Possible Widespread 2018-19 Traction Battery Quick Charge Problems

This was from the log of yesterday's trip. One thing also noticed is the length of time for the batteries to cool off. They lose heat fairly well when very hot but are slow to return to ambient temps. My S30 would return to ambient or near it in less than 12 hours. Yesterday, I started out nearly 19 hours after the previous QC still 16º above ambient temps. In my garage, the Winter ambient temps (due to leakage from furnace I think) does not vary very much running from low to upper 50's over a HUGE range of outside temps. Yesterday's ambient was 57º on a slightly warmer than normal day.

But today, I did see first EVER significant drop in HX dropping from 115.87% to 115.48 %

lorenfb said:

Using your charging data (I assume), the 2018 40 kWh Leaf battery has about the same battery resistance (55 mohms) as the 24 kWh battery.
Given that adding more cells in parallel (effectively) for more energy when using the same chemistry should have resulted in about .60 (24/40)
the battery resistance (on average) of the 24 kWh battery resistance, so one can possibly conclude a change in battery chemistry (worse).
Additionally, since the 2018 battery is running hotter with the approximate same battery resistance, i.e. same internal heat generation,
one would assume that its thermal resistance to ambient has increased. Reg/LeftieBiker have noted/implied this up-thread.

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Am I reading this right -- about 1-2% of power is lost to heat ?

SageBrush said:

lorenfb said:

Using your charging data (I assume), the 2018 40 kWh Leaf battery has about the same battery resistance (55 mohms) as the 24 kWh battery.
Given that adding more cells in parallel (effectively) for more energy when using the same chemistry should have resulted in about .60 (24/40)
the battery resistance (on average) of the 24 kWh battery resistance, so one can possibly conclude a change in battery chemistry (worse).
Additionally, since the 2018 battery is running hotter with the approximate same battery resistance, i.e. same internal heat generation,
one would assume that its thermal resistance to ambient has increased. Reg/LeftieBiker have noted/implied this up-thread.

Click to expand...

Am I reading this right -- about 1-2% of power is lost to heat ?

Click to expand...

You're correct. At about 56 mohms and 100 amps QC charging, that's only .56 kW instantaneous power
loss when supplying about 35 kW actual charging power. Although the relative power loss seems small,
it becomes problematic if not dissipated (TMS) or avoided (charging tapering).

lorenfb said:

SageBrush said:

lorenfb said:

Using your charging data (I assume), the 2018 40 kWh Leaf battery has about the same battery resistance (55 mohms) as the 24 kWh battery.
Given that adding more cells in parallel (effectively) for more energy when using the same chemistry should have resulted in about .60 (24/40)
the battery resistance (on average) of the 24 kWh battery resistance, so one can possibly conclude a change in battery chemistry (worse).
Additionally, since the 2018 battery is running hotter with the approximate same battery resistance, i.e. same internal heat generation,
one would assume that its thermal resistance to ambient has increased. Reg/LeftieBiker have noted/implied this up-thread.

Click to expand...

Am I reading this right -- about 1-2% of power is lost to heat ?

Click to expand...

You're correct. At about 56 mohms and 100 amps QC charging, that's only .56 kW instantaneous power
loss when supplying about 35 kW actual charging power. Although the relative power loss seems small,
it becomes problematic if not dissipated (TMS) or avoided (charging tapering).

Click to expand...

Indeed, it does seem like a small amount.
I imagine a 200 Kg pot of water being heated by a 560 watt element.

SageBrush said:

I imagine a 200 Kg pot of water being heated by a 560 watt element.

Click to expand...

I do as well, but that's because those specs fairly accurately describe the water capacity and maximum power usage for a typically sized heat pump water heater operating in heat pump only mode.

Sorry, now back to topic.

SageBrush said:

Nissan screwed the pooch on QCFC, although it remains to be seen (or figured out) whether even one charging session at 45 kW will be available in warm/hot weather.

