BMS lithium battery protection controller for screwdriver. Converting a cordless screwdriver from ni-cad batteries to li-ion batteries, with BMS and dc-dc down converter
And so, as promised, I will try to describe to you the entire process of switching from ni-cad batteries to li-ion batteries. I’ll say right away that you will still have your original power supply as a charger for new batteries. But the old batteries that you had in cordless drill you can safely recycle. Since in my opinion ni-cad battery is very Low quality due to the fact that in the manufacture of batteries there is a complete saving of materials. Hence they do not shine with their survivability. While li-ion can work for more than five years if used carefully, and they are not afraid of long periods of downtime, unlike ni-cad batteries.
In general, I don’t need to tell you about the advantages, but in the video I’ll tell you more about them and try to demonstrate them.
Yes, in this video and topic we will look at the transition of a 14.4 volt screwdriver. In the future we will consider 18 Volt. Well, now in more detail.
And so what we need.
The most important thing is soldering skills, since remodeling requires making connections using the soldering method:
You need a soldering iron of 25-40 watts or Soldering Station, solder, soldering acid, rosin or flux. Wires with a cross-section of 0.75 kV, and 2 kV, 15-20 cm long, for connecting the battery and the screwdriver itself.
A step-down converter for a current of at least 3A, it serves not only as a charger for batteries but also as a power supply, that is, if we use a 12V 5A power supply, with the help of this device we will not only charge the drill, but also work while charging it from the network. Which has its undeniable advantages.
According to my calculations, it will be optimal to use three LI-ION batteries connected in series, this will be 11.1 V peak 4.2 * 3 = 12.6 V. (Remember the value of 12.6V, we will need it; we will set the charging voltage in relation to this voltage on the step-down converter.)
In order for the batteries to last a long time, I suggest installing a mini charge controller board for each battery. This board will monitor the voltage on each battery, if required, some will be charged before, while others will not be recharged. Simply put, you will get max capacity for a long time! And your batteries will wear out equally.
Such a board is called a balancer in Russian, and it does not have any additional protections.
To search online auctions, use the picture above and the name of the lot: Balance Board for 3 Packs 11.1v 12.6v Li-ion 18650 Battery Charging module
Board characteristics:
Item Description:
This balance board is designed for the Li-ion battery pack without balance charging function. This PCB board, is not a battery protection board,
has not protection function for charging / discharging.
Feature:
Balance voltage for each cell at 4.2v and it is mainly for voltage / current balancing charging.
When translated, it becomes clear that this board is only responsible for supporting the charge of each section not higher than the maximum battery value. Which is exactly what we need.
Diagram for connecting batteries to this board + to the converter board + to the screwdriver.
As you can see from the picture which I tried to show schematically, there is nothing complicated in this assembly.
The advantages of this assembly are obvious.
As for batteries, I use used batteries from old laptop batteries. which greatly reduces the cost of this modification of the screwdriver. And it significantly reduces its final cost. And the use of branded batteries more than doubles the capacity of the screwdriver. Since I use batteries connected in series in pairs, and if you have enough space for 3 more batteries, you can consider connecting batteries like this. :
The capacity of the batteries does not depend on how many of them you have connected in series. And it depends on parallel connection. To increase battery life, I recommend using only proven batteries from the same manufacturer.
Well, what should those who have an old instrument do? Yes, everything is very simple: throw away the Ni-Cd cans and replace them with Li-Ion of the popular 18650 format (the marking indicates a diameter of 18 mm and a length of 65 mm).
What board is needed and what elements are needed to convert a screwdriver to lithium-ion
So, here is my 9.6 V battery with a capacity of 1.3 Ah. At maximum charge level it has a voltage of 10.8 volts. Lithium-ion cells have a nominal voltage of 3.6 volts, a maximum voltage of 4.2. Therefore, to replace the old nickel-cadmium cells with lithium-ion ones, I will need 3 elements, their operating voltage will be 10.8 volts, maximum - 12.6 volts. Exceeding the rated voltage will not harm the motor in any way, it will not burn out, and with a larger difference, there is no need to worry.
Lithium-ion cells, as everyone has long known, categorically do not like overcharging (voltage above 4.2 V) and excessive discharge (below 2.5 V). When the operating range is exceeded in this way, the element degrades very quickly. Therefore, lithium-ion cells are always paired with an electronic board (BMS - Battery Management System), which controls the element and controls both the upper and lower voltage limits. This is a protection board that simply disconnects the can from the electrical circuit when the voltage goes beyond the operating range. Therefore, in addition to the elements themselves, such a BMS board will be required.
