There are many types of battery chargers on the market: rechargeable alkaline battery chargers, nickel-metal hydride battery chargers, and nickel-cadmium battery chargers. When buying a battery charger, I suggest you buy a multi-function battery charger which can reduce some expenses.
Here is a circuit schematic diagram of the battery charger probe that can be tested by using the probe to prevent battery damage, whether the charger starts charging or improperly connected.
This battery charger probe prevents damage to the battery or allows you to test it yourself, whether the charger starts charging or improperly connected. By using the probe, the cable clamp is connected to the battery positive level for the first time, then the test board touches the negative pole of the battery.
Introduction
Battery temperature sensors play an important role in battery management systems by providing temperature monitoring and protection. The measurement of cell, module, and pack temperatures allows the system to optimize charging conditions, prevent damage from overheating, and estimate battery capacity.
This article explores the impacts of temperature on battery performance and lifetime, the consequences of exceeding safe temperature limits, how and where temperature sensors are implemented, and alternatives when temperature sensing may not be required.
Effects of Temperature on Batteries
Battery cell chemistry determines optimal temperature ranges. In general, temperature extremes degrade batteries through the following effects:
High Temperatures
- Accelerated ageing and shorter cycle lifetimes
- Loss of active materials and internal structural changes
- Increased self-discharge rates
- Degradation of internal resistance and power capability
- Thermal runaway risk in some lithium-ion types
Low Temperatures
- Temporary loss of capacity and lower discharge rates
- Increased internal resistance causes voltage drop
- Reduced current and power discharge ability
- Slower charging rates may be required
- Risk of lithium plating in lithium-ion cells
- Higher risk of metal corrosion in some chemistries
Keep batteries within a safe operating range improves performance, lifetime, and safety. Temperature monitoring provides feedback to manage these effects.
Consequences of Exceeding Temperature Limits
Without temperature monitoring and control, the following failure modes can occur when battery temperatures go out of safe limits:
High Temperature Effects
- Pouch cell swelling leading to fire/explosion
- Internal short circuits due to separator damage
- Venting of electrolytes
- Thermal runaway causing cascading cell failures
Low Temperature Impacts
- Permanent capacity loss or premature failure
- Internal battery damage from lithium plating
- Voltage clipping and inability to deliver rated power
These potential risks demonstrate the need for temperature sensing as part of a battery management system.
Implementing Battery Temperature Sensors
To monitor temperature, sensor placement is important:
Cell Surface Mounting
Attaching sensors directly to cell surfaces provides most accurate measurements but increases pack complexity. Higher quantity of sensors required. Useful for validating cell models.
Module/Pack Mounting
Sensor mounted externally on module or pack enclosure is simpler. Provides general temperature for control but may not detect localized hot spots.
Within Pack
Sensors inserted internally between cells provide intermediate monitoring without direct cell contact. Compromise between complexity and localized readings.
Air Intake/Outflow
Measuring inlet cooling air and outlet heat exhaust temperatures provides indirect pack temperature estimates for basic control. Simplest approach.
Thermal Imaging
Infrared cameras used periodically provide non-contact temperature map of pack to identify hotspots not apparent from discrete sensors.
In most cases, a combination of pack surface sensors and selective internal placement provides sufficient temperature monitoring for control and protection.
Temperature Sensor Selection
A variety of sensor options exist for battery temperature monitoring:
- Thermistors – Inexpensive, accurate. Linear and nonlinear types available.
- RTDs – Very linear over wide temperature range. Accurate and precise but higher cost.
- Thermocouples – Low cost sensors. Require compensation circuitry.
- IC Temperature Sensors – On-chip amplification, linearization, and output. Application specific variants.
- Infrared Sensors – Non-contact temperature measurement. Lower accuracy and higher cost than thermistors/RTDs.
- Fiber Optic Sensors – Electrically passive for high voltage isolation. Expensive.
Robustness, cost, accuracy, and measurement range considerations will determine optimal sensor selection for the battery application and environment.
Temperature Sensor Circuit Design
Proper circuit design improves measurement accuracy and noise rejection:
- Linearization – Adding resistive or digital linearization for sensors like thermistors improves temperature correlation.
- Amplification – Sensor signals require buffering and amplification for noise immunity and signal conditioning.
