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Air core transformer question -- help

Started by Unknown January 5, 2016
Could some electronics guru please provide
some hints/suggestions to the following ?
First, I built a simple DC->AC push-pull 
inverter with a 12 Volt 7AH sealed lead 
acid cell battery. The output transformer
is a 120 Volt(primary) and 6-0-6 1.5 Amp
(max) secondary. This configuration worked
fine, and a 60 Watt incandescent lamp          
connected to the transformer output terminals 
provided steady light.

I replaced the transformer with an air core
transformer, obtained by carefully removing
the iron core of the transformer used above,
The winding is completely intact, tested by
measuring the winding resistance of both
the primary and secondary, with the transformer
not connected. I am fully aware of the reluctance
issues but this time the transformer output
is just about 0.5 Volts - 1.0 Volts AC. So
what is going wrong ? All hints/suggestions
are welcome. Thanks in advance for your help.
On Mon, 4 Jan 2016 20:36:18 -0800 (PST), dakupoto@gmail.com Gave us:

>Could some electronics guru please provide >some hints/suggestions to the following ? >First, I built a simple DC->AC push-pull >inverter with a 12 Volt 7AH sealed lead >acid cell battery. The output transformer >is a 120 Volt(primary) and 6-0-6 1.5 Amp >(max) secondary. This configuration worked >fine, and a 60 Watt incandescent lamp >connected to the transformer output terminals >provided steady light. > >I replaced the transformer with an air core >transformer, obtained by carefully removing >the iron core of the transformer used above, >The winding is completely intact, tested by >measuring the winding resistance of both >the primary and secondary, with the transformer >not connected. I am fully aware of the reluctance >issues but this time the transformer output >is just about 0.5 Volts - 1.0 Volts AC. So >what is going wrong ? All hints/suggestions >are welcome. Thanks in advance for your help.
http://www.electrical4u.com/air-core-transformer/ Use for RF. coupling efficiency suffers at low freq. http://www.electronicspoint.com/threads/air-core-transformer-efficiency.18329/
On Mon, 04 Jan 2016 20:36:18 -0800, dakupoto wrote:

> Could some electronics guru please provide some hints/suggestions to the > following ? > First, I built a simple DC->AC push-pull inverter with a 12 Volt 7AH > sealed lead acid cell battery. The output transformer is a 120 > Volt(primary) and 6-0-6 1.5 Amp (max) secondary. This configuration > worked fine, and a 60 Watt incandescent lamp connected to the > transformer output terminals provided steady light. > > I replaced the transformer with an air core transformer, obtained by > carefully removing the iron core of the transformer used above, > The winding is completely intact, tested by measuring the winding > resistance of both the primary and secondary, with the transformer not > connected. I am fully aware of the reluctance issues but this time the > transformer output is just about 0.5 Volts - 1.0 Volts AC. So what is > going wrong ? All hints/suggestions are welcome. Thanks in advance for > your help.
Removing the core reduces the coupling between the coils. If you did the experiment with a 50 or 60Hz switching frequency, you pretty much turned your transformer into a couple of loosely coupled wires. -- www.wescottdesign.com
On Monday, January 4, 2016 at 11:36:22 PM UTC-5, daku...@gmail.com wrote:
> Could some electronics guru please provide > some hints/suggestions to the following ? > First, I built a simple DC->AC push-pull > inverter with a 12 Volt 7AH sealed lead > acid cell battery. The output transformer > is a 120 Volt(primary) and 6-0-6 1.5 Amp > (max) secondary. This configuration worked > fine, and a 60 Watt incandescent lamp > connected to the transformer output terminals > provided steady light. > > I replaced the transformer with an air core > transformer, obtained by carefully removing > the iron core of the transformer used above, > The winding is completely intact, tested by > measuring the winding resistance of both > the primary and secondary, with the transformer > not connected. I am fully aware of the reluctance > issues but this time the transformer output > is just about 0.5 Volts - 1.0 Volts AC. So > what is going wrong ? All hints/suggestions > are welcome. Thanks in advance for your help.
Oops, why did you want to do that? As Tim said there is now little coupling. The voltage is given by the changing magnetic flux through the secondary... no flux, no V. George H.
dakupoto@gmail.com wrote:

