There are several things I really like about this build, and if I was building a daily commuter, a longtail electric cargobike with a large battery pack and a direct drive hubmotor would be at the top of my list.
The header pic is from the youtube channel “skyBridgeConcept”
The Nissan Leaf battery pack
The really unusual thing about this build that immediately jumps out at the reader first is the large battery pack, made from 2016 Nissan Leaf cells. The Nissan Leaf is a car, and although the pack uses flat foil cells, Nissan chose to assemble the cells in metal canisters that are called modules. There are four cells inside each module, and the stock configuration is two cells in series, and two cells in parallel (2S / 2P). For more details, click here.
One of the things that the builders who use Leaf cells seem to like about them, is the handy stock threaded contacts for the positive and negative posts (along with the aluminum cases) They also have a smaller central threaded post for the balancing connection to the Battery Management System (BMS). These contacts make it very easy to build up a pack for a motorcycle, or a home power supply to be used during a power outage.
Due to their large size, it is rare for these cells to be used for an electric bicycle, but I have seen several motorcycle builds that have used them. The side dimensions are 290mm X 216mm (11.4-inches X 8.5).
In the pic above, all of the stock 2S / 2P threaded connectors have been removed, and this pack is now a 1P configuration. These second-generation cells (2015 and newer) are 41 Amp-hours each, so the stock module would be 2P / 82-Ah (the first-gen cells are 33-Ah). The cube of cells shown above is 72V (36V + 36V) and 41-Ah for 3000-Watt Hours (WH) of total power (which could also be called 3-kWH). Its not unusual for a reasonably efficient system to deliver two miles per amp-hour, so 41-Ah would likely provide over 80 miles of range.
The Leaf cells are made by AESC. The early cells have a 3C current rate for an output of (33-Ah X 3C =) 99-amps. The early Nissan Leafs experienced longevity trouble in hot climates, possibly because they are air-fan cooled, rather than the more expensive liquid-cooling used by the Chevy Volt and Tesla. Cold climates did not have the same problems. For instance, Arizona can be 115F in the summer (46C), even before you apply a load to the Nissan Leaf.
One of the things that Nissan improved in 2015, was the C-rate of their new second-gen cells (C-rate is their ability to provide Current). Since the cars performance was not significantly improved, the higher C-rate simply allowed the battery pack to run cooler under load. The second-gen 41-Ah cells have a 10C rate, so they can provide (41-Ah X 10C =) 410 amps. It’s no wonder these cells are popular for motorcycle conversions!
One of the interesting things that this builder did was to configure the twenty cells into two sub-packs with ten cells each. Ten lithium cells in series are commonly called a 36V pack, and two of those in series would be called 72V.
He did this so that he could use two common 36V chargers, and also use a more common pair of 36V BMS’s, since 20S / 72V BMS’s and chargers are rare. The discharge cables that power the controller and motor are not routed through the BMS, so the cells must be capable of providing more amps than the controller will be drawing (the BMS’s control the charging and cell-balancing, but the battery discharge is unrestricted)
If not, any high-amp demand from the controller might damage a low-amp battery pack (without the BMS in-line to protect it). Fortunately, these cells are known to easily provide very high amps, and the controller is only rated for 60A. These BMS’s will only be used for protecting the charging and balancing of the cells.
The controller will only draw the max 60A for a few seconds when accelerating, so these 410A cells will not even get warm when you are using them.
Hubmotors and Moped Rims
Mid drive systems and geared hubmotors have their benefits, but…if you have enough power, like (72V X 60A =) 4300W…a direct drive hubmotor is a robust and simple system that can climb some fairly significant hills without overheating.
But which direct drive hubmotor to use? Joel chose the MXUS 3000W, in the V3 4T version. This motor can easily handle the 4300W that Joel is using. When accelerating, your system might occasionally draw the peak watts, but once you achieve your top speed and then enter a cruise phase…the watts will slide down to a much lower level.
The RPM’s of a motor are the “Voltage times the Kv” of the motor. The MXUS is available in several Kv’s, and the Kv of this 4T model is 8.9 RPM’s per volt, which equals 640-RPMs (when using 72V). Of course, the actual top-speed must also take into consideration the diameter of the tire, plus the air-resistance, and also the weight of the rider, bike, and cargo.
Joel chose a 17-inch motorcycle rim, and a tire with a 21-inch true outside diameter. Bicycle wheels and moped/motorcycle wheels are measured differently, and this 17-inch moto rim is halfway between a 24-inch and 20-inch bicycle wheel. If using a one-cross pattern on the spokes, you can even order a slightly smaller 16-inch rim, which is very close to the size of a 20-inch bicycle wheel. If you are interested in using a moped rim and tire set, you can read our article on them by clicking here.
