BMS for 40 Leaf gen2 modules

Batteries, Chargers, and Battery Management Systems.
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endlessquestions   1 µW

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BMS for 40 Leaf gen2 modules

Post by endlessquestions » Mar 25 2020 10:24am

I recently purchased 40 Nissan Leaf gen2 battery modules with the plan to use 10 of them in my electric motorcycle with an ME-1003 motor and the other 30 on a range extender trailer that will connect to the bike when I want to take longer trips to the beach or out of town.

My plan is to connect 10 modules in series to get 72v and then 4 in parallel to get ~240Ah (the modules are rated for 7.3v 66Ah but are at 92% capacity which is ~60Ah).
10 will live on the bike, the other 30 will live on the trailer.

My question is, what BMS would you recommend? I'm leaning towards the Batrium WatchMon 4 with the LeafMon monitors, but that setup would cost me nearly as much (maybe more!) than I spent on the batteries.

My main concern with having this many batteries laying around is fires, so any extra advise is also welcome. I'm coming from an automechanic and computer repair tech background so I have a fair amount of experience with both fabrication, soldering, and saftley dealing with individual electronics batteries but I'd still love to hear from you all on precautions I might not have considered.

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speedmd   100 MW

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Re: BMS for 40 Leaf gen2 modules

Post by speedmd » Mar 26 2020 6:17am

I just got some leaf modules that I am planning to use in our UTV. 7 in series 2 in parallel (14s4p). Have not pulled the trigger yet on the BMS, but top of my list is the Chargery 16T. You would need the 24T. Direct from china they are under a few hundred $. The various 300 -400a bluetooth BMS units do also look interesting, but also a bit reluctant to get into a brand that may have little to no long term support.

John in CR   100 GW

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Re: BMS for 40 Leaf gen2 modules

Post by John in CR » Mar 26 2020 10:01pm

endlessquestions wrote:
Mar 25 2020 10:24am

My question is, what BMS would you recommend? I'm leaning towards the Batrium WatchMon 4 with the LeafMon monitors, but that setup would cost me nearly as much (maybe more!) than I spent on the batteries.

My main concern with having this many batteries laying around is fires, so any extra advise is also welcome. I'm coming from an automechanic and computer repair tech background so I have a fair amount of experience with both fabrication, soldering, and saftley dealing with individual electronics batteries but I'd still love to hear from you all on precautions I might not have considered.
What kind of charge and discharge levels do you plan to use? I ask because with big capacity packs and running conservatively, it's quite easy to be your own BMS using a multi-meter and easy access to the battery terminals. The only BMS's I've ever used are ones that came built onto battery packs and the BMS's actually killed those packs.

Automotive grade batteries stay incredibly well balanced and the chemistry Nissan uses in their packs is a quite safe one, so your primary risk of fire is from a short circuit or charger failure (ie if over-charging can even light a Leaf module on fire.). At first you'll check the pack for balance frequently, and then as you become familiar with it far less frequency is required. On my packs I only check for balance a few times a year plus if I notice anything different in voltage at rest and/or under load while riding. Checking balance of a 20s pack with easy access to the terminals takes less than a minute.

If you're overly concerned about balance during operation you could use dual voltmeters, each on a 10s half of the pack. Then an out of balance condition will show up as a difference in voltage between the two.

Leaf modules get so saggy at deep discharge that you'll notice the performance decrease long before your pack gets too low.

To make sure you're starting with a perfectly balanced pack, first disconnect all of the series connections after getting the pack to a mostly full charge level, and connect all of the modules together in parallel and leave them connected that way for several days.

Those batteries require compression for best capacity, life and performance, so take that into consideration when building the physical structure. Hopefully it came with the factory rack, so you can measure the compressed and uncompressed thickness of the modules, and so you have all the pieces the factory uses to achieve nice even compressive force.

With such a large pack, your biggest issue will be getting the packs charged before rides requiring the range extender. Unlike lead batteries, leaving lithium packs at full charge for long periods much more rapidly decreases their capacity,. To get the most out of your pack you'll need to plan long rides in advance, so the charge cycle finishes shortly before you leave.

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speedmd   100 MW

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Re: BMS for 40 Leaf gen2 modules

Post by speedmd » Mar 27 2020 10:12am

Thanks John for bringing up some of those important facts on the Leaf cells. Went through a few of the older threads on them and chose them based on their safety record. My situation with the better half running the system most of the time and grand kids here at times that can run it until dead when I am not around or not paying close enough attention, is that I need some obvious (in your face) cell level monitoring and possible alarms -cutoffs that I can adjust. Hate to do it, but not seeing a easy way around it. Not at least in a integrated system.

If I were the only one using it, I would do as you suggest and go without as I do on my bikes that are both made up of 6s rc lipo bricks with nothing else to crap out and just monitor them every charge.
Last edited by speedmd on Mar 27 2020 2:48pm, edited 1 time in total.

john61ct   100 GW

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Re: BMS for 40 Leaf gen2 modules

Post by john61ct » Mar 27 2020 10:20am

Maybe irrelevant for OP

but going to LFP chemistry (3.2-3.3 nominal/halfway voltage) is the best mainstream way to go for safety, near zero chance of thermal runaway even when abused or if protective gear fails.

LTO (2.3V nominal) as well I believe, but much less community experience there.

Main disadvantage with both compared to the usual (3.6-3.7V) LI chemistries, is much lower energy density.

999zip999   100 GW

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Re: BMS for 40 Leaf gen2 modules

Post by 999zip999 » Mar 27 2020 1:40pm

The number one thing you have going for you you're using a high grade automotive cell proven and they keep well balanced and you know what you got..
The drawback is there still big and heavy for an ebike.

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