Summary of Low cost single cell L-Ion battery pack simulator
This article discusses the challenges of testing electronic medical devices with smart battery packs. It highlights issues with using real cells, such as limited charge rates, cycle life, and maintenance needs. Standard fuel gauges are deemed unsuitable for testing because they cannot accept user-defined values. The text concludes by referencing a low-cost single-cell Li-ion battery pack simulator as a solution to these testing constraints.
Parts used in the Electronic Medical Device Testing Project:
- Smart battery pack
- Real battery cells
- Battery fuel gauge
- HDQ one-wire interface
- I2C serial interface
- Low cost single cell L-Ion battery pack simulator
Modern battery operated portable devices use smart battery packs. Every new development of an electronic medical device must follow strict design flow defined by world-wide or local regulatory
directives. The development process of any such device using smart battery pack requires specific operating conditions to meet the testing criteria. When smart battery pack is one of the main power sources the host system should be tested with several battery states. The testing is necessary during development, validation and later in production testing.
Testing process
During development cycle test specifications and pass criteria must be provided base on the product specification. Production test also could be treated as a simplified qualification test, because it has to follow several standard regulations. Efficient production cycle for every product has time constraints on each station. The target of production test is deliver quality products, but it could not go through all engineering details and should be finished within limited time.
Battery cell
There are several problems when using real battery cells for such tasks:
- limited charge and discharge rates,
- limited battery cell charge cycles,
- charge maintenance,
Every battery cell has maximum charge and discharge rates, which must not be exceeded to avoid risks of battery damage, overheating and fire. Charge and discharge rates then limit shortest possible times to set the battery cell to defined state within charge and discharge cycle. As it could have limited usability for development, long testing times are not acceptable for production process and should be avoided.
Next problem with cycling real battery cells is limited number of charge/discharge cycles. Good lithium cell could have about 1000 charge cycles, which is too low for serious production.
And finally, every battery cell needs some maintenance when not in use to keep it in shape and within expected specifications.
Battery fuel gauge
The battery cell usefulness is hampered by the fact that it cannot communicate with the hosting system. Battery gauge is used for capacity monitoring and reporting. The device monitors a charge and discharge activity of the battery cell and provides available time-to-empty information across a wide range of operating conditions. It communicates to the system over a HDQ one-wire or I2C serial interface. Internal registers are updated with battery cell activity and they have no possibility to set user-predefined values. This makes standard fuel gauge devices useless in testing systems.
Read more: Low cost single cell L-Ion battery pack simulator
- Why is testing necessary during development and production?
Testing is required during development, validation, and production to meet specific operating conditions and regulatory directives. - What problems arise when using real battery cells for testing?
Real cells have limited charge/discharge rates, limited charge cycles, and require maintenance when not in use. - How many charge cycles can a good lithium cell typically endure?
A good lithium cell could have about 1000 charge cycles, which is considered too low for serious production testing. - Why are standard fuel gauge devices useless in testing systems?
Standard fuel gauges cannot set user-predefined values because their internal registers only update based on actual battery activity. - How does a battery fuel gauge communicate with the host system?
The device communicates over an HDQ one-wire or I2C serial interface. - What information does a battery fuel gauge provide?
It provides capacity monitoring and reports available time-to-empty information across a wide range of operating conditions. - Can production tests follow all engineering details?
No, production tests must be finished within limited time constraints and cannot go through all engineering details. - What is the target of a production test?
The target is to deliver quality products while adhering to standard regulations and time limits.
