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Transformer testing

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Night Thrasher

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I have a transformer here from a busted ac/dc wall adaptor which has a multiple output voltage, the pcb is burnt so no use of it and i removed it but the problem now is when i test it using digital multi meter i can get the output voltage of each but one thing i forgot is which one is the common? any which of the wires from the transformer i can get a reading, I'm having problem to which wire to connect.
 

mozikluv

New Member
where's the secondary common?

:D hi,

there are two ways to check that, by voltage output test or by resistance. you said you did the voltage check, so do it again this time put your tester on AC and clip your probe to the first wire starting from the left. put the other probe to the last wire, record the value, next probe the second to the last wire down to the other wires. if the value goes down to the lowest voltage, the first wire on the left is the common.

most of those multiple output transfo have the common on the left but there are others situated at the right side. :D

when i say put your tester on AC, it means you check the unrectified voltage out put. :shock:
 

Night Thrasher

New Member
heres what i get.....

from left to right:
5.4, 6.7, 8.2, 9.6, 11.2, 14.5, 17.5

from right to left:
3, 6.4, 8, 9.3, 10.8, 12.1, 17.6

the casing says it has the ff voltage output:

3, 4.5, 6, 7.5, 9, 12 and 15

any replies is highly appreciated thanks...
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Night Thrasher said:
heres what i get.....

from left to right:
5.4, 6.7, 8.2, 9.6, 11.2, 14.5, 17.5

from right to left:
3, 6.4, 8, 9.3, 10.8, 12.1, 17.6

the casing says it has the ff voltage output:

3, 4.5, 6, 7.5, 9, 12 and 15

any replies is highly appreciated thanks...

The top one (left to right) is the correct way. As it's unregulated, all voltages should be a fair bit higher then the specification.
 

Night Thrasher

New Member
I tried using the "left to right" with the full bridge circuit using FR103 diodes and a 16v 1000uf Electrolytic Capacitor, but the caps keep on blowing for just a minute when plugged from the wall outlet.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Night Thrasher said:
I tried using the "left to right" with the full bridge circuit using FR103 diodes and a 16v 1000uf Electrolytic Capacitor, but the caps keep on blowing for just a minute when plugged from the wall outlet.

Make sure the capacitor is the correct way round, also a 16V capacitor isn't high enough for the higher voltage taps on the transformer - the top three taps will probably blow the capacitor.
 

Night Thrasher

New Member
you're right.... i put the capacitor the wrong way.. :oops: :cry: I replace it with a 25v 2200uf and it worked... :D for an hour.... then suddenly i goes on smoke i think the diode got to hot and burn the pcb.

the diode i use are the FR103, do you think I should change it? i'm planning to use a bigger one, a 205?
 
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