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| Rocker switches - imported Chinese rubbbish! (RANT ALERT) |
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| brian_mk:
I needed a SPDT mains rocker switch for a project. Foolishly, I looked on eBay and found a pack of 5 rated at 6A 250V. When they arrived I tested them using my trusty Fluke DMM. One was intermittent and had an ON resistance of 20 Ohms. The others were also intermittent. The ON resistance varied - sometimes up to 1 or 2 Ohms. 2 Ohms at 6A gives a power dissipation of 72W. If a switch gets as hot as a 6OW tungsten light bulb, to me that is worrying. It's a potential fire / safety hazard. I looked up the manufacturer's website. As you might expect, the switches were made in China. The spec stated an ON resistance of 35 milliohms max. Naturally, I have arranged a return & refund. The seller will be receiving negative feedback. I have ordered some from Farnell that will hopefully operate as specified. It seems to me that every time I buy something made in China it turns out to be poor quality rubbish. I had a similar experience with a replacement fan for a NVIDIA 960 GPU card. The existing sleeve bearing fan became noisy after a couple of years. It was impossible to find a replacement in the UK, so I ordered one with the same part number from China. After I fitted it, it lasted just one day before it became as noisy as the original. The fan design and construction is rubbish. I have now ordered an alternative fan that uses two ball bearings - again it had to come from China. I could find no alternatives. I've also had bad experiences with fake ICs from China. I despair that we have to put up with this. |O What has happened to the electronics industry? |
| brian_mk:
Maybe we should be thankful that when the inevitable future war between China and the USA begins, chances are that the Chinese 'launch missiles' button doesn't work. |
| Gyro:
No, there's a lot more to it than that with switch contact materials... Contacts rated for mains use will be something like Silver Nickel or Silver Cadmium oxide. These need a significant voltage (and minimum current) across the closing contacts in order to break down surface contaminants and oxide layers and attain low resistance. In exchange, they are resistant to welding and premature contact erosion though arcing (when interrupting an inductive load). All switches / contact material combinations have a minimum voltage and current spec. A DMM typically won't meet these for unused mains rated contacts. If you want switches for signal level switching then they will typically have Au flashed Ag or Au-Pd contacts - these would be immediately destroyed by switching mains. Some switch and relay contacts these days are 'dual purpose' - they have Au flashed contacts where the Au immediately evaporates when used for high current switching. They are then rendered unsuitable for signal switching. You won't be getting these with a bog standard mains switch though. In all probability, those switches are absolutely fine for their intended mains switching purpose, and so the negative feedback is unwarranted (unless there are other defects). There are entire books written on contact behaviour. P.S. Try not to rant so easily, there's always the possibility that you've missed something, and it's bad for your blood pressure. |
| brian_mk:
Ok - thanks. That's news to me. I will investigate. |
| brian_mk:
The manufacturer's spec doesn't give that information - it just states a maximum on resistance. |
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