18650 battery overcharge protection. Wholesale online store of Chinese goods. What are lithium batteries

• Lithium batteries better than nickel ones in many respects: higher current output and lower voltage drop under load - the screwdriver turns equally well both on a full charge and already discharged. Lithium batteries do not have a memory effect - they can be recharged without sacrificing capacity (unlike nickel ones). The self-discharge of lithium batteries is several times less than nickel ones, the screwdriver will lie quietly for half a year and lose only a couple of tens of percent of the charge, while the nickel one will be discharged to zero.

• Voltage assembly depends on the number of "cans" of lithium. In a fully charged state, one bank has a voltage of 4.2 Volts, while the operating voltage is in the region of 3.7 Volts (in this area, the discharge graph is almost horizontal)

• Number of cans for the battery is selected as follows: look at your old nickel battery. What voltage is on it? Select the number of lithium cans so that their total voltage is close to or slightly higher than the nickel assembly. The voltage of a lithium can in the calculation is 3.7 Volts: 2 cans - 7.4 V, 3 cans - 11.1 V, 4 cans - 14.8 V, 5 cans - 18.5 V. You can also count at the maximum - look at the output voltage of the nickel battery charger, it will be voltage of a fully charged screwdriver. We consider lithium banks as 4.2 Volts per bank: 2 banks - 8.4 V, 3 banks - 12.6 V, 4 banks - 16.8 V, 5 banks - 21 V. THIS WILL NOT BURN. Unless, of course, you hold it in a vice and give it full throttle.

• Security Board (BMS) performs several functions at once: protects the battery from overdischarging (lithium does not like this) and protects against short circuits, saving you from exploding cans. In both cases, the BMS simply disconnects the assembly from the load until the causes of operation are eliminated. Some BMS models do not go off protection until you apply charging voltage to the board. BMS models with cell balancing additionally perform a very important task: they balance the voltage of the cells in the battery during charging, charging them to the same voltage, which ensures the most efficient and safe use of the battery.

• Charge the battery of lithium batteries, you need a special charger that delivers the desired voltage and limits the current, such chargers have “CC CV” in their name, which means constant current constant voltage - the law of charging lithium batteries. ATTENTION! BMS board is not charger! It is necessary to charge the lithium assembly with a separate special charger, the voltage of which is equal to the maximum assembly voltage: 2 cans - 8.4 V, 3 cans - 12.6 V, 4 cans - 16.8 V, 5 cans - 21 V. I will leave links to Chinese charging PSUs below. These chargers automatically turn off the battery at the end of charging. It is very convenient to put a standard 5.5x2.1 mm socket on the battery, because such a plug is on all charging PSUs.

• Indicator the battery charge is a little bit, but it discharges the battery (LEDs are on), so you can’t just connect it to the assembly, you need to do this through a button or switch. You can also connect it directly to the screwdriver motor, but preferably through a diode. Thus, holding “full speed ahead” you will see the battery charge on the indicator!

• What to buy to assemble a lithium battery for a screwdriver?
  High-current batteries, how to count the number of cans I wrote above. You will find links to different batteries below, here I will recommend powerful and capacious SONY VTC6 batteries. With welded strips for easy assembly. And ordinary cans for self-welding / soldering. Slightly cheaper and not as powerful HG2, link one, link two. We have such batteries can be bought in vape shops.
  Security fee (BMS) according to the number of selected cans. There are links to powerful BMS with balancing with connection diagrams. Duplicate here: 3 cans, 3 cans, 4 cans, 4 cans, 5 cans, 5 cans. For particularly powerful screwdrivers, use the powerful BMS. The seller has them for a different number of cans
  Charger for the corresponding number of cans, links are below, I will duplicate here: 3 cans 1 amp, 3 cans 2 amps, 4 cans, 5 cans
  5.5x2.1mm socket for convenient charging, link 1 , link 2
  Charge indicator for the corresponding number of cans: link 1, link 2.