> Could some electronics guru please provide > some hints/suggestions to the following ? > First, I built a simple DC->AC push-pull > inverter with a 12 Volt 7AH sealed lead > acid cell battery. The output transformer > is a 120 Volt(primary) and 6-0-6 1.5 Amp > (max) secondary. This configuration worked > fine, and a 60 Watt incandescent lamp > connected to the transformer output terminals > provided steady light. > > I replaced the transformer with an air core > transformer, obtained by carefully removing > the iron core of the transformer used above, > The winding is completely intact, tested by > measuring the winding resistance of both > the primary and secondary, with the transformer > not connected. I am fully aware of the reluctance > issues but this time the transformer output > is just about 0.5 Volts - 1.0 Volts AC. So > what is going wrong ? All hints/suggestions > are welcome. Thanks in advance for your help.
The iron core couples almost all of the flux from a winding to all other windings. The leakage inductance is a tiny fraction of the total inductance. When you remove the core, the leakage inductance becomes dominant, and the flux from one winding does not couple well at all to the other winding. There are ways to improve the mutual inductance in air-core transforers, such as bifilar winding (interleaving the turns of the two windings). But, now you know WHY they put all that iron in transformers. it is not a mechanical support, it is to capture and couple the flux between windings. And, your results are certainly proof of that! Jon
On Tuesday, January 5, 2016 at 5:10:40 AM UTC-8, George Herold wrote:
> On Monday, January 4, 2016 at 11:36:22 PM UTC-5, daku...@gmail.com wrote: > > Could some electronics guru please provide
> > I replaced the transformer with an air core > > transformer, obtained by carefully removing > > the iron core... this time the transformer output > > is just about 0.5 Volts - 1.0 Volts AC.
> The voltage is given by the changing magnetic flux > through the secondary... no flux, no V.
The reason that there's no flux, is 99% that the B field in iron is magnified from the field (H-field, in physics terminology) that you get with no core. The rest might be that your windings are no longer well-coupled because the core no longer links them, only their geometry does. It is possible to make a transmission-line transformer, very well flux linked, by pairing the primary and secondary wiring, and winding that pair. Your transformer wasn't wound that way (when there is a core, it doesn't matter).
On Wednesday, 6 January 2016 13:09:23 UTC+11, whit3rd  wrote:
> On Tuesday, January 5, 2016 at 5:10:40 AM UTC-8, George Herold wrote: > > On Monday, January 4, 2016 at 11:36:22 PM UTC-5, daku...@gmail.com wrote: > > > Could some electronics guru please provide > > > > I replaced the transformer with an air core > > > transformer, obtained by carefully removing > > > the iron core... this time the transformer output > > > is just about 0.5 Volts - 1.0 Volts AC. > > > The voltage is given by the changing magnetic flux > > through the secondary... no flux, no V. > > The reason that there's no flux, is 99% that the B field > in iron is magnified from the field (H-field, in physics terminology) > that you get with no core. The rest might be that your windings are > no longer well-coupled because the core no longer links them, only > their geometry does. > It is possible to make a transmission-line transformer, very well flux > linked, by pairing the primary and secondary wiring, and winding that pair. > Your transformer wasn't wound that way (when there is a core, it doesn't > matter).
Bifilar winding is used in cored transformers when you really want to minimise leakage inductance. There are situations where even a little leakage inductance can be undesirable. And for precision ratio transformers, each half of a bifilar winding can be identical to the other to one part in 10^9, which can be handy. Most ratio transformers use bundles of more wires, and can't do better than about one part in 10^7. See "Coaxial AC Bridges" by Rayner and Kibble. http://www.amazon.com/Coaxial-Bridges-Kibble-Rayner-Hardcover/dp/B011SK680Q/ref=sr_1_2?s=books&ie=UTF8&qid=1452093542&sr=1-2&keywords=Coaxial+Bridge -- Bill Sloman, Sydney
On Mon, 4 Jan 2016 20:36:18 -0800 (PST), dakupoto@gmail.com wrote:


