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Screwdriver rework on lithium batteries: instruction

The conversion of the screwdriver to lithium batteries makes sense. The advantage is that they have a high electrical density. As a result, having installed such a device in the screwdriver case, we can achieve an increase in the tool life many times. The charging current for high-capacity lithium batteries, especially for new modifications, can reach 1-2 C. It can be recharged in 1 hour, without overestimating the parameters recommended by the manufacturer and not degrading the quality of the product.

What do lithium batteries look like?

Most lithium devices are enclosed in a prismatic case, but some models have a cylindrical shape. In such batteries, roll electrodes and separators are used. The body is made of aluminum or steel. The positive terminal goes to the housing cover.

In prismatic configurations, the electrodes are rectangular plates. To ensure safety in the battery, a device is provided that acts as a regulator for all processes and disconnects the electrical circuit in critical situations. The increased hermetic sealing of the housing does not allow the electrolyte to flow outward and penetrate into the oxygen and moisture.

What measures should be taken to avoid damaging the lithium battery?

  • Due to technology limitations, the charge indicator of lithium batteries should not be higher than 4.25-4.35 V. The discharge should not reach the index of 2.5-2.7. This condition is indicated in the technical passport for each particular model. If you overestimate these values, you can disable the device. Special charge and discharge controllers are used, which keep the voltage on the lithium cell within normal limits. The conversion of a screwdriver to a lithium battery with a controller will protect the device from a malfunction.
  • The voltage indicator of lithium batteries is a multiple of 3.7 V (3.6 V). In Ni-Mh models, this figure is 1.2 V. This phenomenon is understandable. The nominal voltage in lithium devices is stored in a separate cell. A 12 volt lithium battery will never be assembled. The nominal value will be 11.1 V (three consecutive cells) or 14.8 V (four consecutive cells). In addition, the voltage of the lithium cell changes when working at full charge by 4.25 V, and at full discharge - by 2.5 V. The voltage indicator 3S (3 serial - three serial connections) will change when the device functions from 12.6 In (4,2х3) to 7,5 V (2,5х3). For the 4S configuration, this index varies from 16.8 to 10 V.
  • The conversion of a screwdriver to 18650 lithium batteries (the overwhelming majority of products possess this size) requires taking into account the difference in dimensions with Ni-Mh-cells. The diameter of the cell 18 650 is 18 mm, and the height is 65 mm. It is very important to calculate how many cells will fit in the case. It should be remembered that for a model with a capacity of 11.1 V you will need a number of cells, a multiple of three. For a model with a power of 14.8 V - four. The controller and the patch wires must also fit.
  • The charging device for a lithium-based battery is different from the Ni-Mh modification device.

The article will consider how the screwdriver is reworked on lithium Li-Po batteries. The instrument is equipped with a pair of Ni-Mh-storage batteries with a voltage of 12 V and a capacity of 2.6 Ah. We will consider the conversion of the Hitachi screwdriver. Lithium batteries will provide the device with a long service.

Select the nominal voltage

First of all, you should determine the voltage rating for the lithium-based device. The choice should be made between the 3S-model (the range of its voltage is from 12.6 to 7.5 V) and 4S-Li-Ion-battery (voltage range - from 16.8 to 10 V).

The advantages of the second option

The second option is more suitable, because the voltage in the battery falls fairly quickly from the maximum to the lowest level (from 16.8 to 14.8 V). For an electric motor, which, in fact, is a screwdriver, an excess of 2.8 V is not a critical mark.

The lowest voltage in the 3S-Li-Ion modification. It is 7.5 V, which is insufficient for the normal operation of the electrical device. Having mounted four configurations, we will increase the electric capacity of the battery.

How to decide on the choice of lithium cells?

To select the cells based on lithium, it is necessary to outline the limiting factors. Currently, lithium devices are manufactured with an allowable current load of 20-25 A.

Pulse current values (short, up to 1-2 seconds) reach 30-35 A. The battery configuration will not be disturbed.

How many cells fit into the case?

Collect 4S2P (four consecutive connections and two parallel) will not work. The conversion of the screwdriver to lithium batteries 18650 assumes the presence of eight cells. How can they meet at four? Each cell is subjected to the maximum current load.

How to determine the peak current indicator in a screwdriver?

Remaking 12V screwdriver on lithium batteries involves connecting the device to a laboratory power source with an indicator of a maximum current of 30 A. The limiter control is set to the maximum value. Having created the voltage level of the power supply close to the nominal value of the future battery, we start smooth pressing the trigger. The current, which is consumed by the screwdriver, will rise to the mark of 5 A. Now it is necessary to sharply pull the trigger. This shorts the power circuit. The current will reach a power of 20-30 A. Perhaps its indicator would be much higher, but the power supply's power will not let it fix. This will be a short load current when you suddenly press the trigger of the screwdriver. Any model of such a device will react similarly.

