Electrical circuit of the ultra power 18v ​​charger. Charger for screwdriver batteries

Their capacity is on average 12 mAh. In order for the device to always remain in working condition, you need a charger. However, in terms of voltage they are quite different.

Nowadays, models are available 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 look at the standard charger circuit.

Charging circuit

The standard electrical circuit of a screwdriver charger includes a three-channel type microcircuit. In this case, four transistors are required for the 12 V model. They can vary quite a bit in terms of capacity. In order for the device to cope with high clock frequencies, capacitors are attached to the chip. They are used for charging both pulse and transition type. In this case, it is important to take into account the characteristics of specific batteries.

Thyristors themselves are used in devices to stabilize current. Some models have open-type tetrodes. They differ in current conductivity. If we consider modifications for 18 V, then there are often dipole filters. These elements make it easy to cope with network congestion.

12V modifications

A 12 V screwdriver (circuit shown below) is a set of transistors with a capacity of up to 4.4 pF. In this case, the conductivity in the circuit is ensured at a level of 9 microns. To prevent the clock frequency from increasing sharply, capacitors are used. Resistors in models are mainly used as field resistors.

If we talk about charging on tetrodes, then there is an additional phase resistor. It copes well with electromagnetic vibrations. The negative resistance of 12 V chargers is maintained at 30 ohms. They are most often used for 10 mAh batteries. Today they are actively used in models of the Makita brand.

14V chargers

The charger circuit for a screwdriver with 14 V transistors includes five pieces. The microcircuit itself for converting current is only suitable for a four-channel type. Capacitors for 14 V models are pulsed. 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 charging parameters, then the current conductivity in the circuit, as a rule, fluctuates around 5 microns. On average, the resistor capacitance in the circuit does not exceed 6.3 pF.

Direct charging current loads of 14 V can withstand 3.3 A. Triggers are installed in such models quite rarely. However, if we look at Bosch brand screwdrivers, they are often used there. In turn, in Makita models they are replaced by wave resistors. They are good for voltage stabilization. However, the charging frequency can vary greatly.

Circuit diagrams for 18 V models

At 18 V, the charger circuit for a screwdriver involves the use of only transition-type transistors. There are three capacitors on the microcircuit. The tetrode is directly installed with a grid trigger used to stabilize the limiting frequency in the device. If we talk about charging parameters at 18 V, then it should be mentioned that the current conductivity fluctuates around 5.4 microns.

If we consider chargers for Bosch screwdrivers, this figure may be higher. In some cases, chromatic resistors are used to improve signal conductivity. In this case, the capacitance of the capacitors should not exceed 15 pF. If we consider chargers of the Interskol brand, then they use transceivers with increased conductivity. In this case, the maximum current load parameter can reach up to 6 A. Finally, mention should be made of Makita devices. Many of the battery models are equipped with high-quality dipole transistors. They cope well with increased negative resistance. However, problems in some cases arise with magnetic vibrations.

Chargers "Intreskol"

The standard charger for the Interskol screwdriver (the diagram is shown below) includes a two-channel microcircuit. All capacitors are selected for it with a capacity of 3 pF. In this case, transistors for 14 V models are used of the pulse type. If we consider modifications for 18 V, then you can find variable analogues there. The conductivity of these devices can reach up to 6 microns. In this case, the batteries are used on average 12 mAh.

Scheme for the Makita model

The charger circuit 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 ensured in the region of 6 microns.

All this allows you to remove the load from the transistors. The tetrodes themselves are of the open type. If we talk about 14 V modifications, then chargers are produced with special triggers. These elements allow you to cope perfectly with the increased frequency of the device. At the same time, they are not afraid of online surges.

Devices for charging Bosch screwdrivers

A standard Bosch screwdriver includes a three-channel chip. In this case, the transistors are of the pulse type. However, if we talk about 12 V screwdrivers, then adapter analogues are installed there. On average, they have a throughput of 4 microns. Capacitors in devices are used with good conductivity. The chargers of this brand have two diodes.

