If this was NOT a mains transformer then connecting mains to any winding will probably kill it and may kill you.
The transformers in the photos are NOT AC mains input transformers. They have RECTIFIED mains applied as DC and then a high frequency switching circuit uses this DC. Current flow in them is at very high frequency so their AC resistance = = impedance is high. If you connect AC mains to them directly they will "explode" at worst or simply die instantly at best.
What is required for simple AC mains to DIY low voltage is an "iron cored" transformer from a (usually older) piece of equipment that did not use a switching power supply. Older plug packs (wall warts) that are much heavier than usual are often a good source. Something suitable should be available at low or no cost.
Wiring windings in parallel and powering up = near instant death for the transformer in many cases.
You do not say which of the 2 devices (printer/scanner and my old cable tuner) this is from, or whether it was AC mains connected or via a plug pack (wall wart etc) or ... .
Please provide a photo of the transformer.
Stating model and brand of equipment concerned helps greatly.
Were these mains connected?
What is your mains voltage ? (110 VAC, 230 VAC, ...?)
What is the core made of? - ferrite, steel, ...?
How heavy is the transformer and how large? - Does it seem to be steel cored or something less dense?
Again, photo, brand, model will help muchly.
If the sample transformer IS an AC Mains transformer:*
IF you have another transformer with about 6 V*AC* output voltage you can try the following.
**MUST be AC out.
MUST be AC ...**
Identify windings in order of decreasing resistance (highest = A, next highest = B, ...)
Apply a voltmeter set to higher than mains AC to winding B.
Apply
LOW VOLTAGE
AC
about 6V
briefly
to winding A.
Note reading on meter on B, if any.
If meter flickers or has very low or no reading, move meter onto winding A.
Successively apply LOW VOLTAGE, AC to windings B C D E ... watching meter readings on A.
From the above tests you can get a "feel" for the relative winding ratios on the transformer. Some simple arithmetic will allow you to deduce the high and low voltage windings and what the rated voltages should be.
Think about it. Tell us what happens. Ask questions.
You asked:
- what if i scrap the build from scratch project for now, would an omron industrial 24v 1.3a power supply work as a decent 'transformer' to take this ones place? then i can just add in a variable voltage regulator and meter, throw it in a nice wood box and be done for now. :) here is the particular model link octopart.com/s82k-03024-omron-8299
Less good long term.
The Omron supply is VERY expensive for what it does. Much better for much less is possible easily.
If you have one it could be used but it lacks what you need.
The Omron supply datasheet here - specific model PROBABLY on page 57, 3rd line, is apparently fioxed at 24V. 1.3Amax output.
To get lower voltages you will need to convert to the desired voltages with either a switching regulator or a linear regulator. Variable switching regulators are available at low cost on ebay, but add complexity to an already expensive product.
A variable linear regulator will work with moderate complexity BUT to get usual voltages of say 3V3. 5V, 12V you will waste MOST of the energy as heat.
At 5V the efficiency is 5/24 ~= 20%. 80% will be lost as heat. Worse at 3V3. Still bad at 50% at 12V.
Better is to either find a well priced supply that is variable and cheaper OR find a transformer that does what you want and start from there. We can advise if you wish to follow the latter path.
You could try to couple a signal generator with sine signal (e.g 50 or 60 Hz, amplitude starting with just couple of volts -> increase some if needed) into the smaller coil. Then an oscillosscope to to high voltage coil's heads. You should see how many times voltage is multiplied in the magnetic circuit.
Before oscilloscope coupling better to use some multimeter or similar to get clue of the voltage level it outputs..actually you perhaps don't need oscilloscope at all if you get Voltage RMS value of high voltage coil by your multimeter.
If input voltage gets much bigger (like it should) so then it can be ok.
If not so then transformer is basically malfunctioning. Fixing of it may not be practical?
WARNING: The voltage can be still pretty high in the output high voltage coil even if you apply relatively small input signal to the low voltage coil from the signal generator. Be sure to work safely with some dielectric gloves and active monitoring of the situation and its surroundings.
Best Answer
That's the correct indication for the transformer in its original configuration.
With a normal outlet, the neutral and the ground are bonded together at the service entrance, so the tester will light two lights: one between line and neutral and the other between line and ground, since the same voltage appears across both pairings.
With the tester plugged into the transformer, there's voltage between line and neutral created by the transformer secondary, but now there's no path between your isolated neutral and ground, so now that light on the tester no longer lights, indicating "open ground".