>I replaced the transformer with an air core >transformer, obtained by carefully removing >the iron core of the transformer used above, >The winding is completely intact, tested by >measuring the winding resistance of both >the primary and secondary, with the transformer >not connected. I am fully aware of the reluctance >issues but this time the transformer output >is just about 0.5 Volts - 1.0 Volts AC. So >what is going wrong ? All hints/suggestions >are welcome. Thanks in advance for your help.
For your own benefit, instead of removing the core, you might instead reconfigure it so that an adjustible gap is possible. EI stampings can be grouped with 'all E' and 'all I' groupings. Gradually increasing the gap in paper-width-thick increments will show you what's happening as you change the effective permeability of the magnetic core from the initially high value of silicon steel, to that of free space. ( uo = 4 x pi x E-7 ) RL
On Thu, 07 Jan 2016 09:58:04 -0500, legg <legg@nospam.magma.ca> Gave us:

>On Mon, 4 Jan 2016 20:36:18 -0800 (PST), dakupoto@gmail.com wrote: > > >>I replaced the transformer with an air core >>transformer, obtained by carefully removing >>the iron core of the transformer used above, >>The winding is completely intact, tested by >>measuring the winding resistance of both >>the primary and secondary, with the transformer >>not connected. I am fully aware of the reluctance >>issues but this time the transformer output >>is just about 0.5 Volts - 1.0 Volts AC. So >>what is going wrong ? All hints/suggestions >>are welcome. Thanks in advance for your help. > >For your own benefit, instead of removing the core, >you might instead reconfigure it so that an adjustible gap is >possible. > >EI stampings can be grouped with 'all E' and 'all I' groupings. > >Gradually increasing the gap in paper-width-thick increments will show >you what's happening as you change the effective permeability of the >magnetic core from the initially high value of silicon steel, to that >of free space. ( uo = 4 x pi x E-7 ) > >RL
Can we really ever put a price on space?
On Thu, 07 Jan 2016 10:03:02 -0500, DecadentLinuxUserNumeroUno
<DLU1@DecadentLinuxUser.org> wrote:

>On Thu, 07 Jan 2016 09:58:04 -0500, legg <legg@nospam.magma.ca> Gave us: > >>On Mon, 4 Jan 2016 20:36:18 -0800 (PST), dakupoto@gmail.com wrote: >> >> >>>I replaced the transformer with an air core >>>transformer, obtained by carefully removing >>>the iron core of the transformer used above, >>>The winding is completely intact, tested by >>>measuring the winding resistance of both >>>the primary and secondary, with the transformer >>>not connected. I am fully aware of the reluctance >>>issues but this time the transformer output >>>is just about 0.5 Volts - 1.0 Volts AC. So >>>what is going wrong ? All hints/suggestions >>>are welcome. Thanks in advance for your help. >> >>For your own benefit, instead of removing the core, >>you might instead reconfigure it so that an adjustible gap is >>possible. >> >>EI stampings can be grouped with 'all E' and 'all I' groupings. >> >>Gradually increasing the gap in paper-width-thick increments will show >>you what's happening as you change the effective permeability of the >>magnetic core from the initially high value of silicon steel, to that >>of free space. ( uo = 4 x pi x E-7 ) >> >>RL > > Can we really ever put a price on space?
For an awful long time, it seems that there has been no end to the mischief possible, in coveting other people's (or even 'unoccupied') space. Opinions or beliefs, which occupy no physical space what so ever, seem also to end up costing somebody........ Just give it a name and some bright spark will figure out a way to make a buck from it. RL