16 volt Nissan Leaf Battery Management System (BMS) information

In a previous post I have shown how to physically mount six Nissan Leaf battery modules in two series groups of 3 parallel modules to build a 180 Ah by 16 volt Lithium (LiNMC) battery.

The batteries are covered by these very cool laser cut acrylic protective covers (which obscure the BMS wiring).
cover_with_bms_topview

Anthony Felix asked for more information about the BMS units I’m using on my batteries, so here it is! (Jump down to the last picture if you just want to see where the BMS units are attached….all of the text between here and there is an explanation of WHY they are attached there…)
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S-10 EV New J1772 and 120 Volt Charging Inlets

My Chevy S-10 electric truck is about to get a new charger, and the upgrade will also include a new set of charging inlets hiding behind this J1772 novelty front license plate.
IMG_20151129_201443

When you flip the license plate up, it reveals a J1772 inlet, as well as a 15 amp 120 volt RV inlet that any standard extension cord can plug into. I also have a rotary switch to select different charging modes, and a push button with LED indicator light to enable the charger and flash status messages.
IMG_20151129_201401

Here is a video overview of the setup:

YouTube Video

To prevent both inlets from being energized at the same time, I will be routing them through a power relay to the charger. The J1772 inlet will be connected by default. This will make sure that the exposed plugs on the 120 volt inlet are never energized by the 240 volt J1772 source.

If 120 VAC is present on the 15 amp RV inlet, the relay will connect it to the charger (and disconnect the J1772 inlet). I’m not terribly worried about people reaching into the J1772 inlet, as the plugs there are designed to be finger safe, but I don’t want some idiot plugging the J1772 inlet AND an extension cord into the truck at the same time and accidentally connecting 240 volts to a 120 volt circuit.

The rotary switch will allow me to switch between four modes on my charger.
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New S-10 front Air Dam / Air Deflector / Lower Valance Panel

I am getting ready to add a J1772 electric vehicle charger inlet (salvaged from a Nissan Leaf) to the front of my truck. I decided to hide it behind a fold up license plate. [In Georgia, we only need rear license plates, but many vehicles have novelty plates on the front.]

However, the stock front air dam / deflector / lower valance panel that was under the front bumper had a lot of air and foglamp holes molded into it, didn’t really have a good spot to mount the inlet or a fold up license plate bracket, and had a few pieces of plastic cut out where somebody had tried to mount something previously. (Note, the pictures below show the air dams resting upside down on the concrete, the side facing down bolts to the bottom of the bumper.)

Original part

Looking around online, I found an online distributor (getallparts.com) that was apparently closing out their supply of an after-market smooth front air dam that replaces the stock one. (OE # 15658455, Partslink GM1092157)

What really sealed the deal was the fact that they were charging only $9.42 (plus $18 S/H). (Other websites were selling a similar part for $80-90, so this was quite a deal. At that price, I almost ordered two of them…except that the shipping costs were not combined and also doubled…)

A few days later this really large (72″x12″x12″) box arrived:
Really Large Box

The aftermarket air dam is nice and solid, with no holes. It slopes inward at the bottom a bit and has a slightly concavity, but it will be much easier to work with than the previous one, and may even help my aerodynamics slightly.
New Part

As a side note, getting the original part off was a real pain. Access to the bolt heads is inside the bumper, and you really want a ratcheting box wrench, as there isn’t enough room to get a real rachet inside, and various steel pieces keep you from moving a wrench more than 10 degrees at a time on a few of them. I eventually just got out my sawsall and cut through all of the bolts (melting the top of the old part a little in the process). The main problem is that the plastic clip nuts couldn’t be turned, and the bolt heads were the only part that could be turned. I will be replacing them with stainless steel bolts, nuts and fender washers, making it much easier to install/remove by tightening the nuts on from the bottom, and counting on a generous application of Loctite to hold things in place.

Economies of harvesting Nissan Leaf battery modules

rear_of_car_smushed

I purchased a 2013 salvage (wrecked) Nissan Leaf from the CoPart auto auction house for $4081 (including delivery and fees). I consider this to be a very good price for a wrecked Leaf, but if you stalk a lot of auctions and bid on Leafs that have the most damage you can probably get a similar deal with enough patience.

