Comparison of high-capacity resistors

It has become really interesting to compare the foreign high-capacity wire-wound resistors with the ones of the national manufacturing. The number of foreign resistors increases rapidly, and the number of national ones becomes less and less. Although they should be the best in the world like Kalashniko!

Let’s compare and check what resistors are better. So I took two resistors with 10Ohm and 5W for comparison. Here they are 

resistors

There’s one more resistor on the photo because the one of 10 Ohms has the cut lead. Of course I’ll solder the wire to be able to work with it, but I’ve made a photo of another one to make it look good.  The working one is to the left and the one to the right is just to show the looks. So let’s start the comparison:

1.Resistance.

The national resistor has 10.1 Ohm and the international one has 9.9 Ohm. Both are good.

2.Dimensions.

The international is much smaller, which means it will heat up more. Why? Because the electrical energy turns into the heat in resistor. The resistor warms up; the ambient air is cooling it down. So the bigger are the dimensions (the surface area to be exact) of the object, lower is the temperature of heating.

Comparing. Overheating temperature (which means how warmer the resistor is comparing with the environment) when conducting the rated power of 5W:

National – 62º International – 98º . Ours is better!

If the ambient temperature is 28º (it’s much higher inside the unit), the temperature of the body of : National resistor  is 90º International – 126º

That is why if there’s something located next to resistor, it can overheat and get the damages. It’s especially true for the international resistor – 126º for semiconductors is a limit! And it can be even higher!

3.Design.

National C5-5 5W Cutting the body:

resistor 1

Two types of washers (fluoroplastic (low friction and high heat endurance, probably with the aim of the aluminic body construction)) and ceramic are located on both sides. The resistor itself is covered with the insulating material. The insulation is combustible but the resistor is sealed, all my attempts to set the resistor on fire have failed. Let’s go further.

The wire is on the ceramic cylinder and sticks to it (insulated) with some kind of paint. And it’s obviously heat-proof, it stands the heating well. Please note that both ends of the wire are fixed securely.

The resistor leads are welded into the cup. Everything is pretty solid.

International resistor The structure is pretty simple: the resistor itself is inserted into the ceramic body and is closed with some kind of “cement”.


This “cement” (it’s marked with red point on the photo) is very crumby and you can pick it easily. Let’s pick it out:

The ceramic cylinder, the one with the coil, is much smaller. The cover of leads is different – they are just swaged with cups. The wire on the cylinder is not fixed at all – but it’s not obligatory, the wire is well fixed in its place, moreover the “cement” is securing it.

Here are the heating elements of both resistors:

You can tell from the first glance that the national resistor is much bigger and looks “trustworthy”. If to consider the safety, I like our better but I don’t have objective factors to prove that yet. It’s interesting that basing on the complicated structure and used materials our resistor should be 3…5 time more expensive, but I paid only 5 Roules for it at the market and the cost of the international one is 3 Roubles. Looks like the international resistors have the high markup (if there are several agents). So, they are even in this category.

4. Inductance.

Basing on the structure we can assume that the national resistor will have higher inductance than the international one.  Actually it has 25 coils. The inductance of such coil is minimal. Moreover, the aluminic body located outside should reduce the inductance essentially (besides, the body also shields resistor). I didn’t manage to measure the inductance of resistors well –it’s so low that you can hardly measure it with the available equipment. International: is much smaller  - 1 microhenry, ours has 0.5…1 microhenry.  Is it a lot or not? Let’s say that the total resistance of national resistor will become equal to 12 Ohms at the frequency of 1MHz, which means it will 20% increase (not a lot) because of the inductive reactance affect. So you can work with no troubles with the limit frequency of 1MHz.

5. Crush test.

Let’s see how these resistors stand the overloading. Test1. Let’s give the power of ~45W (loading 9 times higher than the normal one). Resistor becomes very hot. It even produced some smoke for a short period of time. Then it stopped. The resistor was working well during 5 minutes. I gave the power of 25W to the international resistor.  It produced smoke during all 5 minutes of conducting the test. Besides, it smelled really badly. Resistor became dark, but remained functional. Results: International – ok Ours – good Test2. Let’s connect the “heaters” of cut resistors to the source of 21.5V. This creates the power of ~45W. National:

became red-hot, smelled badly, but remained functional. When it cooled down, the paint crashed in the center, but remained untouched on the ends! International:

Became even redder than ours and it’s natural because it’s smaller and is cooling worse. Besides it gives more smoke. It was not suffering for a long time and here’s what happened to it in 30 seconds of work:

 It fully burnt down! Results: national – good, international – not good.

CONCLUSIONS

Again I made sure that our military technologies are better than the international ones! It’s better in dimensions and service life (the superiority of all our technologies is unquestionable in what is related to these two parameters!) International resistors can be used in cases when there is no overloading. And vice versa, it’s even better if the resistor is working with under-loading.  The samples of its use are the emitter circuits of transistors of the power amplifier. Because of the big peak-factor of music, the mean power of the resistor is usually much lower than the rated power there. And you should not put or locate the elements prone to heat next to it. And you should not put it tightly to the board, and it would help if you leave a little gap between the board and resistor.National resistors are more resistant to overloading? That is why they are good to be used in the case of overloading. The perfect place is the lift off current limiter in the unit of soft start of power amplifier. It’s really impressing to sustain the loading nine times higher than the normal one during 5 minutes! You shouldn’t put it tightly to the board as this will allow to cool down quicker and won’t heat the board. They will be working better than international resistors in other circuits!