Can this thin wire pass 3A of current?

electricor

This is the circuit board we soldered, but I am worried that the connecting wire at the back is too thin and cannot pass the 3A current. I wonder if this thin wire can be used?

maychang

Wire? Try using a magnet to see if it sticks to you, or a sewing needle to see how well the magnet attracts your wire and sewing needle.

wenyangzeng

You can find the answer by calculating based on 5A per square millimeter of wire cross-section.

qwqwqw2088

3A is a bit thin

maychang

In the electronics industry, there are very few metal wires that can be attracted by magnets. One is glass-encapsulated diodes or transistors, whose leads can be attracted by magnets. That is an alloy with the same thermal expansion coefficient as glass (so that there is no air leakage between the glass and the leads). Another is some axially led resistor lead caps.

wpxm119

Yes, in the past, a thin wire inside the power cord (soft wire with cloth wrapped outside) used by electricians was used as a fuse, and it could pass through a 1000W electric stove. You can also find a 1000W electrical appliance to do the experiment

PowerAnts

wpxm119 posted on 2018-8-19 18:49 Yes, in the past, a thin wire inside the power cord (soft wire wrapped in cloth) used by electricians was used as a fuse, and it could pass a 1000W electric stove. You can also...

Coil wire does not have to be wrapped in cloth. Two strands of wire twisted together like a twist are called cord wire. Thin copper wire can be used as a one-time fuse, but replaceable wire is not recommended. The seat is prone to severe oxidation and it is easy to burn the wire later. There is a reason for using lead-tin alloy for replaceable wire fuses. It can be used once or twice in an emergency, but don't use it as a magic weapon.

LuJianchang

Just in case, tin it directly

bigbat

qwqwqw2088 posted on 2018-8-18 09:58 3A is a bit thin

Haha, even experts get dizzy sometimes! The conductivity mainly depends on the power, W=I*I*R. If the resistance is very small, it doesn't matter, so it depends on the length of the wire, usually in meters. To calculate, take the length into account, the actual length L, R=σ*L/A, that's it, use the value in your table, mm/1000, in the calculation.

PowerAnts

bigbat posted on 2018-8-20 18:28 Haha, even experts get dizzy sometimes! The conductivity mainly depends on the power, W=I*I*R. If the resistance is very small, it doesn't matter, so it depends on...

It has little to do with the length. The length only determines the loss and will not damage the wire. There are many factors that limit the current carrying capacity. The rated temperature rise of the wire determines the allowable current. The rated temperature of the high-voltage line is 80 degrees. The line design is based on a temperature rise of 40 degrees when fully loaded in summer. But in winter, the temperature rise is only 10 degrees when half loaded, and ice may break the line. It needs to be melted. The current (given wire) or cross-sectional area (given current) is determined by the permissible voltage drop. If a house is 10 kilometers away from the transformer, I'm sorry, you can't install an air conditioner. If it's not done well, the refrigerator may not start smoothly. It's okay to light a few energy-saving lamps.

bigbat

PowerAnts posted on 2018-8-20 23:26 It has little to do with the length. The length only determines the loss and will not damage the wire. There are many factors that limit the current carrying capacity. It is determined by the rated temperature rise of the wire...

It subverts my scientific view a bit! According to what I have learned, when a DC current flows through a conductor, a magnetic field perpendicular to the direction of the current is generated. If there is no changing magnetic field around, its energy conversion is mainly determined by the resistance of the conductor, and is mainly converted into "heat". Thermal energy should be the main factor causing temperature rise. W=I*I*R should be the rule. Of course, the temperature rise of long-distance power transmission and distribution lines is also related to the environment and the physical properties of the materials. However, the resistance value of the wire material will be affected by temperature after manufacturing, but it will not be as drastic as semiconductors (temperature refers to -30~150C). Finally, I want to say: when the cross-sectional area of the wire is constant, the resistance is basically determined by the length! The main factor of temperature rise is resistance!!!

dj狂人

bigbat posted on 2018-8-21 08:22 This has somewhat overturned my view of science! According to what I have learned, when a DC current flows through a conductor, a magnetic field perpendicular to the direction of the current will be generated. If there is no magnetic field around...