• Safety when working with lithium batteries plays an extremely important role! Lithium batteries are a powerful and very dangerous thing, if used incorrectly, a lithium battery can bang / catch fire. This can happen for three main reasons: too much load, overheating, and overvoltage. Special cases:
  • Overheat– do not leave batteries in the sun!
  • Short circuit- if you are soldering cans - do it as carefully as possible!
  • Recharge– Use only charger for lithium!
  • Overdischarge- do not force the battery!
  • Hot battery operation
  • Can mechanical damage
• What to do if the battery still banged? Tips from firefighter Andrei Delon:
  • Lithium cannot be extinguished “with absolutely improvised means”, until it burns out, it will create inconvenience and yell loudly about itself.
  • If it catches fire, the most ideal thing is to throw it into a pot, etc. So that it does not smoke much, fill it with something (salt, sand, earth, soda).
    NEVER extinguish with water or foam fire extinguishers.
  • To extinguish lithium, there are special means, powder mixtures PS-11, PS-12 and PS-13 (ordinary fire extinguishers do not work!)
  • Some powder fire extinguishers can even give the opposite effect, for example, with a mixture of PS-2.

The board is designed to protect against short circuit, overcharge and overdischarge of the lithium battery. It is supposed to be used at a maximum current of 3 A, so the 4 A option was taken, there are still almost the same, but 2 A (suffix B instead of A), a little cheaper.

The name clearly indicates the size of the battery, but the board is just as suitable for most lithium batteries with a diameter of 18 mm, for example, 18350, 18490, 18500. .

Testing

Parameters from the seller:

• Maximum battery voltage: 4.275V
• Minimum battery voltage: 2.5V
• Output current: 4A

The seller has no other information, so I decided to test the board's capabilities myself. I tested using two source options - and a battery. The first one was needed to check the operation of the protection by voltage, the second - by current.

Indeed, when it reaches 2.5 V or slightly lower, the board cuts off the input, the output is zero, the bank does not discharge further. In order for the circuit to start flowing current again, the input voltage must already be raised to 3 V. This hysteresis eliminates unnecessary switching when changing states.

Overcharge protection could not be fully tested, but it seems to be working. If you charge with a simple voltage source through a resistor. To check the charge closer to its end, the board turns off the output and, if the voltage on the bank is still low, it turns on charging further. The frequency of the check is approximately once per second. I tested charging through several of my chargers, everywhere the behavior is different, the chargers themselves control the whole process, and the board does not interfere with them.

When the maximum current is exceeded (declared 4 A), the board turns off, the output is zero current. In order for the board to work again, the load must be removed. I closed the battery with protection to a 1 Ohm resistor, the output current went a little more than 2.5 A, the voltage, respectively, is the same. This is the only doubtful moment in this board. It turns out that as soon as I slightly increase the load (lower the resistance), the voltage will still sag, and the board will cut down on voltage. The battery is normal, capable of delivering up to 2.8 A accurately. Perhaps the wires and the multimeter affected. Next, I close the output of the board, and it immediately cuts down. To reset the protection, you need to disconnect the load.

Assembly preparation

The connection diagram is elementary, the contacts on the board are signed, but fixing the board on the battery is not an easy task, mainly due to the need to use special materials. You will definitely need something for laying between the board and the battery, as well as a flat conductor that will stretch from the plus to the minus of the battery.

Since now there will be soldering on the plus side of the battery, it is necessary to add something more convex to the plus so that the load does not fall on the place of this soldering, I already did this.

The electrical connections, again, are fairly simple. The back of the board is completely a contact pad, it is also a “P-“ output, you do not need to solder it. The “P+” pin, like the “B+” pin, must be connected to the positive of the battery. They are already connected on the board, so that the wire-tape can be pulled from any of them. Another wire should connect "B-" to the negative of the battery, it should be short and fit completely into the gap between the board and the battery.

It is best to use a metal tape as a long conductor from the board to the battery plus. Such tapes can even be bought on Ebay, but I only need a couple of strips, it makes sense to look within sight. I found such a copper strip, thickness ~ 0.1 mm, perfect. The need to use a flat conductor is explained by the desire to preserve the overall dimensions of the battery, often in consumer devices there is no extra clearance.

The board must somehow be fixed on the negative pad of the battery. Here you need a compound, sealant, and double-sided tape may be enough. It all depends on whether you plan to serve this scheme in the future. An additional fastening will be a heat-shrinkable tube, so absolute fixation seems optional.

Assembly and results

I decided to try it on a dead battery first. So I can check all actions for errors without risk.

Let's see how the length of the jar changes.

So far, an elongation of only a couple of millimeters is noticeable, but you need to take into account that there will still be soldering on the negative contact (you can save money when soldering along the edge, but you didn’t guess right away, but that’s what the test on the probe is for), as well as the gasket between the board and the battery, beat I don't want chips on iron. It can also be made quite thin, but strong, since there are no great stresses here, but physical strength will be applied often. So far, I decided to put a piece of old heat shrink, quite thick. That is, he did everything as thickly as possible.

