Electronic load with continuously adjustable current. Do-it-yourself electronic load: diagram

For the purpose of testing power supplies, there is an electronic load. This device operates on the principle of signal generation. The main parameters of modifications include threshold voltage, permissible overload, and dissipation coefficient. There are several types of devices. In order to understand the loads, it is first recommended to familiarize yourself with the device diagram.

Modification scheme

Standard scheme The load includes resistors, a rectifier and modulator ports. If we consider low-frequency devices, they use transceivers. These elements operate on open contacts. Comparators are used to transmit the signal. Recently, loads on stabilizers have become popular. First of all, they are allowed to be used in DC networks. They undergo a rapid transformation process. It is also worth noting that an amplifier and regulator are considered an integral element of any load. These devices are short-circuited to the plate. They have quite high conductivity. The modulator is responsible for the generation process in models.

Types of modifications

There are pulsed and programmable devices. IN separate category laboratory ones are allocated that are suitable for powerful power supplies. Modifications also differ in the frequency with which they operate. Low-frequency loads are equipped with transistors with a channel adapter. They are used on the web alternating current. High-frequency models are made on the basis of an open thyristor.

Pulse devices

How is a pulsed electronic load made? First of all, experts recommend choosing a good thyristor for assembly. In this case, the modulator is suitable only for two phases. Experts say that the expander should work alternately. Its operating frequency must be approximately 4000 kHz. The transceiver is installed into the load through a modulator. After soldering the capacitors, it’s worth working on the amplifier.

For stable operation of the load, three channel-directional filters are required. A tester is used to check the device. The resistance should be approximately 55 ohms. At average load the load produces around 200 W. Comparators are used to increase sensitivity. When the system shorts, it is worth checking the circuit from the capacitor. If the resistance at the contacts is too low, then the transceiver needs to be replaced with a capacitive analogue. Many experts point to the possibility of using wave filters that have good conductivity. Regulators for these purposes are used on a triode.

Programmable Models

The electronic programmable load is quite simple to assemble. For this purpose, a 230 V expansion transceiver is used. Three contactors are used to transmit the signal, which extend from the transistor. Regulators are used to control the conversion process. Linear analogues are most often used. The triode is used with an insulator. In this case, you will need a blowtorch. The resistor is directly fixed to the transceiver.

Conventional comparators, which have a low dissipation coefficient, are definitely not suitable for the model. It is also worth noting that many people make the mistake of installing one filter. For normal operation Priora uses only capacitive analogues. The rated output voltage should be approximately 200 V with a resistance of 40 ohms. If you assemble devices using a single-junction expander, then linear models are not suitable.

First of all, the device will not work due to the large overload of the thyristor. It is also worth noting that the model will require a horizontal modulator with low sensitivity. Some experts use stabilizers during assembly. If we are considering a simple modification, then an adjustable type will do. However, inverting elements are most often used.

Laboratory modifications

Assembling a laboratory electronic load with your own hands with a powerful thyristor. Resistors are used with a capacity of 40 pF or more. Experts say that capacitors can only be used of the expansion type. When assembling, special attention should be paid to the modulator. If you use a wired analogue, then the load will require three filters. A simple electronic load has a phase-type modulator with a conductivity of 30 μm. The resistance is approximately 55 ohms. It's also worth noting that loads are often stacked on top of a switched transceiver. The main feature of such devices lies in high pulsation. In this case, conductivity is ensured at around 30 microns.

Field effect transistor device

The electronic load is not made only on the basis of a comparator, and a thyristor is used of an adjustable type. When assembling, first of all, you should select a capacitor unit, which plays a role. In total, three filters will be required for modification. The resistor is installed behind the plates. Experts say that the electronic load on field effect transistor produces a resistance of 40 ohms.

If the conductivity increases significantly, then a capacitive capacitor is installed. It is recommended to use the transceiver itself with two contacts. The relay is installed as standard with a regulator. The rated voltage for loads of this type is no more than 400 W. Experts say that the plate should be fixed behind the resistor. If we consider a high-frequency model for 300 V power supplies, then a modulator will be required of the wave type. In this case, a tetrode is installed behind the thyristor.

Model with continuously adjustable current

The smooth electronic load circuit includes one thyristor. Capacitors for the model will require expansion type with low conductivity. It is also worth noting that one amplifier is placed in the load. The most commonly used are wave analogues that have a phase adapter. The regulator itself is installed behind the modulator, and the rated voltage should be about 300 W.

A simple electronic load with continuously variable current has two contactors for connection. Thyristors can sometimes be used on plates. Comparators in devices are installed with or without stabilizers. In this case, much depends on the operating frequency. If this parameter exceeds 300 kHz, then it is better not to install a stabilizer. Otherwise, the dispersion coefficient will increase significantly.

TL494 based device

The electronic load based on the TL494 is quite easy to assemble. Resistors for modifications are selected as line type. As a rule, they have high capacity. And they are capable of operating in a DC network. When assembling the model, the thyristor is used on two plates. Electronic pulse load based on TL494 works with a phase or pulse type expander.

The first option is the most common. The rated voltage of the loads starts from 220 W. Filters are of the full type, and the conductivity is no more than 4 microns. When installing the regulator, it is important to evaluate the output impedance. If this parameter is not constant, then an amplifier is used for the model. Contactors are installed with or without adapters. Output voltage in the circuit is approximately 300 W for loads. When you turn on devices, the current often increases. This happens due to the heating of the modulator. The user can avoid this problem by reducing sensitivity.

