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Bridge rectifier burning out in power supply circuit

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Smay

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Hi all,
I'm a first time poster here and I apologize if this has been asked before -- I searched but didn't see anything similar. I'm trying to get into some electronics design and thought a good first project would be a variable voltage power supply to power all of my projects. Hopefully I don't make myself look too dumb with this question :)

Problem
I am trying to follow the design at **broken link removed** since it has good descriptions and alternate parts lists, but I am running into a problem where my bridge rectifier keeps burning out. I have disconnected the entire circuit such that it is down to just the transformer, bridge rectifier, and C1, but the same problem happens.

Once I plug the circuit in, I hear a crackling noise coming from the rectifier. After about 5-10 seconds it gets extremely hot and releases the magic smoke. If I have a multimeter attached to the capacitor, I do read a steady voltage though I can't remember what the value is at the moment -- it seemed reasonable when I took the measurement.


Parts
-The transformer I am using is a 12.6V 3A one which I got at radioshack (https://www.radioshack.com/product/index.jsp?productId=2102702).
-I have tried two different bridge rectifiers. The first was an NTE5312 rated at 100V 8A. The second was picked up at radio shack and is rated at 400V 8A
-C1 is a 1000uF 50V electrolytic capacitor.


Connections
I am using an old computer power supply cable to connect to the 120V AC to the transformer. The ground pins of the plug, rectifier (- pin), capacitor, and the center tap (black wire) of the transformer are all connected together. The two other pins of the plug are connected to the two AC inputs of the rectifier. The + output of the rectifier is connected to the + side of the capacitor. I have tried to illustrate this in the attached diagram.


Thanks in advance for any help on this.
 

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Well you diagram doesn't show a transformer, if you're plugging mains straight in, then you will certainly be killing it.

Only possible reasons are connecting it wrong, or faulty components.
 
a 50V bridge might be ok but most likely it is that you probably grabbed a 1A bridge when you need a 3A one.

Dan
 
Not knowing your location.?
Why you have you got the -V side of the bridge and the cap connected to the Ground line,, are you sure it is the ground pin.:confused:
 
Nigel:
There is a transformer, I just forgot to draw it in. My mistake. The AC is connected to the transformer and the two outputs of the transformer (yellow wires) are connected to the two AC inputs of the rectifier.

Ubergeek63:
I'm 100% sure my rectifiers were both rated at 8A. I just double checked.

ericgibbs:
Location is US. I believe you're right, and I just made a stupid mistake in reading the schematic. I went back and checked the circuit and I definitely have the - pin of the rectifier connected to GND, which would explain a lot about why I burnt out the part. I have to go pick up a new rectifier today after work, I'll try changing that connection and see if it works. Thank you.
 
Nigel:
There is a transformer, I just forgot to draw it in. My mistake. The AC is connected to the transformer and the two outputs of the transformer (yellow wires) are connected to the two AC inputs of the rectifier.

Ubergeek63:
I'm 100% sure my rectifiers were both rated at 8A. I just double checked.

ericgibbs:
Location is US. I believe you're right, and I just made a stupid mistake in reading the schematic. I went back and checked the circuit and I definitely have the - pin of the rectifier connected to GND, which would explain a lot about why I burnt out the part. I have to go pick up a new rectifier today after work, I'll try changing that connection and see if it works. Thank you.

hi,
I would fit a 2amp fuse in the secondary of the transformer, they are much cheaper than rectifiers.!:rolleyes:
 
Omit the "ground" wire between the power cord and the negative terminal of the recifier.

The so called "ground" is "Protective Earth" (PE), which has absolutely nothing to do with the rectifier connected to the secondary winding of the transformer.

The same applies to oscilloscopes supplied with mains power. Connecting PE to the enclosure and measuring at mains circuits will cause the same phenomenon producing smoke, this time inside the scope. :D

Boncuk
 
Thanks to everyone for the help. That simple (stupid) mistake was the source of my problems. On the plus side, one of the rectifiers I thought I burnt out is still working, so I didn't need a new one.
 
That regulator won't output 1.25V to 30V and be able to supply 1.5A at the same time.

When the output is reduced below about 18V the LM317's safe area protection will kick-in and reduce the output current.

If 1.5A is drawn when the regulator is set to above 23.5V there will be lots of ripple on the output. The 1000µF capacitor is too small to keep the ripple low enough to give 30VDC. When 1.5A is drawn the ripple on C1 would be 8.3V giving a minimum voltage of 25.7V. The LM317 needs 2.25V (if you're lucky) to regulate properly meaning the highest stable output voltage at 1.5A will be 23.5V.

hi,
I would fit a 2amp fuse in the secondary of the transformer, they are much cheaper than rectifiers.!:rolleyes:
The only problem is a 2A fuse will blow as soon as the power is applied as C1 charges.

It needs to be a slow blow fuse and I'd go for 3A. The LM317's maximum circuit current limit is 3.4A and you don't want the fuse blowing every time the output is shorted. A 3A fuse should be able to pass 3.4A for long enough, a PTC resistor (polyfuse) would be even better.
 
I agree with ericgibbs. Lack of fuses puts your safety at risk. The rectifier is burning from a current overload. It's a miracle the capacitor didn't explode and give you serious burns. That happened to me once before - misread the voltage ( 25VDC, not 35VDC) and popped a capacitor open.
 
Omit the "ground" wire between the power cord and the negative terminal of the recifier.

The so called "ground" is "Protective Earth" (PE), which has absolutely nothing to do with the rectifier connected to the secondary winding of the transformer.

The same applies to oscilloscopes supplied with mains power. Connecting PE to the enclosure and measuring at mains circuits will cause the same phenomenon producing smoke, this time inside the scope. :D

Boncuk

hi, i read the post here. i am also facing the same problem where the rectifier W04 give out "smoke" and "sparks" when i switch on the mains (240V) passing through a 2A 30-0-30 transformer. I am building a 24V PSU using capacitor 4700microF, MC7824 voltage regulator.
Are you saying the ground shouldn't be connected? If so, will the circuit be floating? Is there any possibilty that cause the rectifier to burn?
Thank you.

vp_archer
 
Nigel:
There is a transformer, I just forgot to draw it in. My mistake. The AC is connected to the transformer and the two outputs of the transformer (yellow wires) are connected to the two AC inputs of the rectifier.

Ubergeek63:
I'm 100% sure my rectifiers were both rated at 8A. I just double checked.

ericgibbs:
Location is US. I believe you're right, and I just made a stupid mistake in reading the schematic. I went back and checked the circuit and I definitely have the - pin of the rectifier connected to GND, which would explain a lot about why I burnt out the part. I have to go pick up a new rectifier today after work, I'll try changing that connection and see if it works. Thank you.

hi,
i just want to ask you what changes did you do for your circuit. the bridge rectifier minus-pin is not connect to ground? If so, how/ where do you connect the ground of the circuit?

i did try to build one, the rectifier also gv out magic smoke. the ground of the circuit, i connected it to the chassis of the transformer, which the mains earth wire also connected to.
 
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