DC Fast charging near empty vs. half full

[Anonymous]

I've heard the DC fast charging rate of 90 miles in 30 minutes is reduced if the Bolt battery is half-full or more. If you have DC charged with a half-full battery or more how many miles were added in the 30 minutes?
UPDATE: I used the DC Fast just once, when the battery was very low - only 20 miles of mid-range reading left. Was pleased to get 115 miles added in 28 minutes of charging.

 

[SparkE]

Search this site - question asked and answered several times already.

 

[Zoomit]

Actually SparkE, his specific question has not been asked and answered. I was curious as well and knew I could update my battery models to address the question. I took the opportunity to include the result with 24 kw, 40 kW, 50 kW, and notional 60 kW DC Fast Chargers. These correspond to a maximum amperage of 60A, 100A, 125A, and 150A, respectively.

For the common 50 kW chargers, starting at a 50% State of Charge (SOC) will provide 64 miles EPA range in 30 minutes and 103 miles EPA range in 60 minutes.

My battery charging models assume optimal conditions (car turned off, best battery and ambient temperatures) and can be summarized by this graph showing the power tapering as SOC increases.

Here are the plots for the 30 and 60 minute DC fast charge sessions.

Here is another plot showing how long it would take to charge from empty.

Some other relevant points to consider:
- All the miles in these graphs reference the EPA Combined range of 238 miles. Traveling faster than about 64 mph on the highway will reduce this rapidly. A 20% range hit occurs at 75 mph vs 64 mph.
- The "90 miles in 30 minutes" is not possible, according to my models, with a 125A (50kW) or slower DC fast charger.
- The optimal starting SOC to get as many miles as possible from a 125A (50kW) charger is 17%. In this case, 30 minutes should yield a gain of 36% and end at 53% SOC, just before the first taper begins.
- The charge gained when starting at 50% SOC is basically the same as long as the charger is 100A (40kW) or greater.
- The difference between a 100A (40kW) and a 125A (50kW) is only significant when starting below about 40% SOC.
- The notional 150A Bolt EV charge capability, which is only speculative, has only minor effect on charge durations. The difference between 125A and 150A is only significant when charging for short durations and from low SOC.

 

[devbolt]

I just did a 411 mile road trip with 3 stops and 4 charging sessions, all at 50 kW/125A capable EVgo stations:

First stop, one 30 minute session. Starting SOC 53%, ending SOC 78%, 16.5 kWh delivered, 56 miles added
Second stop, first 30 minute session: starting SOC 18%, ending SOC 56%, kWh not recorded, 82 miles added
Second stop, second 30 minute session: starting SOC 56%, ending SOC 81%, 15.98 kWh delivered, 51 miles added
Third stop, one 30 minute session: starting SOC 30%, ending SOC 65%, 21.96 kWh delivered, 70 miles added.

Car says I used a total of 114.4 kWh to travel 411.4 miles, or an average effeciency of 3.596 miles per kWh. 4% used for Climate Control... Average speed was probably around 70 mph for most of the trip.

 

[GetOffYourGas]

Thanks for the great plots, zoomit! Very informative!

 

[Zoomit]

devbolt--Thanks for the calibration data! It lines up pretty well with my charts.

Here's another two data points on the "90 miles in 30 minutes" claim by GM and referenced by the thread starter.

https://www.youtube.com/watch?v=lY_n1uNKkhk
The video shows, among other things, two 30-minute 125A charge sessions starting at my theorized optimal SOC.

1) Start 17%, end 52%, 22.45kWh delivered
2) Start 18%, end 52%, 22.69kWh delivered

These resulted in a gain of 34-35% SOC in 30 minutes, which is equal to 81-83 miles (EPA Combined) of range gained. This is slightly under what my model predicted (86 miles EPA) but is consistent with what could be expected in the hotter temperatures (~100F) when battery cooling loads are greater.

 

[devbolt]

When I did the charging, each time was after a 100+ mile driving session. Ambient temperatures were in the 90s. I did take a couple of battery temp readings at the end of the sessions and they were between 29C and 30C.

 

[GetOffYourGas]

I did take a couple of battery temp readings at the end of the sessions and they were between 29C and 30C.

How did you take the readings? I thought the Bolt itself didn't provide temperature. Is there a CAN reader or something you are using?

 

[devbolt]

I did take a couple of battery temp readings at the end of the sessions and they were between 29C and 30C.

How did you take the readings? I thought the Bolt itself didn't provide temperature. Is there a CAN reader or something you are using?

I used a Bluetooth OBDII reader and the EngineLink software for the iPad, along with the Volt PIDs.

 

[GetOffYourGas]

Cool. I see it's $5.99 on the App Store, I assume you recommend it for Bolt owners? Also, does it read any kind of battery health metric?

 

[gpsman]

And the ideal temperature for the battery is 77'F (25'C).

