Electronics > Beginners
Power VA and secondary windings.
davelectronic:
I recently acquired a toroidal transformer of single primary and single secondary. The numbers are 100VA at 30 Volts AC, for the use i have in mind, i need a voltage under 20 Volts if possible. The current is 3.3 Amps as the transformer is at 30 Volts at 100VA, i think that right. It looks reasonably easy to remove secondary windings to drop the voltage to something i can make use of. Would i be right in thinking that the power rating would increase as a result of lowering the secondary voltage ? Or is it the case that the power rating would remain the same, regardless of removing secondary windings. I'm asking as although the voltage is lowered, but the secondary wire gauge remains the same. So only design power rating remains the same, but with reduced secondary voltage ?
Thanks for reading, i have googled this in a few different key words, but can't find anything specific to the question above.
Thanks again, thoughts on this appreciated.
Zero999:
Reducing the number of windings on the secondary will not increase the power rating.
If you rewound the secondary with thick enough wire to take over 5A, then the power rating would remain the same. If you simply unwound part of the secondary winding, then the power rating would be reduced, since the secondary winding will not be rated to carry the extra current, so you'd be looking at 20V at 31/3A, which would be power rating of 662/3VA.
madires:
When the OP removes 1/3 of the secondary windings he also reduces the wire's resistance by 1/3. ;)
GromBeestje:
--- Quote from: madires on December 14, 2019, 02:26:01 pm ---When the OP removes 1/3 of the secondary windings he also reduces the wire's resistance by 1/3. ;)
--- End quote ---
In total, yes. But the resistance per centimeter will still remain the same, so the wire itself will not be able to handle more current then it did before.
wraper:
Power rating will remain the same at best. That's given that wire used for secondary winding have higher cross section than minimum needed, so you can safely pull more current at lower voltage (not exceeding total power rating). If wire thickness is bare minimum for rated current, power rating will decrease as output voltage will decrease but you cannot pull more current.
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