>
>In message <6CEB3A36096CD2119FEE00A0C9410EC2228017@excalibur.swindon.msl
>.mitel.com>, Peter Chadwick <Peter_Chadwick@mitel.com> writes
>>
>>A good way of testing a transformer for suitability is to start by measuring
>>the secondary resistance as Rich says. Then measure the primary resistance,
>>and convert that to an equivalent series secondary resistance: sum it with
>>the measured secondary resistance. You can now use the rectifier resistance
>>and the load resistance to come up with the ratio of RL/RS, the load to
>>series resistance ratio. From the graphs in the books, you figure the output
>>voltage for various values of RL for the capacitor. You can use standard
>>formulas to figure the RMS current in the xfmr secondary.
>
>Be careful which standard formulas you use. In a cap. input supply, the
>short duration current spikes give a heating effect which can be much
>higher than a continuous current value calculated from the dc current.
Quite true. The approximation formulae on my Web site are strictly for
capacitor input filters.
>I
>checked some designs using PSpice and found that the *real* rms (heating
>effect) current was 1.7-2.2 x the value calculated from 1.414*Idc - the
>power dissipated in the windings was 3-5x higher than might have been
>expected.
>............ Typically 30-50% of total dissipation is in the iron.
>
As I understand it, copper loss in a Grade-5 Hipersil core transformer
typically accounts for virtually all of total loss.
- later, Steve
Rich. Measures.,www.vcnet.com/measures, 805.386.3734
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