Working with torroid core

[babinton]

Hello every, its been quiet a while I posted in this forum last.

NOTE: please, bear with me if some of my questions seems stupid( this is my first try at constructing an HF transformer by hand ( it is difficult to get my hand of the materials in my country)

I have some issues that I will like everyone to help me with.

I have some toroid core that I removed from an abandoned power panel. my first question is can I used these toroids as transformer core for an inverter transformer?

Next issue, I did some theoretical design of High frequency transformer in which I derived the following parameters

input dc voltage =12v (that is what i can afford right now to power my inverter)

input rms current = 68amps

output voltage DC = 380V dc

number of primary turn = 3 turns

Here is my problem: I can not get my hand on litz wire or coper foil for the primary winding so I thought I should use 4 parallel wire of AWG10. but given my transformer core which is a toroid core, it is difficult to spread and wind the wire to cover the core,
so can I just concentrate my primary winding on some part of the core and cover the other part with the secondary?

Also, is it really okay to parallel wire to form the primary winding?

Furthermore, is it okay for some of the winding to overlap each other?



Please, I will like if you can help with links to sites where I can order Litz wire, copper foils etc.

Best Regards.
BFB babinton.

 

[srizbf]

the Al value of the salvaged core should known before you start using for your design.

 

[babinton]

Please, how can I find the Al value, I was thinking of trying to correlate with mag-inc catalog by checking the size close to the size of what I have, check the coating code etc and use the electrical characteristic of the one that match my core the most. Please, alternative can u suggest a worst case parameter(Al etc.) that I can use for my core to design for the worst case scenario.

Regards

 

[FvM]

There are more manufacturers than Mag Inc, so you shouldn't rely on coating color to identify a core. Even more important than Al value, saturation flux and losses versus frequency would be the most interesting parameters for a power transformer. If you know the core type (ferrite or iron powder), the Al value can give a hint about the core material.

Al value can be easily determined by measuring the inductance of a test coil. The other parameters are more complicated.

For the winding design, you should consider this points:
- multi parallel conductors instead of litz wire can basically work. The wire gauge should be selected for low skin effect. AWG 10 will be only appropriate for low frequencies, I would rather think of 16 -20.
- In addition, the individual wires have to be stranded, otherwise proximity effect will still cause a non-uniform current distribution.
- Asymmetrical position of windings will increase leakage inductance and cause fringing fields, possibly increasing the core losses
- as a special variant, placing partial primary windings around the circumference, connected electrically in parallel may possibly work. I didn't yet try, but it can be expected to give symmetrical field distribution, no proximity effect and moderate leakage inductance.

 

[srizbf]

for salvaged cores that is the method , unless you know the maker of the core.

from some of the catalogues of toroid manufacturers you can match the id and od of the core with color code if any.

then you can get some Al value.
choose the minimum or average if you dont know the core manufactuerer.

if you have instruments you can wind a sample coil and correlate your Al value.

 

[babinton]

Thanks everyone, you replies has been helpful, they confirmed what I already suspected. I will try the different method of finding the AL value.
Also, by the way, I have a salvage EE ferrite transformer, but I decided against using it since I can't find a way of safely separating the two halves without damaging the core or bobbin. Please, any suggestion on how to unglue the two halves from each other will be VERY WELCOME

Regards
Babinton

 

[andre_luis]

the Al value of the salvaged core should known before you start using for your design.

Also is needed to estimate cross sectional area ( Ae ).
It is what define Power limit.

Due you don´t wave other parameters; could comparing with some manufacturers tables wich differs no much.

+++

 

[xaccto]

Thanks everyone, you replies has been helpful, they confirmed what I already suspected. I will try the different method of finding the AL value.
Also, by the way, I have a salvage EE ferrite transformer, but I decided against using it since I can't find a way of safely separating the two halves without damaging the core or bobbin. Please, any suggestion on how to unglue the two halves from each other will be VERY WELCOME

Regards
Babinton

small butane torch flame or large soldering iron to heat up the core. Easily pulls apart then. Welding gloves to handle hot
parts are useful.

---------- Post added at 09:53 ---------- Previous post was at 09:47 ----------

...
- In addition, the individual wires have to be stranded, otherwise proximity effect will still cause a non-uniform current distribution.

Hi Fvm, i'm just a little puzzled, I mean individual wires are already separate strands so to speak, so I'm wondering
if you mean something beyond that, precisely what you mean ? thanks