[GrahamS]

Hi folks,

Well we've had some experience of charging the car at home now. Interesting factoid, unlike the iPace the eTron rarely draws maximum power, and does not draw its charging power consistently over the period of charge. The outlet is a 7Kw tethered 240v Single Phase AC outlet which for our American friends I think is referred to as Level 2. Delivers 32A at 240V. House supply is 100A 240V.

This first chart shows power supplied to the eTron whilst it's charging. Each bar represents the kWh added in each half hour period (plus a bit of background load). It should be more or less flat at about 3.5kWh. Source of data is my Smart Meter.

(UK Date formats so that's 2nd October)

This comparison is with the iPace charged on the same supply a few days before. I picked this example as it covers an identical time period, but the effect is the same every time.

 

[Horia]

Very interesting. Thank you for sharing. I wonder what folks that have similar charging setups in the U.S. (i.e. ChargePoint) are experiencing. I’m in b the process of getting a ChargePoint installed.

 

[JNealCox]

Interesting results. I had not seen a comparison of EV's with Level 2 charging! There are a lot of posts on Youtube, etc., comparing DC charging rates for different EV's. By far these postings show Audi has the most efficient DC charging profile of any EV, due in part to its thermal management. Does your comparison start with both cars at the same initial battery charge level? For DC, maximum charge rate is not the only factor to consider. Tesla's have been touting enormous max charging rates; however, the charging rate after quickly ramping up almost immediately drops drastically in order to reduce thermally induced damage to the battery. In the end, the etron charges in a shorter time. So much so, in fact, that you can toss in an extra charging stop for the Audi and still reach your destination in about the same amount of time. Of course, the downside is that that extra charging station has to exist and be working!

Controlling battery temperature is critical in maintaining batter integrity (and, if the weather is really cold, it significantly affects how fully you can charge the batter). I wonder when you integrate over your two curves, if you end up getting the same total KWH delivered over the same total time. Eyeballing it, it looks close! Maybe Audi is doing some extra coddling of the battery for thermal dissipation purposes to maintain battery integrity, even for Level 2 charging.

 

[GrahamS]

Similar SOC but probably not the same. The point I was trying to make is that AC charging is variable, not that it was better or worse. Why does it tank at times rather than sucking as much as possible. DC charging I agree the eTron wins hands down. Which may destroy the battery...

 

[JNealCox]

Bringing a battery to full charge is very complicated. That is the point: As batteries pull in power, they heat up and degrade, due in part to that heat. The higher the temperature the greater the degradation. All DC charging for ALL EV's is variable. Audi's High DC charging rate is possible because it uses the most advanced thermal management system on the market to keep the battery in the optimal temperature range over the course of the charging. All batteries in DC charging start out with fast rates but slow down--the last 20% in general being very slow. (As you start to fill up the battery with those electrons, they start to get in each others way. That generates even more heat and increases the resistance of the battery to pushing in more charge. It's complicated!) Audi thermal management lets Audi charge with a charging profile that is overall the fastest of all EV's WHILE protecting the battery. (Yes, some degradation can't be avoided.) Even Level 2 charging can cause degradation, especially if you take it to 100% capacity. So, if Audi is using thermal management at Level 2, then the oscillation could be due to the system adjusting the power draw in order to maintain the battery temperature within the optimal limits. It does this, as the integrated plots of your graphs seem to show, while taking up the same amount of power within the same amount of time as the iPace.

 

[GrahamS]

Ok thanks, that's interesting Every day's a schoolday!

 

[Joe]

Totally agree with @JNealCox here. You can notice this effect even on your cell phone if you pay very close attention. The last 10% of charge is actually quite a bit slower than going from say 30%-40% charge. I actually have begun taking this to the next level and charging L2 at 50%, since even at the 4.4 kW rate I am charged up from ~10% to 80% from the time I get home from work to the time I leave in the morning. I'm sure this will have very minimal effect on the battery health over the next decade or so I plan to own the vehicle, but I'm sure it will have SOME effect.

 

[GrahamS]

Well, intellectually interesting but not the point.

iPace - Full whack on AC for hours until full then shuts off
eTron- Varies up and down randomly on AC, takes longer to add the same charge despite the DC charging profile being massively more aggressive, so I cannot believe this is down to temp manmagement. 7Kw vs 150? No way.

I don't get it.

 

[JNealCox]

Remember, it is on DC even when using Level 2. That's what chargers do...convert the AC to a DC current!

 

[GrahamS]

Well yes I know that. I meant fast via onboard charger (aka L2) vs rapid via DC charger (L3)

 

[Joe]

I hate to make assumptions, but this may be the reason: let's assume the temp management system draws 1 or 2 KWH that would be going towards charging the battery. If you're charging at L2 rates (5-10 KWH) this will be very evident. If you're charging L3 ~150 KWH you will not notice, it will appear to be a rounding error on the vehicle's display.

 

[JNealCox]

That is reasonable. Basically, it's a matter of a difference in scale to the L2 vs L3. There are a lot of assumptions in all of this discussion. Too bad Audi tends to be mum on everything. Even the manual is 20% useful info and 80% legal disclaimers.

 

[GrahamS]

Ain't that the truth