BU-304: Why are Protection Circuits Needed?

Batteries can release high energies and the safety requirements for nickel- and lithium-based batteries and cells for portable applications are harmonized under IEC 62133. The standard came into effect in 2012 to reduce the global risk in transporting, storing and operating batteries.

The most basic safety device in a battery is a fuse that opens on high current. Some fuses open permanently and render the battery useless; others are more forgiving and reset. Figure 1 illustrates the top of an 18650 cell for Li-ion with built-in safety features.

The resistance of the positive thermal coefficient (PTC) (blue) is low during normal operation and increases when the temperature rises above a critical level to reduce current flow. The PTC is reversible and returns to high conductivity when the temperature normalizes.

The current interrupt device (CID) is a fuse-type device that cuts off the electrical circuit permanently when triggered by excessive cell pressure, high temperature, or high voltage, depending on design. In Figure 1, the CID operates by pressure. When the internal pressure increases to about 1,000kPa, the scored top disk (orange) breaks, separates from the metallic foil (brown) and disconnects the current flow. This also allows gas to vent.

The last safety device is the vent that releases gas during an anomaly and can be resealed. However, the pressure of a disintegrating cell can be so large that the gases are unable to escape in an orderly way and venting with flame occurs. In some cases the top of the cell escapes like a bullet from a shotgun. Similar to a nuclear meltdown that cannot be stopped once in progress; a Li-ion battery once in disintegration should be allowed to burn out in a safe place with ventilation.

18650 Protection
Figure 1: Typical safety mechanism of the 18650 cell cap [1]

PTC (blue) increases resistance by heat to reduce electrical current. The effect is reversible. CID consists of a top disk (orange) that breaks under pressure and permanently disconnects the current flow.

Protection devices have a residual resistance that causes a slight decrease in overall performance due to a resistive voltage drop. Not all cells have built-in protections and the responsibility for safety in its absence falls to the Battery Management System (BMS).

Further layers of safeguards can include solid-state switches in a circuit that is attached to the battery pack to measure current and voltage and disconnect the circuit if the values are too high. Protection circuits for Li-ion packs are mandatory. (See BU-304b: Making Lithium-ion Safe)

More information on why batteries fail, what the user can do when a battery overheats and simple guidelines using Lithium-ion Batteries are described in BU-304a: Safety Concerns with Li-ion.

Intrinsically Safe Batteries

Safety is vitally important when using electronic devices in hazardous areas. Intrinsic safety (IS) ensures harmless operation in areas where an electric spark could ignite flammable gas or dust. Hazardous areas include oil refineries, chemical plants, grain elevators and textile mills.

All electronic devices entering a hazardous area must be intrinsically safe. This includes two-way radios, mobile phones, laptops, cameras, flashlights, gas detectors, test devices and medical instruments, even when powered with primary AA and AAA cells. Intrinsically safe devices and batteries contain protection circuits that prevent excessive currents that could lead to high heat, sparks and explosion. The hazard levels are subdivided into these four disciplines.

The main classifications for intrinsic safety are divisions and zones. Division is typically used in North America; zone originated in Europe but is now used worldwide. The two classifications have much in common, but there are differences in risk perception.

DIVISIONS (North America)

1. Types of Hazardous Materials and likelihood of presence

Class I Flammable gas/vapors or liquids in petroleum refineries, utility gas plants.
Class II Combustible dust in grain elevators, coal preparations plants.
Class III Ignitable fibers and flyings in textile mills, wood processing creating sawdust, etc.

Division I Hazardous materials likely to exist in ignitable concentrations under normal use.
Division II Hazardous materials unlikely to exist in ignitable concentrations under normal use.

ZONES (Europe and rest of the world)

Zone 0 Gas/vapors exist continuously or for long periods under normal use.
Zone 1 Gas/vapors likely to exist under normal use.
Zone 2 Gas/vapors unlikely to exist under normal use.

Zone 20 Dust exists continuously or for long periods under normal use.
Zone 21 Dust likely to exist under normal use
Zone 22 Dust unlikely to exist under normal use

2. Potency of Hazardous Material (Groups from A to G)

A hazardous material is given a designation of: Acetylene (A), hydrogen (B), ethylene (C), propane, gasoline, etc. (D), metal dust (E), coal dust (F) and grain dust (G).

3. Temperature Codes (from T1 to T6)

The explosion danger of gases or combustible dust is affected by surface temperature. T1 is a hot 450ºC (842ºF); T6 is a moderate 85ºC (185ºF). All other temperatures fall in between.