I believe this was a good decision, since the choice of swapping-in a smaller diameter wheel (compared to the stock 26-inch), helps the potential heat of the motor under load.
Controllers apply amps in an attempt to get the motor up to it’s design RPM’s. The longer it struggles to reach the RPM’s that the throttle is requesting, the hotter the motor will get. The worst-case scenario would be a small-diameter motor with a high Kv, installed into a large diameter rim.
If you move up to a larger diameter motor, you would be placing the magnets farther away from the axle, which will give them more leverage, which improves the torque without increasing the input watts. Then, if you swap to a smaller rim, you will again increase the wheel torque compared to the larger rim, also without raising the input watts. Of course a smaller rim would lower the road speed of the wheel, so you would need to then upgrade to a faster Kv model of your motor, in order to keep the same top-speed. The 4T that Joel chose is an average winding, and it can be found with a faster 3T and also a slower 5T.
Another benefit of using motorcycle rims is that their tires are very resistant to getting a flat from nails or thorns in the road, which is a huge benefit if you are relying on your ebike to get to work every day. The tire Joel chose is from “Gazelle”.
When a powerful hubmotor tries to spin forwards, there is an equal force trying to spin the axle backwards, so…it will need two very strong torque-arms to hold the axle stable. The torque-arm shown above is a great example.
Altering the Yuba frame
Joel knew he would need to alter the Yuba Mundo frame to fit the Leaf cells, but he was certain he wanted to have both of them, no matter how difficult it might turn out to be.
The red square shown above is where Joel wanted to mount the Leaf battery pack, but he also knew there was no way he could pull that off without cutting into the frame. Joel made certain that he bought a version that used a mild steel frame (hi-ten), so he could easily weld onto it (the other options were a cargobike with Chromoly-steel, or possibly aluminum).
The first cut is always the most painful. You have to get it right, because if you cut away too much, you might need additional repairs that are time-consuming and ugly. Once a small portion of the frame was cut away, Joel could insert the battery pack case, and then begin the process of evaluating what strengthening additions would be possible.
As you can see in the pic above, Joel made the repair extra strong, so he could ride this cargobike at high speed, with no fear of the frame breaking.
Below is a pic of the Sabvoton 60A controller Joel is using. He mounted it under the cargo rack, and added a fender to keep road-dirt off of it.
Diverting the Chainline
Once Joel re-attached the drive-chain, he realized that if he moved the battery box far enough over to avoid hitting the chainline, the weight of the battery would be too far to the left. The battery pack as shown is 174mm wide, roughly 6.9-inches. (for those who are interested in something similar, a 14S / 52V pack of Leaf cells would be 43mm thinner for a total of 101mm, roughly four inches wide).
Joel decided to keep the weight of the battery pack in the centerline of the frame, and to accomplish that, he then decided to route the chain to pass under the battery box.
The top run of a bike chain is the part that experiences tension when you are pedaling, and any chain tensioner is typically mounted on the bottom run of chain. However, Joel decided that this was the best compromise for his needs. He also chose cranks from a fatbike to provide additional clearance for the pedals.
Where to get?
The Hybrid Auto Center in Las Vegas has a new website for purchasing used cells from wrecked electric vehicles, called the EV Battery Center (click here). If you are interested in flat foil cells, but you want something smaller than the Leaf cells, I have been reading about many builders using cells from the Chevy Volt, which has a side dimension of 177mm X 127mm (7-inches by 5 inches) and they are 6.3mm thick (1/4-inch).
Leaf cells are 11.4-inches X 8.5…
There are many other brands of hybrid and electric car on the road, so keep an open mind when shopping. However, due to the high number of Nissan Leafs and Chevy Volts produced, these two cells are the most common to find.
The Chevy Volt cells have roughly 45-Ah of range, and are rated for 7C, so 45-Ah X 7C = 315A…still VERY powerful!
If you want another option for cells that are a small size for a hot rod ebike, I have found a 200A cell that is only 190mm X 140mm (7.5-inches by 5.5). They are made for a Chinese company that manufactures hybrid city buses. The Volt cells are the same size, but have many more Amp-hours, however…due to their popularity, the Volt cells can be hard to find.
Since these are constructed for max amps instead of range, they only have 8-Ah each. The company “Battery hookup” sells four of these for $28 plus tax and shipping (click here).
And for your entertainment, I have a video of youtuber “AveRage Joe” assembling a pack of these, at the 26:40 mark (click here).
Written by Ron/spinningmagnets, December 2018