Learn how to convert your electric screwdriver to lithium-ion batteries with your own hands
Electric screwdriver is so tightly squeezed into the life of modern man that no repair or construction work at home and at work can do without it. The main convenience of the tool is in its mobility, which is ensured by a removable self-contained battery. That is why the device in question and received the name “cordless electric screwdriver”. The question of how to convert an electric screwdriver battery often arises during use, because nickel-cadmium batteries have a big disadvantage compared to lithium batteries. it’s low life. To avoid buying a new power tool with a lithium battery, you can upgrade the old battery by replacing the nickel-cadmium banks in it.
The portability of an electric screwdriver is provided by an independent power source. As such source of energy is the rechargeable battery, the principle of work of which is similar to that of a usual battery for a watch or a remote control. Only the battery for power tools has a voltage several tens of times greater than that of an ordinary thumbtack battery.
The battery powers the electric screwdriver’s motor. As the electric motor armature rotates, torque is transmitted to the gearbox. The gearbox increases or decreases the rotation speed (depending on the mode set) of the working body, the chuck, in which the bits are fixed. An independent power source as a battery on an electric screwdriver is a key element without which the device simply cannot work.
Owners of inexpensive screwdrivers are often faced with the situation of a rapidly discharging battery. The reason for this is the material of manufacture of the independent power source. There are three basic types of electric screwdriver batteries:
- Nickel-cadmium. the simplest, inexpensive and short-lived. Another disadvantage of this material is the small charge capacity
- Nickel-metal hydride batteries are an improved version of cadmium batteries, which have higher resistance to frequent charges and discharges (but they discharge quickly). Exposure to low temperatures adversely affects the life of the source
- Lithium-ion batteries are a new era of batteries that not only hold a long charge (slow consumption due to high capacity), but can also last for at least 10 years
Often owners only after buying an electric screwdriver that comes with a nickel-cadmium battery, realize that they “should have chosen a power tool with a lithium battery. The reason for buying a power tool with a nickel-cadmium source is also easy to explain, because with such a battery the device is several times cheaper. If you don’t believe me, you can compare on screwdrivers at Cylinder online store.
Nickel-cadmium and metal hydride. why replace them
One of the earliest batteries to be used in power tools were nickel-hydride sources. The advantages of these devices include optimal capacity reserve and low can heating rates when compared to hydride devices. They are also inexpensive, yet they do their job properly and efficiently.
The advantages of nickel cadmium devices include:
- Lower risk of overheating than hydride batteries
- Nickel-cadmium sources are contained within a metal housing that provides a high degree of stability and tightness
- If properly used, the nickel hydride will serve at least 3-5 years, but precisely because the device is often used in extreme conditions, the battery life is sharply reduced from the first day of purchase
- Low cost, which makes such devices in demand
- Not afraid of deep discharge
To extend the service life of the battery, so as not to ask yourself how to convert the battery of an electric screwdriver to lithium, you need to follow the simple instructions for the use of Ni-Cd batteries:
- You can and should work with the tool until the battery is fully discharged
- It is necessary to charge the source until its capacity is completely replenished
- Unlike lithium batteries, it is better to store cadmium batteries in a discharged state
- The “memory effect” is a disadvantage, but it can easily be eliminated by repeating three charge-discharge cycles
Hydride ones appeared after cadmium ones, but they were not very popular, because they discharge quickly and are not suitable for powerful models of screwdrivers. Hydride batteries have no “memory effect” and are less harmful to the environment than cadmium batteries. If your battery, which consists of cadmium or hydride sources, sooner or later you will need to replace it. Buy a new battery for an electric screwdriver of a little-known brand or outdated model is almost impossible, so it becomes necessary to modernize the old. From an old cadmium battery you can make an even better one, but to do this you will need to figure out how to convert the battery of an electric screwdriver.
How to convert an electric screwdriver to a lithium ion battery
If you have read my previous posts you might remember that after my standard batteries of the electric screwdriver gave out, and I urgently needed to continue working, I soldered up rather powerful converter with 8A rating and up to 15A short-term load. From 24 volts to 15 volts. Two 7 Ah 12 V batteries connected in series. I have an electric screwdriver for 14.4 В.
After exhausting and getting tired of the last construction season building the formwork with this thing, I decided that in the new season I need normal batteries.
