I got a transformer from a CRT tv (it is NOT a flyback transformer). It has four wires, two on each side. One side, theres a Blue and Orange wire, and on the other side theres a White and Yellow. If I plug 9V into the orange one, and touch the negative side to blue, it makes sparks. I have pictures.

If I connected the positive to white and touch the negative to the yellow wire, it does makes sparks but they are less prominent. If I connect + to orange, and - to white and touch white and blue, it measures at 8.42V on my multimeter, but makes some sparks, and shocks me. So I have no idea whats going on, I think it might be a current transformer but then the voltage would be lower.

Pictures: enter image description here

enter image description here

UPDATE 1: @mguima @Marcovecchio That comment made my day ;). I do infact own a multimeter, it's not the best, but it works pretty well. I don't own a sinusoidal generator, and I'm guessing it generates a sine wave. Anyways, back to my multimeter. It's lowest setting for resistance is 200. I've discovered this:

Resistance: Orange/Blue: 1.9 Orange/White: doesn't read Orange/Yellow: doesn't read

Yellow/White: doesn't read Yellow/Orange: 148.2 Yellow/Blue: 0.00

Blue/White: doesn't read Blue/Orange: 3-2 Blue/Yellow: doesn't read

White/Orange: doesn't read White/Yellow: 148.2 White/Blue: doesn't read

For reference, doesn't read means that nothing changed. By default, the multimeter reads "1", until I hook it up. So when I say doesn't read, it means that the one didn't change. If it "didn't read" I would check all the setting for resistance on the multimeter. I think the one might mean a resistance higher than my multimeter, which is 20M. On one hand, I'm spooked. On the other, I think Blue/Orange are a pair and Yellow and White are aswell. I'm actually happy, because that matched exactly with what Marcovecchio said! One winding should be in a few hundred ohms, and one just a few ohms. In this case, yellow and white are the few hundred ohms, and blue and orange are just a few.

I'm going to test the voltage ratio, then report back. Should I use a 9V, or my 6V 2.9Amp battery?

  • 1
    \$\begingroup\$ It's likely that the B/O are one winding, and the W/Y are the other. Measure the DC resistance of each winding, and report. \$\endgroup\$
    – Neil_UK
    Oct 26, 2017 at 15:11
  • \$\begingroup\$ "If I plug 9V into orange one and touch the negative side to blue, it makes sparks". Is it a 9V battery or another DC supply? I'm asking this because spark is an indication to a short circuit. Don't even try to plug a DC supply to a winding. You'll kill the winding or the supply or both. \$\endgroup\$ Oct 26, 2017 at 15:46
  • \$\begingroup\$ @Rohat, if someone uses a 9V battery to test a transformer windings of a huge AC/DC transformer like this on the photo, I don't think he could burn the winding; maybe he willl drain or damage the battery. The funny side is that, if the terminal and batteries are touched / connected in certain ways, this will result in an electrical shock that will not kill, but will teach a lot about electromagnetism. ;-) \$\endgroup\$
    – mguima
    Oct 26, 2017 at 18:11
  • \$\begingroup\$ I'm glad the answer helped, but I think you made all measurements you could do with a meter. The next step (voltage ratio) will require some form of AC power. By the way, when you removed the transformer from the equipment, did you see if it was connected to the mains cable? \$\endgroup\$ Oct 27, 2017 at 12:07
  • \$\begingroup\$ If the readings with the multimeter were consistent, showing a pair of wires with higher resistance, I would suggest to connect this pair to AC. But the readings reported are inconsistent, the same pair of wire shows different values in the measures. \$\endgroup\$
    – mguima
    Oct 27, 2017 at 16:34

2 Answers 2


You should first identify the windings. It's likely that wires on each side form a winding, so blue and orange might be a winding, and white and yellow form another winding. Look for pairs of wires that read low resistence between them.

Once you find the pairs (or windings), do the next check: cross check each winding to be sure the transformer is not shorted. In other words: measure resistence between wires of different windings. If resistence is in the order of MΩ, transformer is good. Lower resistence (in the order of kΩ) may indicate a short between windings.

Now note the resistence of each winding. One should read considerably higher than the other. For example: one winding measures a few ohms, the other one a few hundred ohms. The higher resistence winding will work with higher voltage and less current. The lower resistence one will work at lower voltage and higher current.

