New member, charging question.

[Mick787]

Hi all, new member to the forum living in the UK who has just placed an order for a 'new' i3 Rex. (It's got 4,800 miles on the clock and was previously a Bmw workers/company car.) The sales person was very polite, (as they are when going for the sale), but sadly didn't seem to know much about the car re charging and battery specifics. I'm trying to find out what users have had to do/done re charging points and the installation of them. Our garage is detached from the main house and I wonder if other owners had to upgrade power cables from the main consumer unit in the house to the charging point. Also I am confused as to what will be needed as I have seen that there are different cables (at an additional cost) which should be used to allow the car to be charged at a faster rate.
Any information will be greatly appreciated. We would prefer to be able to charge the car within the 4 hrs rather than have to wait the 12/13hrs I understand happens if the cable that comes with the car is used to plug it into a conventional wall socket.

 

[Tacfoto]

Mick,
This is a difficult question to answer without knowing how your house is set up, and what charger you intend to use. But essentially the fastest at home chargers use about he same amount of power as a full size electric clothing dryer, or an electric oven. Check the breaker or fuse that is supplying power to the garage. If your charger is 20 AMP and your breaker is 15 AMP obviously that is not going to work.

The car does have setting to slow the charge rates so if you plugged in and trip a breaker/blow a fuse, you could go into the car's menu and select a slower rate of charge. Of course this means more time to charge to 100% but it does give you some flexibility. These settings are in the main computer of the car on the center screen. Make sure you check these settings as my car was delivered with them all set to charge as slow as possible, and it was a week before I knew why my care would not charge as fast as I'd been promised. My dealer seemed to know nothing about this.

I'm in the USA and my car (a 2017) included a 12 AMP 110 Volt AC charger. Referred to by BMW as an "occasional Use" charger. From 6% to 100% would take about 30 hours. Obviously that is too slow. But on a typical day I only use 25% of the battery or less so an overnight charge at this rate would bring me back to 100%.

My office provides 240 Volt chargers (not sure on the AMP rating) and these will take my car from 6% to 100% in about 8 hours.

 

[jadnashuanh]

For most customers, the on board charging in the i3 is limited to 7400W, so divide that by your supply voltage would give you the maximum amps. Generally, a 30-32A EVSE is the maximum that the i3 can handle, but because of the protocol, a larger or smaller one will still work...the EVSE announces to the car the maximum that it can provide, and then the car will adjust its draw to never exceed what it was told by the EVSE. IF you choose a smaller EVSE, it will still charge the i3, but it will just take longer.

Most EVSEs are rated for exterior installation, so it could be either outisde or inside. I don't know the rules in the UK, but in the USA, a 30-32A EVSE would require a 40A circuit since the codes require you to derate the circuit capacity to 80% when the device could be on more than a few hours continuously.

In the USA, the charging cable is generally tethered to the EVSE...that isn't necessarily the case in the UK. So, that depends on which EVSE you end up buying as to whether you'll need one. I don't know what the public EVSEs have...you might need a cable for one of those.

Depending on the market, and the model year, the vehicle may only have the ability to recharge at half that 7400W maximum. Also, not all vehicles sold will have a DC charging capability. You can tell if yours does by seeing if the charging port has two sections with a 2-pin one below the main upper one. If you do, you can charge at public DC fast charging locations. Generally, you'll end up with about an 80% charge in about 30-40 minutes.

 

[Nyken]

In the U.K., the basic mains voltage is 230 volts, which is about 2 times the voltage used in North America. So while my 'basic' charge takes about 30 hours, in the U.K. yours will take 15 hours.

I spent about $1000 to install a higher power EVSE at home (240 volts at 32 amps), which charges the i3 in about 5 hours. If a 15 hour charge is too slow, you should be able to install a higher power EVSE in the U.K. as well.

