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Discussion Starter #1
I'm planning to get an EV as my next car. I want to understand how charging at home works. I don't really understand electronics, so go easy.

I have a feeling that residential power supply in the UK is lower than in the US - does this mean we're at a disadvantage when it comes to charging?

I know there's an offer for a charging point from British Gas here:
http://www.britishgas.co.uk/product...ectric-vehicles/electric-charging-offers.html

They say you can upgrade from 16A to 32A at your cost - but what difference does this actually make? Is there an assumption that these 16A and 32A are the same voltage? Does voltage have anything to do with charge time?
 

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Firstly, all home charging in the UK is at 230V unless you have 3-phase and almost no one has that so we can safely say that home charging in the UK is 230V.

BTW, Home charging in the USA can be 110V or 220V but that is USA so I won't cover that here.

Voltage does make a difference but as I have said, we can assume 230V when charging at home so for this purpose we can ignore voltage.

The current you car charges at home is determined firstly by the charger that is on the car. Some cars have a 16A charger, some have a 32A charger... some higher... for example... there is an option on the Leaf to get 16A (standard) or 32A (option). If you only have a car with a 16A charger then you can only charge at 16A and having a 32A charger won't give you anything extra.

So, assuming you do have a car with a 32A charger then having a 32A home charging pod with mean that you can charge in half the time of a 16A pod. This sounds great but most people charge overnight when 32A charging will make little difference to your experience... it will charge more quickly but as you are asleep it generally doesn't matter.

There is one benefit that applies to some people... if you want to charge during the day to allow you to use the car later that day then a 32A option will mean less waiting. 32A charging makes a big difference when charging on plublic charging points too.

I have a British Gas unit but if I were to do it again I would get a Rolec unit rather than British Gas. There are lots of threads here discussing the various merits of BG vs Rolec :)
 

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They say you can upgrade from 16A to 32A at your cost - but what difference does this actually make? Is there an assumption that these 16A and 32A are the same voltage? Does voltage have anything to do with charge time?
The time to charge depends on the power that the charger can supply to the car.

Power (Watts) = Voltage (Volts) x Current (Amps)

Like Paul says, domestic voltage is fixed (230V)

16A charger : Power = 230x16 = 3680W = 3.7kW
32A charger : Power = 230x32 = 7360W = 7.4kW

So the 32A charger has twice the power and will charge a car twice as fast as the 16A charger.

For example, the usable capacity of the i3 battery is 18.8kWh

16A charger : Time to charge = 18.8kWh / 3.7kW = 5 hours
32A charger : Time to charge = 18.8/kWh / 7.4kW = 2.5 hours

In reality, there are charging losses (about 15%) and battery management which means charging takes a bit longer than that.

One other thing to check is the speed at which the car can charge at. It is possible that the car will be the limit rather than the charger. For example, the base level LEAF has a 3.3Kw onboard charger so you can see that is actually less than the 3.7kW power that the 16A charger provides i.e. the car is the bottle-neck.
 

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Well into pedantry land here but it seems that the power draw can be a little higher than 3.7kW for the normal 3.3kW LEAF. From http://en.wikipedia.org/wiki/Nissan_Leaf#Recharging it seems that

"Models with an on-board 3.3 kW charger[81] can be fully recharged from empty in 8 hours from a 220/240-volt 30 amp supply (5.2 kW allowable draw[82]) that can provide the on-board charger its full 3.3 kW of usable power.[83][84] Models with an on-board 6.6 kW charger[27][85] can be fully recharged from empty in 4 hours from a 220/240-volt 40 amp supply (7.7 kW allowable draw[82]) that can provide the on-board charger its full 6.6 kW of usable power.[83][84]"

I actually see a draw of about 4kW on my 32A capable charge point on my Gen 1. Admittedly that's in the margin of error of my measuring system but there might be a small benefit of a 32A charge point for a 3.3kW car.
 

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I can confirm this - my 16a Fluence which stated it will take 6-7hrs to charge when plugged in, invariably completes the task in just 3.5 to 4hrs. If has never taken the estimated time on my 32a Rolec Chargepoint.
 

