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Discussion Starter #1
Hi folks,

This is just the planning stages of the idea, and if it's feasible.
Also, please excuse the ramble, lots of thoughts on the idea.

Me and the girlfriend both love the idea of turning a FWD Qashqai electric, with the guts of a Leaf, but with a self built or modular 18650 packs.

The idea of having the pack underslung under the vehicle sounds an appealing idea.

The way I imagine building the frame and structure of such a pack would be to purchase a cheap Qashqai, and strip that to almost nothing but the framework needed to fabricate what's required, and transfer the mounts to another Qashqai once the fabrications is done. This way I can get the the other stuff done like the motor from the Leaf mounted in there as well.

Is my idea of and underslung pack reserved for the likes of Tesla only, and is a Leaf the best starting point for such a vehicle?

There's a lot of technical questions here too, like can I use other cells with a different BMS and still ask the Leaf to work, to both charge and and power the motor?

What about pack density? Could I fit 60-70KW's worth of cells in that space?
Where else could I build another pack on the underside of the vehicle to get the capacity we could call the idea viable?

On that note, how easy is it to change parameters, like pack capacity, voltage thresholds and maximum current draw?

Are the two car networks the same? Can I cross platform Nissan parts on the same CANBUS?

I'm sure there are more and more questions the further you look and think about it, and possibly quite a lot of unknowns.

We could come to find out that we just don't have the pack density to make it good enough (I would like a good 150+ miles between charges), once we've got a very scrap Qashqai on our hands without thinking about these things fully.

I plan on doing the work myself, and buying the tools and materials required along the way. I have some ideas for pack design, but I feel they might be useless until I've spent some quality time under a Qashqai.

I think that's all for now, but any knowledge, input and thoughts or otherwise is welcome.
 

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Is my idea of and underslung pack reserved for the likes of Tesla only...
No. Nearly every current production EV has the pack under the floor, although only Tesla makes it just a flat pack so even the front row seating has an excessively high floor; other brands make the pack taller under the seats to make it fit better.

Regardless of the details of the pack shape, the floor is modified (from the gas-engine vehicle from which it was derived) to accommodate the pack. Teslas are not based on a gas-engine vehicle, but the floor is still different than it would be without the battery pack: the floor is above the structural rails rather than set down between them, which is why the interior floor is flush with the tops of the door thresholds, instead of below them like a normal car. This sort of modification would be an enormous DIY project, so the rare efforts to put a pack under the floor either have it hanging down lower than the parts under floor on a stock vehicle, or involve custom pack design if there is a space to fit one.

There are three van projects (and probably zero cars and SUVs) in this forum which have placed a pack under a floor:
  • Kevin's 1967 VW Split Screen Van - "ICE Breaker" has a custom-fabricated box between the frame rail, and body modifications to accomodate it, to contain some Tesla battery modules. Post #110 shows the underside in stock form (with components related to the original engine removed), posts #166 and #171 show the box built to hold 8 modules (half of a 85 or 100 kWh pack), and #176 and later posts show it in place... filling the space between frame rails that you won't have in a Qashqai.
  • Yabert's Westfalia T3 with Chevy Bolt drivetrain has a complete Chevrolet Bolt pack (in the original housing!) under the floor and mostly under the frame rails (so it cuts into ground clearance substantially), with floor and structural modifications to accommodate the part which sticks up at the back end of the pack. See post #114 for an idea of the work done under the floor to fit the pack, and how much it (indicated by the structure to hold it) hangs down because the pack is too wide to fit between the frame rails.
  • Steel's Tesla powered Mercedes Vito has a pack under a floor at the same height as stock, other than a box near the back housing ancillary equipment, but is structurally completely custom.
... and is a Leaf the best starting point for such a vehicle?
If all you're using of the Leaf is the drive unit (motor plus gearbox and controller/inverter), it doesn't really have anything to do with the pack design. The drive units (of all brands) sit on and near the axle lines, and underslung packs are all between the axles. The Leaf or any other drive unit with the motor ahead of the axle (which is most modern EVs) is the easiest format to replace the engine and transaxle directly.
 

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Discussion Starter #3
I can't work out how to multiquote on this forum. It's been a while since I've used a forum, to be honest.

Thank you brian_ for those points.

I should have made it clear that I wanted the pack to be flat, a detail that slipped by as I was writing the post.

I was under the impression that on some vehicles, there's a space between the bottom of the sills (going from the closest to the ground) and the bottom of the floorpan, for stuff like RWD driveshafts, exhaust and gas/fuel tank. Would that space be enough? I know the floorpan isn't flat and it is higher or lower in places depending on what's above or below it. The Qashqai is quite high off the ground, so maybe some depth to the pack wouldn't be a showstopper.