100 W models

An electronic load (circuit shown below) of 100 W involves the use of two channel thyristors. The transistor in models is quite often used on an expansion basis. Its conductivity is about 5 microns. It is also worth noting that there are loads on the relay. They are most suitable for powerful power supplies. For self-assembly Wave comparators are additionally used. Homemade devices produce a voltage of no more than 300 V, and the operating frequency starts from 120 kHz.

200 W devices

A 200 W electronic load includes two pairs of thyristors, which are connected in pairs. Many models use wired low-frequency comparators. It is also worth noting that to assemble the modification you will need a modulator. Amplifiers are used to speed up the process. These elements can only operate from wired filters.

The transceiver should be installed behind the covers. In this case, the load voltage is approximately 400 V. Experts say that devices based on conductive transceivers do not work well. They have low conductivity and have problems with overheating. If voltage surges are observed, it is worth changing the comparator. Another problem may be with the resistor.

How to make a 300 W device?

An electronic load of 300 W involves the use of two phase-type thyristors. The rated voltage of the devices is approximately 230 W. The overload indicator in this case depends on the conductivity of the comparator. When assembling this device yourself, you will need a channel-type modulator. A blowtorch is used to install the element.

Regulators are often used with an adapter. The relay is installed as a low-impedance type. The dispersion coefficient of a homemade modification is approximately 80%. It is also worth noting that the contactors used are of low sensitivity. How to check the load before turning it on? This can be done using a tester. Output voltage homemade devices, as a rule, equals 50 Ohms. If we consider models with one comparator, then this parameter may be underestimated.

Models for 10 A units

The electronic load for a 10 A power supply is collected using an expansion thyristor. Transistors are quite often used at 5 pF, which have low conductivity. It is also worth noting that experts do not recommend using linear analogues. They have low sensitivity. They greatly increase the dissipation coefficient. Contactors are used to connect to the block. Modulators are quite often used with adapters.

If we consider the circuit on a capacitor block, then their frequency is on average 400 kHz. In this case, sensitivity may change. Contactors are quite often fixed behind the modulator. Stabilizers should be used on two plates. It is also worth noting that to assemble the modification you will need a pole resistor. It greatly helps to increase the speed of impulse generation.

Devices for 15 A units

The most common loads are for 15 A units. They use open resistors. In this case, transceivers are used with different polarities. In addition, they differ in sensitivity. On average, the voltage of the devices is 320 V. The models differ in conductivity. For the purpose of self-assembly, comparators are used on regulators. Before installing them, stabilizers are attached.

Experts say that expanders can only be installed through the lining. The conductivity at the input must be no more than 6 microns. When installing the regulator, the comparator is thoroughly cleaned. If you assemble a simple model, then the modulator can be used of the inverter type. This will greatly increase the dispersion coefficient. The threshold voltage is on average 200 V. The permissible power parameter is no more than 240 W. It is also worth noting that filters are used for the load different types. In this case, much depends on the conductivity of the comparator.

Device diagram for 20 A units

The electronic load (circuit shown below) for 20 A units is based on binary resistors. They maintain stable high conductivity. The sensitivity is approximately 6 mV. Some modifications are distinguished by a high overload parameter. Relays in models are used on wave transistors. Comparators are used to solve conversion problems. Expanders are often found in the phase type. And they may have several adapters. If necessary, the device can be assembled independently. For this, a capacitor unit is used.

The rated voltage of homemade loads starts from 300 W, and the average frequency is 400 kHz. Experts do not recommend using transient comparators. Regulators are used with plates. To install the comparator you will need an insulator. If we consider loads on two thyristors, then filters are used there. On average, the module capacitance is 3 pF. The dispersion rate for homemade models starts at 50%. When assembling the device, special attention should be paid to the adapter for connecting to the power supply. Contactors are of the pole type. They must withstand heavy overloads and not overheat.

AMETEK devices

Loads of this brand are distinguished by low conductivity. They are great for 15 A power supplies. Among the models of this company there are many pulse modifications. Their specific overload is not high, but they provide a high pulse generation rate. Experts primarily note the good protection of the elements. They use several filters. They cope with phase interference that distorts signals.

If we consider high-frequency models, they have several thyristors. It is also worth noting that modifications based on wired comparators are available on the market. Based on the usual load of this brand, you can assemble an excellent device for different power supplies. The models have excellent stabilizers and very sensitive transistors.

Features of Sorensen series devices

The standard electronic load of this series includes a thyristor and a linear comparator. Many models are manufactured with pole filters that are capable of operating at high frequencies. It is also worth noting that laboratory modifications are available on the market. They have a fairly low dissipation coefficient. Models quite often used are switched type. The average overload indicator is 20 A. Protection systems are used in different classes. Available on store shelves impulse models. They are well suited for testing computer power supplies. Expanders in devices are used with covers.

ITECH series models

The loads of this series are distinguished by their high conductivity. They have good security. In this case, several transceivers are used. The electronic load for the power supply operates at an average frequency of 200 kHz. The overload in this case is 4 A. Amplifiers in the devices are used with contact adapters. Thyristors are used of phase or code type. Among the models in this series there are programmable modifications. They are well suited for testing computer power supplies. Transceivers can be found with or without expanders.

