This.LeftieBiker said:The problem is that the packs will experience similarly high temps in Summer with NO QC.
And QC will routinely be throttled. Nissan made a marketing mistake. The car has a dedicated L2+ charging speed.
This.LeftieBiker said:The problem is that the packs will experience similarly high temps in Summer with NO QC.
Joe6pack said:Perhaps in certain places and even that's not a given being that no new LEAFs have experienced an Arizona summer. Once Summer arrives full force we can find out the delta between ambient and battery temperature under normal driving conditions. I'm willing to bet that it would be difficult to get to 115 degrees Fahrenheit just driving around.
Joe6pack said:Perhaps in certain places and even that's not a given being that no new LEAFs have experienced an Arizona summer. Once Summer arrives full force we can find out the delta between ambient and battery temperature under normal driving conditions. I'm willing to bet that it would be difficult to get to 115 degrees Fahrenheit just driving around.
SageBrush said:Joe6pack said:Perhaps in certain places and even that's not a given being that no new LEAFs have experienced an Arizona summer. Once Summer arrives full force we can find out the delta between ambient and battery temperature under normal driving conditions. I'm willing to bet that it would be difficult to get to 115 degrees Fahrenheit just driving around.
Look up Newton's law of Cooling and Heating and then estimate the pack's specific heat capacity.
It is not difficult to model the '18 LEAF in a summer climate from the information now available.
DaveinOlyWA said:How do we determine internal resistance from LEAF Spy? If you are talking about HX, well my internal resistance is super high. I just checked its 115.75%
Joe6pack said:I am a mechanical engineer, so I get how the heat is generated in the battery and how it is dissipated. Assuming no solar loading, the battery would be at ambient temperature. Once current begins flowing into or out of the battery, it begins to heat up as a function of the internal resistance (as lorenfb pointed out) and the amount of current flowing. Of course, under normal driving conditions, there shouldn't that much current. On the interstate, where you may see higher current draws, you are also going to have a lot of air flow around the battery pack.
I live in Georgia and even on the hottest days, I don't think I've seen the 24 kWh battery hit 115 degrees F just driving around - even on the interstate. If we knew all the variables, we could probably rough something out, but it's probably easier just to take some readings using LEAFSpy.
Joe6pack said:I am a mechanical engineer, so I get how the heat is generated in the battery and how it is dissipated. Assuming no solar loading, the battery would be at ambient temperature. Once current begins flowing into or out of the battery, it begins to heat up as a function of the internal resistance (as lorenfb pointed out) and the amount of current flowing. Of course, under normal driving conditions, there shouldn't that much current. On the interstate, where you may see higher current draws, you are also going to have a lot of air flow around the battery pack.
I live in Georgia and even on the hottest days, I don't think I've seen the 24 kWh battery hit 115 degrees F just driving around - even on the interstate. If we knew all the variables, we could probably rough something out, but it's probably easier just to take some readings using LEAFSpy.
DaveinOlyWA said:How do we determine internal resistance from LEAF Spy? If you are talking about HX, well my internal resistance is super high. I just checked its 115.75%
Ambient air does not circulate in the pack. As for the repackaging and its effect on heat dissipation, ask Nissan. Back in the days of the 24 kWh pack Nissan said that they left space to aid heat dissipation. Today that space does not exist so they either have worse heat dissipation or Nissan found another way to preserve the battery cooling capacity.LeftieBiker said:Joe6pack said:I am a mechanical engineer, so I get how the heat is generated in the battery and how it is dissipated. Assuming no solar loading, the battery would be at ambient temperature. Once current begins flowing into or out of the battery, it begins to heat up as a function of the internal resistance (as lorenfb pointed out) and the amount of current flowing. Of course, under normal driving conditions, there shouldn't that much current. On the interstate, where you may see higher current draws, you are also going to have a lot of air flow around the battery pack.
I live in Georgia and even on the hottest days, I don't think I've seen the 24 kWh battery hit 115 degrees F just driving around - even on the interstate. If we knew all the variables, we could probably rough something out, but it's probably easier just to take some readings using LEAFSpy.
The 24kwh packs have passive air cooling that dissipates heat reasonably well while, driving, as long as the air temp isn't too high. The problem here is that Nissan seems to have reallocated space in the pack previously used for airflow to more battery mass. If not even driving in cool air can cool the core of the pack, it's going to degrade.
SageBrush said:The implication then is that the decrease in heat dissipation that occurs with increasing ambient temperatures will have to be offset by reduced power flow to keep battery temperature constant (though high.) Which brings us back to Newton. Uncertain for now is the improved cooling while driving but it is not difficult to figure that out from the year-round battery experience.
Agree with everything you wrote.Joe6pack said:SageBrush said:The implication then is that the decrease in heat dissipation that occurs with increasing ambient temperatures will have to be offset by reduced power flow to keep battery temperature constant (though high.) Which brings us back to Newton. Uncertain for now is the improved cooling while driving but it is not difficult to figure that out from the year-round battery experience.
Heat transfer is a function of the difference in temperature between the sink (ambient air) and the source (the battery) and the thermal conductivity of the medium through which the heat is being transferred (for conduction). The greater the difference in temperature between the sink and the source, the more heat will be dissipated
The heat is taken away from the battery ultimately by convection. But first the heat has to be conducted away from the source through conduction to the outside of the battery case. We don't know the thermal conductivity of the battery. But, I suppose if we new for a fact that 22kW charging at 35 degrees F resulted in a steady state battery temperature of 115 degrees F, then we could derive the thermal conductivity of the system (convection and conduction). This could then be used to calculate a theoretical steady state temperature for a 95 degree F ambient temperature. This presumes of course that the thermal conductivity doesn't change as a function of temperature as well.
This still wouldn't be an equivalent situation to driving as the convection present when driving would not be present while charging.
Joe6pack said:I am a mechanical engineer, so I get how the heat is generated in the battery and how it is dissipated. Assuming no solar loading, the battery would be at ambient temperature. Once current begins flowing into or out of the battery, it begins to heat up as a function of the internal resistance (as lorenfb pointed out) and the amount of current flowing. Of course, under normal driving conditions, there shouldn't that much current. On the interstate, where you may see higher current draws, you are also going to have a lot of air flow around the battery pack.
I live in Georgia and even on the hottest days, I don't think I've seen the 24 kWh battery hit 115 degrees F just driving around - even on the interstate. If we knew all the variables, we could probably rough something out, but it's probably easier just to take some readings using LEAFSpy.
In the absence of high SOC, temperature is only a minor player in the degradation game.
dhanson865 said:DaveinOlyWA said:How do we determine internal resistance from LEAF Spy? If you are talking about HX, well my internal resistance is super high. I just checked its 115.75%
resistance goes up as a battery degrades, HX goes down as the battery degrades.
It might be that HX is the inverse of resistance but I haven't seen any documentation saying what HX is and I have no reason to say it is or isn't anything else.
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