Fuse Keeps Blowing In Power Supply

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

What rating is the fuse? Switch mode PSUs can take a big surge at start up so a 5A fuse is normally needed even though 360W is only 1.5A.

The other possibility is the PSU is faulty.

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[www.hydraraptor.blogspot.com]

The fuse that it came with was F8AL 250V (fast blow), but the power supply PCB says T6.3A 250V (slow blow). So, I replaced the orginal fuse with a T6.3A 250V and it blew out again.

Edited 1 time(s). Last edit at 02/06/2012 01:55PM by JRMN.

If it blows its own fuse with no load it is faulty.

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[www.hydraraptor.blogspot.com]

... i have an old 24V/80Amps-powersource from the 'German telecom', that blows my main-fuse if plugged in the one way, but is OK if i turn the wall-plug ...

But with blowing its own fuse there is something wrong inside - maybe a long pin produces a short to the housing?

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I just 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?

Not a direct short but it can be quite a low resistance. I just measured a similar one at ~200 ohms.

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[www.hydraraptor.blogspot.com]

I get about 250 ohms between +V and -V.

Can someone tell me why -V is connected to ground in this photo?


Photo is from here.

Yellow-green i think its "safety ground". There is null and phase, these 2 give the power from the electricity company. The 3rd, safety ground its supposed to be a direct local ground, a connection to a grounded, as in a local physically burried underground network made with 6 pieces of 2-3 inch diameter metal tubes, about 1-1,5m tall each, ~3+ meters in between, burried like at least 1m underground, and welded together with very thick metal band like 40mm x 5mm diameter, and with everything tinned. Take a full tour of building outside and if there is a 40mm x 5mm metal band that exits from ground, on the wall of the building, thats it. Its supposed to have very low resistance, measured with a dedicated aparatus should be well under 30 ohms (max acceptable for my local standards). Its meant as safety that connects to cases of equipments, etc, i think to provide a faster and lower resistance ground to shorten eventual currents on a better path than it would go through a human body. I think its generally supposed to be different / have no contact to the phases null.

Thats theory. In practice for households its usually missing (i think). Or its connected to the center null of the 3 phases somewhere, which doesnt make it any different. Its mandatory in industry / factories i think like that.

Since -V is connected to gnd, if there is a real local gnd as it should be, it might help to give it a better ground perhaps. Or if the safety gnd is connected to the null of the 3 phases, that one can get noise from other sources around the neighbours etc, then it might very well alter the potential difference in a bad way. Because when power distribution has issues, that can very well and up with noise on the null line.

I wouldnt do that unless i know for sure what my local situation is like. Although under best of circumstances it shouldnt make much difference at all, under worst circumstances i think it can make a difference either way. If there is a local real safety gnd, i guess it can help. If its instead connected to the null, and this one gets noise from other sources, then it can be a bad thing to do. Hope i am not too far off.

Edited 1 time(s). Last edit at 02/07/2012 02:21AM by NoobMan.

Adrian is from the UK, and all UK sockets have a proper safety ground.

In theory the PSU outputs should be isolated from the mains by split bobbin transformer with double insulation and all the required safety approvals. If that failed the outputs could become live. With a cheap PSU from China the approvals are likely missing, or fake, so it is a good idea to ground the output to prevent it becoming live in the event of a fault.

The downside is that you get a ground loop through the USB cable and the PC which can cause USB comms problems.

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[www.hydraraptor.blogspot.com]

i have the same problem, except i forgot to change the PSU to 240v as this is the current in australia. the fuse burnt out. so i changed the fuse and switched the PSU to 240v to see if it would work. no good, it just keeps blowing fuses. not sure how to fix this? should i replace the PSU?

I dont know how similer your PSU is to the one I fixed last week for a fellow RepRapper but... I was presented with a very similar looking PSU with a blown 6.3A fuse and the problem turned out to be that if the cage wasn't securly fastned the pins on the underside of the Mains selector switch were able to short against the lip of the cage. (which is tucked under the PCB slightly.)

A bit of capton tape and snipping of long pins sorted this out.
Hope that helps someone

I'm confused,

Why do you have a UK Style Plug,
but have 123 and 128 volts running through your house?

That doesn't make any sense.

UK and that plug are 220VAC 50Hz.

@slymike, I wish I had known that before I sent it back. My build has been put on hold.

@ShadowRam, good observation. Short answer, those aren't my photos.

i think i may have the same powersupply... and a similar problem... keeps blowing fuse...
except i think i found my problem, and pretty sure i can blame it on a failing electronic component...
now i would just like to know what it is and where i can find a replacement...

it says: 13009 JT 73 on it. but when i google that i dont get anything too concrete...

thanks for any and all help!
-onus

Quote
onus
it says: 13009 JT 73 on it. but when i google that i dont get anything too concrete...

Probably [www.st.com] or [www.mouser.com] in a slightly different package.

Edited 2 time(s). Last edit at 11/26/2015 03:57PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

so will this do the job: digikey?



THANKS! hopefully i'll be printing soon

Edited 1 time(s). Last edit at 11/30/2015 02:24PM by onus.

The two transistors I listed are equivalent to each other. They are common high-voltage low-cost transistors that I have found used in inverters for larger CFC lamps. However, they both come in a TO220 package, and the ones in your photo appear to be in a different package that I don't recognise. So I suggest you check the lead spacing of the original transistors and the height of the mounting hole above the PCB, and compare it to the dimensions shown at [www.fairchildsemi.com]. The F logo indicates that the original transistors were made by Fairchild Semiconductor. I suggest you replace both of them, because if they are in a half-bridge configuration, when one fails it typically takes the other with it.

Edited 1 time(s). Last edit at 11/30/2015 12:38PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

PS - be very careful! The large capacitor that smooths the rectified AC mains input may hold several hundred volts for a few minutes after the power is removed.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].