- Filtering – Low pass RC filters reduce noise pickup in long sensor leads in electromagnetically noisy environments.
- Isolation – Fiber optic transmitters or galvanic isolators prevent false ground errors.
- Compensation – Correct for errors like thermal junction effects in thermocouples.
- Calibration – Normalize each sensor output at defined temperatures to maximize absolute accuracy.
Careful circuit design ensures the temperature sensor subsystem provides the battery management system with precision temperature data across the operating range.
Alternatives to Temperature Sensors
While temperature sensors are generally recommended, some alternatives exist for low cost or simpler battery packs:
Model Estimation
Use a thermal model of the battery to estimate temperature based on charge/discharge current, voltage response, and ambient temperature. Lower cost but less accurate.
Current Limiting
Conservatively derate maximum current to prevent heating rather than directly sensing temperature rise. Simple but reduces available capacity.
Periodic IR Scanning
Use a handheld thermal camera to periodically scan pack and check for hot spots instead of continuous monitoring. Only detects issues as they arise.
Exterior Thermal Feedback
Rely on skin temperature sensation, temperature labels, or surface mounted thermochromics to indicate unsafe externals temperatures manually. Provides warning but no control.
While workable for very basic systems, the lack of reliable temperature feedback with these alternatives prevents optimization and reduces safety margins compared to proper thermal sensing and control.
Advanced Temperature Monitoring
More advanced battery systems maximize safety and performance using improved thermal monitoring:
- Multiple internal distributed sensors provide temperature maps to the BMS. Detects local hotspots.
- Fiber optic distributed sensing embeds thousands of measuring points within modules to improve resolution.
- Thermal runaway detection monitors rate of temperature increase as an early warning.
- Cell surface insulators with embedded thermistors improve response time and accuracy.
- Actively cooled and heated packs maintain uniform stable temperature regardless of conditions.
With sufficient temperature data, battery thermal models can be further refined to simulate thermal behaviors for different use cases and optimize thermal management strategies.
Thermal Management Integration
Incorporating temperature data into thermal management enables:
- Reducing charge rate when temperature nears limit to avoid overheating rather than simple fixed current charging.
- Proactively cooling the pack when approaching upper limits well before reaching critical temperatures.
- Preventing operation in extremely cold environments by temperature dependent output derating or pack heating.
- Optimizing cooling system controls based on inlet air and internal temperatures.
- Estimating impedances and available capacity based on temperature.
- Triggering safe shutdown and isolation when dangerous temperatures are detected.
Integrating temperature monitoring as part of the overall thermal management and battery management systems is key to maintaining safe, efficient, and optimal battery operation.
Summary
- Battery temperature heavily impacts performance, lifetime, and safety parameters. Exceeding limits degrades batteries.
- Direct temperature monitoring allows optimizing operation as well as preventing failures from overheating or freezing.
- Sensor selection, placement, and circuit design ensure robust and noise-free measurements for the battery management system.
- Alternatives exist for simple batteries but lack protections of active sensing and control. Advanced techniques provide greater resolution.
- Temperature feedback coupled with thermal management strategies maximizes battery efficiency, utilization, and safety.
FAQ
How many temperature sensors are needed in battery pack?
Depends on pack size but a minimum of 3-5 sensors placed at end/middle of pack helps detect basic thermal gradients for control and protection. Larger packs may use 10 or more sensors distributed throughout the modules.
What temperature range do Li-Ion batteries operate in?
Charge: 0°C to 45°C, Discharge: -20°C to 60°C. Wider operating range possible with thermal controls. Lower and upper cutoff limits are used for protection.
What communications bus is used for battery temperature sensors?
A controller area network bus (CAN Bus) is typical for connecting multiple sensors over a common serial data bus. Other options include SPI, ISO-BUS, and I2C. Wireless sensors are also an emerging option.
How often should battery temperature be monitored?
Continuous monitoring provides best results for optimizing charging and prevent over-temperature conditions. For simple packs, occasional sampling may suffice but lacks robust protections.
Why are multiple temperature sensors needed in large battery packs?
A single external measurement cannot detect internal hot spots. Distributed sensors allow finding cells with higher localized heating to properly control charge rates and cooling across large packs.
