DIY Leaf 25-44 kWh

I did some calculations on the back of an envelope and figured out that 16 LG/Sanyo/Panasonic 3500 mAh 18650 cells in parallel (96S) would result in 56 Ah of capacity which is close enough to the capacity of the original LEAF battery (~20 kWh) resulting a total combined raw capacity of 44 kWh.

You'd need exactly 1536 cells to the largest capacity pack. From nkon.nl the cost would be around €5600 excluding delivery (€2800 for 10 kWh). The resulting volume of the cells with spacers and BMS would be around 70 liters and I reckon the resulting enclosure of around size 700 x 700 x 150 mm would fit under the boot floor. The weight of the cells alone would be around 70 kg. Add the weight of casing, BMS, cabling and this would maybe increase to 100 kg. Still a way less than the original battery at around 350 kg for close twice the range.

There a guy in Canada (Leaf xpack) on youtube who's doing a similar installation. His proof of concept battery has 192 cells from recovered laptop batteries. He connected his packs in the main ~400V DC line at the battery pack via isolation contactors. The extra battery cells could be installed in parallel with any multiples of 96 so a pack size between 1.2 to 20 kWh could be constructed that way. The beauty of this approach is that the add on packs would automatically integrate to the car and the power draw would also scale as the add on pack would flow current in/out as the main pack voltage changes during run and charging. The new pack would not need any modifications to the LEAF electronics apart from the connection to the main HV cable which our man constructed so that it can be dismantled without any trace.

Due to the way this addon pack works would actually make cooling it unnecessary (the maximum dis|charge rate would be a tiny fraction of max rated values) and as an additional bonus the more batteries you fit the less current the original pack sees. The original battery would be stressed less and less the more additional capacity there was. As standard the pack is discharged at 4C at maximum and with the 20 kWh extra pack the max rate would reduce down to just over 2C. This approach would be a great way to boost an early car with reduced capacity (although the LEAF mk. 1 do have more stuff installed under the boot floor than the later models).

This definitely would make an interesting project! A lots of soldering and manufacturing is needed. As a bonus how about removing the original modules and filling a dead LEAF main pack with 18650 cells instead?

According to an article I found each of the Nissan LEAF's battery modules are sized 303 x 203 x 35 and there are 48 of them. These could in theory accommodate 18650 cells in 21S 2P (i.e. 42 cells) resulting in capacity of 73.5 Ah per module. The Nissan ones are rated at 33 Ah.

That's 53 kWh in the size of the LEAF pack assembled in same size modules as the OEM ones. At the cell level this would result in discharge rate of about 2C for cells rated at 10C max so passive cooling would probably be grand. The purchase cost for the 2016 cells required from nkon.nl would be approx €7500 and as the the cells weigh at 46 grammes each total weight would be a touch under 100 kg. With clever packaging the pack would actually weigh considerably less than the original Leaf pack.

Edit: Actually the article I was using as a reference to the Leaf 24 kWh battery to made a mistake. Each of the cells (instead of the modules) in Leaf are 33 Ah. The battery modules are nominal 7.5V 66 Ah in 2S-2P configuration and there are 48 of them. So in reality you'd need way more 18650 cells than I estimated to create an unicorn LEAF battery. To reach approx 50 kWh you'd need whopping 3840 battery cells which would cost over €14k retail weighing at 177 kg just for the cells.

On the positive side the resulting 96S-40P battery could output up to constant 400A which at rated 360VDC means that you could increase the LEAF motor from 80 kW to over 150 kW. The standard LEAF battery is rated at 180A constant which is only 64 kW of constant power at rated 360 VDC (and explains why the 80 kW motor needs to be torque restricted at high speeds).

Dardania

Why don't Nissan offer this configuration now?

Batteries are too expensive to play around with without proper methods of construction. These 18650 cells will burst into flames if mistreated and you do not want to risk it.

BMS's fail and can fail with catastrophic consequences . Automotive pouch cells are usually much safer and used for a reason, yes they're a compromise in energy and power density.

Renault will charge 2,500 extra for the 40 Kwh battery , this in my opinion is pretty good.

With such a project you will most likely fail on your first attempt. You got to make your welds absolutely perfect have proper rated fused links etc etc.

It's actually a nightmare of a task, this is all stuff robots do on an assembly line........

Also because a cell is rated for 10C doesn't mean it won't heat enough not to require cooling, even at 2 C you could be surprised how it will heat. Manufacturers have a habit of over rating their performance.

A very, very expensive mistake if something goes wrong.

Manufacturers have the money to test and burn packs, test construction methods etc.

Nissan pouch cells are very safe alright, i.e. you can put knife through them. Don't remember ever hearing a LEAF catching fire unlike many Tesla Model S's.

But it was interesting to confirm with my own maths that there definitely is scope for way more battery capacity even using commodity cells. Looking forward a Kreisel laser welded 53 kWh flooded cooling pack next year.

I don't think there's be a market for after market batteries for electric cars, I could be wrong of course. And I certainly can't imagine them being able to keep the costs as low as Battery manufacturers who will be mass producing cells like never before.

Also, batteries will last a very long time in the next generation electrics.

kirving

In addition to the safety aspects mentioned above, OEM's do an absolutely unbelievable amount of endurance testing on new products to get the reliability spot on.