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I was wondering if anyone knew how many kWh it takes to charge a Nissan Leaf (2nd Gen - with 3.3 kW on board charger? Trying to work out if I would save more by going onto economy 7 or not...
 

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1. 3. Perhaps 5?

It will all depend on whether you start from empty, or any point in between.

My EV starts charging at 0005 when E7 kicks in. Charging usually finishes anytime from 0350 to 0510 which was the latest it has ever been (e7 tariff stopped at 0830). E7 makes sense for me.
 

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I was wondering if anyone knew how many kWh it takes to charge a Nissan Leaf (2nd Gen - with 3.3 kW on board charger? Trying to work out if I would save more by going onto economy 7 or not...
I may have this completely wrong, but I'm sure that the battery is 24 kWh capacity. So with the 3.3 kWh charger it would take roughly 7 hours (24/3.3) for a full charge.

The cost doesn't depend on the rate, it depends on how much electricity you consume and at what time, so IF you charged from flat to full it would at most take seven hours at a steady 3.3 kWh. Although the charge rates do vary too.
 

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Discussion Starter #11
I was wondering about that too - I can't get E7 or any other time-based tariff. Trying to work out what the electricity costs will be to compare them to fuel costs - but it's too complicated :(
 

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It's not too bad but you will need to know your (average or approx) miles per kWh and annual miles to do it.

So for example, if I did an average of 3.8 miles per kWh, and travelled 10,000 miles a year. So to do that 10,000 miles I'm looking at roughly 2,632 kWh. If my electric is 12p per kWh you times your usage by 0.12 and get...

£315.84 for 10k miles of motoring.


PLEASE someone tell me if this is wrong, but I think so far as "fag packet" maths go it's close enough.
 

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Discussion Starter #13
Umn, don't have an EV yet - so guesstimating... this seem reasonable?

==LECCY==
Leaf 24kWh battery capacity
Leccy @ 11.68p per kWh
=> 280.32p per full charge
Leaf range about 80 miles
3.504p per mile
(ish)


==PETROL==
Car does about 10 miles per litre
Fuel is about 130p per litre
=> 13p per mile
(ish)


==SAVING==
8k miles a year
Annual petrol costs: £1,040
Annual leccy costs: £280
 

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Billy, I was just typing out an answer when you posted but your numbers are spot on so I won't bother repeating it.

The only thing to add is that although the LEAF battery is officially 24kWh in reality the 'usuable' size is a bit smaller. From a quick google this is shown to be 21 kWh (I'm sure LEAF owners can correct me if that's not right).

However, there's usually around 15% wastage when charging so that means from empty to full you'd consume 21 x 1.15 = 24.2 kWh which happens to be almost identical to the 24kWh that you used in your calcs so the final answer is the same.
 

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Thanks @Buzby and @Paul that is pretty much exactly what I was after.

I suppose it is fair to say that we all know that it depends how economically you drive but I was after a figure from empty to full. The point being that lets say it is £5, it is then up to me to decide whether I am going to floor it everywhere thereby only getting a few miles or driving ridiculously economically and trying to get the maximum.

I guess I am still used to thinking that a "full tank" in my ICE car was £70 (depending on price per litre at the time). From then, I would sometimes get 340-400 miles from it depending on weather and driving conditions and of course how much lead there was in my right foot that day.

Many thanks for the speedy responses!
 

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I was wondering if anyone knew how many kWh it takes to charge a Nissan Leaf (2nd Gen - with 3.3 kW on board charger? Trying to work out if I would save more by going onto economy 7 or not...
I can't find the page now, but from memory there's 18kWh usable on a Leaf... I think that's from VLBW to full.
 

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What is wrong? The OP wanted a duration. Clearly this is a 'piece of string' scenario - who knows? It all depends on the available capacity when charging commences, the relevant kwh were not mentioned.

My point was the the time to recharge indication on most EV's remains a guestimation but in my case I can complete this wholly within the E7 timeframe.
 

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Fair enough but to give a figure without any justification implies to me, rightly or wrongly, that it is an empty to full time which is what most people ask for.

It is a "piece of string" question but it always is when people ask it. Mentioning a time without saying how much of a charge that gives is pointless. A more accurate reply then is zero to 11 hrs depending on the state of charge when you start and the charger you use... :)
 
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