Voltage at the output of the screwdriver charger
The design of the charger from the screwdriver
The algorithm of the circuit is quite simple.
When connected to a 220V network, the charger does not show its work in any way. Indicators (green and red LEDs) are off. When a removable battery is connected, a green LED lights up, which indicates that the charger is ready for use.
When the “Start” button is pressed, the electromagnetic relay closes its contacts, and the battery is connected to the output of the mains rectifier, and the battery charging process begins. The red LED lights up and the green one goes out. After 50-60 minutes, the relay opens the battery charging circuit. The green LED lights up and the red one goes out. Charging complete.
After charging, the voltage at the battery terminals can reach 16.8 volts.
This operation algorithm is primitive and eventually leads to the so-called “memory effect” of the battery. That is, the capacity of the battery decreases.
If you follow the correct algorithm for charging the battery, first, each of its elements must be discharged to 1 volt. Those. a block of 12 batteries must be discharged to 12 volts. In the charger for the screwdriver, this mode not implemented.
Here is the charging characteristic of one 1.2V Ni-Cd battery cell.
The graph shows how the temperature of the element (temperature), the voltage at its terminals (voltage) and the relative pressure (relative pressure) change during charging.
Specialized charge controllers for Ni-Cd and Ni-MH batteries, as a rule, work according to the so-called delta method.. The figure shows that at the end of the cell charging, the voltage decreases by a small amount. about 10mV (for Ni-Cd) and 4mV (for Ni-MH). Based on this voltage change, the controller determines whether the element is charged.
Also, during charging, the temperature of the element is monitored using a temperature sensor. Immediately on the graph you can see that the temperature of the charged cell is about 45 0 С.
Let’s go back to the charger circuit from the screwdriver. Now it is clear that the JDD-45 thermal switch monitors the temperature of the battery pack and breaks the charge circuit when the temperature reaches somewhere around 45 ° C. Sometimes this happens before the timer on the HCF4060BE microcircuit is triggered. This happens when the battery capacity has decreased due to the “memory effect”. At the same time, a full charge of such a battery occurs a little faster than in 60 minutes.
As you can see from the circuitry, the charging algorithm is not the most optimal and, over time, leads to a loss of the battery’s electrical capacity. Therefore, you can use a universal charger to charge the battery, such as the Turnigy Accucell 6.
The GB1 replaceable battery is a unit in which 12 nickel-cadmium (Ni-Cd) cells are connected in series, each with 1.2 volts.
In the schematic diagram, the elements of the replaceable battery are circled with a dotted line.
The total voltage of such a composite battery is 14.4 volts.
A temperature sensor is also built into the battery pack. In the diagram, it is designated as SA1. In principle, it is similar to the thermal switches of the KSD series. Thermal switch marking JJD-45 2A. Structurally, it is fixed on one of the Ni-Cd cells and fits tightly to it.
One of the terminals of the temperature sensor is connected to the negative terminal of the storage battery. The second pin is connected to a separate, third connector.
Scheme, device, repair
Without a doubt, the power tool greatly facilitates our work, and also reduces the time of routine operations. All kinds of self-powered screwdrivers are now in use.
Consider the device, the schematic diagram and the repair of the battery charger from the Interskol screwdriver.
First, let’s take a look at the schematic diagram. It is copied from a real PCB of the charger.
Charger PCB (CDQ-F06K1).
The power section of the charger consists of a GS-1415 power transformer. Its power is about 25-26 watts. I counted using a simplified formula, which I have already spoken about here.
The reduced alternating voltage 18V from the secondary winding of the transformer is fed to the diode bridge through the fuse FU1. The diode bridge consists of 4 diodes VD1-VD4 type 1N5408. Each of the 1N5408 diodes withstands a forward current of 3 amperes. Electrolytic capacitor C1 smooths the voltage ripple downstream of the diode bridge.
The basis of the control circuit is the HCF4060BE microcircuit, which is a 14-bit counter with elements for the master oscillator. It drives the S9012 pnp bipolar transistor. The transistor is loaded on the S3-12A electromagnetic relay. A kind of timer is implemented on the U1 microcircuit, which turns on the relay for a given charge time. about 60 minutes.
