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Re: Winding a transformer
Hi Kamil,
My, hopefully useful, comments:
> Original Poster: Kamil Kompa <czlonek-at-polbox-dot-com>
>
> Hi !
>
> I have found a transformer core made of metal sheets.
> Metal sheets are shaped like E and I letters.
> It is 1800W and max. inductance in my core is 12000 Gs
Nice find
> I know all the formulea necessary to count number of turns for primary
> and secondary and wire diameter. Unfortinatelly i have a problem with
> it.
> The window in my core is to small ( I mean the space intended for wire
> between real core and frame).
This is often a problem with EI cores in HV applications. Have you factored
in inter-turn insulation as well as the turns thickness?
> My home power system is 220 V and 50 Hz so the primary schould have
> about
> 220 turns (it makes the transformer to take from my power supply about
> 8 A current and it makes about 1760W). I counted that diameter of wire
> schould be about 2,7 mm , but practically 1,7 diameter wire is not
> goaing to be hot while working. My problem appears when i want to make
> secondary.
> There is too little space (of course i remember about isolation and
> sufficient wire diameter). I can make about 3 KV transformer , but its
> not good to use (not very high voltage , very high current).
> This is short description of my problem, and now i want to explain to
> You my solution and ask if it is a good idea.
> All countings (number of turns) were made for a transformer that will
> work properly directly connected to my power supply. In fact to use it
> with a tesla coil i schould connect it with a ballast.
> That fact made me to think about less turns of primary in my
> transformer.
> I mean that i can make about 90 turns primary and about 5000 turns
> secondary (with isolation). It will not work connected to a power supply
> (the fuse will burn), but i thought to connect it with a ballast.
> The ballast will keep current at level of about 8 A and my transformer
> will give about 12KV and about 150mA.
> But this is only theory. How it will work in practice.
Unfortunately it is not even theory. The problem is that the voltage and
therefore power will divide across the ballast and transformer as the ratio
of their inductances - my calcs say you need about 450 turns to take 1800VA
from a 220V 50Hz supply. Therefore you will need another 360 turns on your
ballast. Your transformer will only actually develope 2.4kV on the
secondary because you are only dropping 44 volts across its primary. The
other 176 volts drop across the ballast.
You'd be better off getting hold of a small pole pig or using some MOTs.
The trouble with home made HV transformers is that the cores that are
commonly available are designed for LV applications where the winding window
can be much smaller as the insulation isolation does not have to be as good.
> Will it work , or loss of power will be high?
It won't work.
You could try building it as a rather odd Switch Mode PSU - running at about
250Hz. Then your design would work. However I doubt you can adequately
insulate 12kV in the space you have.
Perhaps you could supply more details of the core's physical dimaensions?
Regards
Nick Field