Transformer power is a square of the cross-section area of the inner leg of the EI core in cm^2. About 20% more for C core.
Square the area. 256VA
Measure the DCR of the primary, then double it
Two rules that I've used over the years are:
1. Load the output until the voltage drops by 10% from the no-load value. I think this rule came from a company that sold electronic surplus.
2. Measure the cross-sectional area of the core. Compare that to published data for similar transformers. I think this rule came from the ARRL.
If there's a disagreement between the two, take the smaller value.
Remember that transformers are rugged beasts. If you overload one slightly, it will just run a bit hotter.
Ed
Two rules that I've used over the years are:
1. Load the output until the voltage drops by 10% from the no-load value. I think this rule came from a company that sold electronic surplus.
2. Measure the cross-sectional area of the core. Compare that to published data for similar transformers. I think this rule came from the ARRL.
If there's a disagreement between the two, take the smaller value.
Remember that transformers are rugged beasts. If you overload one slightly, it will just run a bit hotter.
Ed#1 isn't very good because larger transformers tend to have better regulation. Try that with a transformer rated to a few kVA and you will overload it!
Transformer power is a square of the cross-section area of the inner leg of the EI core in cm^2. About 20% more for C core.
Is this rule for 50 Hz? 60 Hz? 400 Hz?
Don't think I'll add this one to my tips 'n tricks, but if it works for you...
I don't think frequency is a factor in this one
So people building high frequency DC/DC converters to get the size of the magnetics down are on a wild goose chase? I don't think so.
Two rules that I've used over the years are:
1. Load the output until the voltage drops by 10% from the no-load value. I think this rule came from a company that sold electronic surplus.
2. Measure the cross-sectional area of the core. Compare that to published data for similar transformers. I think this rule came from the ARRL.
If there's a disagreement between the two, take the smaller value.
Remember that transformers are rugged beasts. If you overload one slightly, it will just run a bit hotter.
Ed#1 isn't very good because larger transformers tend to have better regulation. Try that with a transformer rated to a few kVA and you will overload it!
My rules are intended for transformers like the one in Jester's photo. Most of us aren't interested in transformers rated for a few kVA.
Ed