Replacing nickel cadmium batteries in an electric screwdriver

How to repair the battery for an electric screwdriver: fault detection and repair

How to repair the battery for an electric screwdriver. this is a frequently asked question among home masters, because this device is in the arsenal of almost every owner. The main advantages of the battery-powered tool are its compact size, the ability to work with it even at height (due to the lack of power supply wires). Nevertheless, the battery of this device can fail, and it is not profitable to buy a new one, because its price sometimes reaches up to 60% of the cost of the tool. Therefore, it is recommended to try to restore the battery. how exactly, we will tell you today.

Despite the variety of models of these tools, the battery in all screwdrivers has a similar appearance. It is a box made of plastic, which contains many constituent elements. They are fastened to each other in a single circuit so that the wires of the “cans” on both sides are shorted to the contacts, which provide power to the screwdriver.

The design of an electric screwdriver

All batteries have a primitive structure, with which even an inexperienced technician, who knows little about electronics, can understand. In addition to the power parts in the box of the unit are often located:

  • A thermistor to allow the temperature of the jars to be controlled during charging;
  • thermal switch. automatically opens parts of the circuit in case of battery overheating;
  • A control and monitoring board (only lithium-ion batteries have one).

2) High-current batteries

Good banks are needed with a current output of at least 15A. Ideal on the price/quality ratio LG HE4 2500mah (yellow “bananas”), Samsung 25R 2500mah, Samsung 30Q 3000mah and LG HG4 3000mah (“chocolate”). Liitokala, Varikore, and other brand repackages will also work for a screwdriver.

LG HG4 3000mah with welded contacts. HERE

Another option with welded contacts is HERE

than a few thousand orders everywhere, normal quality.

Types of batteries

In terms of design features, a distinction is made between batteries in the form of a slider and a cage.

Screwdriver battery in the form of a slider

But these are minor differences compared to the types of batteries. Both the slider and the cradle are used in different types of batteries.

There are three types of screwdriver batteries:

Lithium polymer batteries (Li-Pol) are not made for screwdrivers. Their main applications: smartphones, cell phones, tablets, laptops, radio-controlled devices, electric cars.

Nickelcadmium batteries are the cheapest, fastest to charge, have over a thousand charge cycles. Batteries are resistant to low temperatures. But they have a memory effect. That is, they can only be charged when fully discharged, otherwise the capacity will drop. They have a high self-discharge current. They are made of toxic materials and are difficult to dispose of. These batteries are the most in demand.

Nickel. metal hydride batteries are more expensive, non-toxic, have low memory effect. Self-discharge current is greater than that of nickelcadmium batteries. Higher capacity, charge cycle over five hundred. These batteries can not withstand high rates of discharge. They are less suitable for the maximum capacity of the tool. They need to be constantly recharged.

Lithium-ion batteries are more expensive, powerful, fast-charging. They have no memory effect. Low self-discharge current. Battery cell voltage is greater, so there are fewer cells. Therefore the dimensions and weight of such batteries are smaller than those of nickel batteries. But they must not be completely discharged, otherwise after a few such cycles you have to buy a new one. In order to improve the quality of lithium-ion batteries, manufacturers install in the battery or screwdriver housing a microchip that controls the operation of the battery. A multi-level, multi-stage protection is formed:

  • From high temperature.
  • From complete discharge. These batteries are afraid of total discharge and can not recover if the discharge is below the limit.
  • From short circuits.
  • From overcharging, because it can explode.
  • From overcurrents.

The control board installed in the battery case is more effective. When the battery is not in use, the chip monitors the screwdriver and opens the circuit if there is a problem. The battery is fully protected.

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Replacing electric screwdriver batteries

Without thinking too much, I bought a 18650 lithium-ion battery pack. Since my electric screwdriver is 18 volts, and one battery gives out 3.7 volts, therefore, I needed 5 batteries. 5×3.7=18.5V is what you need.I also bought battery compartments, one for two batteries and one for three. Wired everything in series. Remove the old batteries and replace them with new ones.

Fault Determination and Repair of an Electric Screwdriver Battery

Before proceeding to repair the battery, you should determine its fault, otherwise the repair will be quite difficult or quite impossible. It should be noted that the failure of all cells at the same time the battery is impossible, except in rare cases where there may be a long short circuit of the battery output terminals.

