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 Post subject: Re: How bad is DC charging ?
PostPosted: Fri Apr 13, 2018 8:30 pm 
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f1geek wrote:
. On the rare 100 mile or greater trips I take, I will then charge to 100% immediately prior to leaving so the pack spends very little time at high voltage.


/\ This... is good battery management.

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 Post subject: Re: How bad is DC charging ?
PostPosted: Sun Apr 15, 2018 12:01 am 
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Joined: Wed Apr 04, 2018 12:12 am
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Location: Sunnyvale, CA (NoCa)
Yesterday I fully charged battery at 12:30am
In the morning at 8 am I recognized that almost 1 bar (1/16) is gone. How is it possible ?

Another thing.
If I charge up to 100% right before using it. If should be ok for the battery?

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 Post subject: Re: How bad is DC charging ?
PostPosted: Sun Apr 15, 2018 11:39 am 
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The "loss" in SOC could be due to temperature. What was the ambient temperature at 12:30 am and 8 am? I have noticed I get more range once the battery pack warms up to around 20 to 30 C. Was it warmer at 8 am than it was at 12:30am? Otherwise, I don't think it's a big deal and probably not indicative of any problems.

Yes, for battery longevity, charge up to 100% immediately before using. If you know you need 100% at 8am, I would suggest using the charge timer to have the battery hit 100% at 7:30 am to 7:45 am so that the battery spends the least amount of time at full charge.

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 Post subject: Re: How bad is DC charging ?
PostPosted: Sun Apr 15, 2018 11:54 am 
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Joined: Wed Apr 04, 2018 12:12 am
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Location: Sunnyvale, CA (NoCa)
f1geek wrote:
The "loss" in SOC could be due to temperature. What was the ambient temperature at 12:30 am and 8 am? I have noticed I get more range once the battery pack warms up to around 20 to 30 C. Was it warmer at 8 am than it was at 12:30am? Otherwise, I don't think it's a big deal and probably not indicative of any problems.


I was thinking about difference in temperature too.The temperature at 12:30am was about 10F higher than at 8 am.

f1geek wrote:
Yes, for battery longevity, charge up to 100% immediately before using. If you know you need 100% at 8am, I would suggest using the charge timer to have the battery hit 100% at 7:30 am to 7:45 am so that the battery spends the least amount of time at full charge.


I wish I could do it. I live in apartment. But looks like if I will charge at night up to 90-100% the difference in temperature will lower the SoC.

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 Post subject: Re: How bad is DC charging ?
PostPosted: Fri Apr 27, 2018 3:10 pm 
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Location: Sunnyvale, CA (NoCa)
So. If the only heat is damaging battery then 10-20 min charging on DC should be OK or not ?

Also I checked the charging speed, during the first time I was charging with DC and it shows
from the beginning - 14 min of charging === 39 kw
14 min - 19 min === 38 kw
19 min - 24 min === 35 kw
24 min - 29 min === 28 kw
29 min - 34 min === 20 kw
I think the speed start decreasing because of heat. Maybe the fist 20 min is not damaging the battery.

The second thing about AC charging. Is it batter to charge on 3.3 kw or 6.6 kw or higher. Or maybe even from 110 outlets. Or all these cases are the same for battery ?

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 Post subject: Re: How bad is DC charging ?
PostPosted: Fri Apr 27, 2018 5:30 pm 
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YeGolf wrote:
So. If the only heat is damaging battery then 10-20 min charging on DC should be OK or not ?

Also I checked the charging speed, during the first time I was charging with DC and it shows
from the beginning - 14 min of charging === 39 kw
14 min - 19 min === 38 kw
19 min - 24 min === 35 kw
24 min - 29 min === 28 kw
29 min - 34 min === 20 kw
I think the speed start decreasing because of heat. Maybe the fist 20 min is not damaging the battery.

The second thing about AC charging. Is it batter to charge on 3.3 kw or 6.6 kw or higher. Or maybe even from 110 outlets. Or all these cases are the same for battery ?


Read your owners manual.

VW recommends recharging at night at home, and to use DC fast charging "sparingly".

Any time you exceed a 1C charge rate on any lithium ion battery chemistry, you are doing damage to the battery, by recharging it too fast.
That basically means recharging to full capacity in an hour or mores worth of time is considered "acceptable". Charging to full capacity in less than an hour exceeds the charging rate of the battery, for the sake of convenience, and does long term damage internally to the battery. It's done only for time convenience, but like your smart phone battery, it shortens the life of the battery capacity, permanently. That means less range traveled between recharges.

Avoid fast charging, if you're interested in longevity of your battery and keeping it's range maximized for the life of the car battery. That's just the way it goes with an entry level electric car with a passively cooled battery. Compromise in engineering and cost cutting designs to meet a lower price point. You want to fast recharge, buy a BMW i3 or a Tesla.

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 Post subject: Re: How bad is DC charging ?
PostPosted: Fri Apr 27, 2018 6:34 pm 
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The manual says to avoid “frequent and consecutive” DCFC sessions. It also says to follow a DC session with an AC session. The charge rates you observed are normal and not due to high pack temperature. The charging speed is a function of pack SOC and pack temperature. As long as the pack temperature is not high, the car will charge at the maximum available speed (determined by the amps delivered by the DC charger and the pack voltage) until the SOC gets to about 85%, at which point the rate slows to protect the battery. All lithium ion battery charging systems work this way-watch your smartphone charge and you’ll see the same type of behavior.

For AC, a slower rate will generate less heat in the pack and keep it cooler. I charge at 3.1 kW since I have time to allow slow charging. I would recommend charging with 240V if you can as I believe the on board charger is more efficient at that voltage vs 120 V.

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Last edited by f1geek on Sat Apr 28, 2018 8:22 am, edited 2 times in total.

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 Post subject: Re: How bad is DC charging ?
PostPosted: Fri Apr 27, 2018 9:48 pm 
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Joined: Mon Oct 05, 2015 2:01 pm
Posts: 2105
YeGolf wrote:
So. If the only heat is damaging battery then 10-20 min charging on DC should be OK or not ?

Also I checked the charging speed, during the first time I was charging with DC and it shows
from the beginning - 14 min of charging === 39 kw
14 min - 19 min === 38 kw
19 min - 24 min === 35 kw
24 min - 29 min === 28 kw
29 min - 34 min === 20 kw
I think the speed start decreasing because of heat. Maybe the fist 20 min is not damaging the battery.

The second thing about AC charging. Is it batter to charge on 3.3 kw or 6.6 kw or higher. Or maybe even from 110 outlets. Or all these cases are the same for battery ?


The DC charging rate and taper rate is relative to several conditions. What was state of discharge how many Kw were still stored in the battery when you started charging. If the battery was discharged and cool due to city stop and go driving, versus driving 70 + mph on the freeway and immediately getting off the freeway to fast charge, which will lead to a slower fast charge rate. How hot was the battery, due to previous driving conditions when you started charging.
A cool battery that is just barely in the red on the fuel gauge will take 39 to 40 kWh for perhaps 30 or 35 minutes, before starting to taper off, taking on 20 to 22 kwh. But from there, things will slow down quite a bit in the next 15 to 20 minutes, on a 55 kWh capable DC FC. This is for a 35.8 kWh battery with about 32 useable kWh.

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