Then I spent 439$ on the following tools that I needed to move the car around and extract the battery (the largest amount was for jacks and wheel dollies…)

Car Cover (Keep the neighbors happy) 37.1
Wheel dollies & Jacks 243
Bluetooth OBD II scanner 9.98
Leaf Spy Pro android app (to check battery) 14.99
500V gloves   (Safety first!) 21
2 Jackstands (already had 2) 25
Air Impact Wrench & Sockets 46.5
18mm wrench 12.4
13mm deep socket 8.99
21 mm combination wrench 20.69

This puts my total costs at 4520.75 ($94.18 per module) for a 24 kWh battery pack, which is less expensive than if I bought large format prismatic cells.

Of course, with a lot of time and effort, you can sell all of the other parts from the car. Over the course of six months I made back $3180.46 (including the sale of the smallest of the three jacks I had purchased and 0.46 in change I found in the car.) I’m posting this after selling the main body of the car, leaving me with just a few small items listed on ebay. I may earn a few hundred extra dollars over the course of the next several months, but the overall cost recovery is finished.
final_sale

My current total out of pocket expenses (not including lots of labor!) is 1340.29 (or $27.92 per module) which is quite a significant savings over other options for purchasing large format Lithium Ion batteries.

I’ve seen Nissan Leaf modules selling on Ebay for around $130 each with shipping (in larger quantities), so my ~ $30 per module cost is around 21% of the cost of purchasing them on the used market.

To put this cost savings in perspective, purchasing 20 lead acid golf cart batteries to replace my current pack would probably cost me around $2000-$2200, so the Lithium Ion Nissan leaf battery pack was actually less expensive than a replacement lead acid pack!

However, the process of parting out the wrecked car takes a lot of time and effort. If you are just after the battery and can find one for sale at a salvage/junk yard for less than $2500 it would probably be easier to buy the battery alone without the rest of the car. The one advantage of purchasing the whole car is that you can (sometimes) find out how many miles are on the battery pack. In my case, I was able to use an OBDII scanner with the Leaf Spy Pro application to find out that my battery pack health was still at 98% before I removed it from the car.

If I were to buy a whole car again, I would try much harder to sell the entire car (minus battery) in the $2000-2500 range before parting it out and trade some money for my time.

The Nissan Leaf pack weighs about 650 lbs less than the lead acid batteries currently in my truck. They are capable of providing more amps with less voltage sag due to lower internal resistance, and more of the pack capacity is usable as they don’t suffer from the Peukert effect as much as lead acid batteries.

The overall performance of the truck should be much improved. Also the battery life should be much longer than 2 years. (Cycle life for lithium ion batteries is measured in thousands of charge cycles, instead of hundreds of charge cycles for lead acid batteries.)

However, because I am changing battery chemistries, I am also upgrading my trucks’ charging system (and home EVSE) and those costs are actually more than the battery pack, so the total upgrade cost will be more than just getting another lead acid battery pack. (I will talk more about charger upgrade costs in a later post).

How to build custom length high current cables

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When wiring up an electric vehicle traction pack battery, an off-grid battery backup bank, or other high current power systems, you sometimes need a cable capable of handling high-current with a custom length. If you have a few tools, it is easy to make your own by crimping terminals onto welding cable. This video shows a time-lapse overview of making such a cable:

Here is a set of links to the tools and materials I used:
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Battery carrier compatibility, location specific modifications

battery_pickup_tool

This is a Battery Carrier tool designed for picking up and carrying around lead acid batteries (golf cart or starter batteries). I own one because it’s very useful when removing 20 golf cart batteries from my S-10 electric pickup truck and replacing them with 20 new batteries. While manhandling my Nissan Leaf batteries around my garage, I though “Boy, it sure would be nice to be able to use my battery carrier on these guys.” A few minutes spent rigging up a jig for my trim router and vacuuming up a lot of saw dust later, each of my batteries has a small slot cut in both sides…

plunge_router_with_guide

slots_in_battery

I had thought that I would have to sell my battery carrier and battery filler now that I am upgrading to Lithium Ion…I guess only the battery filler will be obsoleted.