To determine the malfunction, you should:

  • Place the battery on charge and wait until it is fully charged.
  • After that disassemble the case, and measure the voltage of each charging cell. The difference in voltage across the banks for nickel cadmium batteries may be in the range of 1.2-1.4 V, and the difference for lithium batteries may be about 3.8 V.
  • Banks that have less than the rated voltage should be marked. After that, the battery must be reassembled and given a full load until a noticeable discharge.
  • Then disassemble the battery again and measure the voltage of each bank again.
  • Usually the biggest voltage sag will be in the marked cells, which will need to be “resuscitated” or simply replaced.

If the electric screwdriver requires 12 V voltage to work, you can try to find faulty cells in a simpler way. To do this:

  • Make a full charge of the battery, then disassemble it and measure the voltage of each cell.
  • Then use a 12 volt light bulb to discharge it completely and measure the voltage of all the cells again to determine which ones are faulty.

Instead of a light bulb, you can use a suitable voltage resistor.

Repair and replacement of electric screwdriver battery cells

The most effective method, how to restore the battery of an electric screwdriver is a simple replacement of the failed charging elements that were found during their inspection.

To make the repair, you will need a donor, that is, a second battery, which also has failed banks, if such is not available, you can buy new cells online. Today there are enough online stores that are ready to deliver new batteries directly to your home by courier service.

Important. Acquired elements must be exactly the same in their capacity and dimensions as those being replaced.

For the repair you will need to prepare: a soldering iron, tin solder and alcohol flux (preferably).

The process of replacing the charging cells itself does not provide any difficulty, as long as you are skilled in soldering.

Restoring an electric screwdriver battery

Warning. To avoid damaging the battery when working with a soldering iron, soldering must be done quickly.

It is recommended to use the native plates to connect the cells, and if it is impossible to use them, completely replace them with the same size, but made of copper. This is essential for the correct charging process. If the cross-section of the connecting plates between the cells is different, they will heat up, and of course a thermistor will be continuously activated to protect the charging jars.

Care should be taken when assembling the batteries. The connection should be sequential. the minus of each battery is connected to the plus of the next cell.

After all the cells have been completely reassembled, their potentials will be equalized, since they will be different at that time. This requires a certain charging/discharging cycle. The repaired battery is fully charged, after which it should stand for about 24 hours. After one day the voltages of all the cells should be measured separately and if the assembly has been done correctly the voltage reading of each cell should be 1.2 V.

After this time the battery should be fully discharged again. To do this, the assembled battery, with an electric screwdriver, is given a full maximum load until it is completely discharged. The main thing is not to overload the electric screwdriver itself, so it won’t have to be repaired in the future. This charging/discharging procedure must be repeated several times in succession.

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In the same way, about every three months, it is recommended to perform the procedure to erase the “memory effect”, which will prolong the life of the battery and the electric screwdriver itself.

Repairing the battery of an electric screwdriver

Well, now let’s move directly to the restoration of the electric screwdriver. Remove the top cover of the battery pack.

So as not to forget how the batteries are placed inside, I made a peculiar map on paper with their positions and poles. Do the same so you don’t have to worry about where it goes.

Now you can disassemble this bundle to free the power terminals, which are just needed later.

Generally speaking, closed batteries do not solder. The jumpers should be welded by means of contact welding. But since we don’t have one, we use a powerful soldering iron to quickly solder it on.

Flux the pole, put the jumper and solder with the hot soldering iron quickly, keeping the tip for no more than 1-2 seconds.

At the end we glue the common insulating pads back on both sides and assemble the block in reverse order. Measure the voltage at the output terminals. It must be in the neighborhood of 14.4 В. If so, then the sequence of switching on the batteries is correct. Charging.

That is how you can put an electric screwdriver back to work, easily and without unnecessary manipulation, and it will last a very long time, if it is properly maintained.

BMS board

BMS (Battery Management System). The BMS board is extremely important when converting an electric screwdriver to lithium. Why we need it and how it works? It controls the charge and discharge, preventing over-discharge and over-charge of the electric screwdriver battery, it has a built-in “balancer” that separately charges each Li-Ion battery in the assembly. The latter is very important! There are BMS without balancer! 3S. 12v, 4s. 14v, 5s. 18v To choose a BMS board, you must consider that the minimum current must be 30A, otherwise it will go into protection.

The BMS-board option on the link is 2-3 more expensive than some basic versions, but you get 100A instead of 30A or 40A. In my opinion, in terms of functionality, this is the best BMS board from aliexpress and deserves this token overpayment.

But is this a good replacement?

