We hear a lot more about Lithium batteries in the press lately. The articles often only scratch the surface without getting into any particulars.
Since the battery technology is what I have been working with
for the past couple of years, I would like to share with you a few more details
about the larger Lithium batteries or rather battery packs used in
transportation, renewable energy storage, backup power and many other
applications. This is intended for more technical audience curious about what such system is made out of or how to talk about it.
Of course, as this is subject relevant, I have to mention my
perimeter security robotics exploits that can be labeled as a form of
weird transportation for sensors and computing – see my successes page on lubomorhac.com. These unmanned ground vehicles are indeed using Lithium power and electric propulsion.
OK, back to battery packs. There are many different types of Lithium Ion chemistries,
each offering slightly different properties, making the batteries suitable for
one or other application. When you discuss Lithium batteries you want to ask
the right questions, often related to key specifications listed here in no
particular order:
- Cell type (prismatic, pouch, cylindrical)
- Cost
- Cycle life (n cycles at n% DOD)
- Individual cell Voltages
- Power density (Wh/Kg)
- Charge and discharge currents
- Operating temperature ranges
- Heat dissipation requirements at recommended and max. charge / discharge currents
- Safety features
There are many other specs and best practices you need to
factor in when you design power systems using Lithium cells, but this is out of
scope of this blog.At least for now.
A large Lithium packs (array of Lithium cells) are not
complete without the essential component called BMS – Battery Management
System. Here are some functions of a good BMS:
- Monitors packs temperature and each cell individually for various parameters
- Protects battery pack from over charging, over discharging and overheating
- Evaluates and computes State of Charge (your energy gauge), State of Health and other important operational and safety parameters
- Balances cells to maintain the pack’s maximum capacity and health
- Monitoring parameters locally via gauge, computer or remotely over the Internet
The following weekend testing picture gives you an idea what a
battery pack with all the goods attached looks like in action. The netbook computer is connected to the BMS for configuration and pack / cell monitoring. The small, black box with wires attached to the front of the pack
is the BMS. The battery pack and the plywood test jig featured here is the
most expensive electric heater ever! You can see the red glow coming from the electric heater elements - a black box with the duct attached.The test jig is really used for charge / discharge testing, pack protection and current sensing.
For more benefits of Lithium power in large battery packs visit our X4i-LB product page, which is not intended as a shameless self promotion, but to give
you more broad idea about the use of lithium power and show you more design pictures.
Stay tuned for more about the Lithium power...
