Charging the BMW i3 from a 110 V/230 V socket

[Alessandro]

How efficient is the i3 if charged from a 110 V/230 V home socket ? Have you ever tried to charge your i3 at home and, if so, how many kWh does it take from a flat (or near flat) battery to full capacity ?

 

[mindmachine]

How efficient is the i3 if charged from a 110 V/230 V home socket ? Have you ever tried to charge your i3 at home and, if so, how many kWh does it take from a flat (or near flat) battery to full capacity ?

110 volt is not as efficient as 22o volt charging. Figure about 20% charging loss on 110 volts and 15% loss with 220 volt.

So approximately 22 Kwh on 220 volt.

 

[elptex]

Standard European home plug (220-240 volt) will charge to 100% in about 9 hours. I have done this twice.

Total battery capacity is 22kWh, of which ~18kWh is user-consumable, so ~18kWh is what will generally be charged. Losses from charging come into play so actual billable draw will be a bit more (eg. 10% loss = ~20kWh; 15% loss = ~21kWh). I have measured our electric meter/board installed in 2011 to have ~13% loss.

 

[ultraturtle]

So approximately 22 Kwh on 220 volt.

That's exactly what the EPA measured in its tests. 22 kWh out of the wall, 18.8 kWh into the battery => 85% efficiency.

I'll sample the approximate L1 (120 volt) EVSE efficiency later today after a short drive, although the average sample of recharging after many longer drives would be a more useful number.

 

[Alessandro]

Ok. thank you all

So approximately 22 Kwh on 220 volt.

That's exactly what the EPA measured in its tests. 22 kWh out of the wall, 18.8 kWh into the battery => 85% efficiency.

I'll sample the approximate L1 (120 volt) EVSE efficiency later today after a short drive, although the average sample of recharging after many longer drives would be a more useful number.

I'm very keen to know your numbers

 

[KurtEndress]

A couple weeks ago I made careful note of my 120V charging. It took 8.5 hours to recharge from 58% SOC. That's replacing 7.9 kWh at an effective rate of 930 watts. Since it was drawing about 1400 watts from the wall that's about a 66% efficiency.

That probably deserves more than a single test, but since I just got my 240V charger installed I be monitoring that now.

 

[kevinb61]

A couple weeks ago I made careful note of my 120V charging. It took 8.5 hours to recharge from 58% SOC. That's replacing 7.9 kWh at an effective rate of 930 watts. Since it was drawing about 1400 watts from the wall that's about a 66% efficiency.

That probably deserves more than a single test, but since I just got my 240V charger installed I be monitoring that now.

Wow...All I use is the occasional charger (110v), and with my measurements (kill-a-watt, and couple others devices), I have never seen worse than 85%.

 

[mindmachine]

A couple weeks ago I made careful note of my 120V charging. It took 8.5 hours to recharge from 58% SOC. That's replacing 7.9 kWh at an effective rate of 930 watts. Since it was drawing about 1400 watts from the wall that's about a 66% efficiency.

That probably deserves more than a single test, but since I just got my 240V charger installed I be monitoring that now.

Wow...All I use is the occasional charger (110v), and with my measurements (kill-a-watt, and couple others devices), I have never seen worse than 85%.

I too am really surprised at the low efficiency attributed to 120 volt charging.

 

[jadnashuanh]

Some of the energy costs during recharging can increase depending on how much the battery conditioning needs to work to get the battery pack into and keep it at the optimum. For example, if the vehicle is very hot or very cold, some of the energy just goes into heating or cooling it, not recharging it at all. Depending on how much of a charge it needs, that battery temperature control COULD be a significant part of your energy usage, just depends.

 

[WoodlandHills]

A couple weeks ago I made careful note of my 120V charging. It took 8.5 hours to recharge from 58% SOC. That's replacing 7.9 kWh at an effective rate of 930 watts. Since it was drawing about 1400 watts from the wall that's about a 66% efficiency.

That probably deserves more than a single test, but since I just got my 240V charger installed I be monitoring that now.

Wow...All I use is the occasional charger (110v), and with my measurements (kill-a-watt, and couple others devices), I have never seen worse than 85%.

I too am really surprised at the low efficiency attributed to 120 volt charging.

120v is a very small pipe, you just cannot force that much energy through it. 120 is like a drinking straw, 240v like a garden hose and DC is like a firehose!

Oops, my mistake, I reread your post and you are talking about charging efficiency (like you clearly stated, sorry) and not charging rate. Doh!

 

[ultraturtle]

I'll sample the approximate L1 (120 volt) EVSE efficiency later today after a short drive, although the average sample of recharging after many longer drives would be a more useful number.

