Toroidal Transformer Core using Soft iron wire

[btahir90]

Hello!

Dear All, I am Planing to make a toroidal transformer but Silicon iron sheet is costly here in my area, Can i use Soft iron Wire (bare without insulation) to make a toroid shape and start winding on it.

What if i use some varnish on iron wire before making a toroid core to reduce eddy current.

how much power loss i can save by using a varnish coating on bare iron wire.

Attached is an image for the reference.

 

[c_mitra]

Yes but it may not be suitable for high frequency or high power. Intrinsic loss due to hysteresis is large for soft iron because of residual magnetism. If you are planning to use for low power and low frequency perhaps you can use it safely. If it is already has an oxide layer on the surface, then using a varnish in addition is going to reduce some audio noise. If it is having a zinc or tin plating then it will get too hot even at 50-100 Hz (depending on the power handling).

 

[FvM]

Insulating varnish would be absolutely necessary.

Losses of plain "soft iron" compared to silicon steel will be still much higher, the round wire has also a lower packing density than wound tape. I wonder if someone has quantitative data of steel magnetic properties that allow to estimate the losses.

I don't think that it's a promising way to make a transformer.

 

[btahir90]

Power is 1KVA at 50Hz.

- - - Updated - - -

Now having a comparison of Varnished iron Wire core and Varnished Iron sheet Core. Which one will be good for toroidal transformer.

 

[c_mitra]

Commercial toroidal transformers are made from special steel tapes of standard widths. You can get one specially wound or take one commercial transformer of the same or similar capacity and rewind manually. I do not think rewinding a 1 KVA toroidal transformer is fun.

And yes, I think you can forget the varnished iron wire core because it is going to be too much lossy to be useful.

 

[btahir90]

Can You Explain how geometry effect the losses. I think Smaller the Layer smaller the eddy current lesser the loss. In Shape of wire eddy current is divided in many smaller currents. Then how loss could be higher.

What is the effect of air gap in core which will be higher in wire wound core and less in sheet wound core.

Thanks.

 

[c_mitra]

Can You Explain how geometry effect the losses..

Qualitatively speaking: consider the toroid as a bent cylinder that have been joined at the free ends. The magnetic fields are produced along the axis of the cylinder. The induced eddy currents will be perpendicular to the magnetic field lines or they are essentially parallel to the current in the coils (but in opposite direction: Lenz's law say so). Now you can see the effect of lamination.

The effective core area will be determined by the total cross sectional area of the iron wires. The gaps in between the wires will NOT contribute to the core gap in the conventional sense. In the same way, cores made from iron tapes do not have 'core gaps' in the usual sense. They are gapless. However, they have effective cross sectional area less than that of a solid core...

Your losses are due to hysteresis. That is a magnetic loss and is not affected by lamination. Energy lost per cycle is proportional to the area of the hysteresis loop. This is different from eddy current loss. Eddy current loss does take place in all conducting materials but hysteresis loss takes place only in ferromagnetic materials.

 

[btahir90]

This mean that using wire and sheet does not matter if they are laminated. The problem is the iron material. if i choose another material with low hysteresis loss then even wire construction will be OK. Please correct me if i am wrong.
Thanks a lot for the information.

 

[c_mitra]

This mean that using wire and sheet does not matter if they are laminated. The problem is the iron material. if i choose another material with low hysteresis loss then even wire construction will be OK.

Right. If you can get some steel wire with low hysteresis and paint them with high temp varnish and use in a toroidal transformer, you can expect excellent results. Advantage: you can use one wire size and select various core shape and size that will be real hassle with steel tapes (commonly used in conventional toroidal transformers). Disadvantage: you will have a slightly larger size because you will need little bit more area to accommodate the same amount of 'iron'.

You can plot the B-H curve using your wire in any college lab- they will have the full instruments.

 

[FvM]

The whole thing looks to me a bit like re-inventing the wheel. O.K., I concede it's still round. But that's the best you can say about the approach. Suggest you come back when you have found a wire with good soft magnetic characteristic.

 

[btahir90]

Thanks guys. It was too help full for me. I gained a lot.