Loads based on IRGS4062DPBF

Making an electronic load with your own hands based on this transistor is quite simple. The standard circuit of the model includes two capacitor units and one expander. It’s worth noting right away that models of this class are well suited for 10 A power supplies. The voltage parameter for the loads is 200 W. Filters for devices are selected at low frequencies. They are capable of working under heavy loads.

First of all, during assembly, a thyristor is installed, and a comparator can be used of different types. The transistor is installed directly using a soldering iron. If its conductivity exceeds 5 microns, then it is worth installing a dipole filter at the beginning of the circuit. Experts say that the electronic load on the IRGS4062DPBF transistor can be done with transient comparators. However, they have a high dispersion coefficient.

It is also worth noting that models in this series are only suitable for DC circuits. The permissible device overload parameter is 5 A. If we consider devices based on pulse comparators, they have a lot of advantages. The first thing that catches your eye is the high frequency. In this case, the resistance of the devices is shown at 50 Ohms.

They do not have problems with conductivity and sudden voltage surges. Stabilizers can be used in different types. However, they must operate on a DC circuit. Modifications without capacitors are also available on the market. Their dispersion coefficient is approximately 55%. For devices of this class this is very little.

Devices based on KTC8550

Loads based on transistor data are highly valued among professionals. The models are great for testing low-power units. The permissible overload indicator is usually 5 A. Models may use different protection systems. When assembling the modification, it is allowed to use binary modulators with a conductivity of 4 μm. Thus, the devices will output a higher frequency at 300 kHz.

If we talk about the disadvantages, it is worth noting that the modifications are not able to work with 10 A power supplies. First of all, problems arise with pulse surges. Overheating of the capacitor will also make itself felt. To solve this problem, expanders are installed on the loads. Triodes are usually used with two plates and an insulator.

Over time, I have accumulated a certain number of different Chinese AC-DC converters for charging batteries mobile phones, flashlights, tablets, as well as small pulsed sources power supplies for electronics and the batteries themselves. Cases often indicate electrical parameters devices, but since most often you have to deal with Chinese products, where inflating the indicators is sacred, it would not be a bad idea to check the real parameters of the device before using it for crafts. In addition, it is possible to use power supplies without a housing, which do not always contain information about their parameters.

Therefore, I assembled an electronic load for myself using an LM358 operational amplifier and a KT827B composite transistor, testing power supplies with voltages from 3 V to 35 V. In this device, the current through the load element is stabilized, so it is practically not subject to temperature drift and does not depend on the voltage of the source being tested, which is very convenient when taking load characteristics and conducting other tests, especially long-term ones.

Tools:
- soldering iron, solder, flux;
- electric drill;
- jigsaw;
- drill;
- M3 tap.

Instructions for assembling the device:

Operating principle. The device's operating principle is a voltage-controlled current source. A powerful composite bipolar transistor KT 827B with a collector current Ik = 20A, a gain h21e of more than 750 and a maximum power dissipation of 125 W is equivalent to the load. Resistor R1 with a power of 5W is a current sensor. Resistor R5 changes the current through resistor R2 or R3 depending on the position of the switch and, accordingly, the voltage on it. An amplifier with a negative feedback from the emitter of the transistor to the inverting input of the operational amplifier. The action of the OOS is manifested in the fact that the voltage at the output of the op-amp causes such a current through the transistor VT1 that the voltage across the resistor R1 is equal to the voltage across the resistor R2 (R3). Therefore, resistor R5 regulates the voltage across resistor R2 (R3) and, accordingly, the current through the load (transistor VT1). While the op-amp is in linear mode, the indicated value of the current through transistor VT1 does not depend either on the voltage on its collector or on the drift of the transistor parameters when it warms up. The R4C4 circuit suppresses the self-excitation of the transistor and ensures its stable operation in linear mode. To power the device, a voltage of 9 V to 12 V is required, which must be stable, since the stability of the load current depends on it. The device consumes no more than 10 mA.

Perhaps the problem can be solved by installing 1-2 of the same transistors in parallel, but I haven’t practically checked - those same IRF3205 transistors are not available in the required quantity.

The housing for the electronic load was used from a faulty car radio. There is a handle for carrying the device. I installed rubber feet on the bottom to prevent slipping. I used bottle caps for medicines as legs.

I have already written at least three reviews of electronic loads, both completely homemade and assembled from a “designer”, as well as factory-made ones. In this case, both options belong rather to the class of “designers”, since they are not a functionally complete product, although they can work on their own, they require at least a power supply.
I saw them almost a year ago, became interested, and so decided to buy them, and at the same time check how to “buy them on Tao”.
In general, anyone who is interested in this topic will find a lot of interesting things for themselves.

Partly the prerequisite for buying was the difficulty of testing powerful power supplies, when my 300-400 Watts were not enough, partly the expansion of my horizons, and not the least on the list was an attempt to buy on Taobao, because there are some very interesting things there.

There were no problems during the purchase, and as a result, after some time I received a rather large parcel. Here I made a small mistake, delivery is quite expensive, and my pieces of iron are quite heavy.

Everything was packaged just fine, but this was also a small minus, since the more packaging material, the higher the delivery cost :(
In the second photo you see not two products, but one. In this case, on the right is one of the loads, and on the left is what it was packed in.
The second load was packed even better, but in this case it was the seller’s packaging, such a soft box.

