[bro1999]

Now that the weather is not freezing, I was finally able to see how the Bolt fast charges when the battery is already nice and warm. I did 2 back to back 30 minute sessions at the 125A EVgo station near me this morning.
SOC was 12% according to the station (16.9% raw SOC according to Torque Pro), battery temperature was 75F, and ambient temp was 70.

After initiating the session, the charge rate ramped up to 42/43 kW right from the start (finally!). The rate slowly crept up to about 44/45 kW after 15 minutes.

Right around the 15 minute mark of the 1st session, I hear these weird fan noises I’ve never heard before. Turns out when the HV battery hits about 84F, the Bolt’s TMS kicks on, so the fans noise I was hearing was the Bolt cooling the battery. I found the PID for the cooling fan RPM speed, and observed the RPM bounce between 1300-2500 after the initial startup. The TMS was active the last 45 minutes of charging, and the HV temp stayed at 84F the whole time. From my observations, the power draw for the TMS is around 2 kW after initial spool up. Full pull charge rates (43-45 kW) were observed the entire time.

First session results were as follows:

Starting SOC: 12%
Ending SOC: 47%
kWh charged: 22.27
Starting GOM miles: 35
Ending GOM miles: 137
GOM miles added: 102

For the second session, charge rate ramped right up to 44 kW (slightly less than normal due to the TMS). At 52% SOC (according to station), the first taper hit, and charge rates dropped to 37/38 kW and a little over 100A.
At 67% SOC, the 2nd taper hit, and rates dropped further to 23/24 kW and ~60A.

Second session results:

Starting SOC: 47%
Ending SOC: 73%
kWh charged: 17.20
Starting GOM miles: 137
Ending GOM miles: 205
GOM miles added: 68

I have the EVgo On the Go plan, so it costs me 10 cents/minute (in addition to the $14.95 monthly fee). So it cost me $6 to added ~40 kWh, or 15 cents/kWh.

Still think the Bolt can charge faster than 46 kW/125A, but waiting for a juicier station to open...

 

[bxd20]

Very interesting. Thank you.

Some of my thoughts on this... SPECIFICALLY in terms of how it relates to long distance highway travel...

So the first 1/2 hour session increased range by a little over 100 miles of range, or, we can say, a very comfortable 1 hour of driving on the highway at higher end speeds.

The second 1/2 hour session increased range by less than 70 miles, so in the real world, where you have to account for charger locations, cold temperatures, this might have only bought you another 30 minutes of highway driving.

It would therefore appear that for longer highway drives, in areas where chargers are plentiful, charging just enough to keep your SOC under 67% probably makes a lot of sense. It maximizes your charge rates to minimize the time you sit around waiting.

Since EVgo charges by the minute and not by the kWh or by the session, unplugging at the 67% taper and continuing the trip *MIGHT* make sense. All depends on just how far you still have to go and whether there's another charger en route.

 

[PH2]

Great to hear bro1999, this is what many of us postulated many months ago. You've done a great service to many in keeping track of this!

Still unfortunate that Chevy made the tapers so conservative, hopefully they will back off of the conservatism in the future like they did on the Gen2 Volt' s battery.

Convenience in shortening L3 charge times will, for most drivers, outweigh the couple of percentage points in extra loss of capacity (from fewer/steeper tapers) over the life of the battery.

 

[ClarksonCote]

I don't know why they do the stepped taper at the end. Maybe it's simpler hardware circuitry? They should've done a standard constant voltage mode gradual taper, that would give them faster charging overall using the same method every Li-Ion battery chemistry uses.

Also, I'm surprised those EVGo displays use a comma instead of a decimal point in the kWh numbers. I would expect this in Canada perhaps, but you're charging in the US, yes?

 

[Sean Nelson]

Also, I'm surprised those EVGo displays use a comma instead of a decimal point in the kWh numbers. I would expect this in Canada perhaps, but you're charging in the US, yes?

We Canucks use decimal points just like you Yanks do!