I also modified a few of the batteries to better fit in my existing battery bays. Specifically, I decided that batteries 1&2 and 7&8 would be mounted “back to back” and I didn’t need each of them to have a full 1″ of space at the bottom, so I cut a 1/2″ off the bottom of each, giving me an extra inch of room, and leaving them a shared 1″ air vent.
batteries_7_8_back2back

On battery 3, which will be mounted “sideways” with respect to batteries 4,5 & 6, I used a spade bit to sink the washer in a little, and cut off the ends of the threaded rod to make sure they wouldn’t interfere with cables.

battery_3_shortrods

one_inch_indentation

extra_long_rods_cutoff

How to build a 16 volt battery module from six Nissan Leaf cells

I am building 16 volt batteries using six Nissan Leaf LiIon cell modules. (A Nissan Leaf battery has 48 modules, supplying the construction of 8 of my “batteries”.) My Battery is arranged in a 3P2S (two sets of 3 parallel modules in series), giving a 180 Ah capacity and nominally 16 volts (each module from a Nissan Leaf has 2S2P cells inside, so the module goes up to 8.4 volts maximum at 60AH).

This video (playing at 4x-16x speed) shows all of the work that goes into building a battery. Directions with more information are below.

To build a battery, here are the parts you need:

  • Two end plates, made from steel or plywood.
  • Six nissan Leaf modules, sandwiched between the end plates.
  • Four pieces of threaded rod, 10.5 inches in length, with the following hardware for each rod:
    • Two nuts
    • Two lock washers
    • Two fender washers
  • One 7.5″ x 1″ x 0.25″ copper bus bar (to make the series)
  • Two 3.5″ x 1″ copper bus bars (to join the sense terminals) I used 0.25″ thick so that I could source it from the same copper as the series busbar above, but this is overkill, you could use 0.125 or even smaller.
  • Two 3.5″ x 2.5″ x 0.25″ copper bus bars (to be the + and – terminals of the main battery).
  • 12 M6 bolts (can re-use the ones that came with the leaf modules)
  • 12 M6 Locking washers (I used Belleville Spring lock washers)
  • six M4x16 machine screws for the sense terminal bus bars
  • six M4 locking washers (I used Belleville spring lock washers)
  • three M4x8 machine screws for the BMS terminals + 5 more lock washers
  • Two 5/16th bolts (1″ or 0.75″) for the + and – terminals. (could substitute 1/4″ or metric bolts, I used 5/16th because that is what golf cart batteries use.)
  • (very optional) one more 5/16th bolt for the series bus bar if you want to attach a 5/16 ring terminal from an existing battery monitoring system to each “8 volt” half of your battery.
  • 12×12″ acrylic sheet to laser cut battery cover from.

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Laser cut acrylic terminal covers

cover_with_bms_topview

I laser cut some covers that place an acrylic wall between each of the busbars of my battery, as well as covering the top. They are designed to keep a falling screwdriver, wrench, or bolt from bridging the bussbars and causing “excitement”. I have a lot of air holes to try and allow a normal amount of air flow, as well as exposing the bolts and screws for occasional tightness checks.

busbar_layout

You can download the textual openscad design file here:
battery_shield.scad

Or, you can just download the PDF files if you want to laser cut them exactly as they are:
battery_shield
battery_shield_reversed

A “how to assemble” video is here:

Youtube Video link

Acrylic could be a bit brittle for this application, and using 3mm craft plywood could provide a bit more impact resistance. However, the covers are inside the “sidewalls”, plus the batteries will be mounted sideways and the current “top” will be mostly protected by insulating foam in my battery boxes,so I chose to go with the less smoky option. (Plus, I think the semi-transparent nature of the acrylic just looks cooler.)

Building a battery from Leaf Modules – The Plan

I am in the process of replacing the twenty (20) six volt lead acid golf cart batteries that power my electric pickup truck with 48 Nissan Leaf battery modules. Because the battery bays in the truck are specificity designed to hold 20 golf cart batteries (and the Leaf modules have a different form factor), it’s not a straight-forward drop in replacement.

My initial design (not showing the compression plates that hold the six modules together in compression):
sixGroup
In the image above, the black bar is negative, Continue reading