After a little research on internet, I understood the Bosch marketing trick with regards to my original batteries. One new battery costs as much as a new electric screwdriver with two batteries in the set. It didn’t make sense to buy that crap for that kind of money.
There were no lithium ion batteries for my model electric screwdriver. New Li-ion screwdrivers were inadequately priced. It’s like a bacchanal of sucker scams.
So I had the idea to convert my electric screwdriver to lithium by myself. The lithium-ion banks are 3.7 volts, and we need 15-16 volts. We connect four lithium batteries in series and get 16.8V in the fully charged version (at 4.2 V per jar).
If you have a 12 volt electric screwdriver you can connect three banks in series.
Banks that is individual batteries from which is going to be our battery in one big battery, I decided to take a type 18650.
It’s a fashionable thing to use in flashlights these days. They are also found as part of laptop batteries.
These are Sony vtc4 type batteries. Capable of supplying as much as 30 amps to the load (max). Perfect for our purpose.
It’s ok, but lithium is dangerous, you can make a boom if you overcharge it.
In addition, our individual batteries are connected in series and over time there will be a large imbalance, i.e.е. Some cans will be recharged and others on the contrary will be heavily undercharged. In consequence of which the battery will fail very quickly.
Once again, our friends from China came to my rescue. There’s a thing called a balancer. Monitors the voltage during charging at each individual bank and if it is fully charged, disconnects it, and the others continue to charge and so on until all the individual banks in our chain of batteries are fully charged.
This thing costs a penny from the Chinese. But I got a little more than that from them.
It’s a little more expensive, but it’s worth it. The thing is that these batteries have no protection. So I also ordered the battery controller. This thing includes the balancer I was talking about above, as well as a whole set of protections. In particular contains: short circuit protection, overheat protection, overcurrent protection, etc.д.
- B: Batteries plus;
- B3: 1st battery.minus and 2nd battery plus;
- B2-: 2nd battery.minus and 3rd battery plus;
- B1-: 3rd battery.minus and 4th battery plus;
- B: 4th battery.minus;
- P: load/charge V (to the screwdriver / or to the charger);
- P-: load/charge V- (to the screwdriver and/or to the charger).
After piecing everything together, I tried the electric screwdriver in action and oops nothing works. What the heck, did the Chinese sold me a dud, but no they were not to blame. The thing is that in the process of assembling, I must have shorted something somewhere, in general, it triggered a defense, completely disconnecting the battery from the load.
To remove the battery protection (you can guess yourself, it’s not in the manual), you need to apply voltage from the load side, i.e.е. You can just put the battery on the charger. Protection will be removed instantly.
Tucked everything into the original battery case, having previously removed the old nickel-cadmium cans from it. Soldered in to the pads. I used hot melt glue to keep them from falling out.
The new battery is normally charged by the standard charger, although the voltage is a little low (recommended 18V), but I have not got around to it yet. No need to worry about recharging. The controller will disconnect the banks itself after they are fully charged.
Homemade Li-ion battery for an electric screwdriver turned out to 2.1 Ah (2100mAh). Versus the stock capacity of 1.2 Ah. The new battery weighs three times less.
Tested the product on disassembly of floor slabs. Just super, very happy with the result. Works great, doesn’t run down for long, draws power power.
Then I ran into a little disadvantage. When you forget to set the force on the electric screwdriver (drilling mode), especially when it sat down, then at high loads stopping the motor, the protection triggers. I do not know whether it’s good or not. If you’re also going to take not balancer, and a full controller, then buy a bigger load current, otherwise you’ll be sick of removing protection. Or look for a controller with autodischarge.
My controller is for a load current of 8A.
At first I used to take the second old battery with me, plugging it in removes the protection. Then I made a button that switches the circuit to direct operation without the controller and at the same time removes the protection with the battery voltage itself.
If you want you can buy a bank with a large capacity, but be careful in this plan solid fakes. The seller that I bought and constantly buy from has already been tested and its stated capacity corresponds to the real one.
Lithium batteries
Next, I bought 10 lithium batteries and assembled them into batteries, 2 pieces in parallel, and then connected the 5 resulting units in series. Solder the batteries together using pre-tempered copper plates. There is one basic rule for soldering. do not overheat the battery! So you have to solder with a powerful soldering iron and as fast as possible in 1-2 seconds. If you can not immediately make the connection it is better to wait and not to boil the battery.
