Installing a digital voltage and current indicator in a homemade laboratory power supply or car battery charger is a standard procedure for any amateur radio operator. Chinese modules such as DSN-V288 or TN-2880They are widely used due to their low cost and compact size. However, despite the simplicity of appearance, these devices have their own installation features, which must be taken into account to obtain accurate readings.
The main difficulty for beginners is the difference between the circuits of connecting devices with a common and separate power supply. Incorrect connection of wires can lead not only to incorrect operation of the display, but also to failure of the measuring module or even power source. In this article, we will discuss in detail the color marking of wires, calibration methods and ways to eliminate typical problems during operation.
Before you start installing, it is important to understand that most budget models run from a voltage of 3.3-30 V, which allows you to power them directly from the circuit being measured. However, there are models with extended range or requiring a separate source. Accuracy of measurements It directly depends on the quality of soldering and the length of the connecting wires, so the preparation of the tools should be approached responsibly.
Types of voltammeters and their design features
In the modern electronics market, there are many modifications of measuring devices, which are divided into two main groups by type of power. The first group is the devices with meal-inwhere the measuring circuit and the display circuit are connected inside the board. Such models are easier to install, but have restrictions on the minimum measured voltage, as part of the energy is spent on the operation of the backlight.
The second group includes devices with feeding. In such modules, the measurement circuit (thick wires) is galvanically untied from the display supply chain (thin wires). This allows voltage measurements from virtually zero, which is critical when assembling adjustable laboratory power supplies. Visually, they can be distinguished by the number of wires: models with a common power supply have three (red, black, yellow / green), and separate ones have four or more, or there is a lintel on the board.
⚠️ Note: When buying, pay attention to the presence of a jumper on the board. If it is closed, the device operates in general power supply mode. To work in the mode of separate power supply, the jumper must be carefully torn or soldered, otherwise the circuit will burn when connected to high voltage.
The housings of the devices also differ in the method of installation. There are models for insertion into a panel with plastic latches that are fixed without screws, and options for surface installation. DSN-V288 It is usually about 12 mm thick, which requires considering the depth of the case when designing the front panel of the device. Some advanced models are equipped with buttons for calibration directly on the front panel, which eliminates the need to disassemble the device during configuration.
Preparation for installation and necessary tools
The quality of the installation of the voltammeter directly affects the accuracy of its readings and the reliability of the entire device. Before starting work, it is necessary to prepare not only the device itself, but also the appropriate tools. The main requirement is to use a soldering iron with a thin sting, as the contact areas on Chinese modules are often very small and sensitive to overheating.
To connect you will need the following materials:
- 🔌 Copper wire with a cross section of at least 0.5 mm2 for power circuits to minimize voltage drop.
- 🛠️ A soldering iron with a capacity of 25-40 W, solder with flux and tweezers to hold small parts.
- 📏 Multimeter with trusted probes for reference measurements during calibration.
- ✂️ Insulation stripping tool and shrink tubes for insulation of joints.
Particular attention should be paid to the length of the wires going to the measuring contacts. In cheap models, they are often too short or, conversely, too long, which introduces additional errors. Perfect length. The measuring probes are 10-15 cm. If the wires are longer, they should be cut, since the excess length acts as an antenna and can make tips that distort the readings on fractions of a volt.
☑️ Checking before ration
It is also recommended to think in advance about the method of attaching the module in the case. Plastic latches, coming in the kit, over time can dry or break. Many masters prefer to additionally fix the device with the help of thermal glue or small screws, drilling holes in the ears of the body. This is especially true for devices that will be subjected to vibrations, such as in car chargers.
Detailed scheme of wire connection
The most important step is the physical connection of wires. The standard color marking of Chinese voltammeters is usually the same for most models, but it is always best to double-check the signatures on the circuit board. An error in connection even for a couple of seconds can lead to irreversible consequences for the chip.
Consider the classic connection scheme for a device with three wires (shared power):
- 🔴 Red thick wire: It is connected to the plus of the power supply (+V). Through it, power is supplied to the device itself and voltage is measured.
- ⚫ Black thick wire: Connected to the power source minus (-V). It is a common wire (earth) for feeding and measuring.
- 🟡 Thin yellow (or green) wire: It's a measuring probe. It connects to the load plus after contacting the red wire. It is by the voltage drop on the internal shunt or the difference in potentials that the device calculates the current.
In the case of using a separate-powered model, the circuit is complicated by the addition of two additional thin wires to power the display. Thin red and black wires are connected to a separate source of 5-12 volts, or, if the range allows, parallel to the main power wires, but with the obligatory break of the internal lintel on the board. It is important to observe polarity.Because protection against polarization in such modules is often absent.
| Color of wire | Thickness | Function | Connection point |
|---|---|---|---|
| Red. | Fatty. | Nutrition + Measurement V+ | Plus the power source. |
| Black. | Fatty. | Total minus (GND) | Minus the power source |
| Yellow/Green | Thin | Current and load measurement V | Plus loading |
| Blue (rarely) | Thin | Dop. measurement | Depends on the model. |
When soldering, try not to overheat the place of entry of the wire into the device body. The plastic can melt, and the wire will fall off along with a piece of track. It is better to first smear the ends of the wires, and then quickly solder them to the contact board or to the output terminals, if the design allows. Cold rations It is unacceptable, as it will create a transition resistance that will warm and affect the accuracy of the current measurement.
Calibration of readings and accuracy adjustment
Chinese voltammeters often come from a factory with a downed calibration. The error can be as high as 5-10%, which is not acceptable for fine-tuning the car battery charge or laboratory experiments. Fortunately, most models allow manual reading adjustments using adjusting resistors.
