[Amps] Transformers

[Will Matney]

See Below;

*********** REPLY SEPARATOR  ***********

On 7/15/06 at 6:45 AM Tom W8JI wrote:

>> 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.


Does this also include the schematics? Case in point is the SB-1000, and the SB-230.
The SB-230 shows it has an OCV of 2500 volts (really at 25 mA), but at 500 mA current
the sag drops it to 1900 Vdc. That's what I call really bad or, 2500 / 1900 = 1.31 or 31%.
The SB-1000 shows an OCV of 3100 Vdc and a load voltage of 2700 Vdc which comes up
to about 15%. Those would have to be from what the engineers measured before the 
draftsman or engineer drew it.


>
>> 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.

See other post


>
>>>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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Will