No, everything is great, the intermediary not only packed it well, but also sent a letter before that, saying, dear Kirich, we received two incomprehensible pieces of iron, but we have no idea how to check them, we don’t even know what it is...
To which I replied, calm down, don’t panic, compare with the photo in the store, if it’s similar, then send it :)

In general, I got to the bottom of my order and in the end there were only two electronic loads on the table.

I’ll show you the “stupid” one first, i.e. without the ability to connect to a computer, just a load.
Claimed power - up to 300 Watt
Voltage - up to 150 Volts
Current - up to 40 Amperes
Modes - CC\CV

There were many different options in the assortment, which conventionally differ in the voltage of 150/60 Volts, as well as the current of 10/20/30/40 Amps, as well as the adjustment design - a connector on the board, trim resistor on the board or an external variable resistor.

I immediately chose the most sophisticated option and at the same time the most powerful, i.e. 150 Volts, 40 Amps, 300 Watts external resistor.
As you can see, the design consists of essentially two identical modules connected together. There is also an option with a power of 150 Watt, consisting of one module.

An external resistor means a regular variable resistor on a small strip. I’ll jump ahead a little, there’s no point in ordering this way, for convenient control you need to either order a load with a 60 Volt range, or even better, install a multi-turn resistor.

The design of the cooling system (actually the heaviest part) consists of two fans and a special aluminum radiator through which air is blown.
5 points for the design, where can you get hold of such an aluminum profile? It’s even better if the size is not 50x50mm, but for example 80x80, or at least 60x60.

A pair of quite powerful, but also very noisy fans, covered with protective grilles. At first I thought, here are the economists, they put only two screws on the grille, then it turned out that there was simply nowhere to screw in the second pair of screws. No, they are still economists :)

Two control boards are connected together, although it would be more correct to say that they are not disconnected, since this is how they usually go during manufacturing.
Wiring is stretched from one board to another and the idea is clearly visible when one board is made the master, and the second the slave.

Most of the connectors are missing, but I’ll try to explain what’s what.
Ref - regulation by external voltage 0-5 Volts.
Potentiometer - external variable resistor, the middle contact is connected to the same Ref, i.e. changes the voltage in the range of 0-5 Volts.
Fan - connecting a fan, the wires are simply soldered without any connectors.
Con 1, a connector is soldered into the left board - power supply 12-15 Volts.

There is also room for a 74HC connector. In general, this is usually a designation for a series of logical chips, but I don’t know what in this case. One contact goes to ground, four to the microcontroller.
Con 4 - temperature sensor.

The other end of the board has power connectors for connecting the load, as well as:
Con 2 is essentially in series with the power connector Vin, most likely a fuse should be placed there, in fact there is some kind of plate soldered there. Another option is to connect an ammeter, but the connector is kind of flimsy for a current of 20 Amps.
Con 3 - ground, +12 Volts and input voltage Vin are connected to this connector. You can connect a voltmeter here
Fan 2 - Connection of a second fan (working for blowing), connected in parallel to the first.

Four IRFP460A field-effect transistors act as the actual load. It turns out 75 watts per TO-247 case, in my opinion this is a lot, a lot, the power is exceeded by at least 1.5 times. This is due to the fact that field-effect transistors work much harder in linear mode. Actually, that’s why in my homemade one, for a power of 400 Watts, 8 transistors are installed, 50 Watts per case, and even that is a bit much.

But I cannot help but note that the transistors are connected correctly; each transistor has not only its own shunt, but also its own operational amplifier. I used exactly this solution in my version.

The board is screwed with four screws through the stands, the transistors have their own fasteners, and not only thermal paste was not forgotten, but also the correct screws with a flat washer + Grover washer.
When I took it apart, I subconsciously expected that the radiators would fall apart, but no, everything worked out, the radiators seemed to be glued together.
But the racks could have been tightened even more tightly...

From below you can more clearly see how the boards are connected to each other. By the way, for a more correct connection of power wires, you need to connect the plus to one board, and the minus to the other.

If there are no particular questions about the connection of the power connectors, then the wires in varnish insulation for connecting the power supply to the modules look somehow completely wrong. I understand that they are simply hidden there, but one wire was touching the stand and over time, due to vibration, it would scrape the insulation. You will of course ask where the vibration comes from. This is how two fairly powerful fans work, and such wires don’t need more.

One of the “halves” is closer.

1. The power input is protected not only by a 1 Ampere fuse, but also by a diode that protects against polarity reversal. But in addition, they installed a bunch of capacitors along the power supply circuit, it’s even surprising :)
2. Although the load is “stupid”, it still contains a microcontroller. In this case, it controls operating modes, overpower protection, and the fan.
3, 4. Three LM321 operational amplifiers. A pair serves current sensors and transistor control, and one (as far as I understand) is CV mode.

Speaking of fan control. Made very thoughtfully. If the load is cold, the fan is turned off. It turns on stepwise when the power exceeds 20-30 watts per module, gradually increasing the blowing power.
If you turn off the load when the radiators are cold, the fans turn off immediately. But if you warm it up first, they will turn off only when the temperature drops to about 35 degrees.
Those. The fans are controlled in stages depending on power and temperature.

A ceramic capacitor is installed parallel to the input and power terminals. My old one also has a capacitor, but it has a noticeably larger capacity, so sometimes it sparks a little when power is applied to the input.

The less powerful and more “smart” load had noticeably fewer choices, 60/150 Volts and 5/10/20 Amps. And again I chose the most powerful and high-voltage option, and in this case this may have been a mistake.