The no less important question is how hot the battery gets throughout the summer. I asked Joe "the mechanical engineer" in another thread how much heat dissipation drops on a 95F day compared to 35F based on a simple model of conduction but no answer was forthcoming so I'll provide it here: 75%

Ignoring just for a moment other variables in play like specific heat, better ventilation during driving and time, we are starting the game from the sqrt(0.25) = 50%, or about 11 kW based on the reports of 22 kW throttling when the battery reaches 115F. I am not saying that the LEAF will be throttled to 11 kW in the summer or that the battery will live at 115F for months on end. I am saying that the LEAF battery in the 40 kWh model appears to be even more vulnerable in warm climates than prior models and more information is absolutely required to be an informed buyer.

Caveat Emptor. Or just plop down $30k based on "confidence" from Nissan Corporate and a battery warranty that will keep the car running at something over 60% of new range for 8 yrs/ 100k miles.

Click to expand...

I ignored it because it's not relevant. It's obvious that ambient temperature has very little to do with the LEAF's battery temperature rise during quick charging. Your 75% delta, if it's even correct, is only looking at the cooling of the outside of the case which is dependent on ambient temps and the design of the case. However, the issue is that the LEAF's battery cells (and maybe all battery cells) have high thermal capacitance and low thermal conductance. It's analogous to a block of steel which has high thermal capacitance and low thermal conductance. An equivalent block of aluminum, copper or silver would have lower thermal capacitance and higher thermal conductance. This is why steel is never used as a heat sink while aluminum is very common. Any heat generated in the cells tends to stay in the cells and is slow to be conducted away to the outside and that's why battery temps can remain high many hours later. The solution is to cool smaller groups of cells by putting space between the cells and circulating a fluid (air or liquid) thereby reducing the temperature gradient across the cells. Of course the fluid would have to be cooled using a separate radiator or the car's A/C system. This adds cost, increases size, increases weight and decreases efficiency - but it does reduce cell temperatures. It would also have to work while sitting still since we are talking about quick charging thereby increasing charging times - so pick your poison. Nissan looked at "their" markets and "their" customer's use cases and determined this was not necessary. They chose to approach it from the other direction and to limit the amount of heat that is generated in the first place. So there you go.

Joe6pack said:

SageBrush said:

Nissan screwed the pooch on QCFC, although it remains to be seen (or figured out) whether even one charging session at 45 kW will be available in warm/hot weather.

The no less important question is how hot the battery gets throughout the summer. I asked Joe "the mechanical engineer" in another thread how much heat dissipation drops on a 95F day compared to 35F based on a simple model of conduction but no answer was forthcoming so I'll provide it here: 75%

Click to expand...

I ignored it because it's not relevant.

Click to expand...

You mean you cannot see the relevance.

Wait until warmer weather, then even you will wise up. Maybe

Your 75% delta, if it's even correct

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I'm having a hard time believing that you are an engineer, even though I know that competency spans a large range.

iPlug said:

SageBrush said:

I imagine a 200 Kg pot of water being heated by a 560 watt element.

Click to expand...

I do as well, but that's because those specs fairly accurately describe the water capacity and maximum power usage for a typically sized heat pump water heater operating in heat pump only mode.

Sorry, now back to topic.

Click to expand...

Electric tea kettle, not a heat pump ;-)
Resistance heat with a COP of 1.0

Has anyone looked yet to see if the little cabin air exhaust flap in the passenger compartment floor is still there, by the emergency power cutoff?

SageBrush said:

Perhaps we need a new acronym: DCSC "DC slow charging."

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:lol: :lol:

How about "DCFOC" for "DC Fast ONCE Charging"?

SageBrush said:

The 2018 LEAF DCFC should come with a big footnote that reads "up to 45 kW, as battery temperature and other variables allows."

Or just give up on the DCFC sham altogether and advertise DC L2+ speeds

Perhaps we need a new acronym: DCSC "DC slow charging."

Click to expand...

FWIW, in Japan, they have "intermediate" (CHAdeMO) chargers.

