> Why does Heathkit show in their manuals the open circuit
> voltage, and the full load voltage that
> calculates to 15% sag (OCV / FLV )? They show this in
> several of their models.
Manuals are written from other manuals, and the goal was to
always be conservative. Manual writers at Heath were a
completely different group than engineers. I don't think I
talked to a manual writer more than a dozen times.
> I should have worded this different. No they don't
> saturate under load.
That's right, you should have worded it much differently.
>However, the
> amount of iron is what controls the power output in watts.
> Not enough iron and you have
> a high flux density, a higher magnetizing current, and
> more sag.
That's not correct. That still implies flux density controls
maximum power.
>>Maximum flux density, which means closest operation to
>>saturation, occurs with NO load. As load is increased flux
>>levels do not increase. Increased current, because of
>>resistive losses in the primary circuit, actually causes
>>the
>>transformer's flux level to decrease. When a transformer
>>is
>>designed the highest primary voltage under no load is used
>>to set flux density at a safe level.
>
> correct
>
>
>>
>>The actual mechanism inside a transformer is the secondary
>>develops a counter-MMF. This opposing flux would reduce
>>flux
>>density, but primary current increases in order to try and
>>maintain the **same** flux density. When mains and
>>primary
>>resistances carry more current from increased load, the
>>primary voltage drops slightly. This REDUCES flux density,
>>moving the transformer further from saturation. Not closer
>>to it.
>
>
> correct
The idea flux density sets maximum available power is not
correct.
73 Tom
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