Driving more than 500 km in a day in the Nissan Leaf requires careful planning. While rare in my life, my inner engineer is scheming if it would be feasible to add an aftermarket battery cooling system to the Nissan Leaf. As a first step, lets do some thermodynamics and see how much heat we would have to remove. We approach the problem two ways, first we know how much energy a rapid charging session puts into the car, assuming a small loss factor due to heat, we get our heating energy that way. Second, we look up literature values for battery system thermal capacities, and plug in values for the leaf. We find that a few liters of misty water might take away enough heat to counter #rapidgate.
Truth be told, only two or three times a year, I actually need to drive further than 500 km in a day. My Mnt. Tremblant ski trip comes to mind (see this post), where I drove the 600 km or so, in 10 hours, 30 minutes, door to door, including bio-breaks, charge breaks etc. In that post, a theoretical gas car booking it along the 401 would have a door to door time of 8 hours. Had a cooling system been available, that 10 hrs and 30 minutes, might have become 9 hours, so there is something to be gained here.
Lets begin with a charging session approach. On a typical Fast charging session, we might want to put perhaps 25 kWh into the battery. DC charging losses, generally are lower than AC charging losses (DC charging was quoted at 1 %, vs 13% for AC source). I noticed looking at my Ivy receipt, that I pulled 24.5 kWh from the charging station, but my battery state of charge change suggested 23 kWh went into the battery, corresponding to a 5% loss rate. So, lets say, approximately 1.5 kWh of energy went to heating the battery by 16 C.
Next to physics, we know that the 2018 Nissan leaf has a NiMnCo Lithium ion battery, which might have a specific heat of about 1040 J/kg.K (source). It weights about 300 kG (source, source) and during a rapid charging session, we observe a temperature increase of 15 C. This suggests about 1.3 kwH of energy is lost to heat.
So no matter how were slice it, seems we need to remove, say 1-1.5 kWh of heat. How might we go about doing that? Since in my Toronto-Life this is something that comes up not very often, so lets look at a couple of temporary-ish things we could do: Melt Ice and evaporate cooling.
Start with ice. Melting 1 gram of Ice takes about 334 J worth of energy, it takes a little more energy to raise the temperature of the melt-water to say 30C, all-told we would need about 8-12 Kg of ice to remove said 1-1.5 kWh of heat. Grocery stores typically sell a 10 pound bag of ice for a few dollars, hence we would need 2-3 bags of ice, which seems doable.
Misting systems might do better still. Evaporating water is a fairly energy intense exercise, requiring perhaps 2260 J/gr. Hence, it may only take 2.5 Kg of “misted” water to take away that 1-1.5 kWh of heat. Granted, water evaporation is a complex process, and as our battery temperatures are nowhere near the boiling point of water (100 C), I feel we may need to mist a bit more than 2.5 Kg of water. But compared to ice, seems water mist requires a lot less water (frozen or otherwise). Plus, your local hardware store might have a very portable misting fan, this one for example is designed to fit on-top of a water bucket, something the Leaf’s cavernous boot would have no problems with.
We discuss further in my next post, where and how we might use this on the Leaf. But using either ice sourced from a nearby grocery store, or a “misting-fan” are certainly both quite plausible.
Electric car adventures 