 

[jsmay311]

I don't know why they do the stepped taper at the end. Maybe it's simpler hardware circuitry? They should've done a standard constant voltage mode gradual taper, that would give them faster charging overall using the same method every Li-Ion battery chemistry uses.

I agree that the stepped taper is kind of perplexing.

But doing a constant-voltage taper (i.e., charging at the maximum amps until the battery voltage reaches the target voltage) would be more stressful on the battery and would mean zero taper until maybe 80-90% SOC.

I found this graph showing a BMW i3 33kWh charging like this:

It reaches its target voltage around 80% SOC, but the Bolt would take longer since it has a larger-capacity battery pack and the voltage rise for an equivalent current would be less.

Regardless, they could've tapered gradually instead of stepped without relying on a constant-voltage approach. Teslas behave like this, I believe.

 

[hvacman]

Different battery chemistries have different characteristics. I believe the chemistry that GM and LG Chem selected for the Bolt was some new "secret sauce" that had outstanding high temperature kWh capacity/kW power delivery performance characteristics. Perhaps part of the trade-off was it has charging characteristics that requires this conservative step-wise charging taper.

 

[ClarksonCote]

We Canucks use decimal points just like you Yanks do!

Haha! I thought so, but was struggling to think of a reason there'd be a comma in there. So EVgo is based out of Europe then?

 

[ClarksonCote]

I agree that the stepped taper is kind of perplexing.

But doing a constant-voltage taper (i.e., charging at the maximum amps until the battery voltage reaches the target voltage) would be more stressful on the battery and would mean zero taper until maybe 80-90% SOC.

While you're technically correct that it is more stressful, it is certainly not outside the envelope of what Lithium Ion batteries are designed to do.

Any Lithium Ion battery charger available commercially operates this way i.e. charges at Constant Current and then switches to Constant Voltage to top the battery off. Their battery chemistry is no different in regards to being able to accomplish this.

In fact, since the typical Li-Ion cells that are not cooled in any way are designed to do this and complete charging in an hour, I dont' see any reason why a thermally managed battery can't at least do this "slow" 1C rate and complete charging in an hour. Taking it a step further, charging in 30 minutes really shouldn't do much damage either if you're cooling the battery, as many non-cooled cells can charge at a 2C rate now.

As an example supporting that in practice with EVs, I went down Mount Washington in my Volt, and recaptured 70% of my battery's energy in 20 minutes. Given the Volt's margins on state of charge and discharge, that's about a 1.5C charging rate.

Bottom line to me, is that a 1C rate with a standard CC/CV charging profile should be a walk in the park for any thermally managed battery.

 

[gbobman]

...So the first 1/2 hour session increased range by a little over 100 miles of range, or, we can say, a very comfortable 1 hour of driving on the highway at higher end speeds.

The second 1/2 hour session increased range by less than 70 miles, so in the real world, where you have to account for charger locations, cold temperatures, this might have only bought you another 30 minutes of highway driving....

I agree on the general merit of this post but not the estimates. The speeds you would have to reach in order to match those estimated times are outside of the capabilities of the car, even if you were at top speed the whole time.

From those GOM estimates, it looks closer to 3:1 time driving to charging. Not ICE numbers but still respectable.

 

[bxd20]

I agree on the general merit of this post but not the estimates. The speeds you would have to reach in order to match those estimated times are outside of the capabilities of the car, even if you were at top speed the whole time.

From those GOM estimates, it looks closer to 3:1 time driving to charging. Not ICE numbers but still respectable.

Can you explain what I'm missing?

His first charge added 100 miles of range. At 75mph, assuming good weather, you could drive 1 hour and 20 minutes. Assuming there is a charger waiting for you at that exact location. So I think my statement "a very comfortable 1 hour of driving" is accurate, in other words, a little over an hour.

His second charge session added less than 70 miles of range. This was on a warm day. If I'm charging at an Interstate exit, and its winter time, that might mean 50-60 miles of range at 75mph. Perhaps 30 minutes is on the low side, but definitely less than 45 minutes. Again, of course I am describing a worst case scenario. January, 15*F temps, 75mph.

