Chevy Bolt EV Forum banner
  • Hey Guest, welcome to We encourage you to register to engage in conversations about your Bolt.

A little confused about these kW numbers, please help clarify for me.

5426 Views 60 Replies 23 Participants Last post by  GJETSON
I've seen 2 numbers associated with the Bolt.
11 kW, and 55 kW

I saw a public charging station outside of a Denny's restaurant, stopped by to look at the spec. It read "50 kW". This station only charges $0.50 per hour to charge.

So if I hook up my future Bolt EUV to it, will I get 11 kW/hour delivered to the battery, or will I get 50 kW/hour? I know there are losses due to battery SOC and other factors, so the numbers I posted are ideal/theoretical. Let's assume there's no loss to make it easier to understand.

1 - 4 of 61 Posts
Lithium battery designer here...

The two rates are for Level 2 and Level 3 chargers. A Level 2 charger provides 240VAC to the vehicle and its on-board AC to DC converter charges the batteries. A Level 3 charger provides high voltage DC directly to the battery pack and communicates with the battery management system directly. The latter (Level 3) is capable of much higher power because of the higher voltage applied.

The reason you see the 55kW rate fall off at approximately 50% SoC is because the cells have gone from "Bulk" charge to "Absorption" charge. Here are the stages of lithium charging explained:

1) Conditioning charge: This happens at extremely low SoC. The current is small, and the purpose is to take a very dead battery and condition it to be able to accept a higher rate of charge. If you attempt to charge a very dead battery quickly, it will overheat.

2) Bulk Charge: This happens between low SoC and about 50% SoC. During this phase, a constant current is delivered to the battery. The voltage on the cells is increasing during this phase. The end of this phase of charge occurs when the cells reach approximately 4.2V per cell, the "terminal voltage." The voltage on the cells cannot be pushed any higher without damaging them or risking a fire.

3) Absorption Charge: This phase begins when the cells reach terminal voltage. The charger holds the voltage constant and delivers whatever current will continue to flow into the battery. As the batteries continue to charge, the current drops. This is called the "taper." As the current tapers off, the cells are reaching their full state of charge

4) Float: This is not really a charging phase, but the cells are basically held at their termination voltage at very low current. Lithium batteries do not actually need a "float" charge like traditional lead-acid batteries do. Most lithium-specific chargers do not include a float phase, but rather start an absorption phase periodically.

Our Bolts have 96 lithium cells in series, to make 403.2 volts at full charge. The BMS will allow a discharge rate of up to 160kW at full charge, approximately 400 amps from the battery pack.

I hope this helps :)
See less See more
  • Like
  • Helpful
Reactions: 5
There are two ways to charge a battery :
  • using AC
  • using DC
The AC charging can be done on 110V and 240V circuits, thus L1 and L2 names. L1 = AC @ 110 V, L2 = AC @ 240 V.
DC fast charging is NOT a level of AC, thus the use of L3 name is wrong.
If you want to be really technical, there is only ONE way to charge a battery: DC. AC must first be converted to DC before it can be used to charge a battery.

The "Level 3" nomenclature is not necessarily incorrect. SAE defines Level 1 and Level 2 charging standards for both AC and DC charging, but because SAE does not define Level 3 charging standards, doesn't make the colloquial reference to DC Fast Charging as "Level 3" incorrect. It's just not referring to an established SAE standard.

There are currently three different Level 3 (DC Fast Charging) standards: Tesla, CCS, and Chademo. However, the industry has adopted the "Level 3" moniker to apply to all three of these competing standards - basically any DC Fast Charger will be referred to as a "Level 3" on the street.

SAE Level 2 DC charging is the most similar to current non-SAE Level 3 charging. SAE defines Level 2 DC charging as anywhere between 50 and 1000VDC up to 400A.
See less See more
  • Like
Reactions: 3
Distinguishing between Levels 1, 2 and 3 is nothing to really get upset over. (See what I did there?)

I also didn't know, but recently learned, that there are also apparently religious beliefs surrounding the SAE and Chademo connectors. Boggles the mind.
  • Like
Reactions: 2
What will likely happen is that SAE will formally adopt CCS as its Level 3 standard since it is the most widely deployed open standard and has the support of the utility operators.
1 - 4 of 61 Posts