| Electronics > Projects, Designs, and Technical Stuff |
| switching-PSUs: why can't you usually exceed the 50% of declared power? |
| << < (4/21) > >> |
| 0db:
--- Quote from: engrguy42 on May 23, 2020, 10:30:10 pm ---- Are these new or used units? --- End quote --- I bought them from Amazon, declared "new". |
| engrguy42:
For some perspective, here's something very similar to the supervisor circuit on my Dell ATX power supply. And this is from a Dell desktop that's like 5-10 years old. As you can see it's monitoring current AND voltage on 5 outputs (3.3, 5, & 12v). It checks overvoltage, overcurrent, and undervoltage. And it has protection on the input (fuse, MOV's, PFC, etc.). So blowing up really isn't a reasonable likelihood, nor is destroying the motherboard. Hence my skepticism. Of course that won't stop the anti-ATX fanboys from jumping to the assumption that these ATX supplies are just crap, but anyway... |
| 0db:
--- Quote from: engrguy42 on May 23, 2020, 10:30:10 pm ---The reason I ask is that decent ATX power supplies are required to provide some basic protection. --- End quote --- OverCurrent Protection? umm, my old Cooler Master MASTERWATT 550W had a slow OCP protection at 600 Watt. The PSU didn't shutdown immediately, only after 1 sec later with a VDrop of 0.8V at 12V. Paid 50 euro for it, not exactly "cheap", it went back to Amazon. |
| engrguy42:
--- Quote from: 0db on May 23, 2020, 10:59:57 pm --- --- Quote from: engrguy42 on May 23, 2020, 10:30:10 pm ---The reason I ask is that decent ATX power supplies are required to provide some basic protection. --- End quote --- OverCurrent Protection? umm, my old Cooler Master MASTERWATT 550W had a slow OCP protection at 600 Watt. The PSU didn't shutdown immediately, only after 1 sec later with a VDrop of 0.8V at 12V. Paid 50 euro for it, not exactly "cheap", it went back to Amazon. --- End quote --- I suggest you take a look at the Intel ATX power supply design guide. It's extremely informational if you want to understand ATX supplies. Here's a snip of the allowable voltage regulation. Note it says +12V output can get down to 11.4 which is slightly higher than what you measured. I'm not sure how you measured and how accurate you were, but it seems reasonable. And if you were acutally measuring the -12VDC, it says it can get down to -10.8 |
| 0db:
+12V - 0.8V = 11.2V < 11.4V ---> not acceptable! I initially measured it on the oscilloscope, then I repeated the experiment with a multimeter of 3 digits in parallel. Same result. Anyway, OVC means over current protection. If the PSU has a limit of 550Watt, and you try to sink out 600Watt, it should immediately shutdown. Not after 1 sec, but rather the soonest possible! |
| Navigation |
| Message Index |
| Next page |
| Previous page |