The ICE Breaker build battery box seems to be the closest to what I had in mind.

As for the Leaf, I want to recycle/reuse as much as possible, besides the pack, as I don't think I'd get the range that I'd like out of it, and converting it into a powerwall for the home is a better use of those packs, IMO.
The Leaf cells don't seem to have the best packing density, but I would like to be corrected on this assumption.

I'm new to the idea and have never spent any time with either vehicle in any capacity other than a passenger, so this is all on speculation at this point.

I suppose the next step is to find someone with a Qashqai and ask them kindly if I can spend some time under their car with a length of wood and a measuring tape
 

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I should have made it clear that I wanted the pack to be flat, a detail that slipped by as I was writing the post.
The problem with a flat pack is that it is wide and long and there is no chance that a flat box large enough to be useful will fit anywhere under any vehicle not designed to fit it without simply requiring the whole vehicle to be raised by the pack height to avoid losing ground clearance.

I was under the impression that on some vehicles, there's a space between the bottom of the sills (going from the closest to the ground) and the bottom of the floorpan, for stuff like RWD driveshafts, exhaust and gas/fuel tank. Would that space be enough? I know the floorpan isn't flat and it is higher or lower in places depending on what's above or below it.
Yes, but that space occurs as several oddly-shaped "bumps" up in the floor, almost as if someone had made the original by starting with a flat floor and pounding up into it to make room for those components. If a battery were made of putty, you could put a decent amount of it into those spaces... but batteries are made of rigid rectangular boxes.

If you look at images of the Qashqai fuel tank, you'll how Nissan had to mould it to fit a useful amount of fuel (still small compared to the volume needed for an EV battery) into the biggest available space under the floor. (Note: you'll see at least two different shapes, for different generations of the Qashqai) This is very typical of modern vehicles.

The ICE Breaker build battery box seems to be the closest to what I had in mind.
That old bus has a structure that no modern vehicle has, because they are now much more optimized to use the available space. A traditional truck (a heavy truck, or even a pickup to some extent) still has simple frame rails like that, with not much between them after shafts, exhaust components, and fuel tank are removed; however, no car and no unibody vehicle looks like that (and the Qashqai is a unibody car, station wagon format, in the currently fashionable "SUV/crossover" style... tall with big tires).

An early VW Bus is built like you would build a wooden deck for your home: beams (that's the frame rails), with joists laid on top (those are the VW crossmembers). Any modern vehicle other than a motorhome would have the crossmembers between the frame rails, interrupting the potential battery space.

Even in a truck, a big rectangular battery box is hard to fit, because the frame rails are too close together and because there are structural crossmembers through the space.

The Leaf cells don't seem to have the best packing density, but I would like to be corrected on this assumption.
Each Leaf module is simply a stack of four pouch cells, with the required electrical connections and a box tightly fitted around them. They don't even have any cooling hardware included. They're packed as tightly as they reasonably can be. The energy and power density of the cells themselves depends on the generation: 24 kWh, 30 kWh, and 40 kWh batteries are all the same size.

The new Leaf Plus has a 62 kWh battery in almost the same space and overall shape, although it is internally different:
  • all vertical stacks instead of the previous horizontal stack under the rear seat,
  • more stacks of smaller cells,
  • each stack is a single module (appear to be 4S3P, 7S3P, and 9S3P) instead of a stack of 2S2P modules,
  • much less space between cell stacks,
  • 96S 3P instead of 96S 2P overall configuration.
So no, an early Leaf doesn't pack as much energy in the same space or weight as a current EV... even the most recent Leaf. Part of that is chemistry: the Leaf uses NMC cells like some other EVs, but a slightly different composition.

Without active thermal management, Nissan has been conservative in their use of the battery, so they don't push it as hard as, for example, Tesla. If those same Leaf cells were under a Tesla, they would be putting out much more... as long as too much "Ludicrous Mode" didn't kill them. ;)

I suppose the next step is to find someone with a Qashqai and ask them kindly if I can spend some time under their car with a length of wood and a measuring tape
I think that's an excellent idea, if you happen to know someone with one. If a local rental agency has one in their fleet, you could rent it for a day and look all you want.

I understand that you are looking at the Qashqai because it is the same brand as the Leaf (for possible compatibility) and the size and style of vehicle that you want to drive. To understand how things are typically packed under a modern vehicle you don't need a Qashqai, even if that's what you end up converting - just have a look at whatever you're driving now, assuming that it is from this century and isn't a pickup truck.
 
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