Below is the SPI connector, as I understand it, it is more needed to connect the programmer.
Even lower is a long row of contacts; microcontroller ports and power supply are located here.

But I don’t understand what SWIM is, a little to the right and higher. It looks like some kind of jumper is placed there, the middle pin goes to the microcontroller, the outer pins go to ground and power. Those. In this way, you can set three signals - 1, 0 and Z. I tried all the options in the process, but did not notice any difference.

If in the previous load everything was relatively simple, then here there are more components.
1. The actual “brains”, in the form of a microcontroller from STM.
2. Measuring Ultralow Offset opamp OP07, amplifies the signal from the main shunt.
3. Also on the board is a voltage converter LMC7660, it is needed to form the negative pole of the power supply to the operational amplifiers. I did something similar in my electronic load, there was also an OP07 + 7660 combination in the current measurement circuit.
4. The board also contains two precision dual OPA2277 operational amplifiers.

This is where things get a little weird.
The board has space for two operational amplifiers, and even all their wiring is soldered, i.e. just solder another pair of OPA2277.
But the most incomprehensible thing is that the first pair of op-amps serves three transistors, and since the op-amps are dual, there is still one left. I didn’t understand the rest; most likely it is used either to measure voltage or to control three subsequent op-amps.
There is one “half” for each transistor, since there are three transistors installed (I’ll show you below). There is also room for a couple more transistors, but one dual op-amp is enough for them, why another one, and even with a soldered wiring identical to the first? Mystery...

The protection circuit for the input power supply is designed as for the previous load, a polyswitch, a polarity reversal diode and a bunch of capacitors.

And here are the three transistors that I wrote about above. the board is designed for five transistors, and you can even see two thermal sensors located between the first and second, as well as between the fourth and fifth transistors. Both temperature sensors are visible in the control program. In general, the decision is very correct; the manufacturer clearly decided to play it safe.
But here are three transistors from completely different batches, original :)
On the right you can see the space for the connector for the second fan.

As I wrote above, there are shunts installed on the left side of the board. A pair of U-shaped shunts are measuring for the controller itself; data from these shunts are displayed in the program. Shunts are two out of five, five are most likely used in the 50 Amp version.
To the right are three M-shaped pieces - shunts in the circuit of power transistors, they are used to equalize the current for each transistor separately. In this case, each shunt is in a circuit with an operational amplifier and the current is leveled very accurately. I used exactly the same solution in my powerful load, only there were 8 transistors, 8 shunts and 4 op-amps. This solution is the most correct, because it ensures uniform distribution of current between the elements. It can even be applied at all different transistors, the current will still be distributed evenly.

Moreover, what is interesting is that on the product page there are photographs and a funny combination is shown, all the op-amps are soldered, a wide cable is used, i.e. It is assumed that there are 5 transistors installed, but there is only one measuring pin, and two balancing pins.

In terms of review, more powerful load I didn't remove the fans, but judging by the looks of it, there are the same ones there. Quite powerful 50mm fans with a power of almost 3 Watts from Delta.
The fans themselves are the main consumers, so for this load a 12 Volt 0.3-0.35 Ampere power supply is sufficient, and for a powerful version 12 Volt 0.6 Ampere.

Before moving on to testing, I weighed both devices. Most likely you will ask why, if they are clearly not portable.
Since they were ordered through an intermediary, weight begins to play a rather large role.
The total “useful weight” was 1218 grams, the entire package weighed 318 grams, for a total of 1536 grams. By the way, during the process I ended up exceeding the estimated weight, and a debt of 1.3 bucks arose, but the intermediary still sent the parcel. When I asked what to do with the debt, I was told that this will be taken into account during the next purchase.

Since I was the first to examine the powerful option, I will check it first.
We connect the power supply and proceed to the tests.

First, a few words about management.
Each module is controlled by its own button. Short press - turn on/off, long press - switch operating mode. Wherein:
1. If you hold the button for a long time in the off mode, then when you turn it on, the second mode will turn on.
2. The load “remembers” the last used mode.

The first photo shows the correct combination, green-green, SS mode works in this mode.
If you turn on only the second load, nothing will happen; it does not work by itself.
The following two combinations can work, but very incorrectly, so they cannot be used, however, I’d better show you further with examples.

1. Connect to a laboratory power supply and set the output to 30 Volts, the load is turned off.
2. Turn on the leading one (on the left), set the load current at 1 Ampere.
3. Turn on the slave, the current becomes 1.84 Amperes, and not 2, as expected, there is an incorrect calibration.
4. Turn off the master, the current drops to zero, the slave itself cannot work.

Just for fun, I checked the minimum load drop; even taking into account the cable, it was 0.64 Volts at a current of 5.1 Amperes. Somehow I didn’t think to measure how much is realistic, but according to calculations it comes out to about 0.5-0.6 Volts.

CV mode. Actually this was one of the important reasons why I bought these loads. This mode is not needed very often, but it cannot be replaced by the CC mode.
Let me explain, if you check the power supply, then it operates in CV (stabilized voltage) mode and must be loaded in CC (stabilized current) mode. But if you check the charger, then the situation is the opposite, it works in CC mode, and accordingly it must be loaded with a load operating in CV mode.
This mode is more like an analogue of a powerful zener diode, or the equivalent of a battery connected to the charger being tested.
Yes, by charger I mean a charger, and not power supplies with a USB output, which are mistakenly called chargers.