Also, it's interesting to note that I'm spending $500 at our summer home to install a 240v 15 amp circuit for faster charging, which is the basic power circuit used in the U.K. To make this circuit a bit more 'future proof', I'm having heavier wire pulled but to keep costs low, will use a less expensive (but less powerful) EVSE.

 

[Mick787]

Thank you for your replies.
We had an electrician visit our home yesterday and sadly we won't be able to install a 'quick charging' unit as soon as we would have hoped. We have to lay a new cable from our main consumer unit to our detached garage and it won't be a cheap job. The existing cable does not have a high enough amp rating. In addition to that, a new consumer unit will have to be fitted in the garage. :-( Good bye to another few hundred quid and it looks as though it will be a few hours of hard graft for me digging a trench, once the ground softens!
This EV ownership is a costly thing for us to do. OK, should we have done more research before saying 'yes' to the car? Only time will tell. But for the time being we will have to live with using the supplied cable and slow charging via a 3 pin socket and if needs be, the Rex kicking in. There are no charging points where my wife works and she will be the main user of the car. It is planned to always be the second car in our household.
Pick it up today!

 

[JohnKelly]

Have you looked on plugshare.com for stations near you or at work?

 

[Mick787]

Thank you for that information JohnKelly, I guess this is where we start a steep learning curve! That looks to be a very interesting site which we will retain. Re my wife's place of work, no, there is nothing shown in that area.
I wonder how many forum members have found they are managing quite well with just the three pin plug charging lead that comes with the car in the UK and haven't found the need to fit a rapid charger unit. The car is intended to be her commuting vehicle and will be the secondary car in our household.

 

[I33t]

Hi Mick,

If it is expensive to install the charger to your garage, are you able to park the i3 near to the house? Maybe start with the 30amp charger next to the house and later dig the trench and move the charger to the garage later, maybe near the end of summer/autumn.

The REX gives the option of waiting for improving plugshare near the work.

 

[Mick787]

Hi I33t, sadly no. The cost involved in buying a longer connecting cable to reach the closest point the car can be parked to the house, may as well be offset against installing a new supply cable. I will get started on it in a few weeks time once this hot weather we have had here for the last 6 weeks or so breaks and the ground once again returns to the usual conditions of a bog!
Our first charge last night following the mileage done returning from the dealership etc, we got a full charge into the car over the night on the Economy 7, (cheap tariff), we have, so it looks as though there will no rush to do this new cable installation job. We will know more at the end of today once we have put the car through the routine it will mainly experience for the next 5 years or so. I guess the only snag may be when we really run the batteries down, but even then we have the REX to back things up. Thats why we chose that model rather than the 'full' EV.

 

[Donal121]

I think It's quite hard, If your chargers is 20 AMP and your breaker is 15 AMP obviously that is not going to work

 

[Tacfoto]

Congratulations on your purchase and pick-up. Keep us up to date on your progress.

Don't forget to check how the car is set to charge in the center computer. Mine came from the factory set to charge as slowly as possible.

 

[Mick787]

At this very early stage in ownership, my wife is loving the car, she smiles when she talks about it! Yes, I like it too. Because of its intended use, we are starting to think that we may not need a rapid charger. We are topping the charge up using Economy 7 but I wonder if small top ups may not be a wise thing to be doing. I am aware that generally Lithium batteries don't have a memory effect, but is it best practise to let them run down to a low percentage every now and then? If it is, then we may have difficulty in charging the car over one night on E7. I guess it's all about planning ahead.

 

[alohart]

We are topping the charge up using Economy 7 but I wonder if small top ups may not be a wise thing to be doing. I am aware that generally Lithium batteries don't have a memory effect, but is it best practise to let them run down to a low percentage every now and then? If it is, then we may have difficulty in charging the car over one night on E7.

Although BMW doesn't seem to explicitly recommend any charging procedure, I haven't read any suggestion that repeated small top-ups are worse for long-term battery pack life than charging only from low charge levels. In fact, operating a Li-ion battery cell over a small charge level range centered around the 50% charge level is likely better than charging from a low charge level to full, especially when leaving the battery pack full for many hours. However, trying to maintain a 50% charge level average would reduce one's usable range too much for many people, especially those of us with BEV's.