We take the tape, cut off a couple of pieces. The long piece will go along the entire battery, the short one is only needed to close the pad on the board with the minus of the can, you can even use a piece of wire. We tinker all at once and solder one end to the board.




Next, you need to solder the short end to the bank. It is necessary to solder with a minimum amount of solder, everything superfluous will lengthen the finished assembly. At the gasket, I cut off one of the sides a little so that there was a place for the tape. It is necessary to connect everything so that the bends of the tape do not go beyond the battery.


Now solder the remaining tape to the plus side of the can. Here it is very important to ensure that this strip does not touch the body of the can. Add some insulator under the tape. Since this is a test on a dead battery, I was too lazy to do this insulation (in vain, because this is also a test of materials). This isolation is the basis for the safety of working with a battery, since a short to the case will short circuit the battery, bypassing the protection.

Then it remains to pull the tube and seat it so that it wraps slightly over the edge at both ends. And here the main problem appeared - the tube turned out to be too fragile. Additionally, it turned out unfortunate that the fold of the tube fell on one of the edges of the tape, and this immediately led to a break. The edges of the board were too sharp and they also broke the tube.




On the plus side, everything is fine. This tube is afraid of overheating, perhaps this also affected the result.

Unfortunately, I have a limited amount of heat shrink (the last order came with a marriage). Therefore, I decided to postpone the second attempt. Initially, I did not plan to use these boards for their intended purpose, such a form factor is an accident. But during the test, I managed to find out something in case I want to try again:

1. The main thing is that it is better to take a ready-made jar with protection, it will be exactly the same in design. It is unlikely that you will be able to do better and cheaper.
2. Do not overheat the heat shrink. Keep the folds away from the metal tape.
3. Remove burrs from the tape wire. Smooth as much as possible over the surface of the jar. The tape must be well insulated from the case and the external environment.
4. Solder the contact to the negative contact near the edge so that the soldering does not rest against the central part of the board with chips.
5. The heat shrink holds the board strong enough, you should not worry about attaching the board to the battery. But if there is a suitable compound, you should use it.
6. It is advisable to blunt the edges of the board, for example, by putting a layer of electrical tape or the same heat shrink around the perimeter.
7. No matter how hard you try, 3-5 mm will still be added to the battery.

Boards can be used as protection for homemade or finished devices. It is also possible to embed such a board not in the battery, but in the battery holder. Such ready-made designs are on the market.

It is unlikely that I will still try to make a protected battery on my own, it turns out too clumsily for me. I'll stay with the original idea of ​​using consumer devices, not batteries.

I did not understand what kind of third chip is installed on the board, marking 10DB or 100B, the second line is G62S. If anyone knows, hint in the comments. The remaining two chips are FET assemblies, two for each.

The main result here for me is this. Protected battery banks have a significant design flaw in the form of a conductive tape along the entire body. Damage to it, or more likely due to its sharp edges, damage to the insulation under / above it, can lead to contact of the tape with the case, that is, a short circuit of the battery bypassing the protection. Accordingly, it is unlikely that the use of protected cylindrical batteries, especially homemade ones, is safer for all applications.

Safety

But if there is no such equipment, you can get by with a soldering iron. To reduce heating time during tinning, use an active flux, be sure to clean the battery from it afterwards. A low-power soldering iron with a thin tip will be very difficult to tin the battery, use the appropriate tool. Count on 1-2 seconds of continuous contact between the soldering iron and the battery. If it doesn't work that fast, let the battery cool down and adjust the tool kit and/or technique.

I soldered everything with a soldering iron, not paying attention to a slight overheating, since the test battery was killed anyway.

Update July 3, 2017

I often see advice that it is necessary to fix it by resistance welding, it seems like overheating occurs when soldering. Resistance welding also heats the contact point, and to a higher temperature (the melting point of copper is about 1350 ° C, in contrast to the maximum 300 ° C of solder). But with resistance welding, a smaller volume of metal is heated. I'm not sure which way is safer here, but I'm sure both are quite applicable.

This myth has already been overcome, but now I also often see advice on choosing very powerful soldering irons in soldering tips. Also nonsense. The soldering time here is fast, and the only thing that matters is how much energy the sting accumulates, and how quickly it can give it away. Just a thick tip with a flat edge is enough, even a 25-watt soldering iron with a 5-mm tip will do the job.