The calibration process is as follows. First, connect the device to a stable power source and a reference multimeter. Give a voltage, for example, 12.00 V, and compare the readings. If they are different, find a small potentiometer on the back of the board, signed as V-ADJ plainly V. Carefully rotate it with a screwdriver, achieving the coincidence of values on the display of the voltammeter with the reference device.
What to do if there is no scaling resistor?
In some ultra-budget models, the adjustment is software-based and requires a certain voltage to enter when the button is pressed, or there are no resistors at all. In this case, the error can be adjusted programmatically if the device is connected to the microcontroller, or simply remember the correction factor. However, most often the resistor hides under a protective sticker or requires the removal of the back cover.
A similar procedure is performed for calibration of current. To do this, it is necessary to assemble a circuit with a known load (for example, a powerful resistor or an incandescent lamp) and measure the real current with a reference ammeter turned on in series. The control resistor for current is usually indicated as I-ADJ or I. Keep it moving until the readings match. Remember that at high currents, wires can heat up, changing their resistance, so it is better to calibrate in the operating temperature range.
⚠️ Note: When calibrating the current, be careful! Do not leave the circuit closed short to check the maximum current if your power supply does not have reliable protection. This can cause the wires to ignite or damage the source.
Removal of faults and typical errors
During operation, users often face a number of problems that are easily solved without replacing equipment. One of the most common complaints is “floating” readings or a complete lack of glow of the display. Often the reason lies not in marriage, but in improper installation or external tips.
Consider the main symptoms and methods of their elimination:
- 🔥 The display flashes or goes out: Probably lacking the power supply. Make sure the input voltage is higher than 3.5-4 V. If you measure the battery voltage from 0 to 30 V and the appliance requires a minimum of 4.5 V to operate, it won’t turn on at the start of charging. The solution is a separate display power.
- 📉 Large measurement error: Check the quality of soldering of a thin measuring wire. If it is torn off or is not in contact, the device will show nonsense. Also check if the shunt inside the device is heated from a long flow of large current.
- 📟 The testimony will jump: Maybe the long wires of the measuring probe are catching interference. Put them in a harness or shield them. Also, the cause may be the pulsation of the power source itself, if it is poorly filtered.
If the voltammeter shows voltage but zero amperes when the load is connected, check the integrity of the thin yellow wire. He is responsible for taking the readings of the voltage drop. Often it falls off inside the case with careless transportation.
Another common mistake is to try to measure current in a circuit with a voltage above 30 V without taking into account the limitations of the device. Although the range is up to 30V or 100V, cheap Chinese components may not be able to withstand even a short-term exceedance. Always keep a supply of 20-30%. Don't forget about it, too. maximum currentThis is usually limited to 10 Amps for standard models. Exceeding this value will lead to the combustion of the internal shunt.
Modernization and improvement of design
For those who strive for the ideal, standard equipment is not enough. Experienced amateur radio operators often refine these devices to improve their reliability and ease of use. One of the useful improvements is the installation of an external shunt. Built-in shunts in cheap models are thin and warm, which causes drift readings during prolonged work.
Remote shunt made of nichrome wire or ready shop resistor allows you to pass large currents without heating and install it in the break of the chain in a convenient place. To connect an external shunt, it is necessary to unseal the internal (if any) or use contacts designed for this, and dilute the measuring wires directly to the pins of the shunt. This requires recalculation of the gain and recalibration.
Using an external shunt is the most effective way to turn a cheap Chinese indicator into a professional tool for charging powerful batteries, eliminating the problem of heating and drift readings.
Also popular is the replacement of standard wires with higher quality, silicone, 18-16 AWG cross section. Native wires are often rigid and thin, which makes it difficult to install in dense housings. Replacement of the connectors with more reliable ones, for example, XT60 or DC connectorsIt simplifies the process of replacing the device in case of failure. It will not be superfluous to install a fuse in the break of the plus power wire of the voltammeter itself to protect it from accidental voltage surges in the on-board network of the car.
Can this voltammeter be used as a separate voltmeter?
Yes, you can. To do this, you just need not to connect a thin yellow (measuring) wire to the load, but leave it hanging in the air or connect to the plus of the source. In this mode, the device will only show the voltage of the power source and the current consumption (which will be zero if there is no load in the yellow wire circuit). However, to measure the current, the load must be included in the chain of the yellow wire.
Why does the voltammeter show current when the load is off?
This may be due to tips on the long wires of the measuring probe or due to the fact that a thin measuring wire touches the housing or other parts. Also, the reason may be a malfunction of the module itself or the lack of zero calibration. Try twisting the wires of the measuring probe together or shielding them.
What is the maximum power that can be switched through this device?
Voltammeter itself does not switch power, it only measures parameters. However, its built-in shunt is designed for a specific current, usually 10A. At 30V and 10A, the power will be 300W, but for large power, be sure to use an external shunt.
Does the length of the power wires affect the accuracy of the measurement?
Yes, it does. Long and thin power wires create a voltage drop, which is why the device can show less voltage than is actually on the load, if it is powered from the same source. For measuring circuits, use the shortest and thickest wires possible. For the power chains, the display length is not as critical if the cross section is sufficient.
What to do if the lighting diode is burned?
In most models, the backlight is made on the basis of LEDs soldered into a board. If one burns, the whole chain will burn. You can try replacing LEDs with similar in size and voltage (usually 3mm or 5mm LEDs, or SMD). Sometimes it is easier to power the external light from a separate source, if the design of the housing allows.