Why does my PSU KEEP blowing fuses?! - diyAudio
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Old 14th October 2002, 06:45 PM   #1
Rarkov is offline Rarkov  England
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Lightbulb Why does my PSU KEEP blowing fuses?!

Hi,
I have read numerous safety notes about "if you unsure about making a power supply, then don't!" But I figured that there is a first time for everything. Anyway, I have all the bits together. My 500VA transformer is rated as follows:

Prim: 2x115V Brown/White - Black/Pink
Sec: 2x40V Red/Yellow - Blue/Grey

* Because I'm in the UK (240V from the mains), I soldered the White and black together.

* I wanted +-55V so I soldered Yellow and Blue together to be ground.

* I soldered the Brown and Pink to the mains socket, via a 4A fuse and a switch

* I soldered the Red and Grey to the AC sides of the 35A rectifier.

* I didn't have enough solder for the caps, so I soldered two 33k resistors to the + and - of the rectifier to the Yellow/Blue

* Nothing is touching the chassis.

When I turned it on, there was nothing! I was expecting 57V (ish) AC from the rectifier, but the fuse had blown! This happens repeatedly!

Any ideas?! I have included a picture to confuse you even more!

Thanks
Gaz
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Old 14th October 2002, 07:03 PM   #2
CryingDragon
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try taking the center tap off you you have 3: your CT your + and - and test from the + and - to eachother and from them to the CT you should get yes about 56V from - to + and your rated voltage from each one to the CT. It seems like your shorting the secondary (you don't need those resistors).
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Old 14th October 2002, 07:19 PM   #3
CryingDragon
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or like this
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Old 14th October 2002, 07:22 PM   #4
jleaman is offline jleaman  Belgium
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Is this a brand new transofmer and are you ataching the ac to them main ins not the secondary's ive seen people do that.. and desconect your brige and look for straigt ac.
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Old 14th October 2002, 07:28 PM   #5
jleaman is offline jleaman  Belgium
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Is this a brand new transofmer and are you ataching the ac to them main ins not the secondary's ive seen people do that.. and desconect your brige and look for straigt ac.
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Old 14th October 2002, 07:32 PM   #6
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Do you have the CT and the main grounded to the chassis? Your using a 240V 4A fuse right?
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Old 14th October 2002, 07:37 PM   #7
jleaman is offline jleaman  Belgium
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Humm.. yuo should try what i said.. too..
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Old 14th October 2002, 07:42 PM   #8
Rarkov is offline Rarkov  England
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Hi,


OK, thanks for the great response!

* Nothing is touching the chassis nor Earth. Just Live and Neutral.

* The fuse was rated at 250V 4A. Ceramic type.

* All testing must stop until tomorrow when I get new fuses!

* The reason I put the resistors there was so that it would pull a current, albeit under 50mA. I thought power supplies overloaded without a load.

* I did try without the resistors first, but the same thing happened.

It is a brand new xformer and I'm sure that it all connected the right way around.

Gaz
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Old 14th October 2002, 07:44 PM   #9
jleaman is offline jleaman  Belgium
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you should doubble cheak the wireing man..
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Old 14th October 2002, 08:29 PM   #10
Rarkov is offline Rarkov  England
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Hi.
I have the amp here on my lap (it has bass isolation spikes from a loud speaker attached to the bottom, so with the weight of the heatsinks and xformer, it is quite painful!)

I have taken off the resistors, and will get some fuses tomorrow.
The wiring is correct according to your suggestions. The only thing I can think of is that it is dependant on the polarity of the mains in...but it is AC, it shouldn't matter!

There are no short circuits...
I can't even take pictures for u to look at until the 8th Nov when I give my GF a digital camera for her bday!

Gaz
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