Bolt EV Battery Testing ResultsConditions
28-29 DEC 2017
28-29 DEC 2017
Ambient Air Temperature: 12 - 13º F
Garage Temperature: 48º F
Occasional Light Snow
Trip Total: 166.9 mi, 57.1kWh
Interstate Highway: 97 mi (58%)
Odometer: ~3,700 mi
Hybrid/EV Battery Pack Capacity
- HEX: 0739
- DEC: 1849
- Amp-Hours 184.9
- ~ kWh: 64.7
- Hybrid / EV Battery Pack State of Charge Gauge: 100%
- Hybrid / EV Battery Pack State of Charge (Actual): 96%
- Gauge: 16%
- Actual: 19%
AutoEnginuity ScanTool Proline VCI w/ GM Enhanced Interface
GoPro Video Camera
OpenEnergyMonitor emoncms recording OpenEVSE data
The full charge was initiated on a Level 2 40A OpenEVSE at 60% State of Charge, 59% Gauge State of Charge; 361.92VDC. The average battery pack temperature was 46º F. The battery pack resistance at start was 124.5 ohms, falling to 116-117 ohms as the battery warmed, and then climbed rapidly back up to 129 ohms at full charge. The battery heater was engaged at the the start of the charging event, but it seems to only have run for a short period of time. It drew 2.1 kW during operation and the coolant pump was running at ~3200 RPM. The battery heater pump ran at 50 RPM for most or all of the remaining charge cycle with the battery heater off.
During the early charge stages, Maximum Battery Pack Charge Power was at its full 70kW allowance. At full charge, Maximum Charge Power had been restricted to 30.3kW. Maximum Battery Pack Discharge Power was limited to 140.4kW at the starting state of charge and temperature. Discharge Power limits reached the maximum value of 160kW at 384VDC and 81% Gauge SoC.
The charge terminated at ~5.7A on the AC input at 400.4VDC, an average of 4.171V/cell. The vehicle started a full 32A draw from the EVSE immediately following the charge taper completion – we assume that both the passenger compartment and battery heaters were engaged at this time. The heating event lasted 10 minutes and the AC power consumption then fell to zero. *Wife started a precondition without telling me when the charge finished, that was the 10 minute heating event I noticed in the logs*
Road Test Segment
The road test was plotted along interstate highway routes, chosen to hopefully allow the battery to warm to accommodate a more rapid DC fast charge on the return leg. However, the battery did not warm significantly during the trip, and the pack temperature fell a few degrees over the course of the route. The battery heater ran only while connected to the DC fast charger.
There were very little gains to be found by way of waste heat to lower the pack resistance; but as the state of charge decreased the pack resistance fell as expected. The lowest observed pack resistance on this trip was 50 ohms at 37% actual state of charge. The pack resistance increases again at the bottom of the pack, and at 19% actual at the end of the journey, it had risen to 66 ohms.
DC Fast Charge
A free-to-use ChargePoint 50kW 125A CCS charger was used on the return leg, the battery at connection was at 34% actual, and sub-50º F average temperature. At connection the battery was only seeing 17kW, with the remaining going 2kW to the battery heat and 2.5-3.5kW heating the passenger compartment. The battery received ~50A to start and after 24 minutes had risen to about 70A peak when we terminated the charge at about 44%. The charge was unnecessary, but the extra 8kWh or so made the trip range more comfortable and kept us mostly out of the bottom 20% of the pack.
There were several interesting findings. One was the charge voltage reaching 4.171V/cell. The State of Charge of 96% reported reflects closely what you might expect for this charge voltage. Assuming the stored Battery Pack Capacity variable H0739 reflects 184.9 amp hours available at true 100% SOC, we would expect for this vehicle, our 96% “full charge” would reflect a potential of 62.1kWh usable energy. The only other report of capacity we have on this forum is @drdiesel1 with a reported H06E7, equivalent to 176.7 amp-hours, and 61.8kWh total energy capacity. We don’t yet know if a vehicle with a lower capacity will modify its charge voltage in any way to make up for degradation and try to keep available full charge capacity >60kWh for as long as possible.
The battery resistance is a great analog to how much chemical “push-back” is happening. As the temperature falls, chemical reactions are slowed, and the resistance goes up. Likewise, at high and low states of charge the ions are facing a tougher task jumping between the cathode and anode. It’s nice to be able to watch these numbers in real time and verify that these indeed perform much like any other lithium battery.
The charger in the car on AC level 2 reports both the input current and voltage, and the output voltage, current and power. For 32A in and 238-240V AC in (7.61-7.68kW) – the charger reports 7.2-7.25kW on the output side, for an efficiency of 93.5-94.5%.
Also good to note that in cold temperatures, there may be no amount of driving that will warm the pack enough to get a full speed DC fast charge.