The burning of the wire is caused by line loss. In this case, it is indeed related to resistance, but what I have never understood is that the resistance distribution of a wire should be relatively uniform, so that the loss distribution of the wire should be similar within the range of the wire (such as heat), then why is the wire often only burned at one node instead of the entire wire burning?

PowerAnts

bigbat posted on 2018-8-21 08:22 It kind of subverts my view of science! According to what I have learned, when a DC current flows through a conductor, it will generate a magnetic field perpendicular to the direction of the current. If there is nothing around...

Is this also a scientific view? It's just a mountain range when you look at it from the side!

maychang

Dj Madman published on 2018-8-21 08:53 The burning of the wire is caused by line loss. In this sense, it is indeed related to resistance, but what I have never understood is that the resistance distribution of a wire should not be...

The cross-section of the wire is uniform, and the resistance is generally uniform, but the heat dissipation of the wire is not uniform. The heat dissipation capacity of the metal objects (such as wire pressing screws) at both ends of the wire that fix the wire is much stronger than that in the middle of the wire. Whether the wire is burned (melted) is related to the temperature of the wire. Since the heat dissipation at both ends of the wire is better, it is easy to understand that the wire always burns (melts) in the middle.

maychang

Dj Madman published on 2018-8-21 08:53 The burning of the wire is caused by line loss. In this way, it is indeed related to resistance, but what I have never understood is that the resistance distribution of a wire should not be...

The transformer winding is wound with a long wire. The barrel-shaped winding end of a dry transformer (not immersed in oil) dissipates heat better than the inside of the winding, and the outer surface dissipates heat better than the inner layer. When dismantling a burned transformer, the outer surface is often not severely burned, but the copper wire inside has melted.

maychang

bigbat published on 2018-8-21 08:22 This is a bit subverting my scientific view! According to what I have learned, when a DC current flows through a conductor, a magnetic field perpendicular to the direction of the current will be generated. If there is no...

Temperature rise is not only related to the heat generation power (of course, the heat generation power follows the relationship between resistance multiplied by the square of the current), but also to heat dissipation. Wires exposed to the air dissipate heat very well, much easier than wires wound together in a transformer. Therefore, the temperature of transformer windings is easy to rise, while the temperature of wires exposed to the air is not easy to rise. Therefore, the current carrying capacity of bare wires is much higher than that of winding wires in transformers, which is limited by temperature rise. The third floor said, "Calculate it according to 5A per square millimeter of wire cross-section." That is the current density standard for small transformers. For wires exposed to air, the current density can be much greater.

maychang

Feel free to use it. The cross-sectional area of your wire is much larger than the wire corroded on the circuit board. 1. The wire is exposed to the air, so it has good heat dissipation and will not melt. 2. The wire is very short, so the circuit operation will not be affected by excessive resistance.

dj狂人

maychang posted on 2018-8-21 12:05 The cross section of the wire is uniform, and the resistance is generally uniform, but the heat dissipation of the wire is not uniform. The metal objects at both ends of the wire that fix the wire ( ...

So that's the case. I forgot that metal has a strong thermal conductivity.

maychang

bigbat posted on 2018-8-21 08:22 This has somewhat overturned my view of science! According to what I have learned, when a DC current flows through a conductor, a magnetic field perpendicular to the direction of the current will be generated. If there is no...

The current density limited by the temperature rise has nothing to do with the length of the wire. If the length of the wire is doubled and the current of the same magnitude is passed, of course the resistance of the wire will double and the heat will double, but after the length of the wire is doubled, as long as it is not twisted or folded, the heat dissipation capacity will also double.

PowerAnts

dj狂人 posted on 2018-8-21 12:23 So that's how it is. I forgot that metal has strong thermal conductivity.

The heat dissipation of metal wire has little to do with its own thermal conductivity. Heat dissipation depends on surface area. For wires of the same material and diameter, their heat generation and heat dissipation capacity are proportional to the length of the wire, so the current carrying capacity has nothing to do with the length. Don't always talk about scientific views... Personal scientific views are all very one-sided. Remember Su Shi's poem on the 13th floor