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Old 18th December 2006, 11:20 PM   #1
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Default How to lower the secondary voltage of a transformer

Hello, I have a pb with a toroidal transformer which gives 45/0/45 V AC which is a bit higj for my UCD 400. 42 ou 43 V would be better. Is there any possibility to lower this voltage instead of a variac in the primary. I think to a post in a forum, but I am unable to find again. It was suggested to wind a external winding on the core (this I am sure) and connect it in reverse phase to lower secondary voltage (this is what I remerber, but here I ma not sure). I tried, but the wire was too thin and get very hot. Maybe some resistor should be put in series with the new winding to limit current ?
In general, what do you thing of this approach.
Of course, I can order again a new transformer, try to find the correct voltage and wait for x weeks to receive at worse an unusable transfo (last order before this one…).
Thank for reading me, I hope you could help me. Philippe
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Old 18th December 2006, 11:37 PM   #2
paulb is offline paulb  Canada
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You can use the external winding, with a larger wire.
You can use a lower-voltage transformer with its secondary in series with the primary, out of phase, so that it bucks the input voltage.
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Old 19th December 2006, 12:32 PM   #3
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Try to check if your transformer has 200, 220. and 240V ac input, then try to input from the highest 240v if your local supply voltage is lower than, or series a resistor to consume a bit from the primary source.

SUGGESTION IS FOR YOUR REFERENCE, IT MAY CAUSE YOUR CIRCUIT BETTER OR WORSE.
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Old 20th December 2006, 10:30 PM   #4
sss is offline sss  Israel
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adding resistors to the primary winding is a bad idea .
unwind a few turns from the secondary is the best option , but i guess u cant reach it .
if 2V is all u need , u can simply add 2-3 rectifeir diodes to the secondary , that better then using resistors.
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