Intrinsic safety requirements vary from country to country. North America has the Factory Mutual Research Corporation, Underwriters Laboratories (UL) and Canadian Standards Association (CSA); Europe has the ATEX directive; while other countries follow the IECEx standards. Many countries recognize harmonized IEC 60079.


References

[1] Source: CALCE (Center for Advanced Life Cycle Engineering)

Last Updated: 14-Apr-2023
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On June 18, 2019, Julian wrote:
Hi, what is the name of the device to protect a leisure battery from drawing down under 50% or so? So it’s life can be prolonged.
On November 29, 2018, Paul Dalton wrote:
I'm looking into repairing/refurbishing/rebuilding one or more of the several 'bad' Makita 18v LXT battery packs I have. As I read about why these units fail prematurely, a consistently mentioned issue seems to be an imbalance resulting from only two of the cells being used to power the circuitry of the control board. I am definitely NOT a battery expert, but reading about that made me wonder whether it might be possible to eliminate that as an issue by rewiring that board to receive its power insteas from a separate source, perhaps by using two 3.6v LIR2032 coin cell batteries (maybe located externally for easy replacement)? Just curious to learn whether tgat could eork Thanks
On January 23, 2018, Jerry Ratzlaff wrote:
The battery was still operating good when connected to the charger. There are a couple screws to take out so I may open it up and check for a fuse. Thank you.
On January 23, 2018, geoff bryant wrote:
If your battery has a Battery Monitoring System then it's likely that this has operated and disconnected the battery. What state was the battery in before you charged it . If any of the battery cells had dropped below 3.2volts then again the BMS would have disconnected the battery. If there is a fuse fitted it may be worth checking that.
On January 22, 2018, Jerry Ratzlaff wrote:
I have a lithium ion 2100mAh 7.4v 15.54wh battery that came with a 8.4v-1.0A charger. I accidently used a 17.0v-1.0A charger and left it plugged in overnight. Now the battery appears to be completely dead. Do you think the battery would be permanently wrecked? Thank you.
On January 9, 2018, Filip★2805 wrote:
I never believed that 'boring' warnings about LiION bat overcharges. So I didn't care about a phone (flat-Nokia) battery when I charged it without circuit, just directly connected to some lab.supply. Exlposion was so massive, that the battery form (strong stainless steel sheet) become to precise cylinder before activating of pressure fuse. In one moment my table(2sqm) was in fire like spilled gasoline. Believe me, be careful...
On November 19, 2017, georgios papamichael wrote:
I have brought back to life several batteries NI-MH. and they keep streaming at full. , but at work falling quickly . what can happen /
On August 29, 2017, georgios papamichael wrote:
I've built several ni-sd and ni-mh batteries With new cells. I used the old batteries to put it somewhere for retrieval. I decided Since I did not have a job to try to wake old batteries. I tried a 12volt acid battery, and started To supply stream on the dead batteries. Of the hundred batteries reverted to life 80, the other 20 do not keep the stream reasonably they are still dead; I need to recharge? If you can enlighten me. And the other 80 who have been holding. current for several hours, how many. Hours should keep stream to be okei. And what is the current price that must be kept on charging to be an integration?
On August 21, 2017, mukund chitale wrote:
i want to know various ics which are used in lithium ion battery protection circuit..
On June 11, 2017, Tony wrote:
I have an 18v Hitachi toolkit..one of the batteries will not accept a charge via the charger..It will however charge via another battery (jumper) direct one to the other. It seems the charge protection has failed ..can it be fixed
On January 11, 2017, Pete wrote:
I tried replacing the 18650 cells in one of my dewalt li-ion batteries, and it worked for a day... then the voltage across the battery contacts dropped to 14.5V, even though the cell total was still at 20V. Is this the micro-controller detecting a non-dewalt component (the cells)? Additionally, can I see the replies (if any) to the comments/questions?
On November 29, 2016, hussein wrote:
I have traveled from Lebanon to Northern Cyprus since 2 months for education. I have an Toshiba laptop and iPad Air 2 and both of them since I arrived here are being shit. The thing that is happening is that my devices batteries are being over overheated followed by massive unbelievable strange rapid drain in my battery. When I was in Lebanon, both of my devices were running normally and there were neither drain nor overheat in the battery. Also, not only there is an overheating and tremendous battery loss, but also there is slow functioning of the systems. But what I am very angry of is the rapid drainage of my battery since I have to study some of my lectures from the Internet.
On October 18, 2016, wx wrote:
@kelly cheverie: How are the batteries configured internally? Do you have two sets of series batteries connected in parallel? I will presume that t1 and t2 are meant for measuring the temperature on each battery set.
On October 13, 2016, wx wrote:
Hi, i have a question. I opened up a 4S2P battery pack and found a thermistor on one of the cell. My question is, for overtemperature protection, is it adequate only to measure one cell? Can there be an event that occur in which one of the cell in the 4S(or the 2P) overheats? If i only measure the temperature on one cell, will i miss out triggering the protection circuitry? Thanks.
On April 24, 2016, kelly cheverie wrote:
i bought a pair of new ridgid 18 volt 4ah battery packs for a good price. i was planning of removing from case and transplanting in a craftysman c3 case for which i have a full line of tools. besides pos and neg terminals there are two more marked t1 and t2. not totally sure of purpose and would like more info before i adapt to my charger if possible. I think they play a role in determining if battery temperature is in proper range for charging Any help on this thanks
On February 1, 2016, Ramón wrote:
I need to know an integrated circuit to swicht battery on/off by an external push button in order to disconnect my system by the microcontroleror to keep in standby. Thankyou
On January 20, 2016, Chris Humphries wrote:
Hi I am contemplating using two 12 volt 40 watt solar panels mounted on the roof of a motorhome to charge the battery of a 24 volt electric bike battery. Would the 10 amp solar panel controller 12 volt/24volt be satisfactory to control the current , voltage and temperature constraints of the Li Ion battery ?
On January 19, 2016, R P Tiwari wrote:
Hello Sir! . I am new in electronic field. I wish to know about a circuit which can charge a battery of 6/12 V from a solar pannel. This should. have protection of over/ under voltage. Kindly provide the same. Thanks.
On September 29, 2015, Antony wrote:
Hi I have a Bosch 18v li 4ah battery out of a drill, hardly been used charged 5 to 10 times only, I know I shouldn't of done this but used it to power my makita site radio and I think it depleted the battery so much when I go to charge it battery charger doesnt recognize it or something, is the battery fooked? Or is there something I can do to trick the charger to make it charge. Many thanks for any advise antony
On September 23, 2015, VIJAY SONI wrote:
I need intrinsic safe batery of 2700mAh with 3 pin, please suggest some suitable part number.
On September 7, 2015, Robert wrote:
Does a simple li-ion (actually, lifepo4) battery protective circuit board "eat up" a portion of the voltage in the same manner a voltage regulator would? Or does it somehow not drop any of the charging voltage and use the (3.2v) battery, and some little current, to protect the battery from over/under discharge? Thanks in advance.
On July 7, 2015, Absolom Mykhal wrote:
i am in the process of building an 18650 battery pack for a small solar system its a 3s 80ah battery pack with a pcb i just want to find out can i make 2 or 3 of these packs and wire them in parallel to increase amperage as is usually done in solar systems with any problem or effect to the battery packs then also is there a big difference with a pcb or bms that has balancing and one that does not
On May 19, 2015, martyn jenkins wrote:
hi I have a Makita 36v li ion battery drill about 2 years old but unused I have 2 new batteries with it and one good second hand which worked fine when bought I went to charge them this week new ones charged ok but second hand one would not take charge and when in drill the led light comes on but no drill I measured between contacts and shows 36v was thinking of buying CADEX 7400ER to test this and do other batteries any help please thanks martyn
On May 10, 2015, Ed wrote:
Jonathan, Most protecion circuits i looked at disconnect the battery when a overcurrent situation occurs, a ptc for instance allows a larger current for a certain amount of time until it is heated so far that it disconnects or limts the current, electronic protection circuits do the same but disconnect faster. This means that for a short time you can have a large current that is only limited by the total resistance in your circuit. The current of 32 amp you measured could be correct, it could even be higher, looking at the voltage across a resistor in your circuit with a fast digital memory scope can be very interresting (and maybe shocking). I once designed a IS battery pack under the old EX rules and it first failed the short circuit test done by the certifing agency because it diconnected the current instead of limiting it. By adding extra circuits to limit the current i managed to create a pack that passed the certification test
On April 24, 2015, Jonathan wrote:
Yes Edward I am well aware of the danger and it is a test which I carry out almost every day. The test is however conducted in side an explosion proof box and contact is made via an external breaker. As Intrinsic Safety is mentioned above, all cells and batteries used in side of IS equipment must be subjected to the short circuit fault condition tests and a maximum temperature and current obtained (sometimes even with PTC device removed) as per the 60079-11 standard for IS equipment protection. This seems bizarre to a lot of people but these are tests which must be conducted to ensure user safety!! regardless of whether it is in a hazardous or normal location.