When the charger is connected to the network and the battery is connected, the contacts of the JDQK1 relay are open.
The HCF4060BE microcircuit is powered by a VD6 Zener diode. 1N4742A (12V). The zener diode limits the voltage from the mains rectifier to 12 volts, since its output is about 24 volts.
If you look at the diagram, it is not difficult to notice that before pressing the “Start” button, the U1 HCF4060BE microcircuit is de-energized. disconnected from the power source. When the “Start” button is pressed, the supply voltage from the rectifier goes to the 1N4742A zener diode through the resistor R6.
Further, the reduced and stabilized voltage is supplied to the 16th pin of the U1 microcircuit. The microcircuit begins to work, and also the S9012 transistor, which it controls, opens.
The supply voltage through the open transistor S9012 is supplied to the winding of the JDQK1 electromagnetic relay. The relay contacts close and supply voltage is supplied to the battery. The battery starts charging. The VD8 diode (1N4007) shunts the relay and protects the S9012 transistor from a reverse voltage surge that occurs when the relay winding is de-energized.
Diode VD5 (1N5408) protects the battery from discharge if the mains supply is suddenly cut off.
Regulated Voltage Control | PCM Controlled Charging System | AnthonyJ350
What will happen after the contacts of the “Start” button open? The diagram shows that when the contacts of the electromagnetic relay are closed, the positive voltage through the diode VD7 (1N4007) goes to the Zener diode VD6 through the quenching resistor R6. As a result, the U1 microcircuit remains connected to the power source even after the button contacts are open.
Possible charger malfunctions.
Over time, due to wear and tear and moisture, the SK1 “Start” button begins to work poorly, and sometimes even fails. It is clear that if the SK1 button fails, we will not be able to supply power to the U1 microcircuit and start the timer.
There may also be a failure of the VD6 Zener diode (1N4742A) and the U1 microcircuit (HCF4060BE). In this case, when the button is pressed, charging does not turn on, there is no indication.
In my practice, there was a case when a zener diode struck, with a multimeter it “rang” like a piece of wire. After replacing it, the charging began to work properly. Any zener diode for a stabilization voltage of 12V and a power of 1 W is suitable for replacement. You can check the Zener diode for “breakdown” in the same way as a conventional diode. I already talked about checking diodes.
After repair, you need to check the operation of the device. Press the button to start charging the battery. After about an hour, the charger should turn off (the “Network” indicator (green) will light up. Take out the battery and make a “control” measurement of the voltage at its terminals. The battery must be charged.
If the elements of the printed circuit board are in good working order and do not cause suspicion, and the charging mode does not turn on, then the thermal switch SA1 (JDD-45 2A) in the battery pack should be checked.
The scheme is quite primitive and does not cause problems when diagnosing a malfunction and repairing, even for novice radio amateurs.
Voltage at the output of the screwdriver charger
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Indicator for charging a screwdriver 14.4 volts
I bought a cheap Chinese SKIL-2007 screwdriver, a battery of 14.4 V. 1.2A / h, in principle, it is possible to work normally, but it had two drawbacks. First. there is no adjustment of the rotation speed, I coped with it quickly, I put a switch with a speed regulator. The set includes two batteries and a simple charger made in two separate parts. In a small case, which is plugged into an outlet, there is a transformer with a rectifier, it gives out 18 V 200 mA at the output, a piece of wire with a connector leaves from it. The second part of. the charger itself with indicators, here is its diagram. fig. 1.
A green LED indicates that the device is online. Red indicates that the battery is charging, it will remain lit as long as the battery is connected to the charger. According to the mat, the charge time is 3-5 hours. Since it is impossible to control the end of charging with this charger, I decided to add my own. Searches on the Internet did not give anything, came across too abstruse on controllers, the program to which is sent for a separate fee, or schemes according to which the charge is determined by the brightness of the LED glow, but this is also not the best option, since during the day in sunlight, the brightness seems small, but in the dark big.
