Accumulators and batteries What is the difference between a lithium battery and a nickel-cadmium battery. Calculation of t component schemes of alteration. Operating conditions of the lithium battery. Features of alteration of batteries and chargers from different manufacturers.
The meaning and procedure for converting screwdrivers to lithium batteries
Why do nickel-cadmium batteries fail quickly? In a garland of series-connected cans, each is special. The chemical process is individual, the charge in closed systems is different. In the event of a malfunction in one bank, the design does not provide the required voltage. There is no provision for monitoring and balancing the charge in individual components.
- Each Ni-Cd bank provides 1.2V and the li-ion 18650 3.6V.
- The capacity of a lithium battery is 2 times that of a nickel-cadmium battery of similar size.
- An overheated li-ion battery threatens an explosion and fire, therefore, the installation of control of the uniformity of the charge in the banks is mandatory. The manufacturer is not interested in BMS nickel-cadmium batteries.
- Lithium cells have no memory effect, unlike Ni-Cd, they can be charged at any time and within an hour.
- The screwdriver becomes much easier after converting the battery to li-ion, using 18650 cells.
There are only two obstacles to converting a screwdriver for lithium batteries, it is impossible to work with it at minus. The capacity of cans decreases, starting from a decrease already from 10 0 C. Lithium batteries are expensive.
Knowing what input voltage is required for the screwdriver, the charger is reworked, taking into account the placement of the lithium battery cells and control elements in the factory container. You can also do with a flashlight by upgrading the socket for a block of 18650 cells.
Let’s say you need to rework a 12 V screwdriver using Ni-Cd cans on li-ion. If you use 3 cans, the output voltage is not enough: 3.6 x 3 = 10.8 V. With 4 components, the power of the apparatus will be higher: 3.6 x 4 = 14.4 V. This will make the instrument 182 g lighter , its power will slightly increase, the capacity is solid pluses. But when dismantling, it is necessary to leave the terminals and the native thermal sensor.
Converting a Makita screwdriver to a lithium battery
There is a Makita screwdriver with a 1.3 A / h battery and a voltage of 9.6 V. To change the power source to a lithium-ion one, you will need 3 18650 components. Alteration will give the old tool new opportunities: power, as the operating voltage rises to 10.8 V.
The design will require the use of a BMS, a control controller that maintains the lithium cell operating mode within operating limits. With this breaker, each cell will be charged evenly without exceeding 4.2V, lower voltage 2.7V. A built-in balancer is used here.
The parameters of the controller should accompany the operation of the instrument when the operating current rises to 10-20 A. The Sony VTC4 30 A board, designed for a capacity of 2100 A / h, can ensure operation without shutdown. Of the 20 amperes, the Sanyo UR18650NSX accepting energies of 2600A / h is suitable. The board is needed for 3 elements, which is marked in the 3S classification. In this case, the board must have 2 contacts, plus and minus. If the conclusions are designated with the letters P-, P, C-, they are intended for later models of screwdrivers.
A step-by-step instruction on how to convert a Makita screwdriver to lithium batteries looks like this.
- You can disassemble the battery with glue if you tap the junction with a soft-headed hammer while weighing. The direction of impact is downward, into the joint on the lower part of the body.
- Take only contact plates from the old assembly, carefully disconnecting them from the battery. Leave the sensor and breaker.
- Solder 3 elements in series using TAGS flux and insulated jumpers. The wire cross section must be greater than 0.75 mm2.
- Assemble the circuit with the controller, and connect the power supply to the contact connectors with 1.5 square wires.
- Check the functionality of the circuit and reassemble the case by placing it on the glue again.
In a screwdriver with an old DC9710 charger, after charging the 18650 lithium battery, the red LED on the panel will turn off. The built-in controller monitors the charge level.
The Makita DC1414 T charger is used to charge 7.2-14.4 V power sources. While charging, the red light is on. But when charging a lithium battery, its voltage does not fit into the standards of salt products, and after 12 V, the charger will flash red and green. But the required charging is already there. The screwdriver is ready for use.