So, what did I find out?
1. Set the voltage at the output of the power supply to 50-60 Volts, in this case it was 54 Volts.
2. We move the load regulator to the extreme right position and gradually rotate it to the left until the power supply switches to current stabilization mode. That's it, the load operates in CV mode, stabilizing the voltage at a level of 52 Volts. If it were not a laboratory power supply, but a regular one, then it would simply go into defense, since the load would do its best to prevent its normal operation.
3. By rotating the resistor to the left, we reduce the voltage even lower, for example to 16 Volts. There are different currents in the photo, this is not a glitch, the photos were simply collected during different experiments and the settings of the laboratory power supply changed during the experiments.
4. But the first problem became clear - if you turn on the driven load, the voltage drops to zero. It turns out that they cannot work together in this mode.
5, 6. I was able to start the slave load in this mode, but in fact it did not work, this was even evident from the fact that its fan did not start. In addition, the slightest change and it again fell into short circuit mode.

It turns out that in CV mode only the leading load works, therefore the power is limited at 150 Watts, and not 300, as in CC mode.
The second problem was that the load is designed for 150 Volts and this entire range is contained in an incomplete turn of the variable resistor, so there is no way to talk about the accuracy of the adjustment, very roughly. The 60 Volt version would be more accurate, but here you will most likely have to replace the resistor with a multi-turn one.

In addition, I just played around with different powers, 250-300 Watts in CC mode dissipates the load without any problems at all, the noise is really loud. By the way, the fans are controlled independently, and sometimes you can hear how one has reduced speed, while the second is running at full speed.
In CV mode, I was able to load the load at 160-162 Watts, then a short squeak was heard from the speaker and the load was turned off. Stable operation was around 155 watts.

For the next experiment, we used the same things as above plus a USB-RS485 converter and a connecting cable.

I didn’t take any special photographs during the process, and in fact there wasn’t much to photograph, so what follows will be a number of screenshots, tests and some explanations and descriptions of the problems that I encountered along the way.

On the product page there was a link to the Chinese “baida”, where all the necessary software for working with this module was posted.
I changed the name of the main program to a more understandable one - DCL, otherwise “as is”.

The same thing, but with the original file name and additional information. As you can see, they gave a lot of things, but there is one problem, the antivirus and the Win 10 OS protection system (I tried it with Win 7, 8, 10) complain about the Trojan in two files (they both above have the same icon in the form of a red square). Since I still wanted to try, I had to disable the antivirus and run everything at my own peril and risk.

As a result, such software was launched. Or rather, this is how it should be. I tried to follow the link to the developer’s page, it says that the software is in an “experimental” version, so glitches are possible. In general, the manufacturer is engaged in the manufacture of various measuring modules, but more on this towards the end of the review, it will be more logical.
And so the explanation of what and where in this software, some became clear immediately, some already in the process of experimentation, and the last part after translation from Chinese.
1. Parameter entry window.
2. Buttons for setting the parameter value, respectively, in steps of 100, 10, 1, 0.1 and 0.01. The first and last ones are usually not used. The top buttons increase, the bottom buttons decrease, everything is quite logical.
3. Buttons for switching to calibration mode, I understood the purpose by accident, I’ll tell you below.
4. Setting the operating mode - CC, CV, CW, CR
5. Select a COM port and device number on this port (RS485 supports several devices on the same line).
6. Load on/off.
7. And here I had to ask familiar Chinese managers who also know a language that is more understandable to me :). This is recording the results of work to a file.

When I launched the software on my computer, everything was more unclear, and it was from this software that I figured out what and why.
Moreover, exactly the same picture was observed on all home computers and tablets.
I was especially frozen when I saw a current of 655 Amps.

But let’s not talk about sad things, I’ll explain the main operating modes.
1. SS, load DC, set the current to 20 Amperes (actually a maximum of 20.1 Amperes) and if the power does not exceed 150 Watts, then the load goes into operating mode. If there is an excess, it signals and turns off.
2. CV, the same, but we set the limiting voltage. When switching to this mode, a maximum of 151 Volts is displayed, which is quite logical, since it is usually reduced, not raised.
3. CW, quite common mode, constant power. We set the power in Watts and the load will support this power taken from the source.
4. CR, a very rare mode for cheap devices, but quite common for industrial ones. Here you can set the resistance of the “virtual resistor” which will be the load. those. The load current will directly depend on the source voltage. unfortunately this mode
very rough and allows you to choose only with a discreteness of 1 ohm.

It also turned out that the load starts very softly and sometimes it’s even annoying. For example, when setting the current to 3 Amperes, first the current rises sharply to approximately 2.3-2.3 A, and then very smoothly reaches the set value. Total time installation takes about 30 seconds.

Another problem I encountered was that the load was not calibrated for current. But “there was no happiness, but misfortune helped.” The fact is that the voltage calibration was excellent. But I was always confused by the two buttons to the right of the parameter setting buttons. when you click on them, it gives out some strange numbers like 4556 and 65432, obviously some two values. At first I thought that this could be used to simulate interference or ripples, the letter Mu confused me. But at one “wonderful” moment I realized that the load also began to terribly lie in terms of voltage.
and then I remembered that before that I had poked these buttons and tried to select something with the buttons for setting the value. Well, then it’s a matter of technology.
And so, about calibration. To the right of the buttons for setting the value there is another pair, the top one is voltage, the bottom one is current.
I'll show you how to calibrate using current as an example.
We connect the ammeter in series with the load.
1. Select the CC mode, set the current, for example, 4.5 Amperes (the more, the better).
2. Poke the lower right button (near the -0.01 button), a certain constant will be displayed on the screen, it will have great importance, for example 52435 or 65432). Using the parameter setting buttons, we ensure that the real current is equal to the set one.
3. Turn on the CC mode again, set a small current, for example 0.5-1 Ampere.
4. Press the same calibration button twice, it will display a constant with a lower value, for example 3452 or 4321), using the same setting buttons we ensure that the real current value matches the set one.
5. Repeat until you get tired :) After each time, the value of the higher and lower current will correspond more and more to the real one, or rather, the real one will more and more correspond to the set one.

