62 kWh Battery Heater - Quest to Find It!

Well, my math above was off by 10x anyway. 10mA at 400V is only a measly 4W. And 6 parallel shunts would only get you to 24W. Leftie says the pack warmer in the original Leaf uses ~300 watts (https://www.mynissanleaf.com/viewtopic.php?f=17&p=615851#p615851) so nowhere near that.

Where did the 10mA number come from? Is it known to be accurate? For which packs? I checked datasheets for a few BMS chips and they support up to 150mA or 300mA balance current per cell using internal balancing switches. But then there's gonna be a lot of power dissipated in the IC - combined current from multiple cells. So perhaps they used external discharge switches and heat-sinked them to the cells. This configuration is recommended in the datasheets for higher power balancing. It's possible. No reason to believe the 62kWh pack has the same cell balancing circuit as the smaller packs.

I think Nissan just increased the cells from 4 parallel to 6 parallel to increase the capacity 50% (which makes me wonder if the 40kWh pack is really 41.3kWh). The missing dedicated pack heater seems like a compromise made to find space for the extra cells. I'm not suggesting this cell-balancing method would keep up with the dedicated warmer. I'm just saying, what else do you expect a "software pack warmer" to do? Running the microprocessor full speed could generate some heat, but it would be highly localized. My guess is that the pack designers were high-fiving each other just to fit 50% more cells and the software pack warmer solution was just a band-aid to show some effort. A design compromise and perhaps they're mostly relying on the larger pack thermal mass to reduce the liklihood of a low temperature event that lasts long enough to freeze the cells.

I'm in the Dallas area and my Leaf is garaged at night. So, similar to you, my car won't naturally see these conditions. My reaction to that is ... I don't care what the pack warmer does. Why is this a curiosity for you? Are you planning a move to a colder climate? I'm always wary of the damage that could be done with dry ice. Skin contact, fast thermal movement or thermal variations across a rigid structure ... risks I want to avoid.

The shunt resistors are 430 Ohm in the earlier packs; nobody has shown the inside of an LBC [Part Number: 293A0-5SF0B, $850] for a 62kwh pack yet, but i would love to see it.
https://mynissanleaf.com/viewtopic.php?f=8&t=17470&hilit=LBC#p380079

The early packs have a separate internal pack contactor (double-pole?) dedicated for the pack heater strips. It is driven by its own little circuit board that gets the command signal from a drive circuit (FET) on the LBC board. So an active VCM may not be needed for the heaters to function.


Since the FET command comes from the microcontroller on the LBC, then the old packs could be said to be "software pack warmers" also?

The diagram for the 62 packs shows the same looking LBC, and the harness to the control port has 2 small internal connectors. But there are no part numbers for strip heaters or an internal heater contactor.
https://parts.nissanusa.com/a/Nissa.../ELECTRIC-VEHICLE-BATTERY/ZE1U_US_291B_3.html

Snargleblarg said:

I'm in the Dallas area and my Leaf is garaged at night. So, similar to you, my car won't naturally see these conditions. My reaction to that is ... I don't care what the pack warmer does. Why is this a curiosity for you? Are you planning a move to a colder climate? I'm always wary of the damage that could be done with dry ice. Skin contact, fast thermal movement or thermal variations across a rigid structure ... risks I want to avoid.

Click to expand...

Just a scientific curiosity for me.
Yes, exactly what I was thinking of when planning this out, can't have dry ice touching any of the battery compartment, it might just freeze the cells local to contact area instead. I'm looking at making a simple sublimation box to vent the CO2 over the battery compartment instead to cool it down gradually and with some control via fans. If that works, then I would have made a battery cooling system by accident. :lol:

This week is going to be deathly cold with single digit temperatures (F) after tomorrow, so I'm preparing my 2020 Leaf+ for a deep freeze with the aid of some dry ice to see if I can finally catch some LeafSpy readings when this "software heater" mode is suppose to kick in and warm the battery. I'll be monitoring to make sure I don't chill the batteries too low, plus avoid keeping the SoC too high, no QC, etc. to try and keep the battery as cold as possible. Fingers crossed this week.

I am looking forward to your test results!

Me too

The deep freeze is here. So, for where I am, temperatures started out at around 50F, then fell to -1F in about 4 hours. In roughly 12 hours, the battery temperature has only fallen from 50F to 32F in that time. Everything else is frozen solid outside, it's amazing how much thermal mass these batteries have as I figured it would have been a lot colder. Battery was over 90% SoC before the deep freeze, so I have plenty of power to last the rest of the week if I need to drive around, no charging (thus warming) necessary.

I did notice that my 12V lithium battery, the voltage was at around 12.2V this morning. The lowest I've ever seen it (usually +13V all the time no matter when or what temperature I measured usually) I was still about to power on the Leaf and watch the 12V charging power, which was 10 watts :lol:

Interesting. Keep the data coming.

I'm surprised the battery cooled that slowly as well. We are in the middle of multiple days of double-digit subzero temps, a rarity in Denver. I have the Leaf garaged, which means the diesel is outside - also not ideal.

Things will return to normal tomorrow around here.

And btw, what's a "cell-balancing shunt" and how does that make heat?

Just curious.

frontrangeleaf said:

Interesting. Keep the data coming.

I'm surprised the battery cooled that slowly as well. We are in the middle of multiple days of double-digit subzero temps, a rarity in Denver. I have the Leaf garaged, which means the diesel is outside - also not ideal.

Things will return to normal tomorrow around here.

