I am at the moment in the process of re-winding a small transformer with a 0.68 x 0.68 inch core, (0.46 sq in) which would give 13 turns/volt.A rough rule of thumb is to measure the CSA cross sectional area of the transformers core.
Then its inversely 6 turns per volt for every square inch of core.
The easiest way to work out if a transformer is suitable is to work on "watts" VA. If it is a 1,000 VA transformer, you will be able to up to 1kW into a spot-weld. Of course the secondary winding and the leads have to be correct to allow the high current to flow.
Some good explanations in this thread.
As I understand it, there are three main areas of loss in a low frequency (50Hz or 60Hz) transformer:
(1) Copper loss (I↑2R in both primary and secondary)
(2) Core loss
(2.1) Eddy current loss (I↑2R)
(2.2) Coercive force loss (force required to run the core around the BH curve with an AC input)
(2) Leakage inductance (less than perfect coupling between primary and secondary)
Is the coercive force loss significant for a microwave oven transformer?
spec
**broken link removed**
Hi MrAl,Hi there spec,
We could probably look up some typical magnetic materials and try to find out. Grain oriented si steel laminations in every MW transformer i have seen to date.
Pardon for the slight correction, but "leakage inductance" in itself is not considered a loss because it is a storage element and storage elements in theory do not dissipate energy.
Resistance, core losses that result in heat, do result in actual energy losses.
Leakage inductance does cause a loss in voltage, but like any other pure inductance it itself stores and releases energy. It's like connecting an extra inductor in series with the primary that has no losses.
Hi MrAl,
Thanks for info.
Thanks also for the explanation about 'leakage inductance' too. Of course, you are quite right- I had not viewed it as a storage element.
I like the analogy: 'It's like connecting an extra inductor in series with the primary that has no losses'. Am I right in thinking, that because of this, leakage inductance reduces the effective input voltage and thus output voltage so there is a loss of voltage as opposed to power?
spec
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