I decided to make a simple, reliable battery charging indicator from available parts. As a basis, I took a car voltage indicator (found on the shelves in the garage), they are still on sale, it is a cylindrical body that plugs into the car’s cigarette lighter, at the end there are three LEDs arranged in a row, red at the edges, green in the middle. Here is its diagram (Fig. 2.) and passport data.
- red LED VD3. 12V;
- green LED VD4. 12.5 to 14.5 V;
- red LED VD4. more than 15 V.
- red VD3 and green VD4. 12.0 to 12.5 V;
- red VD2 and green VD4. 14.5 to 15.0 V.
This circuit will work without modification for a 12-volt screwdriver. Does not contain scarce parts and can be easily assembled by a novice radio amateur.
In my screwdriver, the voltage of a fully charged battery while charging is 16.5. 16.8 V, it will not rise higher, even though it will charge for a day. The alteration of the car indicator is as follows: the case is disassembled and thrown out, leaving a 16×38 board with three LEDs. Zener diode VD1, replaced by D814G, instead of R2, set a variable resistor of 1 kOhm.
Setting: a power supply with an adjustable voltage of up to 20 V is connected to the input “±” of the indicator. We set the voltage of 16.5 V at the output of the power supply and by rotating the variable resistor slider we achieve that only the green LED is on, as soon as the red VD3 goes out, the rotation stops. This completes the setup.
I got the following charging values: Red VD3. up to 15 V (battery discharged). Red VD3 and green VD4. 15.16.5V (50-80% charged).
Green VD3. 16.5. 19.3 (100% charged). Red VD2. more than 19.3V (this indicator is practically not used).
Then, instead of a variable resistor, set a constant one, in my case it turned out R2 = 470 Ohm, but you can leave the construction one as well. the indicator is connected to the standard charger to the “±” terminals of the battery. Three holes are drilled in the case for the LEDs and the indicator is inserted into the case of the charger, there is a lot of space there, and it is fixed. Everything native remains in its place.
When you turn on the charger without a battery, VD2 lights up. We insert the discharged battery into the charger, VD2 goes out, the VD3 indicator lights up, as the charging voltage reaches 15 V, the green indicator VD4 starts to light up, and the brightness of VD3 decreases and finally VD3 goes out red, and the green VD4 lights up with full glow, charging can be considered completed.
As a result of this addition to the charger, charging, instead of 3-5 hours according to the passport, ends much earlier. At any time, by the glow of the indicators, you can determine at what stage the battery being charged is. According to the tuning method, this circuit is also suitable for other chargers, for a different voltage. To do this, the battery is fully charged, as stated in the instructions for 3-5 hours, then without removing the battery from the charger, the voltage of the fully charged battery is measured. This voltage is set at the output of the regulated power supply and by selecting the Zener diode VD1 and the resistor R2, they achieve a clear operation of the indicator, as mentioned above.
See other articles of the section Chargers, batteries, galvanic cells.
Read and write helpful comments on this article.
Comments on the article:
And where in the VD4 circuit?
It feels like the diagram was drawn by one, and the article was written by another person.
The alteration scheme is not bad, but there are many inaccuracies and confusion in the description.
In most cases, problems with chargers arise for the following common reasons:
- if the fuse has blown;
- the primary winding of the transformer has broken;
It doesn’t matter what brand the screwdriver you own is released under. If, when you turn it on, it simply does not start, then the first thing you need to do is make sure that its battery is charged. To find out, you need to put the battery on charge for a couple of hours. After the specified time, remove the battery and reinsert it into the device. Make sure the battery is working properly. If the screwdriver still does not work, then you will need to carry out a number of manipulations using a device such as a multimeter (you can use a special tester instead). Using this tool, you can diagnose the existing parts of the screwdriver.
If you have a multimeter in your arsenal, then most likely you know how to use it. If not, then you should read the instructions for its use. This tool is very useful and effective.
With the help of these devices, it will be necessary to determine what exactly is the problem of equipment failure to launch. In this case, either the battery or the charger itself is to blame. To find out what the cause of the malfunction is, you will need to carry out the following procedures:
- first, fix the multimeter in the DC voltage measurement mode (set the rating to 20 V);
- if the battery in the screwdriver has a nominal value of 24 V, then the device will need to be set to a nominal value of 200 V;
- insert the plug of the charger into an outlet;
- now measure the output voltage at the terminals of the charging unit.