To extend the battery pack life, BMW has implemented a battery management system that prevents the battery pack charge level from dropping below an actual 10% or above ~93%, the exact percentages depending on temperature, rate of charge/discharge, and likely other factors. So an indicated 0% is really 10% and an indicated 100% is really ~93%. Nevertheless, the cell degradation rate is faster at an actual 93% charge level compared with lower charge levels, especially in hot climates.

Also, the charge levels of the 96 individual battery cells will diverge over time and charge cycles which would reduce the usable battery pack capacity. To rectify this problem, BMW has implemented a passive cell charge level balancing procedure that works more rapidly at full charge. However, it still works at somewhat lower charge levels albeit more slowly.

To try to maximize the life of our battery pack, I usually manually stop charging at an indicated 85-90%. After returning home from a drive, I usually start charging to restore the charge level to 85-90%, especially if I return within our low electricity rate period of 9 am - 5 pm. If I might need full range, I begin charging a couple of hours before departing to increase the charge level to full before departing. In the rare situation in which I need to depart without a full charge and also might need full range, a little-used DC fast charger whose cost is based on the energy delivered is ~½ mile from home, so I could top up there more quickly than with our 3.3 kW charging circuit. This feels like a good compromise between leaving the charge level high enough that some cell balancing will occur and not leaving it so high that the cell degradation rate would increase noticeably.

Most i3 drivers don't bother to manage charge levels and instead just begin charging when they arrive home and disconnect their charging cables when they depart. Particularly in the U.S., most i3's have been leased for no more than 3 years, so battery pack degradation has not been a problem by the end of the lease period. However, for those of us who hope to keep our i3's past when the battery pack warranty expires, doing simple things to minimize degradation could make sense. Only time will tell…

 

[jadnashuanh]

The i3 e-book says that, for example, 10 recharges from 90-100% puts the same wear on the battery as one from 0-100%. I plug mine in when I get home, and it shows the same max range after 4-years as it did when new. IOW, I'm not worrying about it. Now, I don't have a huge number of miles on it, but there's over a thousand partial charges on it now. An i3 is not your cellphone battery chemistry or smarts, it's a lot better.

 

[Mick787]

Thank you for your excellent replies.

 

[Idleup]

Major mistake with BMW only allowing the owner to use 1200 watts to charge. with the larger packs it can take days to charge. While the 1200 watts was acceptable with the first pack - its deficient with the last two upgrades.

Minimum for any EV 110 v charger should be at least 1500 watts or the same as a common space heater.

Regards

 

[alohart]

Major mistake with BMW only allowing the owner to use 1200 watts to charge.

Of course, that's only in countries with 120 V residential branch circuits like in North America. 2014 North American Occasional Use Cables (OUC) were 1440 W devices. Starting in 2015, the maximum OUC charging power is 1200 W. I don't know whether later OUC's are still only 1200 W. In counties with ~230 V residential power, the OUC was considerably more powerful (~2300 W?).

Minimum for any EV 110 v charger should be at least 1500 watts or the same as a common space heater.

It might be that the original 1440 W OUC resulted in too many melted outlets and plugs due to the poor condition of many 15 A outlets and the use of cheap extension cords.

 

[eNate]

...Starting in 2015, the maximum OUC charging power is 1200 W. I don't know whether later OUC's are still only 1200 W...

This is just a semantic point (for clarity) but the car itself is capable utilizing 1at least 6 Amps at Level 1 (120V), or 1900 watts. So regardless of what amperage EVSE the car came with, plugging in a higher current one will.

The 16A EVSE that I'm using roughly charges my car at the rate that my math said it should, and also in comparison to the 12A (1400W) EVSE that came included with my used 2017 BEV.