The consequences of overheating can lead to fires and burns. Be careful!
Who has a spot weld. There will be no problems with the connection. As a result, we have assembled a battery with a voltage of 21 V and a capacity of 5.2 Ah. The connection of the battery to the control board is shown in the figure.
Then everything is packed into the case and tested under load.
I built an LM2596 module into the standard battery charger. The power supply should be a couple of volts more than the voltage of the charged battery. I set the no-load voltage to 21 volts. Then I connected the battery and set the charging current to 0.8 A. Why is it like this?? Because I found a 24V power supply with max. With a current of 0.8 A. I did not buy a special unit. It’s better to let it charge longer. This is not a production version but a home made tool.
In the process of charging revealed a small disadvantage. When the battery reaches full charge voltage, the charger has to switch from CC phase to CV phase. That is, firstly the battery is being charged with the current set (0,8 A in my case), and when you reach 21 V voltage is maintained at this level, and the current gradually decreases to 0,1Iust (in my case 0,08 A, set the middle potentiometer). That’s where the charging process stops. On this module the middle LED indicates this, but only signals that the battery is ready to work, but in fact charging continues, which is not critical in principle. The battery will not recharge anyway. And the downside is that because the control board has its own overcharge protection, it shuts down the charger before it reaches the CV phase.
To get around that, I had to reduce the charger module voltage to about 20.7-20.8V. CV phase starts earlier, but anyway the battery is charged more fully than without it at all. If you do not know about this small disadvantage, then you will not notice the difference in operation.
On the whole I like the finished device. Compared to what it was before it feels like this electric screwdriver. Specially for Radioschemes site. SssaHeKkk.
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Difficulties in remodeling
In Li-Ion batteries have objective disadvantages, such as poor performance at low temperatures. In addition, when converting an electric screwdriver to lithium 18650 batteries, you may encounter a number of difficulties:
- The 18650 standard means that one battery cell has a diameter of 18 mm and a length of 65 mm. These dimensions are not the same as the nickel-cadmium or nickel-metal hydride cells previously installed in an electric screwdriver. Replacing the batteries will require placing them in the regular case of the battery, plus the installation of a protective chip and the connecting wires;
- The output voltage of lithium cells is 3.6 V, while the nickel-cadmium cells are 1.2 V. Let’s assume that the nominal voltage of the old battery is 12 V. This voltage cannot be provided by connecting Li-Ion cells in series. The voltage fluctuation limits during the charge and discharge cycles of an ion battery also vary. Accordingly, converted batteries may not be compatible with an electric screwdriver;
- Ion batteries are specific in their operation. They can hardly withstand overcharge voltages over 4.2V and discharge voltages under 2.7V to the point of failure. Therefore, when remodeling a battery, the electric screwdriver requires the installation of a protection board;
- An existing battery charger may not be suitable for an electric screwdriver with a Li-Ion battery pack. You will also need to convert it or buy another.
Lithium-ion battery
Important! If your drill or electric screwdriver is cheap and not of high quality, it is best not to do the conversion. It can cost more than the tool itself.
Parts and tools for conversion
To convert your existing electric screwdriver to lithium batteries you must buy a battery charger:
- A soldering iron with at least 40 watts of power with a set of consumables, including acid flux;
- Small plumbing tools (screwdrivers, scalpel, etc.).п.).
The process itself is quite creative, depends on the initial conditions and the design of an electric screwdriver, so in the course of alteration, you may need something else. You have to be prepared for that.
Before you modify your power tool to run on Li-Ion batteries, you need to consider the future operating conditions. Lithium-ion cells are not suitable for low temperature applications.
Battery protection and battery controller redesign.
Now that we have the batteries taken care of, let us continue with our Li-ion battery modification of the electric screwdriver.
Lithium needs a protection controller. which will protect the battery banks from overcurrent, overdischarge, overcharging, as well as balance the banks when charging.
Of the ones I tried in terms of price/performance ratio, I liked this controller best.
Works great. Can handle the load. But there is a disadvantage. Protection is not removed automatically. To remove it, apply voltage to the battery or just put it on charge for a couple of seconds.