The reading of this device should be approximately 2 V greater than the rating of the battery being diagnosed. If this indicator turned out to be much lower, or there are no values at all, then this means that the problem lies in the malfunction of the charger itself, and not the battery in the device. It will be possible to repair this part only if you can boast of certain knowledge and skills in electronics. If there are none, and you cannot fix the charging unit, then you will need to purchase a new part of the same brand.
In modern screwdrivers, there is a DC motor in a cylindrical housing with magnetic elements. To check the condition of the engine, you need to disconnect the gearbox, as well as the wires leading to the start button. Measure the resistance of the armature winding (part inside) using a multimeter. If you did not see any readings on the device, then this will indicate that there is an open circuit. Too small values will confirm that a short circuit has occurred in the device.
The collector resistance parameter must be measured on the shaft and on each of the plates. It should be zero. Breakdowns in the anchor can provoke a shutdown of the device during its operation. Power will be lost, sparks and smoke may appear. If the engine breaks down, the gears often remain intact. Because in the lion’s share of engines it is pressed onto the shaft, it can be difficult to remove it. Purchase a specialized removable element or resort to using available tools. Do not do this with a nailer or pliers. ruin the gears. You should act differently.
- Stock up on a piece of profile or channel. Make a neat longitudinally spaced notch using an angle grinder.
- Place the shaft in the groove in a direction perpendicular to the profile. Pry up the gear.
- Lay the prepared profile on 2 rigid bases so that the engine hangs between them.
- Take the nail and hammer. Tap the edges of the shaft gently. After that, the gear will slide smoothly.
- Now you can put the gear on the brand new engine using a hammer and a hard surface.
Having figured out how a modern cordless screwdriver is arranged, you can safely move on and consider what problems are typical for such a tool.
If at any moment you notice that the tool simply does not start, then perhaps it was struck by a certain malfunction. In practice, the situation is that a non-working tool can be such for two main reasons:
- breakdowns, in which such devices stop working, in many cases are caused by problems associated with their electronic “stuffing”;
- many breakdowns of modern screwdrivers occur due to mechanical damage.
If we understand directly the objective reasons for the breakdown of such tools, then we can distinguish a number of characteristic features:
- at some point, the technique stops turning on;
- the speed regulator stops functioning normally (it may stop working altogether);
- the reverse stops its work.
With regard to the mechanical problems of such devices, there is often significant wear on the parts located in the interior of the tool. For example, the characteristic crackling sounds of the mechanism may come from the screwdriver. In most situations, a broken screwdriver will make unusual noises where the bushing is seriously worn or the bearing has collapsed. Hammer tools often encounter these problems.
And also the following problems can be attributed to the most common problems with screwdrivers:
- malfunctioning of the battery (the charger may stop charging it, or the device stops charging);
- severe wear of the brushes located in the inner part of the engine;
- lack of response to turning the device on and off;
- “Uneven” work with noticeable failures.
If repairing the motor or gearbox of a screwdriver seems to you an overwhelming task, then it is permissible to subject these parts to a complete replacement or send them to a workshop, where these elements to be repaired will quickly bring them into working order.
If you find out that the screwdriver’s charger is working fine, and it’s not at all about it, this means that the problem lies in the battery of the equipment. However, do not rush to disassemble the battery soon. Before that, you need to make sure that the screwdriver problems lie in this particular part. There are two methods for this.
- Connect the tester to the terminals of the storage battery. Determine the voltage level at the output. When carrying out these manipulations, you will need to pre-charge the battery, leaving it to charge for 3-4 hours. If the values on the tester turn out to be less than the nominal, then the root of the screwdriver’s malfunction lies precisely in the breakdown of the battery.
- Install another battery in the screwdriver. Make sure the device turns on with it. If this happens, then the first battery is faulty, and the equipment does not start because of it. Modern manufacturers strongly do not recommend resorting to self-repair of batteries. Disassembling them is also not advised. That is why if you moved on to disassembling the device, you need to keep in mind that your every action is completely unsafe. In practice, the situation is that it is still possible to restore the battery, and this is done quite simply. Consider how you can fix a screwdriver battery.
