Lithium batteries provide the very best energy density in contrast with different battery chemistries. Lithium batteries can retailer extra vitality in a smaller, light-weight bundle than another sort of battery. Consequently, Lithium-based batteries are the battery sort of alternative for all sorts of electrical automobiles (EVs). Â Sadly, lithium batteries have a number of downsides. They will endure thermal runaway if broken, below very excessive masses, overcharged, or uncovered to excessive temperatures. Thermal runaway can generate sufficient warmth to ignite the electrolyte and trigger a fireplace or an explosion of a battery pack. Â Such circumstances can severely injury the battery pack and the EV and probably put the passengers in danger.
A brand new know-how that mitigates the danger of battery thermal runaway is now accessible. The most recent know-how developed by Littelfuse, the TTapeâ„¢ Distributed Temperature Monitoring Gadget, permits early detection of localized battery cell overheating. The progressive platform contributes to extending battery life and enhancing the protection of battery installations. TTape is a strip of tape with quite a few intently spaced temperature indicators. In contrast to a discrete thermistor, TTape adheres to battery cells and conforms to the form of the cells, enabling excessive density monitoring of places on a battery pack. The temperature indicating sensors rapidly detect a cell scorching spot stopping battery thermal runaway. With particular person thermistors whose dimension limits the variety of detection places and prevents shut spacing, a battery cell scorching spot that’s not close to the situation of a thermistor may rise to a harmful degree. TTape solves the issue of being unable to detect battery cell scorching spots rapidly.
This text introduces the reader to the advantages of the TTape Distributed Temperature Monitoring Gadget and particulars the product. As well as, a pattern circuit illustrates utilization in a safety scheme. Design engineers will discover TTape a superb and simplified element for guaranteeing lithium-ion batteries have most life and are secure to function.
Description of TTape
TTape is a versatile, skinny band of printed temperature indicators spaced intently collectively for optimum spatially resolved temperature monitoring. Its thickness is lower than 500 µm which permits it to adapt to any battery pack form. Determine 1 exhibits the TTape strip with the printed temperature indicators (PTIs).
The printed temperature indicators are small dots of polymer optimistic temperature coefficient materials. The PTIs are related in sequence. When a PTI detects a temperature above the brink degree, its resistance will increase by an element of over 1000.
Determine 2 offers the dimensional particulars on the TTape Distributed Temperature Monitoring Gadget. Temperature sensors could be spaced round 10 mm aside. The TTape has choices for a slender width of both 8 mm or 10 mm and a regular size of 337 mm. Customized designs could be so long as 1 m. Strain-sensitive adhesives bond the TTape to a floor. The adhesive permits bonding to metallic, polyamide, PET, and polyimide surfaces.
An ordinary tape size of 337 mm contains ten printed thermal indicators. Customized designs can encompass as much as 50 of the PTIs. The printed thermal indicators have a most diameter of 5 mm with a regular spacing of 30 mm.  The slender spacing between the PTIs permits elevated spatial decision for monitoring the temperature of all cells on the battery pack. Discrete temperature sensors can’t obtain such shut monitoring of all particular person battery cells. Moreover, with a thickness of below 500 µm, the TTape can conform to the irregular floor of the battery pack and have direct contact with the person battery pack cells.
The TTape connects to an digital circuit with a 2-wire solder pad interface. Figures 1 and a couple of present the 2 solder pads, and Determine 2 defines their perform.
The TTape has a visit temperature setpoint of 58 ± 3° C for early overheating detection earlier than a battery cell can attain a harmful temperature degree. Lithium-ion and different battery chemistries can cost and discharge at temperatures below 60° C earlier than typical battery administration circuits take motion. The battery administration system will interrupt the load or the charging energy on the battery pack when a temperature above 60° C is detected. Usually, the 58° C setpoint tolerates the battery pack temperature fluctuations that happen when a battery pack is below load or re-charged. The printed thermal indicators have a response time of below one second. If a battery pack temperature exceeds the nominal 58° C threshold for longer than one second, the TTape temperature monitor will reply.
To keep away from speedy on-off biking close to the brink temperature, the TTape PTI materials has a hysteresis attribute which prevents put on on crucial system parts and avoids false alarms. This design method ensures the system responds solely when there’s a real overtemperature situation, contributing to the protection and sturdiness of the battery pack.
Circuit implementation
TTape works in TTL-level l, 5 V circuits, or 3.3 V logic circuits. Determine 3 exhibits a really useful circuit configuration to be used with a TTape monitor. VT is a logic excessive when the TTape printed thermal indicators detect a temperature exceeding 58° C and change to a excessive resistance. VT is a logic low when the temperature is under 58° C or if the temperature has exceeded the brink temperature and has fallen under 42° C. The printed thermal indicators exhibit a hysteresis impact of roughly 16° C as soon as the brink temperature is exceeded. The best facet of Determine 3 presents the hysteresis curve of the TTape machine.
The logic circuit is an easy circuit using a really useful worth of RP as 200 KΩ. VT can present a sign to an A/D converter in a microcontroller. When the TTape will not be detecting a battery scorching spot, the 5 V circuit attracts round 25 µA to eat solely 125 µW. The TTape wants just one A/D enter line on the microcontroller to transmit the temperature state of the battery cells. The microcontroller can both be part of the battery administration system or be an interface to it.
Comparability with discrete thermistor temperature monitoring
With solely 30 mm between the printed thermal-indicating sensors and a skinny adhesive tape kind issue that may conform to any floor, the TTape can detect a battery cell temperature rise earlier than a discrete sensor can until the temperature rise is true below the discrete sensor. Determine 4 illustrates this example. If a thermistor is one cell away from an overheating cell, it may take over two minutes for the thermistor to reply to the excessive temperature situation. With PTIs on every cell, the response is below one second.
In contrast to a NTC sensor, the TTape temperature monitoring platform doesn’t want calibration since it’s basically a two-state machine. As well as, the electronics that course of the TTape sensors don’t require a temperature conversion calibration desk.
As a conforming tape, the TTape consumes negligible area on the battery pack. TTape permits straightforward set up and permits monitoring of any battery pack building. Determine 5 exhibits an instance set up of a TTape monitoring strip on a battery pack.
Excessive-density monitoring for enhanced security
The TTape Temperature Monitoring Platform presents designers with the distinctive skill to have extremely compact temperature monitoring on every group of cells in an EV battery. The high-density monitoring minimizes untimely growing older by detecting and stopping temperature scorching spots on particular person cells or a gaggle of cells. This low-cost, minimal space-consuming answer offers enhanced security and prolonged battery cell life. Moreover, the TTape monitoring machine is AEC-Q200 certified to be used in automotive automobiles.
For extra info on the TTape Distributed Temperature Monitoring Platform together with set up particulars and circuit implementation, see the TTapeâ„¢ Distributed Temperature Monitoring Gadget Software Be aware.
To acquire technical help, go to the TTape product web page and speak to Littelfuse at www.littelfuse.com.