For example I work in automotive manufacturing (not batteries) and even changing a machine which screws two simple components together can see the final product go through literally months vibration and thermal testing.

The same couldn't be said for a home made project unfortunately, particularly where a pierced cell or loose connection could cause a fire. Although it's certainly an interesting idea.

Interesting if you got the money to (Risk) if not then it's a project I certainly wouldn't touch. Building battery packs from hundreds if not thousands of 18650 cells takes a lot of skill and tools, if you are only messing about it's highly likely things will go wrong and terribly wrong at that. The voltages alone will kill you if you're careless, you need the correct PPE equipment also. High voltage gloves, and the likes.

You also can not under any circumstances store these cells in the house of your shed if you value them. In a fire proof location in the shed/workshop then maybe. Make sure you're insured for such a thing.

You need to know the supplier of these cells is reputable, you need recommendations, chances are shipping will be outrageously expensive because no airline will touch Li batteries without proper precautions.

If something goes wrong and you can prove you didn't cause the failure then can you send them back and get a replacement ? you'll have to pay for the shipping back.

You also got to test EVERY SINGLE CELL, I MEAN EVERY SINGLE CELL, you simply can not under any circumstances string hundreds or thousands of cells together without making sure they perform almost exactly the same, and you need to test the internal resistance to make sure the supplier of these cells didn't give you a dud because that dud WILL CAUSE A FIRE.

You need to charge and discharge these cells with proper chargers that log the charging and discharging data.

No cell is exactly the same but you need to make sure they match as close as possible, the whole pack will perform as good as the weakest group of cells.

There's so much you got to know and learn. Fused links, correctly rated cables, components, contractors, relays, pre charge circuits, BMS , the list goes on.

My advise is to start with electric bike projects, go to endless-sphere.com and there's a tonne of information, building high powered electric bikes is a lot of fun but it will give you an idea of what you're up against. Start small. Guaranteed, by the time you stop messing with LiPo battery cells for electric bikes with 500 watt hrs to 1kwh worth of storage you'll never want to tackle 12 Kwh worth, I guarantee it !

BoatMad

samih wrote: »

I did some calculations on the back of an envelope and figured out that 16 LG/Sanyo/Panasonic 3500 mAh 18650 cells in parallel (96S) would result in 56 Ah of capacity which is close enough to the capacity of the original LEAF battery (~20 kWh) resulting a total combined raw capacity of 44 kWh.

You'd need exactly 1536 cells to the largest capacity pack. From nkon.nl the cost would be around €5600 excluding delivery (€2800 for 10 kWh). The resulting volume of the cells with spacers and BMS would be around 70 liters and I reckon the resulting enclosure of around size 700 x 700 x 150 mm would fit under the boot floor. The weight of the cells alone would be around 70 kg. Add the weight of casing, BMS, cabling and this would maybe increase to 100 kg. Still a way less than the original battery at around 350 kg for close twice the range.

There a guy in Canada (Leaf xpack) on youtube who's doing a similar installation. His proof of concept battery has 192 cells from recovered laptop batteries. He connected his packs in the main ~400V DC line at the battery pack via isolation contactors. The extra battery cells could be installed in parallel with any multiples of 96 so a pack size between 1.2 to 20 kWh could be constructed that way. The beauty of this approach is that the add on packs would automatically integrate to the car and the power draw would also scale as the add on pack would flow current in/out as the main pack voltage changes during run and charging. The new pack would not need any modifications to the LEAF electronics apart from the connection to the main HV cable which our man constructed so that it can be dismantled without any trace.

Due to the way this addon pack works would actually make cooling it unnecessary (the maximum dis|charge rate would be a tiny fraction of max rated values) and as an additional bonus the more batteries you fit the less current the original pack sees. The original battery would be stressed less and less the more additional capacity there was. As standard the pack is discharged at 4C at maximum and with the 20 kWh extra pack the max rate would reduce down to just over 2C. This approach would be a great way to boost an early car with reduced capacity (although the LEAF mk. 1 do have more stuff installed under the boot floor than the later models).

This definitely would make an interesting project! A lots of soldering and manufacturing is needed. As a bonus how about removing the original modules and filling a dead LEAF main pack with 18650 cells instead?

Fire away. !!!

BoatMad

BoatMad wrote: »

Fire away. !!!

Haha, pun intended I'm sure....

I have the cells ordered now for extra 20 kWh. Check regularly here for updates.

samih

samih wrote: »

I have the cells ordered now for extra 20 kWh. Check regularly here for updates.

Fair play to you, will be watching with interest. Best of luck but please do take the proper precautions and do not store any quantity of these cells in your house where your family are.

And make sure you check every single cell for the correct voltage and make sure they're all at the same voltage when you connect them up.

I strongly advise running them on a charger that will log the charge/discharge data at the rated specs , this will be time consuming.

Sorry guys for raising false hope but I didn't really order the batteries. Just though I'd see what the reactions were. Have another winter project starting so anything big will have to wait anyway. But I'm really looking forward seeing how your man in Canada fares:

https://youtu.be/Ztejn3YYbvw?list=PL5Nz1FJp-6dtcfy52ArsE6-EyGCAKRlS1