If your battery is exactly 77 (25) degrees and you start in the teens % and end in the 50's % you should get 90 miles in 30 minutes on a 50 kw (46 kw net) charger.

That is: 23 kWh delivered x 3.9 miles per kWh = 89.7 miles.

No doubt, this is the calculation Chevy used for its publicity. A bit presumptuous of them to post the exact, ideal condition, but that is what they did.

I routinely get more than 90 miles in 30 minutes.
This is because I average 4.4 miles per kWh some weeks when I need no heat or A/C.

 

[Zoomit]

That is: 23 kWh delivered x 3.9 miles per kWh = 89.7 miles.

The "delivered" numbers referenced previously are what the DC fast charger reports as being provided to the car, not what the battery stored. There's a ~5% loss primarily due to battery internal resistance and conditioning loads. To get 90 miles of EPA range in 30 minutes, the battery needs to store 22.7 kWh [90/3.97] but the charger needs to provide about 23.9 kWh [22.7/0.95].

 

[gpsman]

Right. I get it.

I get 90 actual miles in 30 minutes sometimes.
Not every time. But it is possible.

That's also why a 50 kw charge station is really a 45 or 46 kw (at best) net charge rate.

 

[Zoomit]

Sure, and I can get 180 miles in 30 minutes if I spend the previous 150 miles moping at 35 mph, but that's not relevant.

 

[GetOffYourGas]

And that's exactly why "miles per minute" is a horrible metric. Yet EVs seem to be enslaved by this measure of charging.

 

[devbolt]

Cool. I see it's $5.99 on the App Store, I assume you recommend it for Bolt owners? Also, does it read any kind of battery health metric?

If the health metric PIDs exist for the Bolt, the app can pull that information out. So far, people are using the Volt PIDs as a basis for the Bolt, but not everything works. You get some very weird data back.

I'm using this LE Bluetooth OBDII reader with the app.

https://www.amazon.com/LELink-Bluetooth-Energy-OBD-II-Diagnostic/dp/B00QJRYMFC/ref=lp_10667160011_1_1?srs=10667160011&ie=UTF8&qid=1500416417&sr=8-1

If you have an Android phone, you can use the same reader with the Torque app. Both apps use the same data file format for the PIDs.

 

[Anonymous]

Actually SparkE, his specific question has not been asked and answered.

Not only that, the "Search" function on this forum is close to worthless, and the format used by this forum lends itself to having information repeated often as new members join the forum, since there is no easy way to find historical important information!

I notice the Moderator never rebutted your remark.

 

[JeffN]

Here are the plots for the 30 and 60 minute DC fast charge sessions....
- The "90 miles in 30 minutes" is not possible, according to my models, with a 125A (50kW) or slower DC fast charger.

Awesome graphs, as usual. Thanks!

The "90 miles in 30 minutes" claim is predicated on the use of a DC charger faster than the 125A "50 kW" ones that are installed today.

As you probably know, the actual quote from the owner manual is:

When using a DC charging station with at least 80 kW of available power, it will take approximately 30 minutes to recharge from a depleted battery to an estimated 145 km (90 mi) of driving range. This time estimate is applicable to nominal temperature ranges.

 

[Anonymous]

The DCFC installed at my dealer, Keyes Chevy in Van Nuys and is available for free (with freshly baked chocolate chip cookies) easily provides 90 miles in 30 minutes [correction] and fills me to 80% from near empty in about 1 hour 12 minutes and full 48 minutes later, given that it slows down substantially after 80%.

 

[Zoomit]

Thanks Jeff--I had forgotten the Owner's Manual had that qualifier for the "90 miles in 30 min". I'm curious to see if the MY18 Bolt EV manual has the same remark. That paragraph was actually removed from the Opel Ampera-e manual, which otherwise appears to be very similar to the Bolt EV manual.

MichaelLAX--For the advertising claim to have any merit, it needs to be referenced to a suitable standard. The EPA Combined range of 238 miles is the obvious standard. (I could argue that the EPA Highway range of 217 miles is actually more appropriate, but I digress.) That's equivalent to 38% [90/238] of the usable battery. If you've managed to gain 38% SoC in 30 min, please let us know! Otherwise, as I passive-aggressively inferred previously, it's not a meaningful demonstration of the GM charging performance claim.

You indicated charging from "near empty" to 80% in 72 minutes, presumably on a 125A charger. My model shows that under optimal conditions, you could charge from 6% to 80% in 72 minutes, which matches your results very closely. At no time in that charge cycle would you have gained 38% in 30 minutes. The peak is 36% or 86 miles EPA in 30 minutes. This is very close, and maybe not a significant difference; however, I don't think anyone has demonstrated GM's claim yet of 90 miles (or more precisely 38% SOC) in 30 minutes on any DC Fast Charger yet.