Now there are two important points that I experimented with unsuccessfully several times until I came to the right choice. This is the maximum permissible operating current of the Li-Ion elements themselves and the maximum operating current of the BMS board.
In a screwdriver, the operating currents at high loads reach 10-20 A. Therefore, you need to buy elements that are capable of delivering high currents. Personally, I successfully use 30-amp 18650 cells manufactured by Sony VTC4 (capacity 2100 mAh) and 20-amp Sanyo UR18650NSX (capacity 2600 mAh). They work fine in my screwdrivers. But, for example, the Chinese TrustFire 2500 mAh and the Japanese light green Panasonic NCR18650B 3400 mAh are not suitable, they are not designed for such currents. Therefore, there is no need to chase the capacity of the elements - even 2100 mAh is more than enough; the main thing when choosing is not to miscalculate the maximum permissible current discharge.
And in the same way, the BMS board must be designed for high operating currents. I saw on Youtube how people assemble batteries on 5 or 10-amp boards - I don’t know, personally, such boards immediately went into protection when I turned on the screwdriver. In my opinion, this is a waste of money. I will say this, that Makita itself puts 30-amp circuit boards in its batteries. That's why I use 25 amp BMS purchased from Aliexpress. They cost about 6-7 dollars and are searched for “BMS 25A”. Since you need a board for an assembly of 3 elements, you need to look for a board with “3S” in its name.
Another important point: for some boards, charging (designation “C”) and load (designation “P”) can be different contacts. For example, the board may have three contacts: “P-”, “P+” and “C-”, like on a native Makita lithium-ion board. Such a fee will not suit us. Charging and discharging (charge/discharge) must be carried out through one contact! That is, there should be 2 working contacts on the board: just “plus” and just “minus”. Because our old charger also only has two pins.
In general, as you might have guessed, with my experiments I wasted a lot of money on both the wrong elements and the wrong boards, making all the mistakes that could be made. But I gained invaluable experience.
How to disassemble a screwdriver battery
How to disassemble an old battery? There are batteries where the case halves are attached with screws, but there are also ones with glue. My batteries are just one of the last ones, and for a long time I generally thought that they were impossible to disassemble. It turns out it's possible if you have a hammer.
In general, with the help of intensive blows to the perimeter of the edge of the lower part of the case (a hammer with a nylon head, the battery must be held suspended in your hand), the gluing area is successfully separated. The case is not damaged in any way, I have already disassembled 4 pieces like this.
The part that interests us.
From old scheme Only contact plates are needed. They are firmly spot welded to the top two elements. You can pick out the weld with a screwdriver or pliers, but you need to pick as carefully as possible so as not to break the plastic.
Everything is almost ready for further work. By the way, I left the standard temperature sensor and circuit breaker, although they are no longer particularly relevant.
But it is very likely that the presence of these elements is necessary for normal operation standard charger. Therefore, I strongly recommend saving them.
Assembling a lithium-ion battery
Here are the new Sanyo UR18650NSX cells (you can find them on Aliexpress using this article number) with a capacity of 2600 mAh. For comparison, the old battery had a capacity of only 1300 mAh, half as much.
You need to solder the wires to the elements. Wires must be taken with a cross-section of at least 0.75 sq. mm, because we will have considerable currents. A wire with this cross-section works normally with currents of more than 20 A at a voltage of 12 V. Lithium-ion cans can be soldered; short-term overheating will not harm them in any way, this has been verified. But you need a good fast-acting flux. I use TAGS glycerin flux. Half a second - and everything is ready.
Solder the other ends of the wires to the board according to the diagram.
I always use even thicker wires of 1.5 sq. mm for the battery contact connectors - because space allows. Before soldering them to the mating contacts, I put a piece on the board heat shrink tube. It is necessary for additional isolation of the board from battery cells. Otherwise, the sharp solder edges can easily rub or pierce the thin film of the lithium-ion cell and cause a short circuit. You don’t have to use heat shrink, but at least putting something insulating between the board and the elements is absolutely necessary.
Now everything is insulated as it should.
The contact part can be strengthened in the battery case with a couple of drops of super glue.
The battery is ready for assembly.
It’s good when the case is on screws, but this is not my case, so I just glue the halves together again with “Moment”.
The battery is charged using a standard charger. True, the operating algorithm is changing.
I have two chargers: DC9710 and DC1414 T. And they work differently now, so I'll tell you exactly how.