See https://teslamotorsclub.com/tmc/threads/chademo-make-model-review-%E2%80%94-using-with-a-tesla.42176/page-8#post-961564 and https://teslamotorsclub.com/tmc/threads/chademo-make-model-review-%E2%80%94-using-with-a-tesla.42176/page-8#post-971287. As the 2nd post mentions, they even have some 10 kW CHAdeMO chargers there.

DaveinOlyWA said:

throttling starts on QC if temp is over about 85º which is almost always going to be the 2nd session but its relatively minor with 16-17 kwh received in 30 mins instead of 22 kwh for a first charge.

The reality is it would not be good for a road trip in Summer over 300 miles. Under that, the additional range more than makes up for the charging speed.

FYI; This sounds bad but puts it on near equal footing with the Bolt. I saw a Bolt charging in temps low 70's in Sept pulling 130 amps from EVGO. I was impressed until it hit 55% and the charge rate dropped like a rock to 62 amps. It was... SHOCKING

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Sorry, I’m just following this thread now so I’m catching up from earlier comments like this one.

Saying that the 2018 LEAF is nearly on the same footing as the Bolt EV for long-distance driving of 300 miles or more is misleading.

I’ve done many road trips since getting my own Bolt in January of 2017 and almost all of the charging during the drive was on 50 kW DC chargers. I’m very familiar with the Bolt’s rampdown pattern. I have even fast charged in Las Vegas at 104F after several hours of driving from near Los Angeles and have not seen a noticeable slowdown due to heat because the TMS does a good job of keeping pack temperatures not much warmer than 86F.

From memory it looks roughly like this:

0-54% at 53 kW or 150A (125A on today’s chargers)
55-68% at 37 kW or 100A
69-84% at 24 kW or 60A
85-92% at 16 kW at 40A

I rarely QC much above 80% so that last line may be slightly off.

So, “dropped like a rock” seems misleading to me.

Even though the Bolt begins ramping down the charge current aggressively at 55% its battery is quite a bit larger in capacity so on road trips its typical to add roughly 80 to 100 miles with a 30 minute charge at an average of around 43 kW on today’s chargers which appears to be at least as fast as a new LEAF can do when not restricted and twice the speed of a heat-restricted LEAF charging.

I have no qualms doing 400 to 500 mile daily segments in hot summer weather while it appears that would be rather tedious in the new LEAF, as you noted.

It sounds like all Leafs from all years and battery sizes thus far would be much better cars if someone would just figure out a way to install a fan that blows fresh air over the traction battery. It might not be enough cooling for those that live in extremely hot areas but it would be better than nothing and might be sufficient in most areas due to the overall thermal stability Nissan designed into all Leaf batteries. The battery fan could even be left on for extended periods by means of a 12V solar panel on the roof.

I just remembered I have a 12V blower just lying in the shed. It or two of them might fit between the traction motor assembly and fire wall. Then I'd just have to figure out the duct work and where the fresh air would come in at (hood scoop maybe?!). Now I want to go grab it and see if I can fit it in there somehow.

IssacZachary said:

It sounds like all Leafs from all years and battery sizes thus far would be much better cars if someone would just figure out a way to install a fan that blows fresh air over the traction battery. It might not be enough cooling for those that live in extremely hot areas but it would be better than nothing and might be sufficient in most areas due to the overall thermal stability Nissan designed into all Leaf batteries. The battery fan could even be left on for extended periods by means of a 12V solar panel on the roof.

I just remembered I have a 12V blower just lying in the shed. It or two of them might fit between the traction motor assembly and fire wall. Then I'd just have to figure out the duct work and where the fresh air would come in at (hood scoop maybe?!). Now I want to go grab it and see if I can fit it in there somehow.

Click to expand...

This idea pops up all the time, but if it was that easy and cheap Nissan would have done it.

IssacZachary said:

It sounds like all Leafs from all years and battery sizes thus far would be much better cars if someone would just figure out a way to install a fan that blows fresh air over the traction battery. It might not be enough cooling for those that live in extremely hot areas but it would be better than nothing and might be sufficient in most areas due to the overall thermal stability Nissan designed into all Leaf batteries. The battery fan could even be left on for extended periods by means of a 12V solar panel on the roof.

