Why does my PSU KEEP blowing fuses?!

Rarkov · 14th October 2002, 06:45 PM

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

14th October 2002, 07:03 PM

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).

14th October 2002, 07:19 PM

or like this

jleaman · 14th October 2002, 07:22 PM

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.

jleaman · 14th October 2002, 07:28 PM

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.

RobPhill33 · 14th October 2002, 07:32 PM

Do you have the CT and the main grounded to the chassis? Your using a 240V 4A fuse right?

jleaman · 14th October 2002, 07:37 PM

Humm.. yuo should try what i said.. too..

Rarkov · 14th October 2002, 07:42 PM

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

jleaman · 14th October 2002, 07:44 PM

you should doubble cheak the wireing man..

Rarkov · 14th October 2002, 08:29 PM

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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14th October 2002, 07:03 PM	#2
CryingDragon Guest	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).

14th October 2002, 07:22 PM	#4
jleaman Banned Join Date: Apr 2002	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.

14th October 2002, 07:28 PM	#5
jleaman Banned Join Date: Apr 2002	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.

14th October 2002, 07:32 PM	#6
RobPhill33 diyAudio Member Join Date: Sep 2002 Location: Milton Ontario	Do you have the CT and the main grounded to the chassis? Your using a 240V 4A fuse right?

14th October 2002, 07:37 PM	#7
jleaman Banned Join Date: Apr 2002	Humm.. yuo should try what i said.. too..

14th October 2002, 07:42 PM	#8
Rarkov diyAudio Member Join Date: Aug 2002 Location: North East, UK	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

14th October 2002, 07:44 PM	#9
jleaman Banned Join Date: Apr 2002	you should doubble cheak the wireing man..

14th October 2002, 08:29 PM	#10
Rarkov diyAudio Member Join Date: Aug 2002 Location: North East, UK	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