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Discussion Starter #1
So my memory is not the greatest, and something that was a major inconvenience during a road trip might have given some valuable data. On a 50 kW charger, it appears that the Bolt EV can recharge from 35% SOC to 69% SOC (roughly 35% capacity) in exactly 30 minutes. Assuming the Bolt EV can charge at a faster rate below 40% SOC than above, this might provide some valuable data about the actual charge rates. I still don't have access to any chargers operating at faster than 50 kW, so we will have to wait and see what the actual fastest charge rates for the Bolt EV are.

 

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So what happened when you reached 80%? Did the charge rate drop below 15kw?
 

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Discussion Starter #3
No. I'll be posting that video soon. The rate actually stayed at 25 kW past 80% SOC. It looks like it continues at that rate until at least 85% SOC.
 

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Thanks for sharing.

Fyi, for DC fast charging the charger is located outside the car in the box behind the cord.

AC charging utilizes the charger in the car. This is why DC charging is a cheap option, basically wires out to the charging port (maybe some safety mechanism there, not sure). An EV company could make a DC charge only car much cheaper, but wouldn't be able to home charge.
 

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Thanks for sharing.

Fyi, for DC fast charging the charger is located outside the car in the box behind the cord.

AC charging utilizes the charger in the car. This is why DC charging is a cheap option, basically wires out to the charging port (maybe some safety mechanism there, not sure). An EV company could make a DC charge only car much cheaper, but wouldn't be able to home charge.
Surely you can home charge. You just need to install a $10k DC charger and 400A service.
 

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Discussion Starter #6
Thanks for sharing.

Fyi, for DC fast charging the charger is located outside the car in the box behind the cord.

AC charging utilizes the charger in the car. This is why DC charging is a cheap option, basically wires out to the charging port (maybe some safety mechanism there, not sure). An EV company could make a DC charge only car much cheaper, but wouldn't be able to home charge.
That was pointed out to me by someone watching my video! :)

I just thought there might be some heat emanating from somewhere, but there wasn't. I think I heard the fans on the Bolt EV kick on one time the entire trip, but it was fairly cold on the trip North.
 

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So my memory is not the greatest, and something that was a major inconvenience during a road trip might have given some valuable data. On a 50 kW charger, it appears that the Bolt EV can recharge from 35% SOC to 69% SOC (roughly 35% capacity) in exactly 30 minutes. Assuming the Bolt EV can charge at a faster rate below 40% SOC than above, this might provide some valuable data about the actual charge rates. I still don't have access to any chargers operating at faster than 50 kW, so we will have to wait and see what the actual fastest charge rates for the Bolt EV are.
You charged at a rate of ~162 EPA miles range per hour. At least one other has demonstrated just over 180 mi range per hour rate, also on a 125A charger.

Calling a charger "50kW" is somewhat meaningless when you're interested in describing the maximum charge rate of the unit. This is because the charger manufacturers don't use a common way to describe their power output. I understand there are at least 3 different kinds of "50kW" class DC fast chargers.

1) 100A @ 500V = 50kW
2) 125A @ 400V = 50kW
3) 125A @ 500V = 62.5kW

But realize that the maximum charge power (eg charge rate) occurs when the charging voltage is at just under 400V and at the maximum current capability of the charger. Let's assume the charging voltage is 390V for the following calculations. Here is the maximum power expected from these chargers:

1) 100A @ 390V = 39.0kW
2) 125A @ 390V = 48.8kW
3) 125A @ 390V = 48.8kW

Here you can see that the charge current, in amps, is actually the most relevant number to know when charging today's EVs with ~400V batteries.

But how do we know the amperage of the charger? Besides looking on the back of the charging unit and looking at the spec plate, the best way to know is if you car is actually charging at more than 40kW. If it is, then you know you're at a 125A charger. Unfortunately PlugShare and similar sites/apps don't make ANY reference to charger power so you may be reliant on looking at their pictures of the site and recognizing specific charger models.

A typical Li-ion charging cycle consists of 2 phases, a constant current (CC) phase first and a constant voltage (CV) phase last. When a battery is charged from empty a constant current is used. As the battery charge increases the voltage rises until the cells reach maximum desired voltage and the charger then holds constant voltage but lets the current drop. The CV phase is when tapering occurs as it's when the charging power is decreasing towards the end of the charge cycle.

Recall that power (kW) is volts (V) times amps (A), so the maximum power and charging rate occurs when the current is highest and the voltage is highest. This occurs just before tapering begins at the transition from CC to CV phases. So charge rate is actually INCREASING until tapering begins.

Today's 400V BEV batteries that can charge at 125A and are on a 125A charger, will start the charge cycle at maybe 330V and will charge at ~41kW [330x125] under optimal conditions. It's not until the battery reaches max voltage that the peak power is produced, and then it's only an instaneous peak as the charger transitions from CC to CV. As shown above, that peak could be ~49kW for today's BEVs on a 125A charger and capable of charging at 125A.

