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Cheap chineese power supply missing short-circuit protection
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Eka:

--- Quote from: dominicM on May 15, 2018, 01:44:05 pm ---The problem with decent PSUs is that they seem to be unreasonably expensive (even compared to high end PC supplies) and harder to source at times.

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The main reason the good power supplies cost more is Non Refundable Engineering (NRE) costs. IE, the costs of designing them, compliance testing, and bringing them to market. Typically they are also produced in much lower volumes than the mass market power supplies like used in PCs. So those NREs need to be spread over fewer devices, and thus cost more per device.
glarsson:

--- Quote from: Eka on May 16, 2018, 10:23:03 am ---The main reason the good power supplies cost more is Non Refundable Engineering (NRE) costs.

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NRE = Non Recurring Engineering
janoc:

--- Quote from: dominicM on May 15, 2018, 01:44:05 pm ---
--- Quote from: glarsson on May 15, 2018, 01:29:11 pm ---Some cheap power supplies fail by leaking high tension from the primary side to the secondary side through a poorly designed transformer (not enough insulation, improper construction, overload damage,...)

You defend this trash power supply against all comments - why?

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I am not defending it. At most I am making a point that cheap stuff has it's place. If it is reasonably safe that is, hence the discussion. The problem with decent PSUs is that they seem to be unreasonably expensive (even compared to high end PC supplies) and harder to source at times.

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But the problem is that you have no means to know it is reasonably safe !!! You are neither qualified to judge something like that nor a lot of this stuff can be just "eyeballed" but needs to be tested, sometimes destructively (e.g. transformer insulation). So the only way one can be somewhat safe is to rely on third party test labs doing their job.

Deciding that something is "safe" because newspapers are not full of stories featuring dead people and burned down houses is ... insane, in my opinion. Especially when the "quality" (or rather lack of it) of these various cheap supplies is a well documented fact.


--- Quote ---When I say occasional I also meant attended. I think you may be exaggerating the dangers a bit. I mean it's in a metal case with grounding. The plug has a fuse. Sockets have an RCD and a main RCD too. As for fire, unless it's covered in newspapers (even then) there is very little to burn inside to cause surrounding areas to catch on fire especially with RCDs etc... And then there's also short-circuit protection on a decent reference design.

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 :palm:

RCDs will not do anything unless there is a short/leakage to ground. There are plenty of failure modes involving high currents (causing a fire) that won't trip neither a breaker nor an RCD.

Also, grounded metal case, RCD, etc. will do zilch, nada against a short on the secondary side (e.g. because a crappy capacitor fails short). If the supply isn't protected properly (good luck with a cheapie), you most likely have a fire now because the supply is dumping all its current into that smouldering cap (or whatever remains of it).

And re fire - you have obviously not seen the board and cables inside a supply to catch on fire yet and how fast that can spread. There is nothing to contain the flames inside and it will ignite anything flammable nearby - enclosure of the device, your desk, etc.

If you want examples of what can happen with a poorly made power supply, just google "power supply fire". I have personally witnessed what kind of mess an ATX supply can make when it goes bang. We got very lucky that it has happened during the day and we have contained the fire right away. Don't want to think what would have been the result if it has happened overnight ... And that was a decent brand, not some low end 10 buck piece of crap.

Feel free to think I am exaggerating. However, with this attitude to safety you are going to get hurt at some point.
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