e-Golf DC Fast Charging

[miimura]

This week I purposely ran down our e-Golf's battery to test fast charging. Yesterday was a bust on the Sunnyvale BTC fast charger because it could not communicate with the e-Golf. I was hoping to use that one because it is supposed to have a higher maximum DC current and its screen shows Volts and Amps continuously during charging. So, this morning, I took the car to the Nob Hill Foods Mountain View station that has two ABB Terra 53CJ (dual CHAdeMO and SAE Combo) chargers. I showed up with the dashboard battery gauge almost exactly at the top of the red zone. These NRG eVgo chargers only run for 30 minutes, so that's all the data that I have. Here are some summary charts for those that are interested. This is just from my notes, but I also have a video of the ABB's screen that I might be able to get more accurate data from. I haven't looked at the video, but just from the viewfinder, it may not be very legible. I would really like to extract minute by minute kWh delivered figures from the video.

This 30 minute session took the ABB reported SOC% from 13% to 92%. I don't have any personal experience with a Leaf, but my impression from reading stuff online is that this data shows that the e-Golf holds the maximum charging rate much longer than the Leaf.

 

[miimura]

I finally extracted the "kWh Delivered" data from the video I took of this same charging session. I recorded the kWh Delivered that was reported by the ABB station at exactly 1 minute intervals according to the timer on the ABB screen. The more precise data shows the charging curve very clearly.

To me, the kW charging rate curve has a very interesting shape. The beginning of the curve is exactly as expected - the station's current limit is constant and the increasing battery voltage is allowing the power delivered to slowly increase. Then, starting in the 21st minute, the car tells the station to quickly ramp down the current and then follows a gentle taper. I would have expected only two slopes to the curve, but there are clearly three distinct slopes.

 

[Jlo]

Thanks Miimura - update on the BTCs, still no fix; BTC was very responsive at first about the fact that their chargers don't work with eGolf's but have now gone dark...no response from them in over a month.

Silver lining (if there is one), EVGO is no longer saying that the problem is with the eGolf...that tomfoolery has stopped, I called in today again to request an update on the Van Nuys Gelson's BTC charger. No update, I put in a new ticket asking them to replace the unit with an ABB...I'm sure that won't go very far but hey, worth a try. I feel kinda dirty asking for such a thing because BTC is a California company (ABB is not even American) but if it don't work, it don't work. Dam good opportunity for enterprising American companies though-

 

[miimura]

I think NRG is using the BTC units because they have a different utility connection than all the other fast chargers. Normal fast chargers use 277Y480V connections. The BTC ones use a 120Y208V connection. This way they can just connect directly into the grocery store's utility service without installing a new utility transformer. So the chance of swapping it out is almost nil. Also, while ABB is a European company, they do make (at least fabricate sheet metal and do assembly) the North American configuration fast chargers in USA.

 

[Jlo]

Good to know Americans are getting some manufacturing jobs out of it.

 

[JoulesThief]

How hard is it on fast charging the batteries in an E-Golf, with no active cooling system for the Li batteries? I know it's early, but are there any reports of similar battery failures like the Leaf's in the Phoenix area, occurring on the E-golf?

What about heat generated at the batteries when using full capacity of the 7.2KW charger on board the SEL versions?

 

[miimura]

How hard is it on fast charging the batteries in an E-Golf, with no active cooling system for the Li batteries? I know it's early, but are there any reports of similar battery failures like the Leaf's in the Phoenix area, occurring on the E-golf?

What about heat generated at the batteries when using full capacity of the 7.2KW charger on board the SEL versions?

The e-Golf has not even been on the market a full year yet, so nobody knows how long the battery will last or if it will fade like the early Leaf batteries. There is a guy in Europe who did a long trip this summer with many consecutive fast charges. As heat accumulates in the battery the car will slow down the fast charging and will reduce the power you can take out of the battery while driving, reducing the possible acceleration. That is the purpose of the power meter, the small gauge on the left side of the dashboard. The available power is also reduced when the battery is low.

You can use the on-board charger as much as you like and it won't generate significant heat in the battery.

 

[JoulesThief]

How hard is it on fast charging the batteries in an E-Golf, with no active cooling system for the Li batteries? I know it's early, but are there any reports of similar battery failures like the Leaf's in the Phoenix area, occurring on the E-golf?

What about heat generated at the batteries when using full capacity of the 7.2KW charger on board the SEL versions?

The e-Golf has not even been on the market a full year yet, so nobody knows how long the battery will last or if it will fade like the early Leaf batteries. There is a guy in Europe who did a long trip this summer with many consecutive fast charges. As heat accumulates in the battery the car will slow down the fast charging and will reduce the power you can take out of the battery while driving, reducing the possible acceleration. That is the purpose of the power meter, the small gauge on the left side of the dashboard. The available power is also reduced when the battery is low.

You can use the on-board charger as much as you like and it won't generate significant heat in the battery.

