transformer windings

[Kevin Weddle]

I learned something new that I would like to share with everybody. I have a transformer with multiple windings. I thought that the taps off the different windings would return to each other. I found out that the voltage is just stepped down to the winding and that the voltage of the windings has nothing to do with the voltage of the input. Here is what I thought happened :

120Vac | |
| |-------80VAc }
| |-------60Vac }different winding
| |-------50Vac
| |
| |-------30Vac
0Vac | |


Instead the voltage is just stepped down and you must connect the separated windings to get something at the same potential. I found this out because I have a power supply that has a bridge for the 5volt and a separate 2 diode rectifier for the +- voltages. I figured that I could take the center tap and use a 2 diode configuration, but there was no return. So now I have a bridge with the center tap that is connected to the ground side to make it the same potential.

 

[Dazza]

I have run into problems in using transformers, and trying to work out how they work, and trying to understand why it didn't work the way I expected. Now I understand better .

Thanks for sharing Kevin.

 

[Kevin Weddle]

Not only that. I found that my meter is only good at measuring sinusoidal waveforms with respect to ground. Sometimes I have to decouple the signal to measure RMS. I even get false readings sometimes. I'll go to measure the voltage, read the voltage, pull the probes away and still measure a voltage. Isn't that the way it goes.

 

[mitesh]

Sir,
Doesn't it seem to be based upon auto-transformer concept? Does it gives good results when all outputs are used at same time? I think there will be a lot of errors due to different losses! :-\

 

[MP1]

Kevin,
With the transformer out of circuit, check the ohm readings between the different taps. This will give you the information you need about the windings and which are connected to which. Then you will be able to draw your own schematic of the transformer windings. It is possible that you have a special transformer that does not follow a standard. In this case, ohm readings will get you where you want to go from there.

MP

 

[prateeksikka]

hi kevin!
Do all the windings have a common ground?
With a good quality multimeter,try out checknig b/w winding-winding point and winding -ground poiint.
Such transformers are used to change turns ratio and thus get varying voltages at the o/p. depending on the requirement.in your case i guess it is much simpler.
why dont you use a t/f with constant turns ratio which gives 5V at the o/p?
:
prateek

 

[Kevin Weddle]

I think it is just a theory problem. You see, I like to follow the polarity of a circuit, especially with transformers. In this case, both supplies share the same ground, but they are different windings. You can only follow the polarity when analyzing each winding separately. Apparently it does not hurt to sneak together two wires and make them the same potential so long as there is not a distinct voltage difference.