Question Of The Week Answers | 25 July 2021

Jul 25, 12:05 AM

Today’s big EV stories: • Your answers to Question of the Week • Patreon thanks

Show #1155.

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With chargers still being rolled out, should they automatically stop charging (and should the car release the cable) at 80%?

Rather than having a DC Fast charger stop at 80% and unlock the cable, I think it makes more sense to use price signals to encourage proper etiquette. For example, perhaps at 80% the pricing should go up by $.25/kWh and at 90% another $.25/kWh. If you desperately need the charge, you can still get it, but if you don’t, you’re encouraged to get out of the way. 

Many EVs can blast through charging at 80%, like my i3 which is good to  86% and the taper only bites at 92% when it’ll drop below 30kW. The old Audi eTron will keep up 45-50kW right to 100% so 80% is a rule of thumb not an ‘ideology’! I think a better idea is for a 50kW rapid to cut off and release the cable when power delivered drops below a certain level, the question is what? Possibly somewhere around 20kW although mine has ‘coldgated’ at 18kW once when I plugged in with a cold soaked battery. So perhaps in the 11-15kW zone. HPCs can have different tougher rules but still need to let e-Golfs and other older cars charge. Furthermore they should fail to initiate charge at 7kw or less to keep out PHEVs etc. on the AC plug [unless a dual charging unit with DC + AC co-charging]. This could possibly be pushed to 11kW although the AC plug is a handy failsafe backup if the CCS is broken.

This takes me back to my laundrette days: If the washing/drying is finished and the owner ain’t there, you move the washing on. That was the ‘rule’. So if we accept that for rapid chargers, unless there is an indication otherwise (like a note), then we can accept that 80% is pretty much finished for Higher powered chargers.  So yes, I’d be happy for them to remove the charger from my Leaf, which is set to 80% anyway. Or… maybe charging should be set to 30 minutes by the charger? After which, the charger stops anyway and is available for others?  If you really need a bit more, restart the charge.  And as you found, most drivers only stop from 20-40 mins anyway.

I haven’t thought this through fully, but what if the first bulk of charging time, say up to 80%, was at the regular rate of cost, and above that is both slower and costs 50% more? Or maybe once it’s fully charged there’s still a fee rate for the parking spot? That would incentivize watching your time and moving on. 

I agree that in the situation where charging is scarce and people are waiting to charge, DC Fast charging should be discontinued once the charge rate drops significantly. For different cars, with different batteries/larger buffers/800V, etc... this point may not occur exactly at 80%. Also some cars, such as the hyundai Ioniq, is still apparently able to charge at 100kW at 80% SOC.  So I would suggest not a cut off at exactly 80%, SOC, but once the  SOC is at at least 80% and the charge curve for that particular vehicle drops to some low level, say 40-45 kW, and it's charging at less than 50% of its peak rate, then a shut off/cable unlock is reasonable. That being said, I would not want to penalize someone who really needs to charge to say 90% to get to their next destination. Perhaps the default would be to shut off charging once rate drops significantly but the user had the option to override if needed.  

CCS/rapid charge above 80%: I'm lucky because I've never yet had to wait for a DC fast charger... There are so few EVs here. That won't be the case forever!! I think why not have a price signal to people charging for that last 20%? Especially here in Oz where distances are greater sometimes I have needed that bit extra in the battery to be sure I'll get to where I'm going, but I do this so occasionally that I wouldn't actually mind if that last part of the charge got a little bit more expensive. That was people that are just opportunity charging will most likely not wanna stick around.

Automatically stopping the charge at a given SOC sounds like a good idea indeed (particularly in North America where charging sites often have only one or two CCS chargers). Tesla does something similar - charge state limit  is automatically set to 80% when using high use superchargers; it helps nudge people in moving on if they can. Having a minimum charge rate might helps also. 

I think it depends on the location. If a DC fast charger is located high volume urban area, and if there are other chargers within an “80% drive” in basically all directions, then I think the limit is a good idea. However, in rural areas where chargers may be scarce, it may be a bad idea, even if high volume, especially for those who cannot charge at home. 