The second drawback on some screwdrivers can trigger protection with a sharp pull of the trigger of an electric screwdriver, and in general it is not set up for our banks (which can easily handle currents and larger), but based on the datasheet on the key transistors (which are also designed for a larger current) battery protection controller, it can be loaded.
Both defects I corrected as follows.
Revamping the lithium battery controller. On the picture of the board you can see two smd resistors labeled R010. Their rating is 0.01 Ohm each. They set the current at which the load will be triggered by the protection.
I added another resistor of the same 0.01 Ohm on their battery controller see. schematic at. You can also add a film capacitor to it, just useful, so that when you suddenly pull the trigger, the protection does not work.
The upper part of the circuit is responsible for the “Power” mode. When the switch is on the transistor switches do not work at all and there is no load on them. But also protection. Therefore this mode is better not to use.
The 15A fuse in this mode protects the current. Set to your liking. A bigger diode. I have two pulse diodes in parallel for 6A each (12A together).
You can connect a small digital voltmeter like this to monitor the discharge control.
Instead of voltmeter I’ve connected a home-made discharge indicator tuned to 12 volt. Its triggering coincides with triggering of the protection board when it works in normal mode.
For clarity, parallel to the discharge indicator (on the schematic is a voltmeter) connected a LED through a 2Kohm resistor to immediately see when the “Power” mode is on.
To work with an electric screwdriver, I practically do not use the “Power” mode, but it is necessary to remove the triggered protection. Just switch it on and off and you’re good to go.
This is how I got the switch to the “Power” mode. It is also used to reset the protection.
On the back are two indicators. The red LED indicates that the “Power” mode is on. The yellow light comes on when the power mode is turned on and the battery is down to 12 volts.
Also added a socket. USB with battery voltage. The main thing that no one by mistake did not put the phone to recharge:) I use it at the construction site to listen to the adapted receiver and LED lamp.
Already a month of testing a new modification of the battery under the lithium, now I like it all. Battery will not run out for a long time. The screwdriver can easily handle heavy loads.
There’s one more thing to do. Fast charging, like in the top models:)
How to rebuild and assemble?
Often the craftsman already has an old cordless electric screwdriver that suits him completely. But the device is equipped with outdated nickel-cadmium batteries. Since the battery pack will have to be replaced anyway, you might want to replace the old battery with something newer. This will not only provide a more comfortable operation, but also eliminate the need to search the market for batteries of an outdated model.
The simplest thing that comes to mind is to assemble a power supply from an electronic transformer in the case of an old battery. Now you can use an electric screwdriver by connecting it to a household power supply.
14 volt models.4 volt can be connected to car batteries. If you assemble the adapter-extender with terminals or the cigarette lighter plug from the casing of the old battery, you get an indispensable device for garage or work “in the field”.
If we are converting an old battery to lithium, we can take into account the fact that lithium cells of the 18650 standard are extremely widespread on the market. Thus, we can make batteries for an electric screwdriver based on readily available parts
over, the prevalence of the 18650 standard allows you to choose batteries from any manufacturer.
It is not difficult to open the case of an old battery and remove the old parts
It is important not to forget to mark on the housing the contact to which previously connected the “plus” of the old battery assembly
Depending on the voltage for which the old battery was designed, it is necessary to select the number of lithium cells connected in series. The standard voltage of a lithium cell is exactly three times that of a nickel cell (3.6 V instead of 1.2 В). Thus, each “lithium” replaces three “nickel” cells connected in series.
By combining three lithium cells in a row, you can make a battery with a voltage of 10 Volts instead of 1 Volt.8 volt. Among nickel batteries, these are found, but not often. If we daisy-chain four lithium cells, we get 14.4 volt. This will allow you to replace the nickel battery at both 12 volts and 14 volts.4 volt is a very common standard for nickel cadmium and nickel metal hydride batteries. It depends on the particular model of electric screwdriver.
Once you have determined the number of consecutive steps, you will probably find that there is still room in the old case. This allows you to connect two cells in each stage in parallel, which doubles the capacity of the battery. To connect lithium batteries together the manufactures use nickel tape. The strips of tape are joined to each other and to the lithium cells by means of contact welding. But soldering is perfectly acceptable in the home.