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It's *warmed" up to around 1F :lol: here , but still, last I checked the battery, it has only fallen to 28F. I did go make a short run to get a pile of dry ice (which helped to further cool it driving directly into the wind chill), so now I have that packed around the battery too and a fan blowing air into it to help wind chill' it.

Will check from time to time to see what the battery temperature has fallen to. I'm hoping that I hit the magic -4F here soon enough, thought at this rate, may take until sun down. :evil:

Darn it! I have the ideal conditions and the laws of physics are defeating me waiting for this battery to freeze.
One take away, if the previous day was above freezing and you only had one day of extreme cold to worry about, you wouldn't need a heater for this battery. Takes so long just to lose all the heat it has.

I have fans blowing -100F dry ice air over this battery and it's still stubborn.
I can watch the temperature tick down about 1/10th of a degree every ten minutes or so. It's like watching paint dry or downloading files over a modem, good thing I took the day off for this. :lol:

^^^
you can come to my area, -10F last night and today it's not even supposed to hit 0! As my Leafs sit outside neither has a temp bar. Too bad I didn't have a newer Leaf as I could do lots of testing on it. I know every couple days I'm switching my EVSE to one or the other Leafs and when I do they are frequently sitting at 60% even though I charge them up to 100% before unplugging them. My '13 seems to be the most prone for the battery heater to turn on, frequently it's on, my '12 much less so, I'm thinking it's outside air sensor might read a little low or have a slightly higher setting as to when the battery heater kicks in. Currently, I'm not driving either Leaf so they just sit outside day and night getting cold.

jjeff said:

^^^
you can come to my area, -10F last night and today it's not even supposed to hit 0! As my Leafs sit outside neither has a temp bar. Too bad I didn't have a newer Leaf as I could do lots of testing on it. I know every couple days I'm switching my EVSE to one or the other Leafs and when I do they are frequently sitting at 60% even though I charge them up to 100% before unplugging them. My '13 seems to be the most prone for the battery heater to turn on, frequently it's on, my '12 much less so, I'm thinking it's outside air sensor might read a little low or have a slightly higher setting as to when the battery heater kicks in. Currently, I'm not driving either Leaf so they just sit outside day and night getting cold.

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I wish I could, just to test this out.

I'm finally down below into the teens for battery temperature. While everyone is worried about keeping their battery warm, I'm trying to freeze mine on purpose. :lol:

Well failure once again. I could never get the battery temperature any lower than 11F. Even with sub-zero temperatures and dry ice, it just takes too long to cool the battery down unless some really cold, sustained temperatures are possible. Our area forecast is just the temperatures going up slowly over time, so it's too bad I missed a chance to see the legend of the "software heater" :lol:

You put up a valiant effort for sure. Too bad I didn't know anyone in my area with a 62 kWh Leaf. I see them on occasion but don't know anyone personally and even then it would have to be someone who didn't drive and charge their Leaf regularly, both of which would heat up the battery. No, they'd need to be someone like me that just has their Leafs mostly sitting day after day where the battery gets basically as low as the ambient temp. In that case like mine, it would be pretty easy to see if A. it dropped SOC% after a few days or B. If they had an EVSE like mine that kept track of charging Watts you could see it on the display if you left it plugged in.
We are also expecting a big heatwave next week, "they say" it's actually supposed to get above freezing by Thursday but I'll believe it when I see it. Currently, it's 1.8 degrees and sunny but still feels bitter outside when I was cleaning up the driveway of snow that had drifted over the last couple of very windy days. Yesterday they shut down basically all the roads in the SW 1/4 corner of my state and many areas had shelter-in-place orders. I was just out of that area and living in a metro area the blizzard was nowhere near as bad as out in the country.

Sorry I didn't instrument our Leaf which was sitting outside in the sub zero temps here in Chicago. We were -2 and below for over 24 hours. I pulled in the car last night putting the garaged leaf outside. The battery was below 7F when I pulled it in. I did notice the % SoC had dropped a few % from when I last saw it.

I'm guessing most of you have seen Kyles Out of Spec deep freeze charging video. While the 2013 Leaf didn't charge due to a dead 12v battery, the 2023 Leaf SV+ began charging almost immediately around 5kw. Kyle unfortunately didn't record any leafspy information but the car had been sitting for several days and the temps were in the -16 to -18f range. The battery was clearly charging as the percentage rose by a decent amount during the half hour charge session. At several points, Kyle cycles through the various Leaf information displays but nothing looks out of the ordinary.

How would a person know if the battery heater was working?

Does anyone have an explanation on how the "software heater" works?

I saw the video and he didn't loose any battery % after sitting for a couple of days....If I remember correctly...it actually went up from 39% to 43%....don't see how that could happen with battery heat running.

The software heater may be the slow charge rate seen in the video to allow the battery to slowly warm up....just a guess.

frontrangeleaf said:

I would just note to ensure that you have adequate ventilation. Otherwise you risk passing out or worse if you raise the CO2 levels too high in your space. CO2 levels don't need to go very high before you will see effects as I understand matters.

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VERY good point

This was/is an amusing thread. Kudos to OP for the MacGuyer type thinking. :lol:

The car is supposed to heat the pack (if possible) more aggressively when connected to shore power, and certainly when charging. So one modification could be to first see how much the pack temp increases per hour with garden variety charging at home, and then to compare it to charging when the pack is properly cold.

If the charging Amps differ, you can correct using I^2*R

The good news is that if the pack shorts and catches fire, it will already be enveloped in a CO2 cloud