Measuring current is a fairly important procedure for calculating and testing electrical circuits. If you are creating a device with power consumption at the level of charging a mobile phone, the usual one is enough to measure.
A typical inexpensive household tester has a current measurement limit of 10 A.
Most of these devices have an additional connector for measuring larger quantities. When rearranging the measuring cable, you probably haven’t thought about why you need to organize an additional circuit, and why you can’t just use the mode switch?
Important! Without knowing it, you have activated the ammeter shunt.
Why can’t one device measure a wide range of quantities?
The operating principle of any ammeter (pointer or coil) is based on converting the measured value into its visual display. Pointer systems operate on a mechanical principle.
A current of a certain magnitude flows through the winding, causing it to deflect in the field of a permanent magnet. An arrow is attached to the reel. The rest is a matter of technique. Scale, markings, etc.
The dependence of the deflection angle on the current strength on the coil is not always linear; this is often compensated by a specially shaped spring.
To ensure measurement accuracy, the scale is made with as many intermediate divisions as possible. In this case, to ensure a wide measurement range, the scale must be of enormous size.
Or you need to have several instruments in your arsenal: an ammeter for tens and hundreds of amperes, a regular ammeter, a milliammeter.
In digital multimeters the picture is similar. The more accurate the scale, the lower the measurement limit. And vice versa - an overestimated value of the limit gives a large error.
A scale that is too busy is inconvenient to use. A large number of positions complicate the design of the device and increase the likelihood of loss of contact.
By applying Ohm's law to a section of the circuit, you can change the sensitivity of the device by installing a shunt for the ammeter.
Many home electricians are dissatisfied with industrial production testers, so they think about how to, as well as how to improve the functionality of the industrial production tester. For this purpose, a special shunt can be made.
Before you begin, you should calculate the shunt for the microammeter and find a material with good conductivity.
Of course, for greater measurement accuracy, you can simply purchase a milliammeter, but such devices are quite expensive, and they are rarely used in practice.
Recently, testers designed for high voltage and resistance have appeared on sale. They do not require a shunt, but their cost is very high. For those who use a classic tester made in Soviet times, or use a homemade one, a shunt is simply necessary.
Selecting a current ammeter is not an easy task. Most devices are produced in the West, in China or in the CIS countries, and each country has its own individual requirements for them. Also, each country has its own permissible values of direct and alternating current, requirements for sockets. In this regard, when connecting a Western-made ammeter to domestic equipment, it may turn out that the device cannot correctly measure current, voltage and resistance.
On the one hand, such devices are very convenient. They are compact, equipped with a charger and easy to use. A classic dial ammeter does not take up much space and has a visually clear interface, but it is often not designed for the existing voltage resistance. As experienced electricians say, there are “not enough amperes” on the scale. Devices designed in this way necessarily require shunting. For example, there are situations when you need to measure a value up to 10a, but there is no number 10 on the instrument scale.
Here are the main ones disadvantages of a classic factory ammeter without a shunt:
- Large error in measurements;
- The range of measured values does not correspond to modern electrical appliances;
- Large calibration does not allow small quantities to be measured;
- When trying to measure a large resistance value, the device goes off scale.
A shunt is necessary in order to correctly measure in cases where the ammeter is not designed to measure such quantities. If a home craftsman often deals with such quantities, it makes sense to make a shunt for an ammeter with your own hands. Shunting significantly improves the accuracy and efficiency of its work. This is an important and necessary device for those who often use the tester. It is usually used by owners of the classic 91s16 ammeter. Here are the main advantages of a homemade shunt:
Manufacturing procedure
Even a freshman at a vocational school or a novice amateur electrician can easily handle making a shunt on his own. If connected properly, this device will greatly increase the accuracy of the ammeter and will last a long time. First of all, it is necessary to calculate the shunt for a DC ammeter. You can learn how to make calculations via the Internet or from specialized literature addressed to home electricians. You can calculate the shunt using a calculator.
To do this, you just need to substitute specific values into the finished formula. In order to use the calculation scheme, you need to know the real voltage and resistance for which a particular tester is designed, and also imagine the range to which you need to expand the capabilities of the tester (this depends on which devices a home electrician most often has to deal with ).
Perfect for making such materials:
- Steel clip;
- Roll of copper wire;
- Manganin;
- Copper wire.
You can purchase materials in specialized stores or use what you have at home.
In fact, a shunt is a source of additional resistance, equipped with four clamps and connected to the device. If steel or copper wire is used to make it, do not twist it into a spiral.
It is better to carefully lay it in the form of “waves”. If the shunt is sized correctly, the tester will perform much better than before.
The metal used to make this device must conduct heat well. But inductance, if a home electrician is dealing with the flow of a large current, can negatively affect the result and contribute to its distortion. This also needs to be kept in mind when making a shunt at home.
If a home electrician decides to purchase a commercially available ammeter, he should choose one with a fine calibration because it will be more accurate. Then, perhaps, you won’t need a homemade shunt.
