I hope this will not be categorized as buying related question because my question is not really on should I buy this or this.

I usually find some parts kits, usually resistor/capacitors/trimpots, like 100 caps for 2€/3$. I've already try one pack of these from Kemo, the values in the pack are totally random but I got some good surprises too (like a bunch of 10K 1% resistors and 550ohm 2% resistors). For the moment I just use them when prototyping the project.

My question is do you know how they can be so "attractive" from a pricing point of view ? I have my little idea, but not sure. I think it's most of them "old parts" or unselled stock from closed companies. (due to the "look" and some have a bit of corrosion). I ask because I've also thinked at a moment about harvested parts from broken electronics as some "feels" like harvested parts.

Do you have any ideas about these cheapos parts ? Is it a dangerous choice ?

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    \$\begingroup\$ This question appears to be off-topic because it is about shopping/economics of product sale/sourcing. \$\endgroup\$ – Passerby Dec 26 '13 at 4:56
  • \$\begingroup\$ It's more security related to know if these parts can be dangerous to use or not and/or if I should take some particular precaution when using them. Nick Alexeev have totally answered to the question. I know it's a bit a border side question but I hope you can see the security focus :/ \$\endgroup\$ – Emmanuel Istace Dec 26 '13 at 5:04
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    \$\begingroup\$ Parts like regular small power resistors and capacitors are usually very cheap when bought in high volume, read: less than a dollar cent. Every second you spend on harvesting parts from eg. PCBs is many times more expensive from labor than they are worth. \$\endgroup\$ – jippie Dec 26 '13 at 10:18

There's a variety of sources. This is, probably not the complete list, but it can give you an idea.

  • Factory overruns. There are accidental overruns, deliberate overages, clandestine overruns. The problem is that you don't know if the overrun was quality controlled or not. In case of clandestine overrun, it's also not know if the manufacturer was following the process, or they were cutting corners.
  • Factory rejects. When quality control decides that the tolerance is out of spec, the whole batch is rejected. Suppose that the batch of 5% resistors falls outside 5%, but within some larger number. These are still viable resistors, only less accurate.
  • So called "new from the old stock". Company cleans out its inventory, which was procured through qualified channels, because they no longer use the part in their designs. The quality of such parts is normal, although shelf life may still apply.

Except for the last type, the history of the parts is usually not known, when you buy the kit.

Don't use these bargain parts in life and death matters: airplanes, cars, weapons, medical devices.

  • \$\begingroup\$ Resistors, and most passives, don't suffer from rejection. If they consistently test out of range, they get re-ranged to the next value up/down. 5% resistors out of tolerance will get labeled as 10% resistors. \$\endgroup\$ – Passerby Dec 26 '13 at 5:24

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