1

Memo 

To: Docket EPA-HQ-OAR-2009-0472 

From: Joseph McDonald 

CC: Ed Nam, U.S. EPA-OTAQ-ASD 

Date: Thursday, March 26, 2010

Re: Lyle Dennis interview of Rob Peterson (GM) regarding the all-electric drive range of the GM 

Volt 

The following document contains an Internet-posted news article summarizing an interview of Rob 

Peterson of GM by Lyle Dennis on the all-electric drive range of the GM Volt. The article is entitled 

“Latest Chevrolet Volt Battery Pack and Generator Details and Clarifications” and was a Accessed on 

the Internet on June 30, 2009 at: 

http://gm-volt.com/2007/08/29/latest-Chevrolet-volt-battery-pack-andgenerator-details-andclarifications/ 
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Latest Chevy Volt Battery Pack and Generator Details and

Clarifications

August 29th, 2007 | Posted in: Battery, Design, Engineering, PHEV 

In some recent posts, we were able to find out and discuss some important details about how the Volt’s li-ion battery pack is 

intended to function. One of the most critical facts we obtained from GM is that the 40 mile all-electric driving range will occur 

within 50% of the batteries maximum charge, or 8 kWh out of 16 kWh total. This translates to 200Wh/mile of energy 

consumption. 

We also looked at the ability of the combustion engine (53 kW maximum) to keep the battery charged and how it might operate 

to do so. This generated some very intriguing discussion and further questions. 

I went back to GM and had some discussion with other sources familiar with the Volt’s engineering, and have been able to 

elucidate the following more accurate facts: 

As per Rob Peterson, GM spokesman, the battery will operate in the 50% “swing” zone, but actually, the batteries full point will 

be 80% (not 100%). So its charge state will actually vary between 30% SOC and 80% SOC. This translates to the following 

analysis of battery capacity: 

theoretical capacity 100% 16.0 kWh (not realized under normal conditions)

highest recharged level 80% 12.8 kWh (after being plugged in)

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Latest Chevy Volt Battery Pack and Generator Details and Clarifications | GM-VOLT : C... Page 1 of 18

http://gm-volt.com/2007/08/29/latest-chevy-volt-battery-pack-and-generator-details-and-cl... 9/11/2009
charge sustaining level 30% 4.8 kWh (after ~40 miles of driving)

empty 0% 0.0 kWh (not realized under normal conditions)

In terms of the on-board generator, the peak power of 53 kW will rarely be used, only in extreme conditions. Peak efficiency will 

be at around 30 kW, which is what the car should require at 65 mph slightly uphill, although the actuals of mass and energy 

requirements are not final yet. 

The engine’s job will be to maintain the battery at a SOC of 30%, and will do so by continuously matching the average power 

requirement of the car once it is turned on. Those energy requirements will roughly be about 8 kWh in the city, and 25 kWh on 

the highway. 

Another interesting note is about the time course of recharging the battery on the road. If one tried to recharge it by maxing 

engine output, the cells’ temperature would get too high, so the idea of rapidly “refilling” it on the fly and then cutting off the 

generator wont apply. Rather, it seems, the engine will continue to run, constantly matching the needs of the car to keep the 

battery at 30% until you stop driving. 

Interestingly, the motor will likely be programmed to increase rpm when you step on the gas and quiet down when you stop to 

“simulate” the driving effect people are already used to. This will avoid the sudden unexpected ons and offs. 

The graph above illustrated how the pack shall operate. 

Related posts: 

Posted by: Lyle

 

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1. NEW FACT: Chevy Volt Generator Starts When Battery Power Hits 50%, Stops Again at 80%

2. Latest Battery Pack Q & A with Denise Gray, GM’s Battery Director

3. FACT: Chevy Volt’s Generator to Start When Battery Power Drops to 50%

4. GM Takes Delivery of Second LG Chem/Compact Power Chevy Volt Battery Pack, and it’s Better Than the First

5. Chevy Volt Mule in Generator Mode Already ‘Prius Quiet’

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Latest Chevy Volt Battery Pack and Generator Details and Clarifications | GM-VOLT : C... Page 2 of 18

http://gm-volt.com/2007/08/29/latest-chevy-volt-battery-pack-and-generator-details-and-cl... 9/11/2009