3:1 at Interstate speeds doesn't seem likely.

 

[CCIE]

Good to hear it's behaving better now that the weather is warmer!

 

[jsmay311]

Bottom line to me, is that a 1C rate with a standard CC/CV charging profile should be a walk in the park for any thermally managed battery.

I'm not in any position to say if that's right or not. But presumably the engineers at GM and Tesla are, and they seem to have a different opinion. ¯\_('-')_/¯

If it was only GM doing it, I might be inclined to think they were being overly cautious. But with both of them? Idk. Tesla generally doesn't play it safe with anything.

 

[ClarksonCote]

If it was only GM doing it, I might be inclined to think they were being overly cautious. But with both of them? Idk. Tesla generally doesn't play it safe with anything.

Well, Tesla actually charges at about a 1C rate and tapers at the end. In fact, they often start a bit higher than a 1C rate which can be seen on many charging graphs online. Some examples here: http://insideevs.com/tesla-ups-supercharger-charging-rate-refreshed-model-s-90d-p90d-video/

With the Spark EV, GM was charging at 2.3C constantly to 80%. See here: http://gm-volt.com/forum/showthread.php?175641-Tesla-Lite-!!

So it seems Tesla comfortably charges around 1C while GM seemingly doesn't with the Bolt EV, yet GM did much more than that with the Spark EV.

To sum it up as you did so well... ¯\_('-')_/¯

 

[Ladogaboy]

Unfortunately, we don't have any public chargers available to charge the Bolt EV at 1 C, so we still don't know what its max charge rate is. However, I doubt that it will charge at 2.3 C (like the Spark EV) even for short periods of time. Until we get access to faster chargers, we are all just guessing.

 

[rob]

With the Spark EV, GM was charging at 2.3C constantly to 80%. See here: http://gm-volt.com/forum/showthread.php?175641-Tesla-Lite-!!

The early Sparks were A123 LiFePO4 cells, which is a chemistry known for having a high charge/discharge rate (but poor energy density).

 

[ClarksonCote]

The early Sparks were A123 LiFePO4 cells, which is a chemistry known for having a high charge/discharge rate (but poor energy density).

True. I guess I wish I knew more about the Bolt's specific chemistry. A 1C rate is just standard for pretty much any LiIon out there. Your phone takes an hour to charge. It is not thermally managed in any way. With lots of cooling capability a car should be able to handle 1C without a second thought.

Unless they somehow used a different chemistry that is much cheaper but far less tolerant of standard charging rates. If that were the case, you'd think that the Bolt would not be capable of 70kW of regen either though, despite that being for shorter bursts, admittedly.

 

[Sean Nelson]

True. I guess I wish I knew more about the Bolt's specific chemistry. A 1C rate is just standard for pretty much any LiIon out there. Your phone takes an hour to charge. It is not thermally managed in any way. With lots of cooling capability a car should be able to handle 1C without a second thought.

I want my car battery to still be working many years after my phone battery has bit the dust, thank you very much.

 

[rob]

True. I guess I wish I knew more about the Bolt's specific chemistry. A 1C rate is just standard for pretty much any LiIon out there. Your phone takes an hour to charge. It is not thermally managed in any way. With lots of cooling capability a car should be able to handle 1C without a second thought.

Remember that California doesn't require your phone's battery to carry a 100,000 mile warranty. The car batteries are likely capable of quite a bit more, but the manufacturers are playing it safe to reduce warranty costs. Hey, it doesn't cost them anything to charge slower.

I want to know more about the Kia Soul battery, 70kW charging on a 27kW pack? 2.6C? Ballsy.

 

[voldar]

Here is an interesting test done by some guys from Quebec. It is in French but you can get the idea pretty quick. http://www.ivisolutions.ca/wp-content/uploads/2017/05/AcquistionRechargeBolt_5Mai_2017.pdf

In short, the cells have to be at a temp of 20C before they can charge full speed. This is why during winter it takes a little longer to get to the full charging speed even though the battery SOC is low.