Then, tighten the tip of the screwdriver with the clamps and observe to what value the consumption current will increase at the operating mode, when the ratchet will operate in the screwdriver. The current index in this case increases to 10-12 A.

So you can determine the value of the load current. In this case, it will be equal to 5 A at idle and 30 A at a sharp start, and with a maximum load of 12 A. The manufacturer must select lithium cells whose nominal load current will be 10-20 A, and the pulse rate will be 25-30 A.

How to choose a controller?

So, there is a reworking of the screwdriver on lithium batteries. Regular charging for the device is required. When choosing a controller, please note that the device must meet two parameters:

  • The indicator of the rated operating voltage;
  • Rated operating current.

With voltage everything is extremely clear: if the battery is 11.1 V, then the controller will have the same voltage.

The term "rated operating current" implies the bandwidth of the protection board. Thus, the controller at 4 A is rated for a current mark of 4 A, and at an indicator of 8 A it is subject to additional load. In this case, the protective device will work. All these technical data are stated in the passport of each modification of the controller. In this case, one modification can have a current limit of 30 A, and the other is 50 A. And both of these devices will formally be suitable for operation. Also, when creating a lithium battery, there is a limitation in size. Therefore, you should purchase a controller that fits in the old battery case.

Disassembly and assembly

The conversion of the screwdriver to lithium batteries includes the following steps:

  • Open the old battery by unscrewing the five screws.
  • Remove the Ni-Mh battery from the case. It will be appreciable that the contact pad, which is engaged with the contact group of the screwdriver, is welded to the minus contact of one of the Ni-Mh cells. The welding points should be cut using a tool with a DREMEL 4000 cut-off stone embedded in it.
  • The wires are soldered to the contacts, the cross section of which is at least 2 mm 2 for the power terminals and 0.2 mm 2 for the thermistor. The contact area is pasted into the battery case by hot melt.
  • On the measure of internal resistance on the meter, four cells are selected. The value must be the same for all four instruments.
  • Lithium cells are glued with hot-melt adhesive so that they are located in the body compactly.
  • Welding of the cells is carried out on the machine for contact welding by means of a welding tape made of nickel (the index of its cross section should be equal to 2X10 mm).

Installing the protection card

This stage can show how much easier the design of the lithium battery is. The weight of the device Ni-Mh was 536 g. The weight of the new device from lithium is 199 g, which will be quite noticeable. The weight managed to win 337 g. At the same time, an increase in the energy capacity is observed.

The battery is mounted in the housing. The voids are filled with soft material from the packaging.

Screwdriver connection

  • A sharp pull on the trigger triggers the current protection mechanism. But in fact, such a protective mode is unlikely to be needed when using the tool. If you do not provoke protection specifically, the work of the screwdriver will be stable.
  • The tip should be clamped in a vice. The battery power freely triggers the operation of a ratchet, which limits the increase in the number of twisting speeds.
  • The lithium battery of the screwdriver is discharged on the electronic load. The discharge current should be equal to 5 A.
  • The battery is inserted into the staff memory. The charge current for the measurement is 3 A, which is acceptable for lithium cells. For the LG INR18650HG2 configuration, the maximum charge current will be 4 A, as indicated in the technical specification.

How long does it take to replace the batteries?

The conversion of the screwdriver to lithium batteries will take approximately 2 hours. If all parameters are checked, then it will take 4 hours.

You can do everything yourself, without the help of another person. But contact welding and the choice of batteries without specialized equipment is not carried out.

How can I test the degree of charge other than the controller?

The screwdriver is reworked on lithium batteries. Stand-by charging, built into the case, is an ideal option. But the cost of the controller is quite high. The device costs $ 30, which is equivalent to the cost of the battery itself.

To test the battery charge level from lithium on the go without using the charger, you can use the special indicator RC helicopter lipo battery AKKU portable voltage meter tester alarm 2-6S AOK. The cost of the device is very low. It has a balance and charging connector similar to the iMax6 device. The device is connected to the battery by means of an adapter. This device for monitoring the voltage level is very convenient. It can measure from two to six consecutively connected cells from lithium, as well as give the total index or voltage of each element individually with the utmost precision.

How much will it cost to replace Ni-Mh with a lithium device?

How much money will it take to re-engineer the screwdriver on a lithium battery?

The price for such a device consists of the cost of several components:

  • The configuration of a lithium-based 4S-battery costs 2200 rubles;
  • The purchase of a controller for charging and discharging plus a balance beam costs 1240 rubles;
  • The cost of welding work and assembly is 800 rubles.

It turns out that the lithium battery made by own hands, costs in 4240 r.

For comparison, let's take a similar configuration from lithium factory production. For example, the device Makita 194065-3 is designed for screwdrivers. It has similar parameters. The cost of such a device is 6500 r. It turns out that the conversion of the screwdriver to lithium batteries saves 2300 r.

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