Electronics > Beginners
Cheap chineese power supply missing short-circuit protection
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bob225:
So around 33 amps at 12v or 8 amps @ 5v ? thats a fair bit of current
janoc:

--- Quote from: dominicM on May 13, 2018, 06:16:34 pm ---Well the upper limit is only exceeded by 3V (12V to 15V) and from what I've read going lower should be safe enough. I mean components won't blow up due to lower voltage... As far as dodgy supplies, I bet most cheap supplies somewhat dodgy. How many hobbyists are going to pay 150€ vs 15€ for a PSU for a non-critical project... I've seen plenty of tear downs of seemingly respectable widely used hardware that have same creepage and other issues so I don't know how worried you can be when it's all around you anyways. I can't imagine for example those 8€ laptop replacement adapters are any better. In the end I don't really know, that's why I asked. In any case I won't be using this particular PSU, will try and get one that at least has all it's components.

--- End quote ---

Components won't blow up because of voltage but the controller IC may stop regulating properly or even start oscillating. If that happens, the supply will likely destroy itself and take out anything connected to it as well.

Keep in mind that that 15€ PSU can become a much more expensive problem once it goes bang and you have a fire. 400W supply is no sneeze, that's a serious amount of energy that will blow shit up and set it on fire should anything go wrong with it. You do get what you pay for here and given that you need a high power supply, trying to go cheap could seriously cost you. When it comes to mains that is a very bad place to be cheap.

I don't know how about you but I don't have any 8€ adapters anywhere (and not buying them neither). I value my life and my property more than that.
dominicM:

--- Quote from: janoc on May 13, 2018, 07:41:02 pm ---
--- Quote from: dominicM on May 13, 2018, 06:16:34 pm ---Well the upper limit is only exceeded by 3V (12V to 15V) and from what I've read going lower should be safe enough. I mean components won't blow up due to lower voltage... As far as dodgy supplies, I bet most cheap supplies somewhat dodgy. How many hobbyists are going to pay 150€ vs 15€ for a PSU for a non-critical project... I've seen plenty of tear downs of seemingly respectable widely used hardware that have same creepage and other issues so I don't know how worried you can be when it's all around you anyways. I can't imagine for example those 8€ laptop replacement adapters are any better. In the end I don't really know, that's why I asked. In any case I won't be using this particular PSU, will try and get one that at least has all it's components.

--- End quote ---

Components won't blow up because of voltage but the controller IC may stop regulating properly or even start oscillating. If that happens, the supply will likely destroy itself and take out anything connected to it as well.

Keep in mind that that 15€ PSU can become a much more expensive problem once it goes bang and you have a fire. 400W supply is no sneeze, that's a serious amount of energy that will blow shit up and set it on fire should anything go wrong with it. You do get what you pay for here and given that you need a high power supply, trying to go cheap could seriously cost you. When it comes to mains that is a very bad place to be cheap.

I don't know how about you but I don't have any 8€ adapters anywhere (and not buying them neither). I value my life and my property more than that.

--- End quote ---

Wouldn't PSU just turn off if the voltage is too low resulting in a on-off loop? That's what I learned with a different PSU I tried to mod. I asked in another thread and there was no suggestion of any danger. Perhaps you can elaborate on exact scenario etc...

Most people aren't on EEVBlog forum so that no indicator of what people use. Phone chargers and such can be cheap crap too even if it's genuine. Even genuine adapters would have issues if you tear it down. It's could be made in the same factory, it's just that chances of fault are lower due to some oversight and QC. Again I don't really know, but it's hard to take someones advice when you don't know the reasons behind that advice that's why I asked.
dominicM:

--- Quote from: bob225 on May 13, 2018, 07:08:14 pm ---So around 33 amps at 12v or 8 amps @ 5v ? thats a fair bit of current

--- End quote ---

It is. It's the max draw possible though, I probably I will only use it at below 100W but would be nice not to be limited or accidentally draw more than PSU can handle. Best I can find on RS is 65€ for 200W Meanwell PSU. Pretty expensive considering PC PSU prices.
abraxa:
It's all about risk management. If you know what you're doing, you can judge whether what you're planning on doing has a risk of causing major damage or not. Comparing that to the risk of a potential worst-case outcome of said damage (burnt-out apartment that you'll have to pay out of your own pocket, assuming no one dies in the fire) allows you to then judge whether it's worth saving $100 and performing the modification or whether the potential for a serious cost penalty is too high and not worth the gamble. Even if you're insured against accidental damage/fire/loss of life, the insurer will be more than happy to hand you the bills once they discover that a PSU that you modified is the origin of the problem.

Since you don't even know what properties the components used in the power supply possess and already being well-aware that the manufacturer of this power supply is cutting cost in scary ways, you're unable to make a proper assessment of how likely the device is to cause major damage. That's the point when you should be jumping ship.


--- Quote from: dominicM on May 13, 2018, 09:44:47 pm ---Wouldn't PSU just turn off if the voltage is too low resulting in a on-off loop? That's what I learned with a different PSU I tried to mod.
--- End quote ---

Low duty cycles at high filter cap discharge rates (i.e. high output current) cause high charge current spikes. What happens if the output filter caps aren't up to the challenge and fail short-circuit? I think you know what a power supply without short circuit protection is going to do then.
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