Soldering lithium elements should be done with extreme care. The connection area should be thoroughly cleaned beforehand and a good flux should be applied. The tinning is done very quickly, with a well heated soldering iron of sufficiently high power.
Soldering itself is made by rapid and sure heating of the place of connection of wire to the lithium element. To avoid the dangerous overheating of the cell, soldering time should not exceed three to five seconds.
The good thing is that now there are ready-made electronic control and balancing modules at fairly low prices. It’s enough to choose the solution that suits your case. Basically such controllers differ from each other by the number of “steps” connected in series, the voltage between which is to be equalized (balanced). In addition, they differ in allowable load current and the way of temperature control.
In any case, you can no longer charge a homemade lithium battery with an old battery charger for nickel batteries. They have fundamentally different charging algorithms and reference voltages. You will need a specialized charger.
How to rebuild and assemble?
Often the handyman already has an old cordless electric screwdriver that suits him completely. But the unit is equipped with outdated nickel-cadmium batteries. Since the battery pack will still have to be replaced, there is a desire to replace the old battery with something newer. This will not only provide a more comfortable operation, but will also eliminate the need to search the market for batteries of an obsolete model.
The easiest thing that comes to mind is to assemble a power supply from an electronic transformer in the housing of the old battery. It will now be possible to use an electric screwdriver by connecting it to a household power supply.
14-volt models.4 volt can be connected to car batteries. If you assemble the adapter-extender with terminals or the cigarette lighter plug from the casing of the old battery you get an indispensable device for the garage or work “in the field.
If you want to convert an old battery into lithium, you can take into account the fact that lithium 18650 cells are extremely widespread on the market. So we can make electric screwdriver batteries from readily available parts
over, the prevalence of the 18650 standard allows you to choose batteries from any manufacturer.
It is not difficult to open the casing of the old battery and remove the old stuffing from it
It is important not to forget to mark on the housing the contact to which the “plus” of the old battery pack was previously connected
Depending on the voltage at which the old battery was designed, you need to find the number of lithium cells in series. The standard voltage of a lithium cell is exactly three times that of a nickel cell (3.6 V instead of 1.2 В). Thus, each “lithium” replaces three “nickels” connected in series.
By providing a battery design in which three lithium cells are connected one after the other, you can get a battery with a voltage of 10.8 volt. There are some of these amongst the nickel batteries, but not very often. If you daisy-chain four lithium cells, you get 14.4 volts. This will replace a 12 volt nickel battery as well as a 14 volt battery.4 volts is a very common standard for Ni-Cd and Ni-MH batteries. It depends on the particular model of electric screwdriver.
After you have managed to determine the number of consecutive steps, you will probably find that there is still room in the old case. This allows two cells to be connected in parallel in each stage, doubling the capacity of the battery. To connect lithium batteries to each other in manufacturing plants, nickel tape is used. The strips are connected to each other and to the lithium cells by means of contact welding. But soldering is okay in the home.
Solder lithium cells with extreme care. The connection place should be carefully cleaned beforehand and good flux should be applied. The tinning is done very quickly, with a well heated soldering iron of sufficiently high power.
Soldering itself is done by quickly and surely warming up the connection point of the wire to the lithium element. To avoid the dangerous overheating of the element, soldering time should not exceed three to five seconds.
The good thing is that electronic control and balancing modules are now available at fairly low prices. Just choose the right solution for your application. In general, such controllers differ in the number of “stages” connected in series, the voltage between which is to be equalized (balancing). They also differ in the permitted load current and the way the temperature is controlled.
In any case, you can no longer charge a homemade lithium battery with the old charger for nickel batteries. They have fundamentally different charging algorithms and reference voltages. You will need a special charger.
Which Lithium Battery to Choose?
In 7 of 10 screwdrivers, 12-volt batteries are used.
Voltage is a decisive factor in your choice. It can be specified in the technical documentation to the device, on the Internet.
- Discharge current value. Screwdrivers are powered by batteries with a high discharge current. Consult the technical documentation to determine the appropriate rating for your particular model. It is a mistake to choose a battery only by its capacity, because the main parameter is the current. It can range from 15-30 A, sometimes up to 40 A.
- Characteristics of lithium-ion cells. 18650 batteries must have the same capacity specifications.