On April 22, 2015, geoff wrote:
Thanks Edward. I've measured the voltage between the battery positive and each of the balancing wires of which there are nine and the potential difference between each is 3.6v .This seems to be correct and wouldn't suggest a bad cell. I'm reluctant to take the cells apart without any indication of a defective cell and I wonder if there could be a malfunction in the control circuit board. This has a number on it : KLH36S88A and I'd be obliged if anyone has any info on this board.
On April 22, 2015, Edward wrote:
geoff , maybe one cell in th pack is failure, you can find the professional person to find the bad cell and change them
On April 12, 2015, geoff wrote:
My 36v 9aH ebike battery's power indicator shows only 20% after charging. The battery voltage measured at the output socket is exactly 36volts. The battery is only just out of warrenty. Any idea about (i) the cause of the problem and (ii) How to resolve it.
On March 25, 2015, veeravalli saibabu wrote:
basics of battery
On August 20, 2014, Edward wrote:
i think there is something wrong with the battery or laptop , you would better find another laptop or battery to check whose wrong?
On August 20, 2014, Paul wrote:
Yes edward, some days ago it was functioning normally but woke up one day and started malfunctioning.. I think it is original
On August 20, 2014, Edward wrote:
is it the original battery??
On August 19, 2014, Paul wrote:
I have a Li-ion laptop battery, it doesnt charge and it only discharges when the laptop is first connected to ac and removed, when u open the BIOS, the laptop shows that the battery isnt present even if it is operating on it. What might be wrong with it? B'se a few days ago it was functioning normally.
On August 19, 2014, Edward wrote:
Jonathan , you are crazy to do the test? it is dangerous? please email to me for more detail information zzrm316@163.com
On August 12, 2014, Jonathan Samuels wrote:
If I have a Li-Ion battery which contains a safety cut off device with a cut off current of 2A is it possible that a current well in excess of the '2A' can be measured and present for a very small amount of time? I have simulated a short circuit fault condition to measure current (using a fluke 287 DMM and fluke i30 current clamp which gives a voltage output) and measuring close to 32A? I was wondering if there is something I am missing or doing completely wrong?
On August 7, 2014, Patrick McEnnerney wrote:
How do you wake up ly-ion battery's
On November 6, 2012, M.Rajashekar wrote:
battery over charge protection circuits
On June 13, 2012, Jason Long wrote:
Are the safety circuit components for Lithium Ion batteries (internal PTC and the safety board) mandatory per any sort of standard, or does industry just do this because it's the right thing to do for consumer safety? Further to that, are the NTC output to chargers and/or temperature monitoring ICs on the safety boards required? Would you deem a battery pack without at least one of these protection mechanisms as unsafe? Would it violate any standards? Thanks!
On June 7, 2012, kurt anderson wrote:
we have a hazardous environment that requires intrinsically safe instrument. Are any low voltage bateries (watch or AAA) acceptable. 2 devices we would liketo approve are a laser pointer for training and a simple disc camera (no flash). Both use 2 AAA batteries. These seem very low risk just trying to determine if any exceptions exist for low voltage devices.
On April 15, 2012, Smac wrote:
How do you wake up a battery that has gone to sleep? I have about 12 bosch 10.8v Li batteries that no longer charge.
On February 23, 2012, Spring Grove Battery LLC wrote:
I rebuild power tool batteries and have been working with the lithium batteries but have found that they have a time out protection device in them. Is it possible to reset this device or replace it. Do you know if the factory scan tool would be able to reset or detect the time out device. Thanks Joel
On November 4, 2011, Ernest Danso wrote:
I have a 7.4V battery that output about 13500mAH but doesn't have any protective circuit. Can someone recommend one for me or know any thing out there that i can design. Thanks
On May 19, 2011, VWFringe wrote:
Need directions for retrofitting CPM to unprotected 18650's. Four pads are given: B+,B-,P+,P-.... Can I leave P+ and P- open, and can I use cat-5 solid conductor wire?
On April 25, 2011, Rudy Gerritsen wrote:
I am charging two 3.2 volt 1500 mAH batteries in parallel wiith a 4.5 volt solar panel. I use a SPDT relay to switch the batteries in seies after the panel goes dark or no sun light, and in parallel for charging when the panel sees sun light. The device I am powering requires 6.4 volts I would like to do this without using a simple relay. I tried using a PFet for switching the batteries in series, without success. Any ideas? Thank you, Rudy