Bridge Rectifier Draws Excessive Current

Thread Starter

alisomay

Joined Jan 30, 2018
29
Hello everyone.

I have a strange phenomenon about my bridge rectifier circuit.

Transformer primary winding : 220VAC.
Transformer secondary windings : 9.4VAC(max 1.5A) , 24VAC(max 700ma), 500VAC(max 100ma).
24VAC and 500VAC are not connected.
The center taps are floating.
There is a cable which is called the shield, the transformer winder told me to connect that to the chasis which i did. He said it is a copper plate between the primary and secondary.
I use the chasis of an old amp which has a switch. The three wire power cable terminals L1 and L2 are connceted to transformer primary through a power switch. Neutral (also probably earth ground and mains transformer center tap) is connected to chasis for safety purposes.

9.4VAC outs, connected to the bridge rectifier inputs.(The anode cathode junctions of the diodes.)
The diodes i am using are 1n5408 (3A Rectified Output Current).
I test them with the scopes component test function and they show a nice L shape. I test them again and again after the operation they don't look that they blew.

I have a couple of questions.

1:
With load, no load, or with a reservoir cap. The circuit draws too much current cables get hot transformer vibrates and if i put an amp meter in series between secondary out and bridge rectifier in it read 2.0 Amps when measuring AC current. The circuit rectifies by the way and ripple calculations are accurate with a 10mF cap and a 33Ohm(15 W heat dissipation capable power resistor network) as the load.
The problem is it draws excessive current from the transformer. I can't and don't want to keep it open more than 4 secs. Why could this be??

An important info is, this does not happen when i install new diodes to circuit, but when i turn the power on and off again the problem starts again.
Inrush current?? but my diodes seem ok. I can't figure the problem out.

2:
There is an AC voltage across chasis to chasis around 6.5 V. Why would that be?

Thank you very much.
 

ericgibbs

Joined Jan 29, 2010
18,766

between the primary and secondary.
I use the chasis of an old amp which has a switch. The three wire power cable terminals L1 and L2 are connceted to transformer primary through a power switch. Neutral (also probably earth ground and mains transformer center tap) is connected to chasis for safety purposes.



hi,
Welcome to AAC

Your description suggests you have the mains input wiring incorrectly connected, UNPLUG the project from the mains.!

Please post a sketch of the mains wiring or a clear photo.

Eric
 
Last edited:

Bordodynov

Joined May 20, 2015
3,177
I had a similar problem because of the use of very old aluminum, oxide capacitors. At the output of the rectifier, there was less voltage than calculated. The transformer was basking. I realized that the capacitor had been formed. I did the forming of the capacitor, gradually increasing the voltage on it. Everything worked for five years. But, after a one-year break in using the stabilizer, the diode bridge blew smoke.
You may have another problem.
 

dl324

Joined Mar 30, 2015
16,839
Welcome to AAC!

When discussing circuits, it's best to post schematics.
Neutral (also probably earth ground and mains transformer center tap) is connected to chasis for safety purposes.
You don't give your locale, but connecting neutral to earth ground as you've done is a code violation in my area.
There is an AC voltage across chasis to chasis around 6.5 V. Why would that be?
Wiring problem. Unplug immediately and check all wiring for shorts and verify receptacle is wired correctly.
 

AnalogKid

Joined Aug 1, 2013
10,986
Disconnect the "neutral " (earth ground?) from everything.
Disconnect the power transformer primary side center tap from everything.
Disconnect the transformer shield from everything.
Disconnect all secondaries from everything.

Try again, no more than 1 second.

If all is well. measure the secondary AC voltage while disconnected from the bridge.

If it is within about +/-10% of nominal, power down and reconnect the bridge.

ak
 

Dodgydave

Joined Jun 22, 2012
11,284
Post a picture of uour transformer with the voltages on each pair of windings, sounds like your secondary output is shorted out.
 

Thread Starter

alisomay

Joined Jan 30, 2018
29
Now i am posting the annonated photos. I will take all of your advises to consideration. Please take a look at this photos i don't at least in my experience see something wrong in the wiring would you explain in detail what i did wrong in mains wiring?

How do i upload an image to this forum should i upload to another image host and link, it didnt work yet.

