Discuss Strange Waveform on Secondary of Mains Transformer in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Reaction score
0
Hi Folks,
Although I'm not an electrical engineer, I've registered on this site in an effort to seek some advice regarding a strange "240v mains" issue I'm seeing in my work shop - I will explain.
The problem first came to my notice whilst trying to locate a 100Hz buzz on my amplifier. I traced to problem back to the 15-0-15v secondary of the mains transformer where I'm seeing a strange "glitch" on the AC waveform (pictures attached). In an effort to try and isolate this, I built a simple replica of the circuit using another transformer connected to a bridge rectifier and a 4700uf capacitor. All looked normal until I connect a load (90mA) across the capacitor and I then see the top of the waveform flatten off and the spike as shown in the pictures. Do I have some king a mains issue as I never seem this before?
Any advice would be appreciated.
Regards
Geoff.

Strange Waveform on Secondary of Mains Transformer Secondary AC - EletriciansForums.net

Strange Waveform on Secondary of Mains Transformer Secondary full waveform - EletriciansForums.net
 
Hi Geoff !
Interesting problem with a few causes ... can you draw the circuit that produces this waveform please :)

(eg - you mention a bridge rectifier but this pic is an AC waveform, where was it seen?)
 
Hi Folks, The amp is a Marshall AS80R (schematic attached).
I've noticed on my replica PSU set-up, its only when the 4700uf cap is connected is the waveform effected.
When I scope the speaker on the amp, I can see a spike occurring every 20mS (100Hz) and this is what I'm hearing. the 20mS spike seems to be everywhere and de-coupling seems to have no effect. I can even see it at different points on the chassis
Regards
Geoff.
 

Attachments

  • Marshall AS80R.pdf
    335.9 KB · Views: 8
If you can measure low volts ac , what is across R301 and associated diodes D301 D302
(whether it how you are measuring or part of the problem - i don't Know )
 
For the top of the wave form to flatten off like that, then either the transformer is not supplying the required current ( impedance too high ), possibly a cheap Chinese transformer, or the filter capacitors are not supplying the current they are required too, possibly they are too large, so they cannot charge up quick enough, or they are faulty. Try a better bigger current transformer, try smaller filter cap's say 2200 uf.
I doubt that an earth loop would cause the waveform distortion.
 

Reply to Strange Waveform on Secondary of Mains Transformer in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock