Let me preface this article with this statement: The following is speculation on my part. I plan on discussing this with Nissan, but as the question seems to be frequently recurring, I thought I would answer it with my own thoughts. I suppose we will find out how accurate these are after I have had a chance to discuss it with the folks who know.
First, the Nissan battery pack has no active thermal management. Tesla’s Roadster and GM’s Volt use active thermal management to cool the battery. In both cases, it can also heat the battery. As anyone who has ever owned a laptop computer knows, heat and batteries don’t work well together. So is this an issue? Not according to Mark Perry, Nissan Director of Product Planning. According to Perry:
We don’t need thermal management for the U.S., but we are looking at the technology for Dubai and other locations like that…. We’ve gone on the record saying that the pack has a 70 to 80 percent capacity after 10 years.
Nissan has been developing Lithium Ion batteries since 1992, giving them an 18 year track record with the technology. In fact, in 2000 Nissan provided a vehicle called the Nissan Prairie EV (introduced in 1995) to the Japanese National North Pole Exploratory Team. The team used the vehicle for 6 years in one of the northernmost settlements in the world. With 38 inhabitants and no Nissan dealership nearby, the Prairie received little to no maintenance. The battery performed flawlessly during this extended durability test.
So, what does all of this have to do with throttling the on-board charger to 3.3kWh? Simple. Heat management. Some Electric Vehicle Supply Equipment (EVSE) is capable of charging above the 3.3kWh rate. By charging at a higher rate, I imagine this would generate additional heat.
Right around now, some of you are thinking “But what about Level 3 charging. Won’t that generate even more heat?” Absolutely. But for a much shorter period of time. A fully depleted battery will take eight hours to charge via Level 2. A fully depleted battery will charge to 80% in under 30 minutes via Level 3. If the Level 2 EVSE provides twice the current, it will reduce the charging time to four hours. There is a significant difference between several hours of residual heat buildup and 30 minutes worth.
We have one other reason for our thinking. Nissan has often stated that expected battery capacity is 70% to 80% in ten years. What would cause the variation in range? Frequent Level 3 charging would bring it to the lower end of the range. Consistent charging with Level 2 will maintain maximum capacity.
In our view, the majority of charging will likely be done via Level 2 equipment while we sleep. Most of us sleep for more than four hours. Also, the battery will not be fully depleted the majority of the time when charging. This will provide for shorter charge cycles as well. For those times when a fast charge is needed, there will be an ever expanding network of Level 3 equipment as time goes by.
{ 7 comments… read them below or add one }
I’ve heard that when TN starts making the Leaf, it will have a 6.6kw charger. And that it might be possible to swap the 3.3 for the newer 6.6.
I would be interested in your source. Much of the information on LEAF I’ve found to be speculative. If I find that this is from Nissan corporate, I’ll be happy to pass it along. Not to put a damper on things, just trying to provide accurate info.
I think the 3.3kW limitation is not heat related. While driving you’ll be pulling more than 3.3kW out of the battery on a continuous basis anyway. So heat in the battery or the inverter should not be an issue. Even 6.6kW … should not be a problem; that would be the equivalent of driving 40-45mph for a few hours. I think the reason is the infrastructure (and the most common outlet available). And I believe the decisions made by Nissan focused not on the US market, but the rest of the world being standardized at 220-240V: 13A standard household outlet in the U.K. at 240V. (13*240=3.1kW). Some think the 3.3kW came about from the use of the (incorrect) 220V on a 15A USA circuit (15*220=3.3kW). Again, neither is heat related.
Thanks for that. As I prefaced the article – this was speculation on my part. I’ve also since corrected the bit about the Tesla active thermal management. I missed that in my research.
BTW, the Tesla Roadster can also heat the battery; that feature is not exclusive to the Volt.
I have 240vAC, 30amp service in my garage. That’s 7.2Kw. AeroEnvironment says no good, has to be 40amp and will cost $2600 incl. charger. If Leaf limits charging to 3.3Kw, what is going on here?
Hi Allen, Welcome to Living LEAF! Essentially, there are two different engineering thought processes here. While AeroVironment’s (AV) in-home EVSE draws 30 amps max, the breaker must be a 40 amp breaker so as not to over tax the circuit. And you are correct – this will provide 7.2Kw charge capability. Currently the LEAF on-board charger will charge the battery at the rate of 3.3Kw. This is thought to be because in Europe, the EV charge standard is 230V 16A. Nissan has already discussed the possibility of 6.6Kw, but will not likely be available until LEAF 2.0 in three to five years, or perhaps when the Smyrna, Tennessee plant comes online in late 2012. No official word from Nissan on this yet. So it looks as if AV (and others) are future-proofing their EVSE for a potential upgrade in the US on-board charger.
For more on EVSE than you could possibly ever want to know, you can check out this thread on the MyNissanLeaf forum. Very experienced EV owners discuss the various EVSE alternatives. You don’t have to accept the Nissan recommended equipment supplied by AV, however Nissan will request that you sign a waiver. And depending on your driving needs, you may not need any L2 installed in your home. In fact, you just gave me an idea for my story today – a slight expansion on this comment response! Thanks!