In fact, a much bigger problem is the mechanical strength of the solder joint. If you do not use special tricks (described), then the tape from the can can be very easily torn off.

This board had been lying in the bins for a long time, until the chance to use it for its intended purpose came up. If you like schemes and tools - it will be interesting.

If anyone remembers, I have a converted screwdriver
For more than 2 years, he actively and regularly worked, discharged and charged it 40 times.
Until he brutally overloaded it himself, making a vent hole in the OSB with a 102 mm crown, barely holding the tool with both hands :)


The corded screwdriver also did not cope with such work, and there was no powerful drill at hand. The result - one of the batteries could not stand the bullying and went into a cliff. At all:(
After partial disassembly of the battery, it turned out that the aluminum tape contact to the roll had burnt out. I don't know how to repair batteries yet :(




The tool was urgently needed, so the first thought is to buy the same 26650 LiMn2O4 battery and quickly rebuild the battery pack. But in stores, the same battery was not found. Order from China and wait - too long ...
In addition, I decided to add a BMS protection board to the block so that this does not happen again. But here's the problem - there is absolutely no free space in the battery pack :(
In short, I bought relatively inexpensive high-current SONY US18650VTC4 (2100mAh 30A peak 60A). They cost 750 rubles for 3 pieces - this is slightly more expensive than ordering from China, but here and now! took
The capacity of 2100mAh is, of course, significantly less than the former 3500mAh, but I will survive it somehow, you still get tired faster than it discharges. During the next smoke break, you can recharge it, especially now I will charge it with a new charge with a high current :)
The remaining two 26650 3500mAh batteries that worked previously were checked for residual capacity - I received 3140mAh. A drop in capacity of 10% is quite acceptable and the batteries can still be used somewhere.

If desired, this board can be easily converted to 2S by simply closing B2 and B + with a jumper, while the power switches can heat up more by increasing the resistance of the fieldworker channels.
Controllers provide protection

Without violating his principles, he copied the original circuit diagram.


The scheme, although it looks complicated, works simply and clearly. Mistakes, of course, have not gone away - the Chinese keep their mark :)
The numbering of transistors is shown conditionally.
On p-n-n transistors Q1-Q6, a level converter and a signal adder with HY2210 are assembled
On npn transistors Q7-Q9 assembled a simple transistor logic for controlling power switches
Q7 is unlocked when any battery is over-discharged to a voltage below 2.40V, recovery occurs at a voltage above 3.0V (after removing the load or connecting to charging).
Q8 ensures that the protection is snapped in after it has tripped until the load is completely removed. At the same time, high-speed protection is organized on it in case of a short circuit of the load, when the current jumps over 100A.
Q9 is unlocked when any battery is recharged to a voltage above 4.28V, recovery occurs under load at a voltage below 4.08V. In this case, the power switches do not interfere with the flow of the discharge current.
I did not check the exact thresholds of all controllers, because. this is time consuming, but in reality they do not differ much from those stated in the specification.

S1 and S2 are just control points, they have nothing to do with thermal protection. Moreover, they cannot be closed to each other. How to connect thermal protection normally - I will tell and show below.
A signal appears on S1 when any element is overdischarged.
A signal appears on S2 when any element is recharged, and also after the current protection is triggered.
The current consumption by the board is very small (several microamps).

New batteries

The batteries are signed and tested, the capacity corresponds to the nominal

Despite the presence of a contact welding machine, I soldered the batteries, because. in this case, this is the best solution.
Batteries must be well tinned before soldering.

Batteries are soldered and installed in place

The board is soldered (the board has already been redone in the photo)
Be careful not to short-circuit the ends of the batteries

Power wires - in silicone insulation 1.5 sq. mm
Control wires - MGTF-0.2

The typical scheme for connecting the board is not optimal, because There are 4 power wires going to the board. I connected according to a simpler scheme, when only 2 power wires go to the board. Such a connection is allowed with a short length of connecting wires to the batteries

Under load, when the trigger is pressed sharply, the protection of the board immediately works :(
At first, I logically assumed that it was cut off due to current overload, but closing the shunt of the board did not change anything. It became clear that a non-current overload of the board causes the protection to trip.
Next, I connected the oscilloscope in recording mode to the batteries and checked the voltage on them under load. The voltage managed to fall below 7V and the protection immediately worked :(
That's the reason for the protection. Why did the voltage drop so much, because the batteries are high-current? Let's take measurements and calculations:
- battery voltage 11.4V (HP890CN)
- the internal resistance of the batteries from the datasheet on DC DC-IR 66mOhm (3x22mOhm)
- measured motor resistance 63mΩ
- resistance of connecting wires and screwdriver switch - 23mOhm
- protection board resistance - shunt + MOSFET + connection wires - 10mΩ
Total circuit resistance 66+63+23+10=162mΩ
Circuit current 11.4/0.162= 70A
A lot, however...

