Determining Resistor Wattage: Identify Watt Rating by Resistance, Tolerance & Size Factors

Question

How to check how much watt is a resistor? On the barcode, they only give resistance and tolerance, and how to check whether it is, for example, 1W or 2W or more, I noticed that the size of the resistor does matter, but how big is how much Watt?

Paweł Es. · Answer

There is no simple dependency. You can try, for example, by comparing with other resistors of known power and, just in case, take the next larger value from the power series.

w1m · Answer

Measurement of the diameter gives a full picture, however, it is dependent on the age of the resistor very old resistors, although they are large, have low power

If it is about more modern ones, I had only these at hand, about 2.3mm, 0.125W, 3.6mm, 0.25W, 4.5mm, 0.5W

boomerang · Answer

I propose an experiment.
Adjustable voltage power supply, increasing the voltage until the long-term operation does not cause a significant increase in temperature. Then, from the basic formulas, calculate the power released and adopt a little lower values for operation.

Kondrax · Answer

I did not think that there is an easier way, but I see, to be sure, it is better to go to the store and buy a new one, how to look for old resistors, and I asked for watts after doing a JIG to a speaker workshop and there it is very important how much watt has.

Added after 1 [minutes]:

And tell me how it is with watts when connected in series or in parallel because I did not find it in the electrical engineering book.

szymon188 · Answer

If you give a resistor too strong, nothing will happen. Gay, if you give it too weak and it will burn out.

Kondrax · Answer

Super cool szymon188 but which one is the stronger one, you haven't thought about it.

szymon188 · Answer

It is best to go to the electronic one and ask the seller when buying, because when using old recycled resistors, you can never be sure how long it will last,

Kondrax · Answer

How is it with watts when connected in series or in parallel because I did not find it in the electrical engineering book. Do they add up or how?

Paweł Es. · Answer

When you connect in series, the total power is divided into resistors depending on the voltages on them

The same current flows through all the resistors.

Pcałk = U1 * I + U2 * I + ... + Un * I

With a parallel connection, the power is distributed among the resistors depending on the current that flows through the resistor:

There is the same voltage across all resistors.

Pcałk = U * I1 + U * I2 + ... + U * In

Note that the voltage across any resistor must not exceed the maximum allowable for a given construction type, because it may result in its breakdown)

It is similar with maximum power

Both of the above conditions must be met so that the resistor is not damaged.

pendzel_no1 · Answer

That was it?

CYRUS2 · Answer

Fellow advisers - skip your advice.
It will not work - you have to take it from the catalog.
The power is specified by the manufacturer.
Power various types of resistors of the same dimensions may be different.
Example :
2W MŁT resistors from "Omig" are much larger than the current 2W resistors.

JoteR · Answer

Yeah, sure. Each of us keeps resistors in a drawer with labels with the manufacturer's name and catalogs dangling next to them.

_jta_ · Answer

And very much: I just had resistors of very similar sizes, one of which had a power of 0.5W (the ones with flat tips transverse to the resistor, used in the past in tube circuits), the other 5W (covered with some enamel); I also have dark green resistors (they are probably wire painted) of similar size and also a lot of power.

jarek_lnx · Answer

The higher the operating temperature allowed by the manufacturer, the higher the power can be at a given surface of the resistor.

You need to be careful with power resistors, because if the manufacturer specifies that the resistor will withstand 5W, but at the same time it has the temperature of a hot soldering iron, it may be better not to use these "possibilities" and not to smell the burned dust and not have a brown laminate under the resistor and overheated parts nearby .

CYRUS2 · Answer

This colleague will not find out what the rated power of the resistors is.

klamocik · Answer

As with watts, if you connect two 1 watt resistors, whether in series or in parallel, the power will be 2 watts.

_jta_ · Answer

Unless he gets to know the resistors so that he knows which is which - they are slightly different, you just need to know what and be able to see it.

398216 Usunięty · Answer

Yes. This is due to Kirchhoff's laws.

Adamcyn · Answer

I connected a 1 M? resistor to a regulated power supply, and it won't heat up too damn well. Am i doing something wrong?

CYRUS2 · Answer

Resistor power.
This is not a direct link to the destruction of the resistor.

This is the power curve of the resistor.
The resistor is able to discharge the rated power at an ambient temperature of max 70 ° C.
At higher temperatures, the power of the resistor decreases.

hasek123 · Answer

This should help.

Anonymous · Answer

Only this is true for two resistors with the same resistance. If they have different resistance values it will not sum 1 + 1 = 2W, but between 1W and 2W. You have to count on currents and tensions. I just write to myself because the phrases were ambiguous. By the way - I am built by the local CYRUS2 posts. Really. Keep it up.

^ToM^ · Answer

Adaś, you have a weak power supply. I connected 10 M? to a 0-3000 V regulated power supply and I can certainly confirm that it heats up, while 1 M? even burns

Determining Resistor Wattage: Identify Watt Rating by Resistance, Tolerance & Size Factors

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