Guru
Joined: 09/08/2007
Location: AustraliaPosts: 4406
| Posted: 09:46pm 11 Apr 2021 |
Roger,
You might care to go to the trouble of measuring the idling power loss of each of those cores before you go any further.
First wrap a decent number of turns of any old wire roughly around the bare core.
From whatever number of turns you finally end up with, use the on line flux calculator to find an applied rms voltage to reach one Tesla with that number of turns, and that core cross sectional area.
It might work out to 0.73 volts per turn or something (???) for just one core.
That is just an imaginary number I guessed.
If there are seventeen turns, 17 x 0.73 = 12.41 volts for example = one Tesla
Find a way to get 12.41 volts to energise the winding with, maybe a variac, or another transformer with some appropriate resistors, light bulbs. Whatever....
Measure the current in your toroidal test winding at 12.41 volts. Around 10 Va to 15Va for each core would be a reasonable expectation, probably a bit less than one amp in this example.
Idling power is a very good indication of the overall quality of the core. The grade of steel, any internal air voids, or lumps of weld will all tend to degrade the idling efficiency.
That may be excellent top quality steel you have there, but some Chinese guy has probably bought a lot of odd offcuts fairly cheaply as scrap, which all ends up looking a lot worse than it actually is. So you may be in luck.
But its probably worth knowing what you have before putting a LOT of time and effort into doing the winding.
The big commercial transformer manufacturers buy massive bulk rolls of steel strip and copper wire, and when getting near the end of a roll, will not attempt to load their machine if there is insufficient to wind one last core without a join. So odd lengths get sold cheap for scrap price. Its just not worth the time and trouble to mess about with joins on their big fully automated machine.