With voltage it’s about the same, but there are two ways, right and wrong:
1. Incorrect, we supply a stabilized voltage and by changing the constants we ensure that the load indicator shows accurately. This method is very fast, but due to the large display discreteness it is also less accurate.
2. Correct. We apply a current-limited voltage to the input, for example a power supply connected through a light bulb, but a power supply with current limitation is better.
We connect a voltmeter to the load terminals.
We switch the load to CV mode, apply a certain voltage to the input, for example 20-60 Volts (the more, the better) and set, for example, 5 Volts less than the supplied one. Now the input voltage should be equal to the set one, since it is set by the electronic load.
We click on the upper right calibration button (to the right of +0.01), get into the calibration mode and use the parameter setting buttons to adjust the mode so that our external voltmeter shows what is set.
After this, we go back to the CV mode, set, for example, 5 Volts (2-5), and repeat everything with the second constant as in the current calibration example.
Then I think everything is clear, by successive approximation we achieve precise setting of both the upper and lower values.

I didn’t take any specific measurements specifically for the review, but there is at least one informative photo left.
On the left is an example of work before calibration, it is clear that the current was clearly overestimated, I raised it with a discrete of 1 Ampere, i.e. 0-1-2-3-4.
In addition to the incorrect current setting, the entire installation process took a long time, approximately 1 minute 40 seconds.
On the right is an example after calibration, I raised it to 5 Amps, 0-1-2-3-4-5, the current was set accurately and everything took about one minute.

In addition to the basic parameters themselves, you can measure (calculate) quantities such as mAh and Wh; for this, there are three windows below that display the corresponding measurements. The clock runs while the load is on, regardless of the set operating mode; I don’t know how to reset all these values, since the unit itself remembers them. I tried not only rebooting the software, but also launching a second copy of the program from a different folder, because to reset it I have to juggle the power supply to the load itself, which is inconvenient.
But the Chinese would not be Chinese if they had not messed up here too.

Remembering how the USB tester worked, I decided to conduct a similar experiment here, set the current to 4 Amperes, and started taking screenshots every 6 minutes, respectively, the values ​​​​should be 400 mAh, 4 Wh / 800 mAh, 8 Wh, etc.
But it turned out that the mAh readings were underestimated by exactly 10 times, however, I noticed this when I was experimenting before, but I just decided to double-check.
Well, how is that?
I even remembered a fragment from the book False Mirrors.
He has a small box in his palm. We crowd around, trying to see what it is.
“Warlock-9300,” Shurka answers. - Finally it turned out the way I planned...
The box is a tiny elevator cabin. The most ordinary one, brown, with sliding doors, with a piece of cable at the top.
But the elevator is ten centimeters high.
“The most convenient form,” says Maniac. - “Nine-thousander” was also supposed to work like this, but it didn’t work out...
“Sasha... Sasha, my dear,” Padla says hoarsely. - Are you sure you didn’t make a mistake with the size? A?
“I somehow didn’t think about the size,” Maniac says self-critically, and I understand that the bastard will face another stage of punishment for the joke.
- Apparently, I made a mistake with a comma somewhere...

I wrote above that regarding one point I had to ask for help from those for whom Chinese is their native language. At the bottom right of the program's working window, recording of the work log is enabled; as a result, a csv file with such incomprehensible values ​​is formed in the folder with the program.

In general, a lot of means are provided for working with the load, and partly for this reason there will be no continuation in the form of the final assembly of the device, since I feel that everything is still ahead.
For example, there is a hypothetical possibility of building graphs -

As far as I understand, the graphs are built based on data from another program, I downloaded it and it even tries to work, although it displays nonsense, so the screenshot is from the developer.

But an even greater reason for the temporary pause in the assembly was that in the process of searching for information I came across a module that can measure, display and control the operation of the device.

But all this is implemented somewhat strangely, the module has its own circuits for measuring current and voltage, on the left you can see the wires that go to the current-measuring resistor (and a very correct one, with four pins), but the module is also connected to the 485 interface.
In addition to the basic capabilities, it is stated that this addition allows -
Optional - bluetooth control.
Setting load shedding thresholds, such as minimum voltage or current, as well as limiting operation by time.
Mode memory.
Compensation for voltage drop on wires
Current up to 50 Amps
Coulometer
18 bit ADC.
Language selection - Chinese, English.

There is a truth and a minus, even on Tao this module costs about 28 bucks: (But it’s quite possible that I’ll fork out the cash.

But the idea to switch to such control was also caused by software glitches.
1. Spontaneous values ​​flash on the screen periodically, fortunately for a short time and do not interfere in any way
2. Management. Comrades, this is a bummer. I understand that the software version is test, but so.....
Even in the mode of simply selecting the current/voltage value, etc. Changing each parameter takes about 3 seconds.
For example, you need to set 1.2 Amperes, it will look like this -
press 1,
3 seconds pause,
press 0.1
3 seconds pause
press 0.1
3 seconds pause.