I've tried to describe optimal and generic charging. There are a multitude of factors that result in lower charging performance.
 

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Discussion Starter #8
Thank you for your information, Zoomit! That actually explains some of my experiences. The EVgo charger in San Luis Obispo is a 50 kW charger rated at 400 V @ 125 A, which is why I was able to charge at a net rate of 45 kW. The EVgo charger in Gillroy must be a 500 V @ 100 A, because the max rate I was able to charge on that station was 37-38 kW. Also, regarding the 162 mi per 30 minutes is starting with 35% SOC. It might be much faster had I started at 10% SOC.

Your information also explains why some of the chargers are listed as 60 kW because I think several of them are 500 V @ 125 A. The Bolt EV can't take advantage of the higher voltage, but it can take advantage of the higher current. Of course, we don't know what the Bolt EV's upper limit is for current yet (especially under 40% SOC). One of GM's videos showed it hooked to a 500 V @ 175 A charger, but that wasn't a production Bolt, and we don't know exactly what amperage it was accepting. I have a feeling the Bolt EV will accept a max charge rate of 400 V @ 150 A (ideal circumstances), but we need to verify that when higher current stations come online.

I need to do a better job of checking the modules at the EVgo stations. The one in San Luis Obispo was ABB (I think they are all 125 A), but the one it Gilroy is different. It might be a Sumitomo or other that only provides 100 A.
 

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Under optimal conditions the Bolt EV might gain 38% SoC in 30 minutes on a 125A charger. However, I haven't seen that demonstrated, so I don't yet know the taper point for Bolt EV. Let's make the assumption that the taper point is 65%. That means the fastest 30min charge session would be from 27% SoC [65-38] up to 65% SoC. So starting a fast charging session around 20-35% SoC is the likely region where the most energy will be gained in 30min.

Other ways to optimize the session could be to have 65-75F ambient temperatures and have the car turned off.

Can you point out which GM video showed the Bolt EV connected to a 175A charger?
 

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Discussion Starter #10 (Edited)
Regarding the taper, these are my observations so far:
< 45% SOC: At least 45 kW
55%-75% SOC: ~ 35 kW
75%-85% SOC: ~ 25 kW
85%-90/95% SOC: ~ 15 kW

Unfortunately, one of the few ways I have to track current charge rates is with the Bolt EV on, which draws ~ 1 kW of additional power. I wish ChargePoint would get off their butts and start putting out faster charging stations. At least with them, I can track charging rates through their app.

As for the GM video, I'll try to find a link. It was one of their promotional videos about the Bolt EV at their testing facility.
 

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The EVgo charger in Gillroy must be a 500 V @ 100 A, because the max rate I was able to charge on that station was 37-38 kW.

// cut //

The one in San Luis Obispo was ABB (I think they are all 125 A), but the one it Gilroy is different. It might be a Sumitomo or other that only provides 100 A.
Yep, looks like at least one DC fast charger at Gilroy is 100A. Someone took a picture of the spec plate and put it on PlugShare. Some of the comments also reference 100A service.
 

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The max charger current is available in at least one other EV market, Norway. The Charge & Drive app that supports Nordic countries doesn't even reference power output; it only shows voltage and current. Here's an example of a listing for a DCFC station at a random McDonalds in Norway.


 

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As for the GM video, I'll try to find a link. It was one of their promotional videos about the Bolt EV at their testing facility.
Found it: https://youtu.be/uOc4b81VzGI?t=52s

That brings back memories. I watched that video a few times when it came out in mid-'15.

The charger is clearly an ABB unit with a plug label warning of 175A and 500V. ABB's current line-up does not have anything with a similar amperage. Nevertheless, that unit would put out 70kW at 400V. If it could maintain the 175A all the way up to 500V, that would be 87.5kW which is a very interesting coincidence with this text from the Bolt EV Owner's Manual: "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." (p.232)
 

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I hadn't looked closely enough, but apparently some of the ABB charge stations indicate max current on the plug holder frame. Here's a picture of a station in Santa Barbara from PlugShare that's capable of 125A from the CCS plug:
 

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Discussion Starter #16
Ah, good. You found the video. I had been searching, and was just getting a bunch of crap search results.

Great catch on the plug holder. I never noticed the small text with the voltage and amperage.

Regardless, I never saw the Bolt EV charging at faster than ~380 V, and I don't know whether an increased current would change that number. Either way, it will be interesting to see if the Bolt EV can accept as high as 175 A.
 

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Why don't folks simply make 3kW DC home chargers, presumably for $1000 or less? Then the car would be $1000 cheaper without the AC charger (which is simply that very 3kW DC charger)?
 

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I stopped by 3 local DCFC stations in my area, 2 EVgo and 1 Chargepoint. All rated up to 500V, 120-125A output.



 

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