Mains power supply for electric screwdriver
- Disassemble the battery (at your own risk. do not forget about the manufacturer’s recommendations). Many manufacturers manufacture batteries from a pair of plastic bases that are connected with screws.
- After removing the top lid, a certain number of small barrels (cans) will appear in front of you. Their number depends on the direct voltage of the battery. Banks issue 1 V. To get a nominal value of 12 or 15 V (or other values), the jars will need to be connected in series.
- Now we need to make sure that the contacts are reliable. If there is a break in the connections between the banks, then we can conclude that the breakdown has been directly identified. But it must be borne in mind that these problems occur in rare cases. In most situations, one or a certain number of cans fail.
- Next, you should check if there is voltage in each of the cans. If they all have a voltage of 1 V, and one of 0.8 V, then this means that the problems with starting the screwdriver lie in this particular part. They cannot be repaired, but it is quite possible to replace them in order to fix the device’s battery.
To replace the jars, it will be necessary to carry out such manipulations.
- Detach the damaged keg with a soldering iron.
- In its place, solder a brand new jar of the same size. When choosing a new part, you will need to take into account its face value and filling.
- Collect the battery back, charge and test the correct functioning of the equipment.
How to disassemble?
Often it will be possible to identify this or that malfunction of the screwdriver, as well as to repair it, only after correct disassembly. Since almost all such tools are similar to each other and have the shape of a kind of angle pistol, useful recommendations should be followed when disassembling them.
- The first step is to disconnect the battery pack from the device battery. For this purpose, it will be necessary to gently press the latch and unfasten the module equally carefully.
- You will need to unscrew the screws around the perimeter of the tool using a small Phillips screwdriver.
- By unscrewing all the fasteners, the two parts of the body base can be easily disconnected from each other. But at the same time, it is extremely important to hold the remaining elements of the existing structure, which are fixed in the grooves.
- Very carefully it is necessary to remove the part responsible for gear shifting. Together with it, carefully remove the start button and the reverse mechanism.
- After that, you can further carefully disassemble the technique. Remove the reducer from the removed housing half. To remove it from its place, you will need to turn the gearbox at the landing site.
If you find out that both the battery and the charging unit are operating normally, then you will need to look for the source of the breakdown a little deeper. Disassemble the screwdriver. Next, you need to perform a series of actions to identify and eliminate breakdowns.
- Measure the voltage that comes from the battery to the terminals of the start button. If there is voltage, this means that the necessary power is supplied to the button. If the voltage was not detected, then this means that the wire was damaged in a certain area, or some of the important contacts was broken. Continue down the chain to troubleshoot.
- Check the operation of the button that turns on the device. Remove the battery in order to carry out the necessary checks. Short-circuit the contacts. The output elements of the button will require the connection of the multimeter probes. Set the device to resistance measurement mode. If the button works properly, the readings on the device will tend to zero. If the specified part is still faulty, then the parameters will tend to infinity.
A broken start button can be replaced with a new one or it can be repaired. If this component is collapsible, then it is permissible to disassemble it, clean the contacts. Often, buttons break if one of them burns out. It can be cleaned with sandpaper. The screwdriver will then work as before. If the button is not separable, then you will need to purchase a new one.
The graphite brushes are located at the end of the engine at the junction with the button. They can be located in the inside of the case, or outside. If at least one brush is worn out, then both will have to be changed. To do this, you will need to disassemble the engine, carefully bend the flare with pliers. Then a part with brushes is taken out. Old elements are extracted from it and new ones are installed. After that, you need to assemble the base back.
Scheme for the model “Makita
The charger circuit of the “Makita” screwdriver has a three-channel type microcircuit. There are three transistors in total in the circuit. If we talk about 18 V screwdrivers, then in this case the capacitors are installed with a capacity of 4.5 pF. Conductivity is provided in the region of 6 microns.
All this allows you to remove the load from the transistors. Directly used tetrodes are of open type. If we talk about modifications for 14 V, then the chargers are available with special triggers. These elements allow you to perfectly cope with the increased frequency of the device. At the same time, they are not afraid of online jumps.