Makita DC9710 charger and lithium-ion battery
Previously, the battery charge was controlled by the device itself. When the full level was reached, it stopped the process and signaled the completion of charging with a green indicator. But now the BMS circuit we installed is responsible for level control and power shutdown. Therefore, when charging is complete, the red LED on the charger will simply turn off.
If you have such an old device, you're in luck. Because everything is simple with him. The diode is on - charging is in progress. Goes off – charging is complete, the battery is fully charged.
Makita DC1414 T charger and lithium-ion battery
There is small nuance, which you need to know. This charger is newer and is designed to charge a wider range of batteries from 7.2 to 14.4 V. The charging process on it proceeds as usual, the red LED is on:
But when the battery (which in the case of NiMH cells is supposed to have a maximum voltage of 10.8 V) reaches 12 volts (we have Li-Ion cells, for which the maximum total voltage can be 12.6 V), the charger will go crazy. Because he will not understand which battery he is charging: either a 9.6-volt one or a 14.4-volt one. And at this moment, the Makita DC1414 will enter error mode, flashing the red and green LED alternately.
This is fine! Yours new battery It will still charge - though not completely. The voltage will be approximately 12 volts.
That is, you will miss some part of the capacity with this charger, but it seems to me that this can be survived.
In total, upgrading the battery cost about 1000 rubles. The new Makita PA09 costs twice as much. Moreover, we ended up with twice the capacity, and further repairs (in the event of a short-term failure) will only consist of replacing lithium-ion elements.
Many craftsmen have in their service cordless screwdriver. Over time, the battery degrades and holds a charge less and less. Battery wear greatly affects the time battery life. Constant recharging doesn't help. In this situation, “repacking” the battery with the same elements helps. The most commonly used elements in screwdriver batteries are the “SC” size type. But the most valuable thing a master has is repairing things with his own hands.
Let's remake a screwdriver with a 14.4 volt battery. Screwdrivers often use a motor for a wide range of supply voltage. So in in this case You can use only three Li-ion cells of the 18650 format. I will not use control boards. The discharge of elements will be visible in operation. As soon as the self-tapping screw does not tighten, for example, it’s time to put it on charge.
Converting a screwdriver to Li-ion without a BMS board
First, let's disassemble our battery. There are 12 elements inside it. 10 pieces in one row and 2 in the second row. A contact group is welded to the second row of elements. We leave a couple of elements with a contact group, and dispose of the rest.
Now you need to solder the wires for further work. The contacts turned out to be made of a material that cannot be tinned, so we soldered the wires to the elements. Minus to the body of the element, and plus directly to the positive patch. The old elements act as a support and do not participate in the work.
I will use lithium-ion batteries of the 18650 format. The elements are used. High-current elements are needed for modification. I “changed” my elements into heat-shrink from Sanyo, the old one was pretty shabby. I checked the residual capacity Imax.
We connect the batteries in series and solder the head elements. The battery is almost ready.
Now let's ensure comfortable charging. You need to install a four-pin connector. I used the connector from the old one motherboard for the number of contacts I need. I took the mating part from an old computer power supply.
Cut a hole for the connector. Fill the connector epoxy glue or super glue with soda. We also solder the wires.
Solder the wires to the elements. Wire from the first contact of the connector to the battery positive. A wire from the second contact of the connector to the plus of the second element, which is also the minus of the first element, and so on. Since I will be charging with a “smart” charger, I need to make a balancing wire.
As a connector for connecting to the charger, I will use the wire from the computer's power supply. The wire through which the floppy drive was powered. We cut off all the keys from the connector and it fits perfectly into the charger. It unsolders easily. Red wire to the first contact of the battery connector. Black wire to the second pin of the battery connector, etc.
The cordless tool is more mobile and easier to use compared to its networked counterparts. But we must not forget about the significant disadvantage of cordless tools; as you yourself understand, the fragility of batteries. Buying new batteries separately is comparable in price to purchasing a new tool.
After four years of service, my first screwdriver, or rather the batteries, began to lose capacity. To begin with, I assembled one from two batteries by choosing working “banks,” but this modernization did not last long. I converted my screwdriver to a corded one - it turned out to be very inconvenient. I had to buy the same, but new 12 volt “Interskol DA-12ER”. The batteries in the new screwdriver lasted even less. As a result, two working screwdrivers and more than one working battery.