The image of the mains in my area (Turkey).
https://ibb.co/mOp94R
Image of my plug.
https://ibb.co/nPmYW6
Images of transformer, connections and the chasis.
https://ibb.co/jvWBJm
https://ibb.co/hvE3W6
https://ibb.co/grG6jR
Schematics.
https://ibb.co/nn8xr6





 
Last edited:

Thread Starter

alisomay

Joined Jan 30, 2018
29
Welcome to AAC!

When discussing circuits, it's best to post schematics.
You don't give your locale, but connecting neutral to earth ground as you've done is a code violation in my area.
Wiring problem. Unplug immediately and check all wiring for shorts and verify receptacle is wired correctly.
It could be my misunderstanding of the terms. I provided the photos, am i labeling the terminals in my receptacle correctly. The simplest i understand is the ground section in receptacle is connected to the center tap of the street transformer. I believe that is connected to the earth ground at some point. That is the thing i called neutral.
 

Thread Starter

alisomay

Joined Jan 30, 2018
29
Disconnect the "neutral " (earth ground?) from everything.
Disconnect the power transformer primary side center tap from everything.
Disconnect the transformer shield from everything.
Disconnect all secondaries from everything.

Try again, no more than 1 second.

If all is well. measure the secondary AC voltage while disconnected from the bridge.

If it is within about +/-10% of nominal, power down and reconnect the bridge.

ak
The transformer works as expected without the bridge connected. The current draw anly happens when the bridge is connected son probably no short in transformer.
 

ericgibbs

Joined Jan 29, 2010
18,766
hi,
This image shows the connections I would expect to see, it looks OK.
Do not connect the centre tap to the mains.

Either the bridge or smoothing cap that's a problem.

Use your resistance measure meter to check for short circuits on the bridge or cap.

Disconnect the transformer from the mains while doing these tests.

E
 

Attachments

BobaMosfet

Joined Jul 1, 2009
2,110
So essentially the 'shield' is a copper plate between the primary and secondary windings tied to ground which will limit/mitigate high-frequency noise, as I understand it via capacitive coupling between the windings on the primary side and the shield.

I clipped the rest of this, as other posts have come in since I began writing it and you're sure your transformer is good.
 

Thread Starter

alisomay

Joined Jan 30, 2018
29
hi,
This image shows the connections I would expect to see, it looks OK.
Do not connect the centre tap to the mains.

Either the bridge or smoothing cap that's a problem.

Use your resistance measure meter to check for short circuits on the bridge or cap.

Disconnect the transformer from the mains while doing these tests.

E
The current draw happens apart from the existence of a cap or load. Also diodes seem ok. Connections seem ok. These are my 4th quartet of diodes. I test them in my scope they show a nice L shape. Really i did all the general controls. This problem comes cryptic to me. I even installed varistors to mains.
 

Thread Starter

alisomay

Joined Jan 30, 2018
29
Will it help if i took a video and upload it to vimeo? I will measure mains voltage, the voltage in secondary. The voltage from chasis to chasis. I will test all the diodes fastly. Power on the transformer when nothing is connected. Then i will connect the bridge with the amp meter. Or if you want me to perform another tests i can do them in the video also.
 

BobaMosfet

Joined Jul 1, 2009
2,110
The current draw happens apart from the existence of a cap or load. Also diodes seem ok. Connections seem ok. These are my 4th quartet of diodes. I test them in my scope they show a nice L shape. Really i did all the general controls. This problem comes cryptic to me. I even installed varistors to mains.
This doesn't make sense. Without a capacitor and a load, there is only the bridge-- so no current should flow because the circuit isn't closed. Makes me suspicious of how you're connecting the bridge.
 

Thread Starter

alisomay

Joined Jan 30, 2018
29
This doesn't make sense. Without a capacitor and a load, there is only the bridge-- so no current should flow because the circuit isn't closed. Makes me suspicious of how you're connecting the bridge.
No really i checked it many many times. Transformer outs to anode cathode junctions. Outputs are anode anode junction
(to use as load ground) cathode cathode junction for the positive side. I dosen't make sense to me also that is why i suggested that i make a video. I will do that, i will be home in 45 minutes or so.
 
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