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 Post subject: charging to 100%
PostPosted: Wed May 08, 2019 2:23 pm 
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Joined: Tue May 07, 2019 10:01 am
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I hope this post is not needlessly repetitive, but I DID search first.
My Mercedes B Class Electric Drive has a Tesla drive train, and Tesla says, to maximize battery life, to keep the car plugged in when it is not being driven. The Mercedes has an active battery cooling system, and will always be charged to max (which is really about 80% of total battery capacity).
My new (to me) 2016 eGolf has, I know, a passive battery cooling system.
My question: can I safely leave my eGolf plugged in all the time, or should I not? I want maximum battery life, but am retired and there is no scheduled time when I regularly need the car, so cannot really use the pre-programmed charging feature.
If I MUST NOT regularly charge to 100%, how can I set the upper limit to 90% without having a programmed departure time?
Thanks,
Craig


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 Post subject: Re: charging to 100%
PostPosted: Wed May 08, 2019 5:05 pm 
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You can leave the car plugged in all the time, but the only way to ensure you don't charge beyond 80% is to use charge timers. Why not charge the car to be at 80% every morning at 6am? If the car is always plugged in, then you'll always be ready to go. 80% is even better than 90% for battery longevity: so says VW and Tesla (Musk says there's not much difference, but he agrees that 80% is better).

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 Post subject: Re: charging to 100%
PostPosted: Wed May 08, 2019 9:21 pm 
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Thanks, I'll try that! If I do that, then want to recharge later in the day after running errands and push the 'charge now' button, will it charge to 100% if left hooked up, or will it continue to limit charging to 80%?


Last edited by Craig on Wed May 08, 2019 9:48 pm, edited 1 time in total.

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 Post subject: Re: charging to 100%
PostPosted: Wed May 08, 2019 9:24 pm 
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Joined: Fri Mar 27, 2015 4:13 pm
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Location: Los Altos, CA
This video may be helpful for setting up charge timers on the car's screen in the 2016 e-Golf, US model.
https://knowyourvw.com/model/52/asset=5386

You want to set the Max Battery Charge Level.

However, keep in mind that VW builds in more of a buffer at the top of the battery (100% SOC) than Tesla does. So, Tesla's warnings don't apply with the same strength to the e-Golf.

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 Post subject: Re: charging to 100%
PostPosted: Wed May 08, 2019 9:53 pm 
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Are you saying that charging to full SOC in an eGolf is not really charging to 100% of the battery's capacity?
The Tesla battery in the b250e is really 36kw, but they claim 28kw, because the computer limits charging to that amount, unless you push the bypass button, so charging to 'full' is really only charging to 80% of the battery's capacity.


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 Post subject: Re: charging to 100%
PostPosted: Thu May 09, 2019 8:50 am 
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Craig wrote:
Are you saying that charging to full SOC in an eGolf is not really charging to 100% of the battery's capacity?
The Tesla battery in the b250e is really 36kw, but they claim 28kw, because the computer limits charging to that amount, unless you push the bypass button, so charging to 'full' is really only charging to 80% of the battery's capacity.


Yes, full SOC doesn't truly represent the actual physical capacity of the battery, as some is kept in reserve for lifetime management - or something very similar to that. Full SOC represents the capacity that is availabe for you to use.

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 Post subject: Re: charging to 100%
PostPosted: Thu May 09, 2019 9:21 am 
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Location: Los Altos, CA
Craig wrote:
Are you saying that charging to full SOC in an eGolf is not really charging to 100% of the battery's capacity?
The Tesla battery in the b250e is really 36kw, but they claim 28kw, because the computer limits charging to that amount, unless you push the bypass button, so charging to 'full' is really only charging to 80% of the battery's capacity.

Yes, the e-Golf has a significant inaccessible buffer in the battery capacity.

I also have a RAV4 EV and it has the same kind of charging regime that the B Class does. Normally it only charges to about 80-83% of the raw capacity of the battery. As it degrades, the "Extended Charge" capacity is reduced because the "Standard Charge" is normalized to about 35kWh of the new raw capacity of 41.8kWh. There are now some of these cars where the usable capacity is less than 35kWh and the 16th capacity bar on the dash never illuminates when fully charged.

The 2016 e-Golf has a traction battery raw capacity of 24kWh when new, but you can only use about 20kWh when new. I'm not exactly sure how it manages degradation. It may take all the degradation out of the usable capacity or it may take some from the buffer capacity that was not originally available to the user.

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2015 e-Golf LE (returned) | 2018 Tesla Model 3 LR | 2012 RAV4 EV Shoreline w/JdeMO | Leviton EVB40 & Jesla Home Charging | 4.32kW Motech/Enphase PV + 2x Powerwall 2 AC


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 Post subject: Re: charging to 100%
PostPosted: Thu May 09, 2019 10:15 am 
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miimura wrote:
The 2016 e-Golf has a traction battery raw capacity of 24kWh when new, but you can only use about 20kWh when new. I'm not exactly sure how it manages degradation. It may take all the degradation out of the usable capacity or it may take some from the buffer capacity that was not originally available to the user.


An interesting thing that I've noted is that charging a 24kWh e-Golf to 100% basically cuts Regen completely until you burn some battery, but charging a 36kWh e-Golf to 100% still gives pretty significant, if weakened, regen right off the charger. There must be more room at the top end on the 36kWh batteries.

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 Post subject: Re: charging to 100%
PostPosted: Thu May 09, 2019 2:38 pm 
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Combing through recommendations from people like Jeff Dahn, you don't want the cell voltage to be at or above 4.1 V when hot, and 3.9 V is better under all temperatures. Also, you don't want to go too low, but I don't think the e-Golf will allow too low of a voltage. That being said, I looked into the data on my car and saw at "Full" on the fuel gauge, the cell voltage was approx 4.1 V (some second decimal point variation from cell to cell). and at 80%, the cell voltage was about 3.94 V. Therefore, I would recommend 80% SoC for maximum longevity of the 36 kWh battery pack. You can, of course, do what you like, but there may be consequences.

I used to see a taper of the charge when reaching 100% on my 24 kWh e-Golf pack but have not observed a taper on the very few occasions I charged my 36 kWh e-Golf to 100%, so there is most certainly more of a buffer at the top SoC of the pack. Regardless, if you don't need the range, why not charge to only 80% and add hundreds if not thousands of full charge cycles to the pack lifetime?

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 Post subject: Re: charging to 100%
PostPosted: Thu May 09, 2019 4:39 pm 
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I know it was a newbie question, but I appreciate everyone's input: thanks!


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