- Number of new batteries. Easy to calculate. The ratio is as follows: 3 Ni-CDs equal 1 Li-ion. Replace the old 12 volt block with a block of 3 lithium-ion cells.
When calculating the number of new sources remember that higher voltage (for example, instead of 3 Li-ion instead of 10 Ni-CD take 4 lithium batteries) will increase wear and tear of the equipment, reduce the life of. But the power will increase. You therefore have to weigh up the pros and cons. Do not rush the installation of sources in the tool. They need to be fully charged first.
which lithium battery to choose?
In 7 out of 10 screwdrivers, 12 volt batteries are used.
Voltage is a decisive factor when choosing a battery. You can look it up in the tool’s data sheet, on the Internet.
- What is the Discharge Current. Screwdrivers are powered by batteries with a high discharge current. Check the datasheet to determine the appropriate setting for your particular model. It is a mistake to choose a battery only by its capacity, because the main parameter is the current. It can range from 15-30 A, sometimes up to 40 A.
- Characteristics of lithium-ion cells. Batteries of 18650 standard must have the same capacity.
- The number of new batteries. Easy to calculate. Ratio is as follows: 3 Ni-CD equals 1 Li-ion. Replace 12 volt old block with a block of 3 lithium-ion cells.
When calculating the number of new sources remember that the increased voltage (for example, instead of 3 Li-ion instead of 10 Ni-CD take 4 lithium) will increase wear and tear of the equipment, will shorten its life. But the power will increase. So you need to weigh the pros and cons. Do not rush with the installation of sources in the tool. Firstly they must be fully charged.
Instructions for setting up the charger
Everything fits the snaggy description)). Works fine. I will use it to charge my converted electric screwdriver. Reached Samara in 25 days. For those who can’t figure out how LEDs work, I found a great description:
upper LED is light until inverter is able to supply the load with the current laid down (in case of using it as a charging one it will be a CC phase indicator, as soon as it goes out. CV phase has started) middle LED is light until the current in the load comes down to 0.1 set, went out. charge terminated.
value 0.1 is set by default, if you want it can be adjusted upwards (charging faster, capacity less) or downwards (charging time increases, the battery is charged more fully) with the middle potentiometer. But the charge continues even after it is turned off, it is only an indication that the battery is basically charged and ready for use. lower LED is just an indicator of the working of the inverter.
charge. this indicator is lit until the current in the output circuit is above the set value. This value is set in relation to the maximum current. If you set a large maximum current (units of amperes) it may not be possible to set the display to a small current (units and tens of milliamps).
Which BMS card is needed and how to connect it
Lithium 18650 batteries are afraid of overcharging and deep discharging. no synchronized cell operation can be guaranteed when cells are connected in series. If one bank has a lower capacity, it will replenish energy faster than the others when charging, and overcharging will occur. If a lower capacity battery is used, it will discharge faster than the others and may lead to a deep discharge.
All of these problems can be solved by the balancing protection board. BMS boards:
- protect against short circuits;
- recover when the protection is triggered;
- monitor the voltage of each bank and disconnect the load when at least one of the cells is completely discharged (deep discharge protection);
- Perform balancing (overcharge protection).
BMS board for electric screwdriver must be able to withstand a maximum peak current of at least 30A. In addition, when selecting, you should be guided by the number of banks connected in series. A 12 volt electric screwdriver requires 3 batteries, choose a 3S board. If you need 14 volts, you buy a 4S, and for 18 volts, you buy a 5S.
How to connect 2, 3 or 4 banks in series to BMS board is shown in picture.
You can also use a mixed, series-parallel connection. In this case, connect the same number of batteries in parallel to the banks connected in series.
charger
Just need to figure out how to charge the tool. It cannot be connected to a standard power supply. You need a battery charger.
In most cases, native accessories have no problem charging lithium batteries.
Charge comes through the controller. If the factory unit is not suitable, it is remade by adding the missing circuit elements. These include charging termination assemblies, safety components, etc. The circuit is finalized for the main determinant, the charging current.
It is not cost-effective to retrofit the charger circuit if it is thoroughly reworked. Easily interchangeable with general-purpose equipment or buy new. Even with the purchase of the charger, the owner of an electric screwdriver acquires a powerful tool with extended battery life at a minimal cost.