I just remembered I have a 12V blower just lying in the shed. It or two of them might fit between the traction motor assembly and fire wall. Then I'd just have to figure out the duct work and where the fresh air would come in at (hood scoop maybe?!). Now I want to go grab it and see if I can fit it in there somehow.

Click to expand...

Remember, to remove heat from the battery cells you have three thermal resistances (inverse of thermal conductance) to contend with,
i.e. cells to battery case, battery case to vehicle chassis, chassis to ambient. The last has the lowest thermal resistance. The next lowest is
the battery case to chassis. The most problematic thermal resistance is the cells to battery case. So blowing ambient air on the battery case
will have negligible effect on reducing the cells temperature. That's why an effective TMS has to be integrated into the design of the battery.

lorenfb said:

IssacZachary said:

It sounds like all Leafs from all years and battery sizes thus far would be much better cars if someone would just figure out a way to install a fan that blows fresh air over the traction battery. It might not be enough cooling for those that live in extremely hot areas but it would be better than nothing and might be sufficient in most areas due to the overall thermal stability Nissan designed into all Leaf batteries. The battery fan could even be left on for extended periods by means of a 12V solar panel on the roof.

I just remembered I have a 12V blower just lying in the shed. It or two of them might fit between the traction motor assembly and fire wall. Then I'd just have to figure out the duct work and where the fresh air would come in at (hood scoop maybe?!). Now I want to go grab it and see if I can fit it in there somehow.

Click to expand...

Remember, to remove heat from the battery cells you have three thermal resistances (inverse of thermal conductance) to contend with,
i.e. cells to battery case, battery case to vehicle chassis, chassis to ambient. The last has the lowest thermal resistance. The next lowest is
the battery case to chassis. The most problematic thermal resistance is the cells to battery case. So blowing ambient air on the battery case
will have negligible effect on reducing the cells temperature. That's why an effective TMS has to be integrated into the design of the battery.

Click to expand...

And yet driving is pretty effective compared to standing still, at least in the 24 kWh packs.
My take on this question is that parking in an unventilated space like a closed garage is a BAD idea; but once outside I doubt a fan is going to help much.

Isn't there a space above and below the battery for cooling purposes? I don't recall that heat has to travel through the chasis to exit the battery.

Anyhow, it's not a lot of heat that needs to be removed.

SageBrush said:

lorenfb said:

IssacZachary said:

It sounds like all Leafs from all years and battery sizes thus far would be much better cars if someone would just figure out a way to install a fan that blows fresh air over the traction battery. It might not be enough cooling for those that live in extremely hot areas but it would be better than nothing and might be sufficient in most areas due to the overall thermal stability Nissan designed into all Leaf batteries. The battery fan could even be left on for extended periods by means of a 12V solar panel on the roof.

I just remembered I have a 12V blower just lying in the shed. It or two of them might fit between the traction motor assembly and fire wall. Then I'd just have to figure out the duct work and where the fresh air would come in at (hood scoop maybe?!). Now I want to go grab it and see if I can fit it in there somehow.

Click to expand...

Remember, to remove heat from the battery cells you have three thermal resistances (inverse of thermal conductance) to contend with,
i.e. cells to battery case, battery case to vehicle chassis, chassis to ambient. The last has the lowest thermal resistance. The next lowest is
the battery case to chassis. The most problematic thermal resistance is the cells to battery case. So blowing ambient air on the battery case
will have negligible effect on reducing the cells temperature. That's why an effective TMS has to be integrated into the design of the battery.

Click to expand...

And yet driving is pretty effective compared to standing still, at least in the 24 kWh packs.
My take on this question is that parking in an unventilated space like a closed garage is a BAD idea; but once outside I doubt a fan is going to help much.

Click to expand...

Right. Then there's the thermal time constant, i.e. the time for the cells' temperatures to reach ambient - assuming a higher temp (from driving/charging).

IssacZachary said:

Isn't there a space above and below the battery for cooling purposes? I don't recall that heat has to travel through the chasis to exit the battery.

Click to expand...

You need to know how the battery is attached to the chassis.