Conditions were 78 degree garage, BMW Occasional Use Charge Cable (Nominal 12 amp, 120 volt, Level 1 EVSE), unloaded wall socket voltage 119.8 volts, dropping to 111.0 volts under load, initially drawing 1.22 to 1.31 kW. Charge took 5 hours 45 minutes:

Battery kWh charged: 5.6 kWh (13.7 to 19.3 kWh, or 73% to 100% SOC) measured from the i3 display
Drawn from wall outlet: 7.36 kWh - measured by Kill-A-Watt
Efficiency: 76%

My observation is that the significant efficiency drop is largely due to thermal management of the battery system. L1 charging takes 2.5 to 5 times as long as L2 charging, which means that much more time the battery pack and charging systems need to be cooled. I don't have a T.E.D. system monitoring this residence, so cannot repeat the exercise with my L2 EVSE at this time. Can anyone else help out so we have a basis for comparison?

Interesting that the car shows 19.3 to 19.4 kWh capacity.

 

[Alessandro]

Battery kWh charged: 5.6 kWh (13.7 to 19.3 kWh, or 73% to 100% SOC) measured from the i3 display
Drawn from wall outlet: 7.36 kWh - measured by Kill-A-Watt
Efficiency: 76%



Interesting that the car shows 19.3 to 19.4 kWh capacity.

my understating is that it's much more difficult to charge the "last" kWh than the previous ones, a cleverer sample should be to charge the battery from zero to 100% - if you have time and opportunity to do this experiment

 

[elptex]

my understating is that it's much more difficult to charge the "last" kWh than the previous ones, a cleverer sample should be to charge the battery from zero to 100% - if you have time and opportunity to do this experiment

That has to do with the battery, not the electricity supply. It isn't a matter of 'difficult', it is to protect the battery.

 

[Alessandro]

my understating is that it's much more difficult to charge the "last" kWh than the previous ones, a cleverer sample should be to charge the battery from zero to 100% - if you have time and opportunity to do this experiment

That has to do with the battery, not the electricity supply. It isn't a matter of 'difficult', it is to protect the battery.

I'm not sure it' s like this, I hope to see inthe next future a balanced test (from 0% to 100%) to figure out that

 

[ultraturtle]

a cleverer sample should be to charge the battery from zero to 100% - if you have time and opportunity to do this experiment

I will not do it, as I not only seldom deplete the battery capacity (only once in 1,500 miles), am confident that L2 charging is significantly more efficient (having measured both on other EVs), and do not have a planned 20 hour block of time for the car to sit on a charger.

It's largely an academic exercise for you, however, since your i3 will come equipped with a 220 volt (L2) EVSE, capable of charging it from depletion to 100% at 12 amps in a bit over 10 hours. You can decrease that time by a factor of roughly 2.5 with a 30 or 32 amp wall mounted EVSE (assuming yours includes the upgraded KLE and software).

 

[Alessandro]

I' m rather interested to the kWh consumption to fill up the i3, not in particular a comparison between 230 V and less efficient 110 V (and not the time to charge it, either)

 

[ultraturtle]

I' m rather interested to the kWh consumption to fill up the i3, not in particular a comparison between 230 V and less efficient 110 V (and not the time to charge it, either)

The EPA measured it at 22 kWh:

• From 124 MPGe, we get 272 Wh per mile using EPA's formula of: Wh per mile = 33,704/MPGe.
  Multiplied by measured range of 81 miles, we get 22.0 kWh.
  22.0 kWh to fill 18.8 kWh of capacity results in 85% efficiency.

 

[KurtEndress]

22 kWh to recharge from 0% to 100% is the usual amount at 240V. Under certain conditions you may find it takes more than that, if its really cold out for example.

I did my first overnight charge last night with my new level 2 charger. I was a little surprised when I looked at the TED graph this morning. It started at 51% SOC as reported by i Remote and charged for a couple hours with the power slowly ramping down toward the end. That charge calculated out to about 85% efficiency as advertised. But then an hour later there was another spike for 15 minutes starting at about 2 kW and ramping down to 1. Then another spike for 10 minutes an hour later and another at my scheduled departure of 7:00am.

Each spike consumed an additional 0.3 kWh or so and dragged down the over-all charge efficiency to under 80%.

Was it trying to keep the car or battery conditioned for my scheduled departure? It wasn't all that cold last night with a low of 56 and I hadn't set it to pre-condition the car.

 

[jadnashuanh]

Here's my take...to charge any battery, the supply voltage must be higher than the battery. The logic can try to measure how much current is going into the battery to assess its state, but sometimes, it's more accurate to essentially stop charging and measure the battery voltage itself. It will quickly taper to its nominal state and is a fair assessment of its state of charge. If it isn't full, the charging circuit reactivates to fill it up to max. If the battery pack cools off in the interim, it may also need to use some of that energy to warm the pack up some. When it is hotter outside, it may need a fairly constant cooling operation to keep the battery temp at an ideal state. This is independent of preconditioning the interior of the car. THe temperature of any battery determines a lot of what its ultimate storage capacity is.

Keep in mind, that there's a buffer both on the top end and at the bottom end of the battery capacity that you can see as the user. The top end is probably where they could store some regenerated power right after leaving with a 'full' battery, and the bottom end is to prevent damage to the battery. Keeping it in that happy middle ground is what is supposed to make the battery last longer.