Use of BC847 transistors
The charger circuit for the BC847 screwdriver is quite simple. The specified elements are used most often by the “Makita” company. They are suitable for 12 mAh batteries. In this case, the microcircuits are of a three-channel type. Capacitors are used with double diodes.
Directly triggers are used of an open type, and their current conductivity is at the level of 5.5 microns. A total of three transistors for charging 12 V are required. One of them is installed at the capacitors. The rest in this case are located behind the reference diodes. If we talk about voltage, then 12 V overload charges with these transistors are capable of carrying 5 A.
Application of the LM7805 regulator
The charger circuit for a screwdriver with an LM7805 regulator includes only two-channel microcircuits. Capacitors are used on it with a capacity of 3 to 10 pF. Regulators of this type can most often be found in models of the “Bosch” trademark. They are not suitable directly for 12 V chargers. In this case, the negative resistance parameter in the circuit reaches 30 ohms.
If we talk about transistors, then they are used in models of a pulse type. Triggers for regulators can be used. There are three diodes in the circuit. If we talk about modifications to 14 V, then tetrodes are suitable for them only wave type.
Charger circuit for a screwdriver. Electric circuit of the charger of the screwdriver
Many modern screwdrivers operate on a rechargeable battery. Their capacity is on average 12 mAh. In order for the device to always remain in working order, a charger is needed. However, in terms of voltage, they are quite different.
Nowadays, models are produced for 12, 14 and 18 V. It is also important to note that manufacturers use various components for chargers. In order to understand this issue, you should take a look at the standard charger circuit.
14 volt chargers
The charger circuit for a 14 V transistor screwdriver includes five pieces. Directly, the microcircuit for converting current is only suitable for a four-channel type. Capacitors for 14 V models use impulse capacitors. If we talk about batteries with a capacity of 12 mAh, then tetrodes are additionally installed there. In this case, there are two diodes on the microcircuit. If we talk about the charging parameters, then the current conductivity in the circuit, as a rule, fluctuates around 5 microns. On average, the capacitance of the resistor in the circuit does not exceed 6.3 pF.
Directly loads of charging current at 14 V can withstand 3.3 A. Triggers in such models are installed quite rarely. However, if we consider the Bosch brand screwdrivers, they are often used there. In turn, in the “Makita” models, they are replaced by wave resistors. In order to stabilize the voltage, they fit well. However, the charging frequency can vary greatly.
The standard charger of the Interskol screwdriver (the diagram is shown below) includes a two-channel microcircuit. Capacitors are selected for it all with a capacity of 3 pF. In this case, the transistors for 14 V models are of the pulse type. If we consider modifications for 18 V, then there you can find variable analogs. The conductivity of these devices is capable of reaching 6 microns. In this case, the batteries are used on average 12 mAh.
Chargers for Bosch screwdrivers
The standard charger circuit of the Bosch screwdriver includes a three-channel type microcircuit. In this case, the transistors are of the pulse type. However, if we talk about 12 V screwdrivers, then transitional analogs are installed there. On average, they have a bandwidth of 4 microns. Capacitors in devices are used with good conductivity. The chargers of the presented brand have two diodes.
Triggers in devices are used only for 12 V. If we talk about the protection system, then only open transceivers are used. On average, they are capable of carrying a current load of 6 A. In this case, the negative resistance in the circuit does not exceed 33 ohms. If we talk separately about modifications for 14 V, then they are produced for 15 mAh batteries. Triggers are not used. In this case, there are three capacitors in the circuit.
Scheme for the Skill model
The Skil screwdriver charger circuitry includes a three-channel IC. In this case, the models on the market are presented at 12 and 14 V. If we consider the first option, then the transistors in the circuit are of the pulse type. Their current reducibility is no more than 5 microns. In this case, triggers are used in all configurations. In turn, thyristors are used only for charging at 14 V.
Capacitors for 12 V models are installed with a varicap. In this case, they are not able to withstand large overloads. In this case, the transistors overheat rather quickly. There are three diodes directly in the 12V charging.