  • 1. Li-ion batteries are more expensive. You will have to shell out 250- 500 for one.
  • 2. The next disadvantage is their fastidiousness to charging. they don’t tolerate overcharging or overdischarging and, frankly, they are better charged with a “smart” charger that reduces the current delivered to the batteries when they reach a certain voltage.

In order not to overpay and get exactly what you need look at the specifications of your electric screwdriver. It should indicate the power consumption and voltage. The first needs to be divided by the second. you get the maximum current draw of the electric screwdriver. When choosing a battery, first of all pay attention to its current absorption capacity (you can see it in the data sheet), because if the battery draws too much current, it can cause a fire, heating or release gases that are hazardous to health. Among the batteries with a high current output the following models are popular: Samsung 25R, LG HE2, LG HE4, Sony VTC5.

What you need

Disassembling the battery case

Every battery case is collapsible. Consists of two parts that are connected with small screws or glue. In the first case, everything is simple: you only need to unscrew the screws and separate the parts. If the case is glued, you will have to work hard to accurately get to the cells without damaging them. First you need to stick the blade of the knife at any point on the junction of the parts, then insert something sharp there, such as a screw. In this way, it is possible to wedge a single piece. Then carefully pass the blade all around the perimeter separating the glued parts. The housing is disassembled. After the repair it must be glued again.

Fault detection

When you get to the battery cells you will see that they are jars connected in series. So, a single faulty element can cause the electric screwdriver to work poorly. An important step in repairing the battery of an electric screwdriver with your own hands is to find that weak link.

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The test must be carried out with a fully charged battery. It is necessary to remove all the cells from the case and for convenience lay them out on the table so that there is free access to the connection pins. Using multimeter probe measure the voltage at each bank, be sure to record the reading. For convenience, you can draw a scheme on a piece of paper and record there the readings. You can mark them directly on the cells.

For nickel cadmium batteries, the voltage of each cell must be between 1.2 and 1.4 V, and between 3.6 and 3.8 V for lithium ion batteries.

After measuring the voltage, the battery is assembled and operated with an electric screwdriver until the loss of power. Then disassemble and re-measure and record again. The cells that had the lowest voltage values during the first measurement have the highest losses. It is worth noting that a significant difference in the voltage of the banks is considered 0.5. 0.7 V. These are the cells which must be replaced.

Please Note! When repairing an electric screwdriver battery with your own hands, replacing the cells is considered more effective than repairing them. The fact is that the restored banks will not last long, and soon they will have to be replaced anyway. So it is better not to do double work, and immediately make a replacement.

We replace the damaged cells

With the upcoming self-repair of the battery of an electric screwdriver, many users face the question of where to get new banks. You can find an old battery, for example, from acquaintances or visitors of thematic forums. Use it as a donor and select working cells from it. You can buy the cells separately. They are sold in radio and electrical stores or on private ads sites. Some craftsmen order batteries from Chinese websites. You should agree that it is not that much money compared to buying a new battery.

Tip: When choosing, make sure that the new cells have the same dimensions and current values as the cells you are replacing.

The process of replacing damaged cells is quite simple. It will not cause difficulties for those who have dealt with the soldering. First it is necessary to carefully cut the connecting plate and remove the faulty jar. Try to keep this plate for reattaching the new element. Installing the new bank, observe the correct position of the plus and minus. When connecting in series, place the cell so that the minus of the previous one goes to the plus of the new one. To hold the cans securely, you can fasten them around the perimeter with duct tape.

Warning! When soldering, try not to overheat the parts and work quickly. It is important to observe this rule to avoid overheating the battery. Otherwise there is a risk of damaging it.

Charge and discharge the repaired battery

After repairing the electric screwdriver battery potentials on the cells will be different, so they must be aligned. Charge the assembled cell for a long time, possibly overnight. Then let it sit and let it cool down for about 24 hours. After that check the voltage of all cells. If all processes are performed correctly, the reading on each jar will be the same, for example 1.2. 1.3 V.

The next step will be to fully discharge the power cell. Work the electric screwdriver until the charge is gone. After that, fully charge the cell. Repeat the charge/discharge cycle two more times. This will help to extend the life of the battery when it does come back to life.

Say that you should not take this article as an exact guide in repairing the battery of an electric screwdriver with your own hands. This is just one way to bring a battery back to life. If the subject interests you, study it on tool forums, communicate with craftsmen who share their experience, ask them questions. Try to repeat their experience and you will probably do just as well.

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