newbie transformer question

[cwats]

hey guys,
was playing around with some solenoids (as in the picture) and found that as the core is passed from left to right through the transformer the output voltage is increased. Can anybody tell me why?

As mentioned I am a real newbie, and I hope not to waste your time with what could be a really dumb question

Any answer is appreciated. thanks

 

[cowboybob]

Google "Transformer Flux".

 

[colin55]

The magnetic flux produced by the first winding is passed to the core.
The core passes the magnetic flux to the other coil.

 

[cwats]

thanks,
I understand about induced currents and what-not, but why does the out put voltage increase as the core is moved further though the transformer? Maximum output voltage is achieved when only 60mm of the core is in the primary coil (each coil is 150mm long). I can upload a graph showing the relationship if that would be of any help.

 

[cowboybob]

In your photo example, you're inducing flux into the entire core length, most of which is outside of the coil(s), thus being "wasted" or "lost" or "not used" (no conductors to induce current into).

Were you to use a core rod of 300mm, you would see max secondary output with the core flush at each end of the transformer.

 

[cwats]

thank,
yep thats what i would have thought as well but it is not the case, i did test with a 300mm core and max output voltage was still when there was only 60mm in the primary coil. I have been searching around for a few weeks now and the closest thing to an answer that i have been able to find is a lvdt transformer, but from what i understand the same principles do not apply?

 

[cwats]

it may also be worth noting that the further the core is passed through there is a noticeable increase in a humming noise and the core begins to vibrate

 

[MrAl]

Hi,


There could be several reasons why this might happen.

As the core is moved into the primary coil, it is subject to more and more ampere turns. If there is any DC current present in the coil it could saturate the core once it gets far enough in, or even the AC part could be affecting the saturation of the core. Also, as the core enters the primary center it is excited more and more, which could mean more core loss and so attenuation of the signal.

The 'core' does not look like it is made for magnetic applications, and this means it will function very poorly anyway even if it did work at all. Cores made for magnetic applications are made from special materials that are known to have good magnetic properties. A steel nail for example has some 100 to 1000 times LESS effectiveness as a core than a real transformer core made from real transformer metal.

You could try other materials, but you probably dont have anything worthy of a magnetic application laying around.

You could also try reducing the AC input amplitude to the primary and see if you get better results. Less excitation could mean better performance.

 

[cowboybob]

MrAl makes a very good point, that I missed, concerning core material.

 

[cwats]

thanks for the help,