18650s in a Leaf anyone?

I've got to admit to a bit of fascination with the higher energy density of 18650 format cells, especially the Panasonic NCR18650B which boasts 11Wh in a 50g weight battery. I built up a 500Wh pack for an electric scooter last year & found the cells to be beautifully balanced, so much so that I charge them without a BMS.

Recently prices on these cells have tumbled from $10-$12 down to $3-$4 ea. Has anyone else considered the possibility of paralleling the Leaf traction pack with a few extra kwh worth of these cells? A 384 cell pack (2p192s) in the trunk would add an extra 4kwh (~20%) to the Leaf, would weigh only 20kg & cost about $1500 to build. I'd make the connection at the charger behind the back seat on my 2012 model & simply let the AUX pack charge & discharge with the main pack. Maybe stick a 10A fuse in there somewhere just to be safe.

Thoughts anybody?

The battery experts here will know more about it, but my understanding is that the chemistry used in those cells is too much of a fire hazard to be safe in cars without some sort of effective cooling system (such as what Tesla uses for its battery packs).

dgpcolorado said:

The battery experts here will know more about it, but my understanding is that the chemistry used in those cells is too much of a fire hazard to be safe in cars without some sort of effective cooling system (such as what Tesla uses for its battery packs).

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I believe you are correct! Maybe the price drop was to get in on the Boeing contract :lol:

Kris1 said:

A 384 cell pack (2p192s)

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You probably want a 96S pack or so, same as the current LEAF, so perhaps a 4P96S pack.

It would take some work and experimentation to determine if the pack can handle the load.

The biggest challenge will be designing a cost-effective BMS for the pack to keep yourself from blowing it up.

So, you're thinking that Nissan has built in a charger and BMS that can't tell if there is a short circuit in the car (which the extra batteries would be seen as) and just keeps pumping in power even if the battery isn't receiving it? I'm not saying they have, but I would have tended to build a system that monitors current from the charger and current into the battery pack, and if it was out by some tolerance then it would not charge.

What sort of '10A' fuse do you think it needs, and where would you put it. 10A!? If you add 20% to the battery, and the motor can pull 300A, then you need to have your 20% addendum rated for 60A at least. A 10A fuse on a 20% extra pack would go 'pop' as soon as you hit 15kW on the motor.

So all your interconnections, relays (you'd need that too) and fuses would need to be 100A capable, I would say. The relay would have to open with the car's own HV relay, you'd have to disable any BMS interference, etc..

dgpcolorado said:

The battery experts here will know more about it, but my understanding is that the chemistry used in those cells is too much of a fire hazard to be safe in cars without some sort of effective cooling system (such as what Tesla uses for its battery packs).

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I'm definitely no expert on this but excerpts of the post at http://gm-volt.com/forum/showthread.php?5243-Volt-thermal-management-system-temperature-band&p=43732#post43732" onclick="window.open(this.href);return false; have been quoted here on MNL before.

So that's $350 per kWh retail? Wow, that's pretty good. I can only imagine what Tesla would pay. They may be making a lot of money if the 85 packs are only 25 grand!

donald said:

So, you're thinking that Nissan has built in a charger and BMS that can't tell if there is a short circuit in the car (which the extra batteries would be seen as) and just keeps pumping in power even if the battery isn't receiving it? I'm not saying they have, but I would have tended to build a system that monitors current from the charger and current into the battery pack, and if it was out by some tolerance then it would not charge.

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Well I'm doing something like this when I charge my car with two chargers. The original charger puts out about 8-9 amps and I'm pumping in 16-18 total. The car doesn't seem to mind! The BMS shows the true amperage while charging and stops the charge as it normally would... I've got almost 10,000 miles on my second charger.

The extra batteries would not appear as a short, as they have internal resistance much like the rest of the pack. The total combined battery resistance would be lower, however.

Do note that the OBC has its own HV contactor. I'm not sure where it is, check the service manual. I think it’s in the HV junction box near the DC/DC converter. This means the HV lines going to the charger are probably not energized unless the car is charging. But then again the Ingineer upgrade used those lines so there's probably a way to do it... I remember that there were issues with this though. Keep in mind those lines aren't exactly meant to take any sort of serious amperage like you desire. The OBC is only putting 8A on them. I don't remember the gauge off hand but I don't think it's much.

Good luck. Be safe.