Converting an electric screwdriver battery to 12 volt lithium
Conversion to lithium batteries Sturm
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Battery assembly process
The first step is to determine if the new elements will fit into the old case. It should be borne in mind that in addition to batteries, you will also have to place a BMS board (about it below). In most cases, there will not be enough space in the old case, and first you need to try to remove everything unnecessary from there (partitions, unnecessary fasteners, etc.)
An alternative option is to “print” the new body on a 3D printer. Not everyone has such an opportunity, but if it works out, the elements can be placed in an optimal way.
It is not known what material the strips are made of (manufacturers claim that they are made of nickel), but they are easily soldered. This means you can eliminate the acidic flux and use a conventional rosin-based formulation. Eliminates additional corrosion factor.
If you wish, you can glue a miniature digital voltmeter or a voltage indicator in the form of a light strip into the case. Usability will improve slightly. Such a device is connected in parallel to the battery chain through a button. so as not to increase the discharge of the batteries in the pauses of work.
The next step is to install the BMS board in the case and connect it according to the diagram.
The board is connected to the contact group with conductors with a cross section of at least 2.5 sq. Mm. To do this, it is convenient to use wires in soft silicone insulation. it is not afraid of overheating (it can occur during soldering or during operation).
This completes the battery replacement, you can finally assemble the battery pack, charge the battery and try the electric screwdriver in operation.
How to convert an electric screwdriver to lithium batteries
It is known that the resource of the mechanical part of the power tool in most cases is much higher than the battery life. The batteries are nearing the end of their life and the electric screwdriver may well continue to work. It is only necessary to resolve the issue of nutrition. In some cases, purchasing new batteries of the same type is difficult, expensive, or even impossible. Therefore, you will have to make a decision. to alter the power tool for operation from the network, while losing mobility, or to adapt a different type of battery to work.
Ryobi 12v Cordless Drill converted to direct wire [ by WW4OK]
If the second option is chosen, then it is most rational to use lithium-ion batteries. they have an increased electrical capacity per unit of geometric volume, they have practically no memory effect (although this type of batteries also has certain disadvantages).
For all its merits, lithium-ion cells are sensitive to:
- deep discharge;
- excessive charging current;
It is difficult to independently control these parameters for several hours, which will be required to replenish the battery energy. Therefore, these functions are assigned to the PCB system (Power Control Board) or SOF (function support system). It is a small board, which is often built into the battery case (because of this, the length of the 18650 cell is slightly longer than the promised 65 mm). This system stops charging when the required voltage is reached and disconnects the battery when discharging to the set level. These elements are labeled Protected on the body. If the marking is absent or Unprotected is directly indicated, then the battery is not equipped with such a system and the charge parameters will have to be controlled manually or this function must be assigned to an external device.
Cordless Drill Lithium Battery Conversion using 18650 Cells
Do not confuse PCB (SOF) with BMS system. Battery Management System or PCM. Power Charge Module. This system is designed for element-by-element control of the charge of the accumulators connected to the battery according to a sequential scheme. The elements that make up the battery have a certain range of parameters, so a situation is possible when some of the cells are already charged, and the other part still needs to be charged. Obviously, this mode is unfavorable for batteries. This problem is designed to solve the BMS (“balancer”). And in the case under consideration, this system cannot be dispensed with.
A typical BMS connection diagram is shown in the figure. When the nominal parameters are reached, the cell is shunted with an internal key, the rest of the batteries continue to charge.
For boards from different manufacturers, the marking may slightly differ (instead of “B-” there is the designation “0V”, instead of the serial number of the battery, the total voltage at the connection point). You can buy a ready-made device on the Internet at well-known trading platforms. You need to choose according to the following parameters:
- operating current. not less than 30 A;
- the number of connected cells must correspond to the number of batteries in the battery.
And, of course, you need to measure the dimensions of the board with the available mounting space.
Safety measures when working with batteries
When assembling the battery, it should be remembered that the currents during the operation of an electric screwdriver can reach 11-12 amperes, therefore the area of the contact patch of the connecting buses between the elements should be maximum. Therefore, the spot welding option often offered on the Internet is not the best. Better to solder the busbars over the entire contact area of the battery. It should be understood that the elements are very sensitive to overheating, therefore, they must be soldered quickly and confidently, using acid fluxes. the battery cases are not made of copper or brass. It is advisable to use heat sinks, which can be pliers, etc.
Care must be taken that acid splashes during soldering do not fall on other surfaces, because this will subsequently lead to corrosion in these places. Places of rations must be thoroughly rinsed.
Parts and tools for rework
To convert an existing electric screwdriver to lithium, you need to purchase:
- set of Li-Ion batteries;
- charge controller board (BMS):
- wires with a cross section of at least 2.5 sq. mm (better in silicone insulation).
- a soldering iron with a capacity of at least 40 watts with a set of consumables, including an acid flux;
- small locksmith tools (screwdrivers, scalpel, etc.).
The process itself is quite creative, depending on the existing initial conditions and the design of the electric screwdriver, so something else may be needed along the way. You need to be ready for this.
Before converting a power tool to use Li-Ion batteries, future operating conditions must be considered. Lithium ion cells are not suitable for low temperature environments.
How many and which batteries to buy
In most cases, 18650 cells are used to convert any electric screwdriver to lithium batteries. This figure means the linear dimensions:
- length 65 mm (actually a little more);
- diameter 18 mm.
These batteries are classified as finger-type batteries. have a cylindrical shape with positive and negative terminals on opposite sides. The voltage of one cell in a fully charged state is 3.6 volts. For each electric screwdriver, you need to dial the required voltage. It can be found on the case of an old battery.
|12||3-4||10.8 or 14.4|
Assembling the charger
Charging lithium-ion batteries has its own peculiarities. It is done in two stages:
BOSCH Upgrade Battery / Change Old Dead Li Ion Cell / GSR BAT411
- at the first stage, energy is replenished with a constant current (the voltage for this should increase smoothly), this stage allows you to charge the battery to about 80% of the nominal capacity;
- at the second stage, the battery is charged with constant voltage (the current falls).
The graph also shows the preliminary stage of trickle charging. It is needed for deeply discharged cells. Obviously, in order to execute such an algorithm and to fully use the battery resource, a specific charger must be used. Failure to comply with the algorithm leads to incomplete use of the battery capacity and a decrease in its resource. A device with such functions must be purchased ready-made or assembled independently, if qualifications allow. Such memory devices are based on specialized microcircuits. Converting a ready-made charger from other batteries is difficult and impractical.
Not all inexpensive chargers provide the required charging algorithm for Li-Ion cells. Many manufacturers from Southeast Asia produce chargers that charge cells only with a stabilized current.
The second stage of charging with constant voltage is not provided. Monitoring the charge level is reduced to measuring time. after a specified period, the current source is turned off, and the functions of protection against excessive charge are assigned to the internal battery protection circuit (if it is absent, then to the owner of the battery).
We recommend the video series “The Second Life of the Electric Screwdriver”
Replacing old electric screwdriver batteries with lithium batteries is a smart move. You can do it yourself, but you need to take into account the peculiarities of operating a battery of this type. After reading the materials of this review, the user will not have any fundamental questions.