At this point, you already know what you asked: to identify the wires/windings. Now you can optionally test the voltage ratio of your transformer, if you have an AC power source: get a resistor between 10kΩ and 100kΩ and connect it to the lower resistence winding, and apply a 5V, 60Hz AC (preferably sinusoidal) voltage to the higher resistence winding. Then, measure voltage across the resistor. You should read a voltage lower than 5V. The ratio between this voltage and 5V will give you the voltage conversion rate of your transformer.

The values I suggested (5V, 10kΩ / 100kΩ) are quite conservative, and are not likely to cause accidents, sparks or anything. Just be sure it's an AC voltage about 60Hz, not DC!

  • 3
    \$\begingroup\$ kilo with lowercase k. \$\endgroup\$
    – winny
    Oct 26, 2017 at 16:20
  • 3
    \$\begingroup\$ It's not about looks. K is kelvin. k is kilo. \$\endgroup\$
    – winny
    Oct 26, 2017 at 16:31
  • 2
    \$\begingroup\$ @Marcovecchio, I voted +1 for this answer that talks about using three resistors and also a 5V 60Hz sinusoidal generator, because it is technically perfect, but, for a perfect world. I fear that this answer will not help an OP who is trying to test a transformer using a 9v battery and watching the sparks! He probably doesn't have a multimeter neither a continuity tester, and maybe don't know what those equipments are. Sinusoidal generator is too much for him! \$\endgroup\$
    – mguima
    Oct 26, 2017 at 19:06
  • \$\begingroup\$ @mguima, I agree! But anyway, the AC generator is not necessary for wire identification, which is what the OP asked in the first place. I added this last test using AC just for completeness. However, he will need at least a cheap meter, otherwise he will have to guess! \$\endgroup\$ Oct 26, 2017 at 19:14
  • 2
    \$\begingroup\$ @Barry Maybe the OP has a bicycle dynamo, a hamster wheel, and a suitable rodent? \$\endgroup\$ Oct 27, 2017 at 13:03

It's complicated! Every time you report a different reading from multimeter, the posts were edited many times...

White / Yellow, which reading should be about 148 ohms in both directions, is the primary winding, that connects to AC mains. White and Yellow should, both, "doesn't read" when each of then is probed with orange and blue in the other probe point.

Orange/Blue, which reading should be just a few ohms, and reading should be the same in both directions (Orange/blue and blue/orange), is the secondary winding.

Next step: Connect a wire to yellow and another to white. Get a switch; certify that the switch if at off position. Connect one of the wires (yellow or white) to the switch, and connect the other pin of the switch to another wire, and this wire to AC output.

Connect the OTHER primary winding (white or yellow) to the other AC output.

Put the transformer on a clean and empty surface, keep some distance, and turn the switch on (but be prepared to turn the switch off immediatelly, if necessary). If it sparks, or makes loud noise, turn it off.

99.9% chances of nothing happens when you turn the switch on, which is a good thing (a transformer should work quietly). Take the multimeter, adjust to AC 400V or AC 1000V. Touch BLUE with one multimeter probe and touch ORANGE with the another probe, and read the voltage in the multimeter, this is the secondary winding voltage.

By now, with some luck, you know what you wanted to know, the transformer wires are identified. A transformer like can be used in a power supply.

  • \$\begingroup\$ It's difficult to figure out which are OP quotes in you answer. Use the > symbol at the start of the line to change it to a formatted quote. \$\endgroup\$
    – Transistor
    Oct 27, 2017 at 15:32
  • \$\begingroup\$ Please edit your answer to fix issues instead of deleting old versions and posting a new one. \$\endgroup\$
    – W5VO
    Oct 27, 2017 at 16:28
  • \$\begingroup\$ Thanks, @W5VO. I mistakenly tought that there were a time limit to edit answers, as there is to comments. \$\endgroup\$
    – mguima
    Oct 27, 2017 at 16:39
  • \$\begingroup\$ I had a typo, it was Yellow/Orange thet didn't read, and yellow white that had 148.2 ohms of resistance \$\endgroup\$
    – HXGamer
    Nov 9, 2017 at 14:53
  • \$\begingroup\$ I wrote another answer. \$\endgroup\$
    – mguima
    Nov 9, 2017 at 18:01

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