As above, if you run a 7kWh charger for an hour, you’ll have used 7 kWh. I am charged 11p per kWh.

11p x 7 = 77p to run my 7 kWh charger, for an hour.

Car battery is 22 kWh, but someone above states due to efficiency around 32 kWh are needed.

32 divided by 7 will give the number of hours I need to run the charger for to fully charge.

Times that number of hours by my earlier 77p per hour figure, and voila.

It really depends on what your energy supplier is charging you per kWh, this is the crucial figure.

32 kWh required to charge 22 kWh battery

Just checked my own charge last night and it seems the efficiency is a lot lower at 3kW.. Must do the sums but I think I am looking at about a 60% efficiency at that level..

@jit187

Mike – if your tariff has ECO7 the cost for elec is even less. my ECO7 tariff I pay £0.05 per KW. so my total cost to charge my car overnight is £1.10 (22 kw X £0.05)

so if anyone does want to charge at mine please come between the hours of 0100 am to 0700 am…. 🙂

I woudl change to this, but the Wife works from home 3 days a week, so my day rate would be higher, and therefore I doubt any saving would be had… might even cost more. As I say it’ll go on charge every night, but realistically I am only going to need 1 and a bit “full” charges a week.

@Valeri

Actually the total cost is more than 22 kWh*x£. That is because efficiency of charging is not anywhere near 100%. It might be 70% at low rates. Considering that the amount of taken KW would be around 22/0.7=31.4 kW for a total charge

Interesting… that equates to (lets say 32 kWh):

32 kWh required to charge 22 kWh battery, 7 kWh chargepoint, and 11p/kWh elec tariff.

32/7 = 4.5
7*0.11 = 0.77
0.77*4.5 = £3.47

Call it £3.50 to fully charge. Not bad, considering I’ll only be doing around 100 miles a week. Based on 100 mile per charge (here is wishing…) thats 3.5p a mile.

Interestingly I’ve just done some sums. 22 kWh battery, 7 kWh chargepoint, and 11p/kWh elec tariff.

£2.40 to fully charge, +/- 10% for loss temperature changes etc. Nto bad, considering I’ll only be doing around 100 miles a week. Based on 100 mile per charge (here is wishing…) thats 2.4p a mile.

Compared to the Mustang at 80/215 which is 37p a mile (on fuel alone!).

Quite chuffed

I wonder if they might have to SORN it to stop paying the battery rental.

As buchanan says, it’s officially 22kWh and, as I’ve mentioned in another thread, when I’ve run the battery right down it has said it used 22kWh.

I’m collecting an ex-demo this Friday – glad I’ve checked this list… Point 3 (tax disc) made me check the tax status on the DVLA website, and discovered my car is declared off-road and has SORN status.

Therefore, additional checkpoint for anyone buying an ex-demo…
11) Check the DVLA website that it’s not declared SORN (otherwise would be illegal to drive away)

Also, given mine has been sat on a forecourt for a good while, I’m asking them to check for software updates, battery condition and make sure it’s roadworthy (tire pressures, brakes etc.) Probably not a checklist item for most people buying brand new, but an additional thought in my case.

Also, presumably you get two ‘keyless’ keys? If so, checkpoint to make sure I get both of them.

I’m a bit bemused why they would SORN it when it’s free to tax it! They’ve just created admin for themselves, I think.

Finally, another checkpoint item (for myself), bring driving licence (my dealer specifically asked I bring this), and make sure I have the debit card for the account where all the money is too!

The battery initially charges at constant voltage constant current, but when the battery reaches a certain voltage, the charging regime changes to constant voltage, variable current; the current gradually dropping off until the battery reaches maximum voltage.

Which is why as it gets closer and closer to 100%, the charging gets longer and longer.

You can see this clearly if you have one of those new electric meters at home that has a graphical display – it will stay at 7KW for a couple of hours then there will be a fairly linear drop off.

The battery is made up of lots of 3volt cells, and the voltage range is 4.2(Full) to 3.7 (Empty). If the voltage drops below 3.7 volts, then that will damage the cell.

As the battery ages, the cells will start to discharge at different rates, doing a full charge cycle re-balances all the cells back to the same voltage.

What this means is constantly using hi-speed chargers and stopping at 80-90% doesn’t do the battery a lot of good as eventually the cells will get very much out of balance and some will start to drop below that 3.7 volt threshold.

This I think can be proven – if you use a fast charger often, see how long it takes to do a proper home charge after using a fast charger for a few cycles and compare it with how long it takes to do a proper home charge without using the fast charger.