When working with the tester, you should follow basic safety precautions. This will help prevent serious injury caused by electrical shock.
If the tester systematically goes off scale, you should not use it.
It is possible that the device is either faulty or is not able to show the correct measurement result without additional equipment. It is best to purchase modern, domestically produced ammeters, because they are better suited for testing new generation electrical appliances. Before you start working with the tester, you should carefully read the operating instructions.
A shunt is a great way to optimize the work of a home electrician when testing electrical circuits. In order to make this device with your own hands, you will only need a working industrial production tester, available materials and basic knowledge in the field of electrical engineering.
♦ In the previous article: to control the charging current it is used ammeter for 5 - 8 amperes.
An ammeter is a rather scarce thing and you can’t always find one for such a current. Let's try to make an ammeter with our own hands. 
To do this, you will need a pointer measuring device of the magnetic-electric system for any current of the full deviation of the needle on the scale.
It is necessary to ensure that it does not have an internal shunt or additional resistance for the voltmeter.
♦ The measuring pointer device has an internal resistance of the movable frame and the current of the full deflection of the pointer. The pointer device can be used as a voltmeter (additional resistance is connected in series with the device) and as an ammeter (additional resistance is connected in parallel with the device).
♦ The circuit for the ammeter is on the right in the figure.
Additional resistance - shunt calculated using special formulas... We will make it in a practical way, using only a calibration ammeter on current up to 5 - 8 amperes, or by using a tester, if it has such a measurement limit.
♦ Let's assemble a simple circuit from a charging rectifier, a standard ammeter, a wire for a shunt and a chargeable battery. See the picture... 
♦ A thick wire made of steel or copper can be used as a shunt. The best and easiest way is to take the same wire that was used to wind the secondary winding, or a little thicker.
You need to take a piece of copper or steel wire about 80 centimeters, remove the insulation from it. At two ends of the segment, make rings for bolt fastening. Connect this segment in series with a reference ammeter.
Solder one end from our pointer device to the end of the shunt, and run the other along the shunt wire. Turn on the power, set the charge current using the regulator or toggle switches according to the control ammeter - 5 amp.
Starting from the soldering point, run the other end from the pointer device along the wire. Set the readings of both ammeters to the same level. Depending on the frame resistance of your pointer gauge, different pointer gauges will have different shunt wire lengths, sometimes up to one meter.
This, of course, is not always convenient, but if you have free space in the case, you can carefully place it.
♦ The shunt wire can be wound into a spiral as in the figure, or in some other way depending on the circumstances. Stretch the turns a little so that they do not touch each other, or put rings made of vinyl chloride tubes along the entire length of the shunt. 
♦ You can first determine the length of the shunt wire, and then use insulated wire instead of bare wire and wind it in bulk onto the workpiece.
You must select carefully, performing all operations several times, the more accurate the readings of your ammeter will be.
The connecting wires from the device must be soldered directly to the shunt, otherwise the device arrow will read incorrectly.
♦ The connecting wires can be of any length, and therefore the shunt can be located anywhere in the rectifier body.
♦ It is necessary to select a scale for the ammeter. The ammeter scale for measuring direct current is uniform.
The other day I was reminded of another idea for computer modding. We will talk about how to connect a fluorescent (VFD) indicator from a Soviet tape recorder to a computer.
Once upon a time, a long time ago, I had a Mayak 240-S1 tape recorder. Due to obsolescence, the tape recorder was scrapped. All that was left of him of value was the electroluminescent indicator, which I had lying around collecting dust. Once upon a time, a couple of years ago, I already tried to install it on a computer, but it did not fit the design.
The indicator looks like this:
And today I will tell you how to connect this or a similar indicator to a computer.
So, let's start with the schematic diagram:
but we don’t need the entire scheme, we are only interested in part
As can be seen in the diagram, the indicator has dual power: bipolar ±15 volts and alternating 5 volts. But the indicator remains operational when powered by a bipolar voltage of ±12 volts and a constant voltage of +5 volts.
Let's connect XP1 as follows (designations according to the diagram):
1 - zero
2 - +5
3 - +12
4 - -12
5 - zero
To make it more convenient to connect, I took a non-working and half-soldered motherboard
and soldered the wires on the back of the ATX connector and connected the power supply.
Now that power is supplied to the indicator, you need to send some signal to it. I will use an mp3 player as a signal source.
The XP2 connection diagram is very simple (designations according to the diagram):
1 - left channel
2 - right channel
3 - Fe tape type indicator
4 - indicator of the PN noise reduction system
5 - Cr tape type indicator
6 - microphone on indicator
7 - speaker on indicator
8 - recording indicator
Taking out from your supplies a cable to connect the CD-ROM drive to the sound card
And having removed the original connectors from it, I soldered one end to the indicator board, and soldered a 3.5mm jack to the second
In general, this gray cable is a very good help in such cases, because there is a shielded two-channel stranded wire inside the insulation and it is long enough for many applications. But, unfortunately, recently, very often these cables are not shielded. But I got distracted, let’s continue.
