10-12-2021, 04:53 PM
(This post was last modified: 10-12-2021, 04:56 PM by AdrianPH.
Edit Reason: mistakes
)
Hello Jeffrey;
No unfortunately I do not have a variac.
The following was described to me once if making mains transformers without details of the core saturation, the numbers are going off memory.
If I had a variac, I could wind say a few hundred turns on a bobbin and slowly bring the variac volts up until I saw a knee in the current drawn and then back off a little, so that if I had 250 turns on the bobbin and just below the knee was 30 Volts then use the formula of 250/30 = 8.33 turns per volt, so for 240 Volt mains input it would be 2000 turns and for secondary use 8.33 x 1.04 to allow for some loss. So for 30 Volts output use 30 x 8.33 x 1.04 = 260 turns per volt. But how that would apply to lower or higher frequencies was not mentioned.
I have not come across a reasonably priced fully isolating variac, so never picked one up.
Adrian
No unfortunately I do not have a variac.
The following was described to me once if making mains transformers without details of the core saturation, the numbers are going off memory.
If I had a variac, I could wind say a few hundred turns on a bobbin and slowly bring the variac volts up until I saw a knee in the current drawn and then back off a little, so that if I had 250 turns on the bobbin and just below the knee was 30 Volts then use the formula of 250/30 = 8.33 turns per volt, so for 240 Volt mains input it would be 2000 turns and for secondary use 8.33 x 1.04 to allow for some loss. So for 30 Volts output use 30 x 8.33 x 1.04 = 260 turns per volt. But how that would apply to lower or higher frequencies was not mentioned.
I have not come across a reasonably priced fully isolating variac, so never picked one up.
Adrian
Learning as I go!
Youtube EF91 Valve
Youtube EF91 Valve
