Charging at work

[gt1]

I have access to a 120V outlet at work. How many miles of range should I be able to add after an 8 hour charge?

 

[Jeffj]

When set to max charging, the car will pull 12 amps x 120 volts for a maximum of 1400 watts. So each hour, you'll add 1.4 kWh to your car. That translates to ~5-6 miles/hour of charging, depending on how you drive. Charging will be slower once the battery gets above 85% or so.

 

[janner]

It's also important to get an hour or so at full charge and still connected so the battery management system can 'smooth out' the individual cell charge: the system will check every cell and then lower all to the lowest charge then top up again to full. The charge rate for 120v is between 0.66 and 1.33kW so with an 18.8kW battery you may never quite get to maximum charge. If that is the case then try and find a time when you can leave it connected for longer.

 

[Leasi3]

I have access to a 120V outlet at work. How many miles of range should I be able to add after an 8 hour charge?

Real world figure under four miles per hour (4 mph). There is some fixed overhead for the cars control systems, power losses due to the inefficiencies of boosting the voltage up high enough to charge the batteries and the loss of converting DC to battery charge itself.

Until recently I charged this way at work (They just installed two level 2 (30 AMP) EVSEs, so .)

I used a 20A 120V GFCI outlet, and at the 12 amp charge rate it took 8 to 9 hours to fully charge back to 100% to make up for my 23 mile commute.

 

[Jeffj]

The last percentages, especially above 95% charge far slower than the percentages "in the middle". Getting back to 100% charge from, say 80%, will take significantly longer than getting from 60% to 80%.

 

[alohart]

In early 2015, BMW starting equipping i3's with 10 amp rather than 12 amp EVSE's. If you have a 10 amp EVSE, your charging rate will be even slower.

 

[gt1]

Thanks. Looks like I should be able to cover or almost cover my 40 miles R/T commute if I don't keep the battery fully charged. Which is also an advantage- charging the battery to 100% reduces its lifespan. IIRC, Nissan LEAF even has an option to limit charging to 80%.

 

[jadnashuanh]

Thanks. Looks like I should be able to cover or almost cover my 40 miles R/T commute if I don't keep the battery fully charged. Which is also an advantage- charging the battery to 100% reduces its lifespan. IIRC, Nissan LEAF even has an option to limit charging to 80%.

FWIW, the i3 never charges the battery to an actual 100% nor will it let you discharge it fully...it will shut itself off, though, and, with the (I think) much better logic and better temperature control on the batteries than the Nissan, especially their first generation I really doubt you'll have battery issues related to using an EVSE. The i3 is not like a cellphone..it shuts off the input power when it thinks it's full...it does not sit there constantly with the charging circuits trying to pump energy into the batteries...the analogy is not exactly the same regarding charging.

What you will likely find out though, is that the Level 1 EVSE provided in the USA, you won't be able to use a departure time with preconditioning and expect to leave with 100% like you could if you had a higher capacity EVSE hooked up.

 

[gt1]

Cell phone charging controllers use the same logic- they limit charge and discharge voltages, and slow down the charging when nearly full. Of course a phone battery has only one cell and doesn't need to deal with the extreme temperatures.

 

[jadnashuanh]

I think one major difference is, that on EV's, they can disconnect the input power at will to control the charging. And, with active heating and cooling on the i3, they can keep things in the sweet spot to coddle the batteries for long life.

 

[gt1]

I did a little bit of reading on the battery tech when i considered getting a LEAF for my parents (they didn't want it after all) At that time, it wasn't much data about long time Lithium battery performance. Amazingly, the longest and most detailed publicly available information came from the Mars rovers! The consensus was that the longest life could be achieved by minimizing the temperature extremes, avoiding full charges and discharges and charging slowly. In practice it means that if an average commute uses 40% of the capacity, it is better to keep the battery between 40 and 80%, rather than between 60 and 100. You're right about the Nissans, they have no thermal management and it lead to problems in the hot Southwestern states. i3 battery should last longer.

 

[jadnashuanh]

FWIW, the BMW i3 never charges to an actual 100% nor discharges to 0 for exactly those reasons. What is shown to the operator is the usable value, not the actual battery capacity.

 

[gt1]

I skimmed through the factory i3 presentation materials. It says that the battery charges to 100%, but discharges to 10% when it displays 0%.

 

[alohart]

I skimmed through the factory i3 presentation materials. It says that the battery charges to 100%, but discharges to 10% when it displays 0%.

That doesn't square with 18.8 of 22 kWh, or 85%, being usable. If the battery pack has a 10% buffer at the low charge end, then it would have to have a 5% buffer at the high charge end. The life of a Li-ion battery cell is shortened if it is repeatedly fully charged and discharged, so I'm confident that BMW would not guarantee 70% capacity after 8 years or 100,000 miles, whichever occurs first, if its battery management system allowed 100% charges.