Triggers in devices are used only at 12 V. If we talk about the protection system, then transceivers are used only of the open type. On average, they can carry 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 14 V modifications, 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 charger circuit includes a three-channel microcircuit. In this case, models on the market are presented at 12 and 14 V. If we consider the first option, then the transistors in the circuit are used of the pulse type. Their current conductivity is no more than 5 microns. In this case, triggers are used in all configurations. In turn, thyristors are used only for 14 V charging.

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 quite quickly. There are three diodes directly in the 12 V charger.

Application of 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. You can most often find regulators of this type in models of the Bosch brand. They are not suitable for 12V chargers directly. 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 the pulse type. Triggers for regulators can be used. There are three diodes in the circuit. If we talk about 14 V modifications, then tetrodes are only suitable for them of the wave type.

Using BC847 transistors

The charger circuit for the BC847 transistorized screwdriver is quite simple. These elements are most often used by Makita. They are suitable for 12 mAh batteries. In this case, the microcircuits are of a three-channel type. Capacitors are used with dual diodes.

The triggers themselves are of the open type, and their current conductivity is at the level of 5.5 microns. A total of three transistors are required for charging at 12 V. One of them is installed near the capacitors. The rest in this case are located behind the reference diodes. If we talk about voltage, then 12 V charges with these transistors can handle overloads of 5 A.

Transistor device IRLML2230

Charging circuits with transistors of this type are found quite often. The Intreskol company uses them in 14 and 18 V versions. In this case, the microcircuits are used only of the three-channel type. The direct capacity of these transistors is 2 pF.

They tolerate current overloads from the network well. In this case, the conductivity indicator in the charges does not exceed 4 A. If we talk about other components, then the capacitors are installed of the pulse type. In this case, three of them will be required. If we talk about 14 V models, then they have thyristors for voltage stabilization.

When I came up with the circuit, I tried to simplify it as much as possible, using a minimum of components.
1. Relay - any with a winding voltage of 12 Volts (for options with 3-4 batteries) and contacts designed for a current of at least 2x the charging current.
2. Transistor - BC846, 847, or the well-known KT315, KT3102, as well as analogues.
3. Diode - any low-power diode.
4. Resistors - any in the range of 15 - 33 kOhm
5. Capacitor - 33-47 µF 25-50 Volts.
6. Optocoupler - PC817, found on most power supply boards.

Collected the fee.

Slightly different values ​​are used here, although essentially only the value of resistors R4 and R5 is important. The value of R5 must be at least 2 times less than that of R4.

We select components for the future board. Unfortunately, you will most likely have to buy a transistor, since such devices are rarely used in finished devices; they can be found on motherboards, but extremely rarely.

The board is universal, you can use a relay and make it according to the previous circuit, or you can use a field-effect transistor.

Now the charger block diagram will look like this:
A transformer, then a diode bridge and a filter capacitor, then a DC-DC converter board, and finally a shutdown board.
I did not sign the polarity of the charge indication pins, since it can be different on different boards; if something doesn’t work, then you just need to swap them, thereby changing the polarity to the opposite.

Let's move on to the actual alteration.
First of all, I cut the tracks from the output of the diode bridge, the battery connection terminals and the charge indication LED. The goal is to disconnect them from the rest of the circuit so it doesn't interfere with the "process". You can, of course, simply unsolder all the parts except the bridge diodes, it will be the same, but it was easier for me to cut the tracks.

Then we solder the filter capacitor. I soldered it directly to the diode terminals, but you can install a separate diode bridge, as I showed above.
Remember that a terminal with a stripe is a plus, without a stripe a minus. The capacitor has a long lead - plus.

The printed circuit boards on top did not fit at all, constantly resting against the top cover, so we had to place them from below. Here, of course, everything was not so smooth, they had to bite out one stand and saw down the plastic a little, but in any case, they were much better here.
They even increased in height with a margin.

