Charging 2 cars in the UK (single phase circuit)

[markmobi]

Hi,

I have a Model S on order and my partner is thinking about getting a BMW i3 too. However this made me wonder what to do about charging. My usage pattern is I leave for work before 7am and return just before 7pm, having done about 120 miles during the day.

Her usage is a lot less miles (10-20) and they are done during the day. Things like the school run, popping to the shops and such.

Should we buy two different wall chargers? Can we run them at the same time? Is this very impractical considering my Model S will be charging through a large portion of the night?

Thanks for any thoughts

 

[Brunel]

2 EVs here. 2 wall chargers - Rolec 32 amp & Chargemaster 30amp. Separate fuses and main 100amp fuse into the property. To save money on wall chargers you could get a switched commando socket for the Tesla (I think BMW offer a free to heavily discounted wall charger). If you are flash then get 2 Tesla wall-chargers that spread the electric load in a chain ie balance like 2 linked superchargers and that will only take one fuse from your consumer unit and avoid any possible upgrading of electrics eg 60 amp to 100 amp.

 

[markmobi]

2 EVs here. 2 wall chargers - Rolec 32 amp & Chargemaster 30amp. Separate fuses and main 100amp fuse into the property. To save money on wall chargers you could get a switched commando socket for the Tesla (I think BMW offer a free to heavily discounted wall charger). If you are flash then get 2 Tesla wall-chargers that spread the electric load in a chain ie balance like 2 linked superchargers and that will only take one fuse from your consumer unit and avoid any possible upgrading of electrics eg 60 amp to 100 amp.

Thanks Brunel. The Tesla system spreading the load sounds interesting. I'll look into that and also what it would take to get electrics upgraded to the 100amp at the same time anyway. We may be getting a solar system fitted with a battery, so there's a chance we could have this all done at the same time.

 

[Brunel]

Good stuff. I have almost 7kw solar already and might get a couple of Powerwall 2s.

You might have a 100amp fuse already. Also, I have my 2 EV chargers on different sides of my consumer unit, so if something trips one side I can still use one EV charger (some water was getting into the outside junction box for the 30 amp charger and it was constantly tripping until the sparky could come round and sort it, so it was great having the resilience for a few days).

 

[markmobi]

I was on the phone to a solar company this morning to get a quote, and they seem liked a great company because rather than hard sell to get a system in right now, they actually heard about my needs and have suggested that we speak in February when the Powerwall 2 is out. Otherwise they were going to fix a Powerwall 1. Good idea on the charger being on opposite sides of the consumer unit. Resilience is good as I expect to use half the Tesla's battery each day, so want to ensure I can charge it.

 

[tga]

The Tesla system spreading the load sounds interesting.

Can you charge a European i3 with a European HPWC? Are they all Mennekes type 2? The load sharing only works between Tesla HPWC's, not a HPWC and some other generic charging station (for a non-Tesla car).

I would guess that you'll be fine with 1 charging station, assuming you can dedicate at least 30A to charging. Unplug the i3 and plug in the Tesla when you get home, and it'll be charged in ~6 hours. In the morning when you leave, plug the Tesla and plug in the i3. When she gets home from errands, she should plug in the i3 (ie, keep it plugged in during the day). The i3 should only need an hour or 2 of charge time for 20 miles.

This assumes you can charge during the daytime, and don't have discounted night rates, limits on daytime usage, etc. I don't know how that works in the UK.

Depending on how complicated the installation is, you could also have the electrician install a wire for a second circuit when installing the first charging station (leave it unconnected). The extra labor and wire cost should be minimal, but it'll be a lot simpler to add a second charging station later if you decide it's needed. If your electrical panel is in the garage and it's a 1 foot run, don't bother. If they have to drill through concrete and run cables through walls and attics, definitely consider the second wire (or a bigger circuit to a subpanel in the garage).

 

[markmobi]

Thanks tga. It looks like the i3 has a type 2 connector. And I checked the meter for power into my house and see I have a 100amp fuse at the meter. So running two wall chargers looks feasible. However I like what you say tga, and will try with one wall charger first - but the Tesla one so I can have the unit spread the load with a second unit if I get a second one. It looks like we'll have the i3 first as my build date on the Model S is currently Jan 9th and then it needs to be shipped to the UK. So the i3 will be Tesla powered.

 

[grahamsimmonds]

I have a Model S and an I3. I have two Rolec 32a chargers fitted to their own RCDs on the consumer unit. I have a 100a supply. Both bought under the OLEV scheme total cost £199. Both are maintained by Earth Electricals. I charge overnight using E7.

 

[markmobi]

Thanks Graham. It's great to know you're doing exactly the use case I am looking at. How does the Rolec compare to the tesla unit in terms of charge time?

How are you finding the mix of a Model S and an i3?

And what does E7 mean?

 

[WannabeOwner]

Otherwise they were going to fix a Powerwall 1

I'm sceptical about the benefit / economics / payback of at-home static storage - happy to be educated though. If you are out during the day [and don't use all the solar you generate] and can store your solar until the night that's great. Either way you will be paid (assume that is still available on new installs?) the FIT payment on 50% of what you generate. You could just export your excess into the grid and then buy electricity at night, when you are charging. (Your FIT contract may explicitly disallow static-storage?)

And what does E7 mean?

Economy-7 off-peak night-time electricity tariff. Typically its 50%, or less, of normal day rate, but the E7 day rate is then a bit higher (than normal). Its midnight-to-7AM in Winter and 1AM to 8AM in Summer (if I've got that the right way round!!). I'll bet you a beer that there will be a charge to change your meter if you aren't currently on E7 and don't have a Smart Meter

If you are going to charge two cars overnight you won't want to be going out in the middle of the night to swap the plugs over so I would recommend having two separate supplies & "wall sockets" and then both can be used at once. I expect you will also have times during the day (e.g. weekend) where you both want to charge - probably not often, but likely to happen at some point in time, maybe most likely for some sort of "emergency".

You can set the MS to "schedule charge" at, say, 12:05. There is a grace period, so if you are out at a cracking party and roll home at 2AM it will still charge, and if you want to charge during the day you can override that. Scheduled Charging is based on geo-location so if, for example, you also charge at work you won't have to manually fiddle with any settings when you get to work.

You should get about 20 miles-per-hour of charge at home (single phase, 240V). (By contrast sticking a plug in a 13AMP socket will give you about 4 MPH)