Protection Systems for Industrial Applications
VPW provides PTC (Positive Temperature Coefficient) thermistors, PCM (Protection Circuit Modules) and BMS (Battery Management Systems) for a wide variety of batteries and chemistries. Using these control systems greatly improves safety, performance and longevity of any battery system.
Many rechargeable batteries have very high energy density and very specific charging and discharging requirements. Not properly caring for these batteries can lead to irreversible battery damage and in severe cases battery rupture and even fire. To help assure safe battery operation, peak performance and maximum longevity, battery protection circuits are often included within the battery pack, wired in line with the device being powered or integrated into the device itself.
PTC (Positive Temperature Coefficient)
Some times referred to as a resettable fuse or polymeric positive temperature coefficient device (PPTC), the PTC is typically utilized with Nickel battery chemistries to provide basic resettable protection for over current and short circuit. These simple devices come in a variety of sizes and mounting options to fit virtually any application and can be implemented quickly and cost effectively.
PCM (Protection Circuit Module)
Typically designed to provide basic protections such as overcharge, over discharge and short circuit protection, these are fairly simple circuits offering a limited degree of control and safety. Because they do not require software integration they can be implemented quickly and cost-effectively making them an excellent first-line approach to improving battery safety and cycle life.
BMS (Battery Management System)
When a higher degree of control is required a BMS system can be utilized to perform a much broader range of controls including short circuit protection, cell balancing, individual cell monitoring for internal resistance, temperature and more.
BMS modules are available as stand-alone circuits or as Smart BMS for communicating with your computer, charging system and flight controller. Many communication methods are available including I2C, SMB, USB, RS232, among others. Because software integration is required integration of battery management systems requires additional lead-time and development cost.
Protection circuits may not be utilized in instances where power requirements are very high, cost requirements are low and the development schedule is limited. Risk assessment is a large part of the decision to exclude protection circuitry for customers that may be willing to accept the potential risks or where the device the battery is utilized with contains the means for proper battery protection. VPW strongly urges customers to consider the use of some means for proper battery protection both for safety and longevity of the battery system. Some form of protection will be required for lithium battery chemistries to ensure compliance with UN38.3 transportation requirements for a lithium battery.
Since battery protection requirements can vary widely, Vertical Partners West works closely with our customers to make sure the selected protection device is properly specified and implemented to the specific customers project requirements.
For most industrial applications, battery life and system safety are critical and a PTC device is a first line approach to improving battery safety and cycle life for Nickel based battery chemistries.
PTCs or positive temperature coefficient thermistors have been a long time standard solution for over current and short circuit protection and are offered in a variety of current ratings and mounting styles to fit most applications.
As current passes through the PTC its temperature increases and when the current exceeds the rated trip current it heats suddenly breaking connection between the conductive particles in the device. As current is removed from the PTC the device cools and returns to a low resistance state allowing current flow to resume.
For proper operation, when selecting a PTC, consideration should be given to the various factors that may affect its operating temperature.
Typically PCM devices are utilized for Lithium chemistries and offer many safety features, which are a requirement for transportation safety of lithium batteries per UN38.3 specifications. PCM circuits also help to extend battery life while improving battery safety.
Safety functions commonly offered in a PCM are:
- Cell balancing (lithium chemistries)
- Over charge and over discharge protection
- Over temperature protection (NTC thermistor)
- Over current and short circuit protection
Overcharging can cause excessive heat, and shorten battery life and in extremes it can cause a fire. To safe guard against this, PCM devices are equipped with a FET switch that disconnects the battery from the voltage supply at a predetermined level.
If a battery voltage drops below the specified voltage, the PCM disconnects the battery to protect it. One of the dangers of over-discharging is that the weakest cell’s voltage may reverse. This can cause improper recognition of the battery by the charger and individual cells in the pack can become grossly overcharged and lead to the battery overheating and potentially rupturing.
The PCM monitors the battery temperature usually by monitoring the temperature of the hottest cell, that one which testing shows becomes the warmest in operation and in charging. If an over temperature condition occurs, the PCM disconnects the battery from the circuit until the battery cools to within specification then it automatically reconnects the circuit.
The PCM monitors current flow and disconnects the battery should over current condition exist. Over-current operation can cause the battery to overheat, shortening the battery life expectancy and in extreme cases cause the battery to vent or catch fire. Over-current protection usually keeps the battery circuit open until the over current situation is resolved.
If a hard short circuit occurs the PCM’s FET switch is designed to fail. This destroys the PCM and usually makes the battery useless but prevents fires, cell rupture with electrolyte leakage or other issues.
In addition to handling the same safety management as a PCM, a BMS incorporates a microprocessor that monitors, controls and reports on a variety of parameters. It is designed to manage and monitor the battery and communicate with the outside, which is usually a microprocessor or master computer.
Through software, a user can control the battery operation, keep track of statistics such as how many times the battery has been used, how many times it has been charged, the temperature, depth of discharge, current capacity and the degradation of capacity over time. The BMS can also communicate the state of charge (SOC) so that the robot or drone can be sure to have enough energy left to return to its starting point (ET Call Home).
FCC Testing Required:
BMS circuits contain a low power microprocessor to perform its functions and control. This means that these batteries must be tested and approved to FCC Part 15 emissions and susceptibility regulations. Look for the FCC logo on these batteries.
Communicating with the BMS
BMS communications are available through a variety of protocols. The most common are the I2C/SMB and CAN bus protocols. Also available are Ethernet, WiFi, RS485 and others depending upon requirements. VPW provides a full technical description of the protocol and works closely with customers to meet specific communication requirements.