Now imagine how much time it takes to set, for example, a current of 5.55 Amperes....

But I’ll be honest, I still haven’t lost hope that the software will be “finished”, and besides, I can say that there are essentially no special comments on the load itself (i.e. on the hardware), they work on their own not bad, and besides, they have a quite reasonable price both for functionality and for workmanship.
Actually, that’s why I have a question, maybe one of the programmers who also wants a similar device will be able to help in terms of the program. Perhaps there is an option to attach an arduino with a normal screen, buttons and an encoder. In this case, I can do the “hardware” part in terms of redrawing the circuit for repetition, and together we can make a quite good device.

For a heavy load, I am slowly looking for a good ammeter with a voltmeter, as well as a multi-turn resistor and a housing + power supply. But maybe I’ll think about converting it to digital control. In any case, at least one more review with application is planned.

That's probably all I have. I ordered the load through an intermediary

Recently it became necessary to test various very powerful rechargeable batteries voltage from 24 to 55 V. Since it is impossible to select resistors for such high currents, we had to build something completely electronic. The artificial load design served as the base. Since its power was too low, it intensified somewhat.

Electrical circuit diagram EN

The power element uses 8 0.68 Ohm resistors connected to an IGBT power transistor. Why IGBT? During testing, several conventional MOSFETs failed, but the IGBTs turned out to be noticeably more stable. Resistors are installed on radiators, 4 pcs each. Depending on the needs included sequentially for more high voltage load or in parallel - for weaker ones. The radiators are screwed at a distance of 1 cm from the bottom of the case, holes are drilled under the radiators, the cooling air flow is significant.

The power transistor is installed on a heatsink from the PC processor and is cooled by two fans.

A 0.01 Ohm resistor is used as a measuring element and standard for the operational amplifier, and counters on ICL7107 microcircuits are used as meters - current accuracy is 0.1 A, voltage - 0.1 V.

Electrical supply for meters and fans - removed from some pulse device with parameters + 5 V at 5 A (indicators), +/- 12 V at 2 A (fans and op-amp). There was a cool metal case from some old device available, and it was decided to use it. The front panel is made from a piece of 3mm PVC plate. Holes for fans are cut out in the back.

Load operation test

1. Circuit tested at 28V at 20A - power dissipated in 560W IGBT resistors and transistors - cooled and under load for one hour - 40 degree temperature.
2. Another artificial load test was carried out with a 55 V battery at 11 A/h - here the load was 15 - 20 A, which means the power reached 1 kW - the radiators became hot, especially those on which power resistors were installed. The resistors heated up to about 110 degrees, the IGBT transistor to a temperature of 90 degrees, in principle acceptable.
3. Naturally you can easily test car batteries with a 12 V 20 A mode - the temperature was 80 degrees, which is normal.

Ways to improve the device

In the future, we will further improve this homemade electronic load by adding a power meter and a mode controller on Arduino (from Aliexpress).

The construction of the device was mainly spent on power resistors - the rest was lying around from disassembling all sorts of things.
Multiple sockets will also be added to allow multiple voltage ranges for testing without switching power resistors.

The power-regulated load is part of the test equipment needed when setting up various electronic projects. For example, when building a laboratory power supply, it can "simulate" the connected current sink to see how well your circuit performs not only on Idling, but also on the load. Adding power resistors for the output can only be done as a last resort, but not everyone has them and they can’t last long - they get very hot. This article will show how a variable electronic load bank can be built using inexpensive components available to hobbyists.

Electronic load circuit using transistors

In this design maximum current should be about 7 amps and is limited by the 5W resistor that was used and the relatively weak FET. Even higher load currents can be achieved using a 10 or 20 W resistor. The input voltage should not exceed 60 volts (maximum for these field-effect transistors). The basis is an op-amp LM324 and 4 field-effect transistors.

Two "spare" operational amplifiers of the LM324 chip are used to protect and control the cooling fan. U2C forms a simple comparator between the voltage set by the thermistor and the voltage divider R5, R6. The hysteresis is controlled by the positive feedback received by R4. The thermistor is placed in direct contact with the transistors on the heatsinks and its resistance decreases as the temperature increases. When the temperature exceeds the set threshold, the U2C output will be high. You can replace R5 and R6 with an adjustable variable and manually select the response threshold. When setting up, make sure that the protection is triggered when the temperature of the MOSFET transistors is slightly below the maximum permissible specified in the datasheet. LED D2 signals when the overload protection function is activated - it is installed on the front panel.

The op-amp element U2B also has voltage comparator hysteresis and is used to control a 12V fan (can be used from older PCs). The 1N4001 diode protects the MOSFET BS170 from inductive voltage surges. The lower temperature threshold for activating the fan is controlled by resistor RV2.

Assembling the device

An old aluminum switch box was used for the case, with plenty of internal space for components. In the electronic load I used old AC/DC adapters to supply 12 V for the main circuit and 9 V for dashboard- she has digital ammeter, to immediately see the current consumption. You can already calculate the power yourself using the well-known formula.

Here's a photo of the test setup. Laboratory block The power supply is set to 5 V. The load shows 0.49A. A multimeter is also connected to the load, so that the load current and voltage are monitored simultaneously. You can verify for yourself that the entire module is working smoothly.