Conversion of a screwdriver to lithium batteries 18650
Every craftsman is faced with the problem of reduced tool performance, or complete failure due to the battery. Manufacturers use nickel-cadmium batteries in 12, 14, 18 volt screwdrivers. The sequential assembly of several elements creates the required voltage. Replacing nickel-cadmium batteries with lithium batteries extends battery life, making the design easier. Mandatory BMS board installation adds reliability. Therefore, the conversion of a screwdriver to lithium batteries, mainly to the 18650 form factor, is justified.
The arguments against
- Lithium battery cells cannot be charged above 4.2 volts and discharged below 2.7 volts. In real conditions, this interval is even narrower. If you go beyond these limits, the battery can be damaged. Therefore, in addition to the lithium cans themselves, you will need to connect and install a charge-discharge controller in the screwdriver;
- The voltage of one Li─Ion cell is 3.6─3.7 volts, and for Ni─Cd and Ni─MH this value is 1.2 volts. That is, there are problems with assembling a battery for screwdrivers with a voltage rating of 12 volts. From three lithium cans connected in series, you can assemble a battery with a nominal value of 11.1 volts. Out of four ─ 14.8, out of five ─ 18.5 volts, and so on. Naturally, the voltage limits during charge-discharge will also be different. That is, there may be problems with the compatibility of the converted battery with a screwdriver;
- In most cases, 18650 standard cans are used in the role of lithium cells for conversion. They differ in size from Ni─Cd and Ni─MH cans. In addition, you will need space for a charge-discharge controller and wires. All this will need to fit in a standard battery case of a screwdriver. Otherwise, it will be extremely inconvenient for them to work;
- A cadmium battery charger may not be suitable for recharging a battery after a redesign. You may need to revise the charger or use universal chargers;
- Lithium batteries lose their performance at low temperatures. This is critical for those who use a screwdriver outdoors;
- The price of lithium batteries is higher than cadmium batteries.
What do you need to estimate before starting work?
Also, more lithium cells will give more capacity. This means more operating time of the screwdriver.
Lithium battery cells 18650
The nominal voltage of lithium cells is 3.6-3.7 volts, and the capacity in most cases is 2000-3000 mAh. If the battery case allows, you can take not 4, but 8 cells. Connect them two by two in 4 parallel assemblies, and then connect them in series. As a result, you will be able to increase the battery capacity. But not every case will be able to pack 8 cans of 18650.
And the last preparatory stage is choosing a controller. According to its characteristics, it must correspond to the rated voltage and discharge current. That is, if you decide to assemble a 14.4 volt battery, then choose a controller with this voltage. The working discharge current is usually chosen to be two times less than the maximum permissible current.
Charge-Discharge Controller Board
Converting the battery of a screwdriver to lithium cells
Many screwdriver owners want to convert their batteries to lithium battery cells. Many articles have been written on this topic and in this material I would like to summarize information on this issue. First of all, we will consider the arguments in favor of converting a screwdriver to lithium batteries and against it. And also we will consider certain moments of the process of replacing batteries itself.
Conversion of a screwdriver to lithium batteries 18650
The first question that arises when it comes to replacing batteries in a screwdriver with lithium is the expediency of the time and effort expended and what benefits we will get in the end. So let’s take a look at the pros and cons.
Redesigning the charger for a lithium battery screwdriver will give the following advantages:
Increasing the operating time of the screwdriver several times.
Device recharge speeds. You can charge the screwdriver in 1 hour.
High power charging current. New generation batteries have up to 1-2C.
Save money on battery replacement.
Lithium-ion batteries have no memory effect.
Where to begin?
- We determine the nominal voltage value, for this we calculate the number of elements. For three cells 12.6 volts, for four 16.8 volts.
