EXTREME POWER NMC Lithium
Ion 48v 16Ah battery pack
Our new LiIon battery packs are being built from 32mm cylindrical
cells. We are using 32650 cells, these are Lithium
NMC 3.7v 8Ah capacity and 5c discharge rate. I have been told Mercedes is
using the same cells in their EV packs! (hard to
find out if this is true of course!) These cells are rated at 40A discharge,
two in parallel gets us 80A discharge rating. Perfect for the 40-50A load
from our 2000w mid drive kit as you never want to load your cells up more
than around 50% of their rating if possible.
am trying 32mm cells is they are much easier to build into packs, with only 2
cells in parallel it is easier to find a bad one and easier to replace it if
needed. 18650 cells have come a long way in the last 5-10 years and you can
get some amazing high power versions (not cheap though) but you still need
5-6 cells in parallel to get the capacity high enough for a bike. 5c
discharge means 2500-3000mah per cell maximum, larger capacity cells don’t have
the same discharge ratings so a 4000mah cell might only be 2c, this means 8A
max, 5 of them in parallel gets you a 20Ah pack with a max rating of 40A
discharge, its just not enough for high power bikes like ours.
building the packs with a quality BMS board that features balancing circuit,
over charge and over discharge protection, a 40A constant output stage that
will take up to 60A short term and has a 100A short circuit protection built
shipment is a semi triangle, approx 200mm across the top and 200mm down the
back, it fits our LUNA triangle bag. We use AMASS XT90s antispark
plugs for main connection, you charge through the same plug as the BMS is
shared port design. Pack weight is 4.4kg.
We plan on building these packs here in Australia in the coming months,
and will be building them as a rectangular pack that will be approx 230mm
long, 130mm wide, 70mm thick.
ABOUT OUR BATTERIES
NMC LiIon PACKS (Lithium Nickel Manganese Cobalt Oxide)
One of the most successful Li-ion systems is a cathode combination of
nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be
tailored to serve as Energy Cells or Power Cells. For example, NMC in an
18650 cell for moderate load condition has a capacity of about 2,800mAh and
can deliver 4A to 5A; NMC in the same cell optimized for specific power has a
capacity of only about 2,000mAh but delivers a continuous discharge current
of 20A. A silicon-based anode will go to 4,000mAh and higher but at reduced
loading capability and shorter cycle life. Silicon added to graphite has the
drawback that the anode grows and shrinks with charge and discharge, making
the cell mechanically unstable.
The secret of NMC lies in combining nickel and manganese. An analogy of this
is table salt in which the main ingredients, sodium and chloride, are toxic
on their own but mixing them serves as seasoning salt and food preserver.
Nickel is known for its high specific energy but poor stability; manganese
has the benefit of forming a spinal structure to achieve low internal
resistance but offers a low specific energy. Combining the metals enhances
each other strengths.
NMC is the battery of choice for power tools, e-bikes and other electric
power trains. The cathode combination is typically one-third nickel,
one-third manganese and one-third cobalt, also known as 1-1-1. This offers a unique blend that also
lowers the raw material cost due to reduced cobalt content. Another
successful combination is NCM with 5 parts nickel, 3 parts cobalt and 2 parts
manganese (5-3-2). Other
combinations using various amounts of cathode materials are possible.
Battery manufacturers move away from cobalt systems toward
nickel cathodes because of the high cost of cobalt. Nickel-based systems have
higher energy density, lower cost, and longer cycle life than the
cobalt-based cells but they have a slightly lower voltage.
NOTE: Using a quality charger and storing batteries
safely in a steel tool box are necessary habits to get in to with Lithium batteries and
something we expect our customers to do. We do not warranty
overcharged batteries that are charged with 3rd party chargers.
inside your house! We say this to every customer, it’s in our battery
instruction notes, and it NEEDS TO BE FOLLOWED. We will not be held responsible for you damaging your property by
charging or storing these batteries inside the house! Charge outside under
cover, or in the garage on a non flammable surface away from everything!
Lithium cells start to degrade as soon as they are manufactured, they have a
finite shelf life, storing them correctly at 50-60%
capacity increases their lifespan a lot. It is this reason that claims from
sellers of thousands of cycles is completely pointless, as most of these
batteries will fail due to age and not cycles!!
strict guidelines will get the most life from your batteries, being careless
with how you use and store them will result in shorter lifespan. Storing them
for weeks on end fully charged degrades the cells over time,
we suggest charging the battery back to 48v before storing it, 54.6v is fully
charged, 48v is nominal and a good voltage for long term storage. Get
yourself a cheap $15 multimeter from Jaycar so that you can measure the voltage of your
battery pack via the XT90 plug, its cheap and easy to do.