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Old 19th March 2011, 02:03 AM   #1
tomes is offline tomes  Malaysia
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Default Unbalance sec ac voltage

Hi,Need help from your opinion,recently i bought a tranformer for class a project,300va 24v-0-24,the problem is the sec is 25-0&30-0,i dont know may be they wind it wrong,it stated 24-0,24-0, so any body know how to solve it or change new one,i need +-36v.
Thank
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Old 19th March 2011, 12:17 PM   #2
DF96 is online now DF96  England
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How did you measure it? If off-load (apart from the voltmeter) then you might get a misleading reading due to saturation. Add a power resistor to the secondary to take some power (not a lot, a few W or 10's of W should be enough) then measure again.

24-0-24V rms is not enough to give you 36V DC, even off load. You might get 32-35V. Absolute maximum you can get is Vrms x 1.414 - diode drops (1.2V?).
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Old 19th March 2011, 01:21 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
before you try to measure voltages you must identify windings.

Does the primary have one winding or two windings?
You use a resistance meter to measure the windings.
If the resistance meter indicates an open circuit then you have mixed up the primary windings. Change one of the wires.

The Primary winding is usually quite a high resistance 10r to 1k

The secondary is two windings with four ends. The 24-0,24-0 tells us it has four ends.

Again you must find and label each winding. This time the resistance will be quite low expect 0r2 to 2r0 for a 24Vac winding.

Now connect the secondaries in series. Measure the resistance of the two open ends. This should be double the individual winding resistance.

Don't connect it to the mains yet !!!!!!!!!!!!

Build a mains light bulb tester.
This puts an incandescent filament in series with the Primary winding.
This prevents you blowing up a mis-wired transformer.
This protects from injury.

If the bulb lights up when the transformer is plugged in then you have a fault. FIND THE FAULT !!!!

Once you have the transformer properly wired up only then are you ready to measure voltages.
Tell us when you arrive here.
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regards Andrew T.
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Old 20th March 2011, 03:47 PM   #4
tomes is offline tomes  Malaysia
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Hi DF 96& Andrew T,
I done as yours suggestion in the late aftrn,i wire it up become sec av 24-0-30,then after the bridge ritifier it become 41-0-41 dc,i put a load with 10w 220v light bulb it become 39-0-39(+-78) dc,it seen balance v after the diode.
Thank for yours help,will continue the project.
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Old 21st March 2011, 12:24 PM   #5
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
Now the DC voltages appear to be matched.
That implies the AC voltages were matched.

What did you do that gave the erroneous voltage you quoted earlier?
This way you can inform other beginners of "what to avoid".
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