As will charging the last 8 to 10% to 98 to 100% charged. And the stock walwart 1.3kw factory charger is a non issue, charging as slow as molasses, in terms of heat.

 

[JoulesThief]

Do you recall what your electron "gas" gauge level was at, or what it read, before you started charging? Perhaps take a picture of the gauge reading before you try this again the next time, and if you re log everything, it might give us a correlation as to what useable battery capacity is on these 24kwh batteries.

The gauge shows what the batteries took, it doesn't reflect what the batteries actually ended up with, due to thermal, and other charging losses.

 

[miimura]

Do you recall what your electron "gas" gauge level was at, or what it read, before you started charging? Perhaps take a picture of the gauge reading before you try this again the next time, and if you re log everything, it might give us a correlation as to what useable battery capacity is on these 24kwh batteries.

The gauge shows what the batteries took, it doesn't reflect what the batteries actually ended up with, due to thermal, and other charging losses.

From the first post in this thread:

I showed up with the dashboard battery gauge almost exactly at the top of the red zone.

The top of the red zone is 1/8 of the usable capacity remaining. When it finished, the charging station reported 92%, which is 14.72/16ths. The gauge was also in that position, which is not a surprise, since the fast charger is just displaying what the car is telling it. The nominal total capacity is 24 point something kWh. I don't recall the actual number. So, VW is probably letting us use about 90% of the nominal capacity before it completely shuts down. The power reduction and warnings and red zone strongly discourage use of the bottom 1/8, or 12.5%

I also did some math on the car's "Since Charge" screen and battery gauge and it suggested that the usable capacity is 22kWh. This is a copy-paste from a post at the Facebook "VW e-Golf" group.

This picture shows the battery level that matches the previous screen shot. You will notice that we drove 29 miles with an efficiency of 4.2mi/kWh and consumed 5/16ths of the battery. Simple math (29/4.2) shows that we used 6.9kWh of battery today. Dividing by 5/16 shows that you should be able to use 22kWh from completely full to completely empty. If we continued to drive with the same efficiency, the car would probably run out of juice at about 92 miles (4.2*22). This happens to match the sum of the GOM and the distance already covered (63+29).

In any case, I think you're overthinking the batteries. I honestly believe that the gauge is displaying the actual usable capacity of the battery pack. Any losses would have to be calculated from external sources like the actual DC Volts and Amps from a fast charger, or the AC Volts and Amps going into the car from the wall. Those losses are real and do reflect losses from actually storing energy into the battery and losses converting AC to DC. However, once it is in the battery, it will be reflected on the gauge and you will be able to use that energy to drive the car. I find all the figures presented inside the car to be internally consistent.

 

[JoulesThief]

Trip to Santa Barbara Tesla, then back to beach to charge, while on the Wharf.

Electron fuel needle.

Driving habits: First 6 miles to 101 freeway, Blvd speeds, traffic, red lights. Rest of trip is almost all 60 mph. Used regen as much as possible, I tend to now brake with the shifter, if at all possible, by planning ahead. Very hot thin air at 97F. Hardly ran the AC at all, rolled the windows down and sweated it out for the eMPG's. 16.0 c per KWh at home rate.

96 miles / 5.8 miles per kwh = 16.55 Kwh. Started charging at 2:20 pm, I believe I stopped charging at around 5:17, with 125 out of 129 miles range showing, didn't want to wait longer.

Drive home, got on the road about 5:20 pm

Electron fuel needle.

82/5.0 = 16.4 Kwh.

 

[miimura]

I successfully charged our e-Golf on the BTC charger at the now closed Fresh & Easy store in Sunnyvale at Tasman and Fair Oaks. The software on the chargers has been updated. The unit on the left has a very large screen and shows Version 7.9.2 while the unit on the right has a very small screen and shows Version 7.8. I charged our car on the unit on the left with the higher version number. Both of these units how have a note on the welcome screen regarding the e-Golf.

The 30 minute charging session on my car took it from 37% to 94%. This charger shows the battery percentage (SOC, State of Charge), Charger Voltage, Charger Current, and remaining time. I took a video of the charging session and copied the data from the screen shown in the video into a spreadsheet at 1 minute intervals. Here is the chart of the data.

The curve still looks strange to me. I was expecting a simple constant current charge to the max battery voltage, then constant voltage with a tapering current. However, it looks to me like VW has 4 segments.
1. Constant current at the charger's max output.
2. Constant voltage at 355VDC until the current drops to 60A.
3. Slowly increasing voltage and slowly decreasing current until 360VDC.
4. Constant voltage at 360VDC with decreasing current until full.

I was hoping to get more of the taper at the full end of the charge than I did on the ABB charger, but since the BTC has a lower maximum charging current, I only got 2% more than the ABB, which took me from 13% to 92% in the same 30 minutes. The BTC was pushing 99 amps until 80% SOC. I suspect that the ABB was pushing 109 or 110 amps until the same 80% SOC.

Here is a chart comparing the two charging sessions.