Decades ago, electronic components were not as easy to acquire as they are today. Sure, you could get some things at Radio Shack. But you might not have many choices, and the price would be on the high side. TV repair components were another option, but, again, big bucks. Some places sold surplus parts, which could be cheap. These often came from manufacturing runs where a company bought 10,000 components and made 8,000 products. But today, you can order parts inexpensively and get them on your doorstep in a day or, sometimes, even less. Are these inexpensive parts really any good? [Denki Otaku] likes to find out. In a recent video, he checks out some Amazon-supplied 1% resistors to find out how good they are. You can watch his results below.
He starts with two resistor kits and examines them quite closely. For example, a magnet revealed that one brand of resistor had iron leads which are not as conductive as copper leads. They look the same because they are both coated with tin, but the magnet tells the difference.
The Elegoo kit measured the expected resistance value within the tolerance band. The sample size was a little small to draw a solid conclusion, but it does look like the resistor were well within their advertised tolerance. The Longrunner resistors, however, did not fall in range. Some of the resistors were within 1% of the marked value, but others were as far out as 1.4%. That doesn’t sound like much, but if you bought them for their 1% tolerance, a 1.4% error is way off the mark.
We liked the test jig he built to do the four-wire resistance measurements more easily. Simple but effective. He did some experiments with hot air to determine the temperature coefficient and the power handling capability of the resistors. That led to an accidental smoke release. Later, he had more of a planned smoke release.
If you need general-purpose resistors that are within a few percent of their marked values, these kits are probably fine. But if you are relying on precise values, you might be disappointed. On the other hand, you would probably hand-match anything important, anyway, but it is still good to be aware that the markings on the resistors might not reflect reality.
We recently saw a case where being out of spec with cheap parts was much more dangerous. If you want to know more about 4-wire resistance measurements, you are in the right place.