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11kwh and 22kwh home chargers...

the fatty Sep 1, 2018

  1. the fatty

    the fatty New Member

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    I think I must be miscalculating, but based on the specs I have read online, the e Tron range will have a 11kwh charger, which takes aboit 12 hours, and a 22kwh charger which takes about 8 hours to charge. Going off the 11kwh charger and using an average of 14p per unit of electric, that's (11*0.14)*12=£18.48 for a full charge, for a maximum of a 250mile journey. That works out at 7.3p per mile. Comparing that with a normal car that can do 50mpg, and at a average fuel price of £1.18, that works out at 10.7p per mile. The batteries are going to deteriorate with age so will hold less charge and take longer to charge. So is there really enough in this to make e Tron worth it at the moment?
     
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  3. desertstorm

    desertstorm Moderator Staff Member Moderator VCDS Map User TDi quattro Audi A4 Audi Avant Owner Group

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  4. DrEskimo

    DrEskimo Well-Known Member

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    I take it you are talking about the new e-Tron pure EV, rather than the Q7 hybrid?

    In which case yes, I'm afraid there are lots of mistakes in your post.

    The 11kWh and 22kWh charger is referring to the recuperation rate of the regenerative braking. The e-Tron will have DC charging and is rumoured to be able charge as high as 150kWh from a rapid charger.

    This is not accurate. Let's just assume you are charging at 11kWh (this will only be possible from a home charger if you have 3-phase supply, which many don't. The highest rated charger you can get on a single phase supply is 7.2kWh, which is what most people will have). The car will not draw 11kWh for the entire 12hours. That would mean the car has a 132kWh battery, which it doesn't...! The last 10% will always take the longest, as it can only draw a small amount of power. You've probably noticed this on your phone or laptop.
    In any case, the important number is the battery capacity, which is rumoured to be 95kWh. It's irrelevant how fast or slow this is charged, it will only draw and hold 95kWh. Think of it like petrol tank that can hold 95litres. It's irrelevant how fast you pump the petrol in, it will only take 95litres, and there is a set price per litre.
    So at 14p per kWh, from 0-100%, it will cost 95*0.14p = £13.30. You would be doing this overnight though, and be daft to not take advantage of cheap off-peak charging at 7p kWh, so more like £6.65.

    The range of a 95kWh battery will not be 250 max, 300+ miles is more than realistic. Tesla 100D's (100kWh battery) can achieve this with ease in all conditions and normal driving. General rule of thumb is that normal driving will give you about 3-4miles per kWh. So 95kWh will give you around 330.

    So that's 4p a mile (2p if using off-peak rates), which is about the standard on all EV's.

    Current average diesel prices are £1.30 (and rising...). So at 50MPG that is 12p a mile. Around 4-6x the cost per mile. Typically, you would charge the car form 20% to 90% every week or so, depending on how many miles you do. You would do this over night and take advantage of off-peak economy 7 prices of 7p per kWh. This would take around 8hours and give you about 60kWh of energy into the battery. This equates to £4.20 a week, as apposed to £40 in diesel a week. That's the real world cost difference.

    Battery degradation has been absolutely minimal on EV's. Thermal battery management and battery management software ensures that the batteries remain in good condition. This is why comparisons with phones or laptops with respect to degradation are spurious, as they do not have thermal management of the battery, and the CPU can cause the batteries to reach temperatures in excess 90C. Some high mileage Tesla's have seen just 10% degradation after 160k miles. In any case, battery degradation will only affect range, not power or charging time. Therefore charging time is reduced, not increased (If your 150k mile e-Tron has 10% degradation, it essentially has a 85kWh battery now, so smaller batteries charge in less time). Without getting even more technical, the e-Tron probably has a 100kWh battery, but has software to reduce it to 95kWh. Holding 5kWh back means you don't get the problem of slow charging for the last 100% (because it really is 95%). So if your battery did degrade, they could always 'unlock' the 5kWh and give some capacity back.
    In any case, the battery is likely to warrantied for 8yrs/unlimited miles. Any excessive degradation would be covered and repaired/replaced. Not sure I know many ICE that have that sort of warranty on their engines....

    If you can charge from home, looking to spend similar money on a new SUV from Audi that can do 0-60 in<6secs, then yes it will be substantially cheaper than a diesel on fuel costs alone, not to mention markedly reduced servicing costs (it's completely optional on the Tesla and does not affect the warranty, since it just entails a battery health check and pollen filter change) and hardly any maintenance (brakes will likely never need changing due to regen braking, so it's just tyres...and windscreen fluid...).

    Hope that clears up any confusion. Any other questions just let me know :)
     
    Last edited: Sep 2, 2018
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  5. the fatty

    the fatty New Member

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  6. DrEskimo

    DrEskimo Well-Known Member

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    Ah OK. Apologies I confused it with the regen stats. In which case they are offering options to charge it up to 22kWh from AC. You can charge up to 43kWh max on AC currently from public chargers. As I said though, this will be limited by the electrical supply to your house. The majority of houses have only a single phase supply, and you can only install a 7.2kWh at 32amp on a single phase. To get 11 or 22kWh you need a three phase supply, which is costly to install.

    To be honest, 7kWh at home is plenty though. Just plug it in whenever you want at night...could wake up every morning with a full charge if wanted! Whether you run it down and wait till the weekend and do a big charge, or do small charges everyday, it will cost the same (very little :p). You have plenty of sleeping hours to charge however you want...you quickly realise just how inconvenient visiting petrol stations are...!

    The higher AC charging would be useful for work charger though, assuming they have higher rated chargers you can use.

    What's more interesting is the ability to rapid charge up to 150kWh on the road. This means you could drive 300miles, then get back to 100% in around 30mins and do another 300miles. Any notion of 'range anxiety' just wouldn't exist (not that it's an issue on this battery capacity anyway. I have driven 200miles in a Tesla with just a 60kWh battery and it was a complete breeze....).

    Looking forward to seeing the confirmed specs and details though.
     
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