We take a battery with a voltage of 14.4 volts as a basis. In this case, it is more correct to take four elements, this will not only equalize the slight difference in volts, but a larger number of elements will increase the capacity, and hence the operating time of your screwdriver.
- Choosing lithium cells. In our opinion, the best option is the 18650.
- Let’s figure out the discharge current and capacity. During normal operation of the screwdriver, the current consumption is in the range of 5-10 amperes, with a sharp start, the current jumps to 25 amperes. Therefore, we select cells with a high discharge current value of up to 30 amperes, so as not to damage the battery during current surges.
- Body capacity and capacity increase. It is possible to use 8 cans, instead of 4. To do this, connect two elements in parallel, and then connect the connected pairs in series. However, not every battery case can accommodate 8 18650 cells.
- Choosing a controller. The controller must match the rated voltage and discharge current. That is, the voltage should be the same for the controller and the battery, but the operating discharge current is two times lower than the limit. In numbers, it looks like this: the charge-discharge controller is calculated for 12-15 amperes, then the protection will work with a sharp jump in current up to 30 amperes. We also remind you about the size of the protective board, it must fit into the battery case of the screwdriver.
Alteration of the charger of the screwdriver for lithium batteries
When all the elements are ready, we begin the collection process. For example, we considered the conversion of a 12v screwdriver to lithium batteries, inside which there are 12 nickel-cadmium cans of 1.2 volts each. First, we disassemble the battery case and remove the nickel-cadmium batteries using wire cutters. Leave the connector in place.
We install the controller and the thermocouple instead of the temperature sensor. Remember to carefully select the correct size for your case.
Next, we turn to the main task: it is necessary to sequentially solder the prepared elements. Then solder the controller according to the diagram. Remember to connect the balancing points. As a rule, a connector and wires are provided for them on the board.
When the battery is ready, you need to solder the leads for plus and minus and place the structure in the case.
This completes the process.
As a rule, there are no difficulties with a standard charger when charging lithium cells. And since the charge goes through the controller, you don’t have to worry about a new battery.
External power supply
The idea is not as absurd as it might seem. Even a large and heavy buck rectifier can just stand near the outlet.
You are equally tied to the power supply, and to the stuck mains plug. And the low-voltage cord can be made of any length.
IMPORTANT! Ohm’s law says at the same power, by decreasing the voltage, we increase the current strength! Accordingly, the 12-19 volt supply cord should have a larger cross section than 220 volts.
Making a homemade power supply
If you are familiar with the principles of building electrical circuits, you can make your own power supply. Diagram giving general concepts in the illustration.
The transformer can be picked up from an old tube TV, or other household appliances. Power 220 volts 250-350W. The main thing is that the donor power supply should not be pulsed.
The voltage on the secondary winding is 24-30 volts. The secondary winding is made from a wire of the corresponding section.
However, if the output winding current is at least 15 amperes (see transformer specification) there is nothing to worry about.
After the losses on the diode bridge (1-1.5 V on the diode), you will get the required output value.
If you have an electrical engineering education, make the calculation yourself. Or in a practical way: by connecting a 220 volt 100W incandescent lamp as a load, measure the output voltage. E
If it exceeds the needs of the screwdriver, reduce the number of turns of the secondary winding of the transformer.
Using a power supply from a personal computer
On the radio market, you can purchase an old power supply from a personal computer for a small cost. We need a variant of the AT format, which had to be turned off with the key after exiting the operating system.
Experienced users remember such system blocks. The advantage of such a power supply is also that it indicates an honest power. If it says 300W, it means you can safely remove 15-16 amperes from the 12-volt output (again referring to Ohm’s law). This is enough to power an average screwdriver.
Such blocks have a power button in the kit. Another advantage is the presence of a cooling fan and an advanced overload protection system.
If you will hide the power supply in a beautiful case, do not forget to leave a hole for ventilation.
The connection is very simple. Black wire (-), yellow wire (12V).
Limitations A screwdriver with a supply voltage higher than 14 volts will not work.