There is a lot written on the Internet about how to solve this problem. It is proposed to convert old Ni-Cd batteries to Li-ion batteries of size 18650. At first glance, there is nothing complicated about this. You remove the old Ni-Cd batteries from the case and install new Li-ion ones. But it turned out that not everything is so simple. The following describes what you should pay attention to when upgrading your cordless tool.
For the remodel you will need:
I'll start with 18650 lithium-ion batteries. Purchased at.
The nominal voltage of the elements is 18650 - 3.7 V. According to the seller, the capacity is 2600 mAh, marking ICR18650 26F, dimensions 18 by 65 mm.
The advantages of Li-ion batteries over Ni-Cd are smaller dimensions and weight, with larger capacity, as well as the absence of the so-called “memory effect”. But lithium-ion batteries have serious disadvantages, namely:
1. Negative temperatures sharply reduce capacity, which cannot be said about nickel cadmium batteries. Hence the conclusion - if the tool is often used at subzero temperatures, then replacing it with Li-ion will not solve the problem.
2. Discharge below 2.9 - 2.5V and overcharge above 4.2V can be critical, and complete failure is possible. Therefore, a BMS board is needed to control charge and discharge; if it is not installed, the new batteries will quickly fail.
The Internet mainly describes how to convert a 14-volt screwdriver - it is ideal for modernization. With four 18650 cells connected in series and a nominal voltage of 3.7V. we get 14.8V. - just what you need, even with a full charge plus another 2V, this is not terrible for the electric motor. What about a 12V instrument? There are two options: install 3 or 4 18650 elements, if three then seem to be not enough, especially with partial discharge, and if four - a bit too much. I chose four and in my opinion I made the right choice.
And now about the BMS board, it is also from AliExpress.
This is the so-called battery charge and discharge control board, specifically in my case CF-4S30A-A. As you can see from the markings, it is designed for a battery of four 18650 “cans” and a discharge current of up to 30A. It also has a built-in so-called “balancer”, which controls the charge of each element separately and eliminates uneven charging. For proper operation The batteries for assembly are taken from the same capacity and preferably from the same batch.
In general, there are a great variety of BMS boards on sale with different characteristics. I don’t recommend taking it for a current lower than 30A - the board will constantly go into protection and to restore operation, some boards need to be briefly supplied with charging current, and to do this you need to remove the battery and connect it to a charger. The board we are considering does not have such a drawback; you simply release the trigger of the screwdriver and in the absence of short circuit currents, the board will turn on itself.
The original universal charger was perfect for charging the converted battery. IN last years Interskol began to equip its tools with universal chargers.
The photo shows to what voltage the BMS board charges my battery together with the standard charger. The voltage on the battery after charging is 14.95V, slightly higher than what is needed for a 12-volt screwdriver, but this is probably even better. My old screwdriver became faster and more powerful, and the fears that it would burn out gradually dissipated after four months of use. That seems to be all the main nuances, you can start remaking.
We disassemble the old battery.
We solder the old cans and leave the terminals along with the temperature sensor. If you also remove the sensor, it will not turn on when using the standard charger.
According to the diagram in the photo, we solder 18650 cells into one battery. The jumpers between the “banks” must be made with a thick wire of at least 2.5 square meters. mm, since the currents when operating a screwdriver are large, and with a small cross-section, the power of the tool will sharply drop. They write online that Li-ion batteries cannot be soldered as they are afraid of overheating, and they recommend connecting them using spot welding. You can only solder by needing a soldering iron with at least 60 watts of power. The most important thing is to solder quickly so as not to overheat the element itself.
It should be approximately so that it fits into the battery case.
Lithium batteries are most often used in the form of individual sections connected in series. This is necessary to obtain the required output voltage. The number of sections that make up the battery varies within very wide limits - from several units to several dozen. There are two main ways to charge such batteries.
Sequential method, when charging is carried out from a single power source, with a voltage equal to the full voltage of the battery. A parallel method, when each section is charged independently from a special charger.
Consisting of large quantity voltage sources galvanically not connected to each other, and individual control devices for each section.
The most widespread, due to its greater simplicity, is the sequential charging method. The balancer discussed in the article is not used in parallel charging systems, so parallel charging systems will not be considered in this article.
With the sequential charging method, one of the main requirements that must be met is the following: the voltage in any section of the charged lithium battery during charging must not exceed a certain value (the value of this threshold depends on the type of lithium element).
It is impossible to ensure the fulfillment of this requirement during sequential charging without taking special measures... The reason is obvious - the individual sections of the battery are not identical, therefore, achieving the maximum permissible voltage on each of the sections during charging occurs in different time. Required Balancer control board.
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