you buy computers you can check the charging cycles, is this relevant for an ED Smart. Do I look at the power gauges ( which is apart of the discussion in this thread ) do I look at the amount of charge held when the unit is recharged, is there a "sapping rate" that is generally acceptable.

I do not have range anxiety but I don't wish to buy a paper weight either. Any ideas please...

Rp

 

[YIMGreen]

From all I've read, Smart EDs are very reliable. I've had mine for two years without a single problem and, being electric, there's not a lot that can go wrong. However, you should probably check the service records to see if the car's had past problems (that it's not been a lemon right out of the box). If that's clean, and it's a low mileage car, you shouldn't have any problems. If there's a Smart center nearby that's reliable (and that's a rarity) you could ask for a reading of the state of the battery, (to tell you if any cells in the battery are degraded and by how much). This is something that's supposed to be done annually at the car's service but many dealers don't know how to do it, or don't have the equipment.

After that, enjoy the car.

 

[marc hanna]

Okay, so I am a complete newbie to electric cars. I firmly believe in them and I intend to lease ( I am told the only way to own one ) a Smart ED. ( to be honest I find it ironic that a 65 year old is contemplating anything that ends in ED....) but I have a question.

If I buy used ( and I have asked this before but did not get an answer to my question ) what do I look for? With gas engines I can see the condition of the engine and checkout the mileage. But what do you look for with electrics .... When you buy computers you can check the charging cycles, is this relevant for an ED Smart. Do I look at the power gauges ( which is apart of the discussion in this thread ) do I look at the amount of charge held when the unit is recharged, is there a "sapping rate" that is generally acceptable.

I do not have range anxiety but I don't wish to buy a paper weight either. Any ideas please...

Rp

As far as suspension and body and all non-engine related stuff, it's pretty much identical to the gasoline models. As far as the battery goes, you can take it to the dealer and have them run a diagnostic test on the battery to see if it's lost any capacity. I was one of the first North American owners of an Gen III ED, and I have almost 50,000kms on it now, and my battery test shows no degradation whatsoever - in fact it reads a little higher than what the original nominal Ah's are supposed to be (there is a margin of error on the measurement). So if you're going to test drive a used one, see if you can schedule a test at a local dealer the same time, so you can drive it right over and get it tested - or ask the seller to get it done and provide the report.

Hope that helps.

 

[Banjoguy]

YIMGreen, thanx for your reply, this helps a lot!

 

[MB DNA]

Most sellers aren't going to pay to prove the battery capacity unless you are buying from a smart Center.

Know what the title reads as a "branded" title may have a tell all back story?

Be prepared to deal with non-smart car dealers who know little about ED. Ask how many batteries the smart has, 2 would be the appropriate answer - the BP and a 12V. May want to know if the purchase price includes the BP most resales are complete sled + BP.

Best plan, be certain that the OEM Battery Pack warranty is still in place. Some (US) CARB states may impose even longer warranties which may be influenced by the original purchase state?

As others have said, fewer moving parts than an ICE have shown ED to be pretty reliable although cold weather can reduce your range.

 

[Banjoguy]

Marc Hanna, thanx for your reply it helps a lot! One of the issues I have noticed is that the MB dealers, even though they have Smart Centres, know little about the cars, and the sales reps even less. YINGreen in the post above has the same opinion, I think.

MB needs to establish dealer protocols for its dealers to sell Smarts or the dealerships lack of expertise will kill the brand.

 

[jimvw57]

Same old story. Dealers would much rather sell a car with a higher profit margin than they get on a smart.

 

[MB DNA]

Marc Hanna, thanx for your reply it helps a lot! One of the issues I have noticed is that the MB dealers, even though they have Smart Centres, know little about the cars, and the sales reps even less. YINGreen in the post above has the same opinion, I think.

MB needs to establish dealer protocols for its dealers to sell Smarts or the dealerships lack of expertise will kill the brand.

The SCoA choir has been singing this song since 2008.

While there are a few well informed/staffed smart Centers, YMMV.

 

[marc hanna]

Yup, different dealers will treat the brand very differently. I see you're down in Windsor, so I don't know what the dealers are like down there, but up here, Victoria Star in Kitchener charged me $305 for a B service which includes desiccant cartridge change and a brake flush, whereas Burlington MB wanted $560 plus materials.

 

[marc hanna]

Most sellers aren't going to pay to prove the battery capacity unless you are buying from a smart Center.

I agree, but I think things will change, and battery reports will be like CarFax. Especially with the potential cost of replacement of a bad battery - if a person wants to sell the electric car for a good price they will need to prove the state of the battery.

 

[SmartElectric]

I think things will change, and battery reports will be like CarFax. Especially with the potential cost of replacement of a bad battery - if a person wants to sell the electric car for a good price they will need to prove the state of the battery.

Exactly! I was in the market for a used electric car (in addition to my Smart ED) and found it difficult to get the sellers to report the range on a max charge. Even the manufacturer whom I bought my recent EV from did not disclose the full range, though when I picked up the car I did check that out and was pleasantly surprised, so there was no problem, but it was something I was interested in knowing for sure!

In the end, I think like Marc says, it will be come a requirement to report battery health just like a CarFax (my compliments Marc, I like that analogy!).

Buyers will need to become more informed, that would be a good first step.

 

[Be a star]

After a round trip to the local Y, which is 2 miles each way, my dash readout says 5.2 m/kwh. This is with extreme hypermiling. Temp is in the mid 40s. Never went more than 30 mph and much of it I did at 10 or 15 mph. Acceleration extremely slow and smooth and almost no use of brakes. There is some up and down, but nothing extreme.

Something cool -- I like to think in terms of miles per dollar equivalent of a gallon of gas. Since my electric rate is 25 cents/kwh and gas is around $2.50, the conversion is just a matter of moving the decimal point. 5.2 m/kwh is for me is 52 miles to the gallon (dollar equivalent thereof, that is) and 3.2 is 32 miles to the "gallon," etc.

My average is 3.3 m/kwh over the life of the car so far (2100 miles on a 2015 car bought new in 2017). Most of my driving is highway.

 

[InjuredAgain]

Wow! Gas is about $3.30 a gallon for regular, and we pay around 11 cents per kWh. Now that it has warmed up a bit, into the 45-60 degree range, we back to over 80 miles when just running around the city. Right now, we're at 41 miles driven and about 53% SOC remaining.

I've always considered the onboard calculation of miles per kWh as the power coming out of the outlet. Otherwise, it is terribly pessimistic, kind of like the range remaining display.