Tesla already does this in the USA.  I’ve stopped at two superchargers already that limited me to 80%, with a screen message declaring that station a high volume station. One of them, however, was at the edge of a remote area of northern New Hampshire that borders Canada. It’s understandable that it’s high volume being the last supercharger in line before the first Canada supercharger 192 miles away. Vacationers, or multi-family unit dwellers might have a problem and be forced to return to the charger often too. 

Cables should not release but pricing should be higher after 80%. If you have a low range EV (like the e-Golf that I have), I need every ounce of electricity that I can get. Sometimes I need to charge up to 85% to be able to make it to my destination.

Here is an example of why chargers or government cannot make a blanket statement about stopping charges at 80%. 73% to 89% in 8 minutes pulling 13kWh.
That’s 97kW average speed. Started at 105kW and slowed to 85kW at 88kW. It’s a Taycan. Even when doing long trips I try to stop charging at 95% when it slows to 25kW or so. I know my Chevy Bolt would be dog slow past 80% so I understand the idea. My other email had more thinking, short cables on DCFC is the main reason it makes no sense.

I would say NO. It might be necessary to charge more then 80% to get to your destination without any trouble.
I´m aware of that above 80% HPCharging is more like… hunting snails or riding a turtle, but… 

I would prefer, that the companies who are running these charging stations are offering a Knigge for EV-Owners with all the DOs and DONTs
Printed on a flyer, brochure, small case for your charging cards, parking disc…. 
Made in a very gentle way without patronizing somebody. You got the idea :-)

Hi, I live in West Virginia USA.  We have very few fast chargers. Only 1 or 2 fast chargers at car dealers which is really not for general public. In other words we need to charge to neat 100 percent when on a trip. 

I think the car should release the cable once the charge is complete, so someone else can plug in. However I don’t see the need for the charge to stop at 80%. I know some cars’ charge curve rapidly slows down after 80% but that’s due to the battery management software of individual models. We have two 28kwh Ioniqs which can rapid charge up to 69kw speed and maintain a fast rate all the way up to 94% state of charge, at which point the car stops the charge, so we’re often done long before other EVs charging at below 50kw, even though we fill up more than 80%. I think the simple answer is we need many more high powered chargers to be installed to cope with the rapid uptake of EVs.

On my 28klw Ioniq if the auto button is activated the cable can be removed once the charging as completed no need to unlock the car. If I was selfish enough to leave my car unattended for a long period on a rapid I would expect it to be unplugged. Having said that I only take what I need for the journey so my average time on a rapid is 15 minutes. 

Auto disconnect service and releasing plug lock at a predetermined percentage makes no sense on DCFC as the cables are too short and parking too constrained to virtually ever get another car in without hitting the current car and DCFC is really the only place auto disconnect at 80% would make sense.  Also this would have to be an option anyway because sometimes you do need to go above 80% to make it to the next charger on your trip.

Auto-release at 80% should be an option you select when you activate the plug. Maybe even remind the user of the reduced efficiency for an affirmation.

The charger definitely should automatically turn off at 80% and disconnect. I'd add to that, it should also ping the owner's phone and keep sending notifications until they move their car. "Hey, your car is t charging anymore! Hey! People are waiting for your spot!"

Do I think DC fast chargers should stop at 80%, no I don’t think so, especially here in the US where we have somewhat limited infrastructure, I know that could be used as an argument to stop at 80% but sometimes we might need that extra charge to get to the next charger on a road trip. Perhaps something like that could eventually be implemented with more chargers around. I think an alternative would be to increase the cost when the cars charging rate drops below a certain percentage of its max wattage, some cars may still take a faster rate up to 90 instead of 80 making the time at the charger more useful. I think perhaps being kicked off after 95% might be fair though. 


With 2877 Superchargers globally and 25000 stalls, what do you think about Tesla’s plan to open up the network to everyone?

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