Power Supply Keeps Blowing Fuse

Community General Discussion
1

I purchased a 12V 30A DC Universal Regulated Switching Power Supply from ebay and everytime I plug it in the wall outlet the fuse blows. It's set to 115 volts and I'm getting between 123 and 128 volts throughout my house. I talked to my cousin who works for the local power company and he said it doesn't matter that it's that high. He also said that if it wasn't all the electronics in house would have fried by now.

This is how I have it wirded:

Does anyone have an idea why the fuse keeps blowing.

2

A few questions:

  1. Do you have the input power wired correctly (sanity check)?
  2. Which fuse - the one on the supply, or breaker for the house circuit?
  3. Does this problem happen on any outlet in the house?
  4. What do you have wired to the power supply 12V output (how much current is being drawn)?
  5. What happens when nothing is wired to the 12V output?
3
  1. Yup, doubled and trippled check the wiring.
  2. The fuse inside of the power supply.
  3. It happened at another outlet in the same room.
  4. I don't have anything hooked up at the moment.
  5. The fuse inside fo the power supply blows.
4

Obviously there's a short somewhere; with the power supply off, and unplugged from the wall, let it sit for an hour or so (?). Then set your meter to resistance measurement (you might want to use an el-cheapo harbor freight freebie for this, in case there is any residual charge on any caps - the whole point of letting it sit to discharge, but you never know), and do some continuity checks between the output terminals; if you see 0 resistance, then the problem is somewhere "close" to the output terminals. If not, then it is deeper in the supply, and may not be easily found. I am not an expert in power supplies - but I would suggest you might try the Electro Tech forums (there's some guys there who really know their stuff). You may have just gotten a bad supply (was the vendor a reputable vendor? can you exchange it?).

5

I did continuity tests between ground and hot or neutral. I got no continuity. I also did a continuity test on +V and -V of the power supply and I got continuity. That's not supposed to be the case right?

6

JRMN:
I did continuity tests between ground and hot or neutral. I got no continuity. I also did a continuity test on +V and -V of the power supply and I got continuity. That's not supposed to be the case right?

I wouldn't worry about the "incoming side", as that would've popped your breaker.

But on the output side - that does sound weird (by continuity - do you mean zero resistance?)...

You might try removing the PCB from the case - then retest out of the case - if it goes away, then maybe the case is shorting it? If not, then start tracing (visual inspection and such). Homebrew schematics may be needed...

7