EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: dentaku on March 13, 2014, 02:00:06 am
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I have this transformer from an old stereo that seems to have 3 secondaries. They're completely independent of each other too.
The bleu-blue and red-red wires both connected to the circuit board to little B20S rectifiers plus each a single large-ish 25V cap and the Orange-White-Orange connected to a larger 205N rectifier and two 3300uF 35V caps so obviously the different parts of this system had different power requirements (tape, radio, turntable, amp etc.).
Checking the AC voltage with my meter I get
RED = 14.6V
BLUE = 15.25V
orange-white-orange = around 17V per side
Question?
I checked the resistance between the different windings and RED = 0.7ohm, BLUE = 1.2ohm, ORANGE-WHITE-ORANGE = 0.5ohm on each side of the center tap (so 1ohm total)
Can the resistance tell me anything about this transformer?
Why would the blue one be higher than the others?
Even though it's a rather large thing, it's really 3 smaller windings in one package so would this mean that it's not as capable a transformer as something that just has ONE large secondary?
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The resistances will tell you about the thickness of the wire used in the secondaries, and therefore about how much current each was designed to supply. Given that they all produce about the same voltage (and thus have a similar number of turns), you can assume to a first approximation that the available current is in inverse proportion to the resistance. So a 0.5 ohm winding can provide more than twice as much current as a 1.2 ohm winding.
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The resistances will tell you about the thickness of the wire used in the secondaries, and therefore about how much current each was designed to supply. Given that they all produce about the same voltage (and thus have a similar number of turns), you can assume to a first approximation that the available current is in inverse proportion to the resistance. So a 0.5 ohm winding can provide more than twice as much current as a 1.2 ohm winding.
Great. At least it's just the blue one that measures higher than the others because it's the orange and white center tapped one that I'm interested in.
I built an LM317 circuit on a breadboard and it supplies me with voltages high enough for what I need it for.
I'm not sure how to test how much current the transformer is able to safely supply but I'm assuming it's more than the 1.5A the LM317/337 is rated for anyway.