Let's move on to the electrical connections. To begin with, we solder the wires, at first I wanted to use thicker ones, but then I realized that I simply couldn’t turn around with them in a cramped case and took ordinary multi-core wires with a cross-section of 0.22mm.sq.
I soldered the wires to the top board:
1. On the left is the power input of the converter board, connected to the diode bridge.
2. On the right - white and blue - the output of the converter board. If a disconnect board is used, then to it, if not, then to the battery contacts.
3. Red and blue - output indicating the charging process, if with a shutdown board, then to it, if not, then to the indication LED.
4. Black with green - Indication of the end of the charge, if with a disconnect board, then to the LED, if not, then we do not connect it anywhere.

So far only the wires to the battery are soldered to the bottom board.

Yes, I completely forgot, you can see the LED on the left board. The fact is that I completely forgot and unsoldered all the LEDs that were on the board, but the problem is that if you unsolder the current limit indication LED, the current will not be limited, so it must be left (marked on the board as CC/CV) , be careful.

In general, we connect everything as shown, the photo is clickable.

Then we glue double-sided tape to the bottom of the case, since the bottom of the boards is not entirely smooth, it is better to use thick tape. In general, everyone does this moment as conveniently as possible, you can glue it with hot glue, screw it with self-tapping screws, nail down :)

We glue the boards and hide the wires.
As a result, we should have 6 wires left free - 2 to the battery, 2 to the diode bridge and 2 to the LED.

Don’t pay attention to the yellow wire, this is a special case, I only had a 24 Volt relay, so I powered it from the converter input.
When preparing wires, always try to follow the color coding, red/white is positive, black/blue is negative.

We connect the wires to the original charger board. Here, of course, everyone will have their own way, but I think the general principle is clear. You need to especially carefully check that the connection to the battery terminals is correct; it is better to first check with a tester where the plus and minus are; however, the same applies to the power input.

After all these manipulations, it is imperative to check and possibly reset the output voltage of the converter board, since during the installation process you can reset the setting and get at the output not 12.6 Volts (the voltage of three lithium batteries), but for example 12.79.
You can also adjust the charge current.

Since setting the threshold for indicating the end of charge is not very convenient, I recommend buying a board with two trimming resistors, it’s easier. If you bought a board with three trimming resistors, then to configure it you need to connect to the output a load approximately corresponding to 1/10 - 1/5 of the set charge current. Those. if the charge current is 1.5 Amperes and the voltage is 12 Volts, then it can be a resistor with a nominal value of 51-100 Ohms with a power of about 1-2 Watts.

We've set it up and check it before assembly.
If you did everything correctly, then when you connect the battery, the relay should activate and the charge will turn on. In my case, the indication LED goes out and turns on when the charge is complete. If you want to do the opposite, you can turn on this LED in series with the input of the optocoupler, then the LED will shine while charging is in progress.

Since the title of the review still mentions the board, and the review is about redesigning the charger, I decided to check the board itself. After half an hour of operation at a charge current of 1 Ampere, the temperature of the microcircuit was about 60 degrees, so I can say that this board can be used up to a current of 1.5 Amperes. However, I suspected this from the very beginning; with a current of 3 Amps, the board will most likely fail due to overheating. The maximum current at which the board can still be used relatively safely is 2 Amperes, but since the board is in a case and the cooling is not very good, I recommend 1.5 Amperes.

That's it, we twist the body and set it to full run. I actually had to drain the battery before this, since I charged it in the process of preparing the last part.
If a charged battery is connected to the charger, then the relay is activated for 1.5-2 seconds, then turns off again, since the current is low and blocking does not occur.