But the problem is not in the current, but in the voltage drop on the batteries.
At a current of 70A, the voltage of each battery decreases by 70*0.022=1.54V and becomes 3.8-1.54=2.26V. Here it is, the real reason for the operation of the protection!
It is undesirable to correct or remove the protection - the safety of use is reduced, so it must simply be slowed down for the duration of the engine start. Add a 0.47uF capacitor to the right place and the delay is ready :)
If it is difficult for someone to solder a trifle to the board, you can solder the capacitor by surface mounting between S1 and B-
It was easier for me to put an SMD capacitor :)
Now there is enough time for the engine to spin up under load. When the engine is hard blocked at full throttle, the protection is activated after 0.3 seconds, and not instantly, as before.
Converted board


Do not pay attention to the 470kΩ resistor - the native 510kΩ resistor suffered as a result of experiments and was replaced with whatever came to hand :)
The board contains high-resistance circuits, so after soldering it is necessary to thoroughly wash the board.

Scheme after alteration

Description of all modifications
1. An unnecessary 0.1uF capacitor was soldered from 2 pins of HY2210 to the shunt. Why it was installed at all is not clear, it is missing in the datasheet on the HY2210. Does not affect the work, but soldered it out of harm's way.
2. Added base-emitter resistor for normal recovery after protection operation.
Without it, auto-recovery of protection after removing the load is extremely unstable, because. the slightest interference on P- interferes with resetting protection. A suitable resistor value is 1-3MΩ. I soldered this resistor neatly directly to the terminals of the transistor. Be careful not to overheat it!
3. Added a 0.47uF capacitor to slow down the overdischarge protection from 25ms (typical for HY2210) to 300ms. I tried to connect a 0.1uF capacitor - the protection works too quickly for a hefty RS-775 motor. If the engine is completely brutal, you may need to install a more capacious capacitor, for example 1uF

Now a sharp pull on the trigger under load does not trigger the protection :)

Connection of the protective thermoswitch.
Both NO and NC thermal switches can be connected to this board.
I give the schemes below.


I used NO thermal switch KSD 9700 5A 70ºC

Glued it to the batteries

At the same time, I decided to abandon charging from the PSU through current-limiting resistors and charge the batteries with a converted 3S 12.6V 3A charger

The final scheme turned out like this

Charging Colaier 12.6V 3A

already did SW on it. kirich but as always I have something to add

In its original form, charging does not hold the declared current of 3A and overheats. In addition, it emits noticeable interference to a nearby radio receiver.
The charger was disassembled before the tests :)

Charging differs from simple PSUs by additionally installed elements of the current limiting circuit

I'll be brief with revisions :)
- Put the missing input filter. Now the radio does not respond to a working charge.
- Moved the thermistor NTC1 (5D-9) and fuse LF1 (T2A) to the right places
- The board has a place to install discharge resistors R1 + R2. They are needed to discharge CX1 after turning off charging from the network. I put a discharge resistor OMLT-0.5 620 kOhm in parallel with CX1 :)

I put the output choke L1 instead of jumpers. The work was not affected in any way, because the output ripple for charging is not of great importance.

Reduced the output voltage from 12.8V to 12.65V by connecting a 390kΩ resistor in parallel with the R29 8.2kΩ resistor
- Reduced the output current from 3.2A to 2A by replacing the R26 1.6kΩ resistor with a 1kΩ resistor


The current was reduced because, firstly, this charge cannot deliver a current of 3A without overheating, and secondly, because US18650VTC4 batteries have a maximum charging current of 2A.
The PCB layout is incorrect, because of this there is no good stability of the output voltage and current. I did not change because it is not very critical.

Conclusions:
- SONY US18650VTC4 batteries have only one drawback - a small capacity
- BMS 3S 25A board is able to work normally after a little modification
- Charging 3S 12.6V 3A in its original form works unsatisfactorily and requires significant improvement, I can not recommend it, sorry

After the alteration, the screwdriver has been working normally for 4 months. Power reduction is not felt, it charges quickly, a little over an hour.

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