So, now about the good and the not so good.
The good thing is that the conversion was a success, the charge is on, the board disconnects the battery, in general it’s simple, convenient and practical.
The bad - If you turn off the charger's power during charging and then turn it on again, the charge will not turn on automatically.
But there is a much bigger problem. During the preparation process, I used the board from the previous review, but I also wrote there that the board does not have a controller, and therefore cannot be completely blocked. But more “smart” boards completely turn off the output in a critical situation, and since it is also an input, when connected to the charger that I modified above, it will not start. To start, you need voltage, and the board needs voltage to start:(

There are several solutions to this problem.
1. Place a resistor between the input and output of the protection board, through which current will flow to the terminals to start the charger, but I don’t know how the protection board will behave, there is nothing to check.
2. Connect the charger input to a separate battery terminal, this is often done with cordless tools with lithium batteries. Those. We charge through some contacts, discharge through others.
3. Do not install a shutdown board at all.
4. Instead of automation, install a button as in this diagram.

At the top there is an option without a protection board, at the bottom there is just a relay, an optocoupler and a button. The principle is simple, we inserted the battery into the charger, pressed the button, the charge began, and we went to rest. Once the charge is complete, the relay will completely disconnect the battery from the charger.

Conventional chargers constantly try to supply voltage to the output if it is below a certain value, but this modification option is inconvenient, and with a relay it is not very applicable. But for now I think it might be possible to do it beautifully.

What advice can you give regarding choosing battery charging options:
1. Just use a board with two trimming resistors (it’s in the review), it’s simple, quite correct, but it’s better not to forget that the charger is on. I don’t think there will be any problems for a day or two, but I wouldn’t recommend going on vacation and forgetting the charger is on.
2. Do as in the review. Difficult, with limitations, but more correct.
3. Use a separate charger, for example the well-known Imax.
4. If your battery has an assembly of two or three batteries, then you can use B3.
It is quite simple and convenient, in addition there is a complete description in it from the author Onegin45.

5. Take the power supply and modify it a little. I did something similar in this.

6. Make your own charger, with all automatic shutdowns, correct charging and extended display. The most difficult option. But this is the topic of the third part of the review, however, it will most likely also include converting the power supply into a charger.

7. Use a charger like this.

In addition, I often encounter questions about balancing the elements in the battery. Personally, I think that this is unnecessary, since high-quality and selected batteries are not so easy to unbalance. If you want something simple and high quality, then it’s much easier to buy a protection board with a balancing function.

Recently there was a question whether it is possible to make the charger able to charge both lithium and cadmium batteries. Yes, it can be done, but it’s better not to, since in addition to different chemistry, batteries also have different voltages. For example, an assembly of 10 cadmium batteries requires 14.3-15 Volts, and an assembly of three lithium batteries requires 12.6 Volts. In this regard, you need a switch that you can accidentally forget to switch. A universal option is only possible if the number of cadmium batteries is a multiple of three, 9-12-15, then they can be charged as lithium assemblies 3-4-5. But common tool batteries cost assemblies of 10 pieces.

That seems to be all, I tried to answer some questions that people ask me in private. In addition, the review will likely be supplemented with answers to your next questions.

The purchased boards are quite functional, but the chips are most likely fake, so it is better to load no more than 50-60% of the declared value.

In the meantime, I’m thinking that you need to have it in a proper charger, which will be made from scratch. So far from the plans -
1. Automatic start of charging when installing the battery
2. Restart in case of power failure.
3. Several stages of charging process indication
4. Select the number of batteries and their type using jumpers on the board.
5. Microprocessor control

I would also like to know what would be interesting for you to see in the third part of the review (you can PM me).

I wanted to use a specialized microcircuit (it seems that you can even order a free sample), but it only works in linear mode, and this causes heating:((((

It might be useful to have an archive with traces and diagrams, but as I wrote above, the additional board most likely will not work with boards that completely disconnect the batteries.

In addition, such conversion methods are only suitable for batteries up to 14.4 Volts (approximately), since chargers for 18 Volt batteries produce voltages above 35 Volts, and DC-DC boards are designed only up to 35-40.