How to Find the Primary and the Secondary Coils of a FlyBack Transformer

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Introduction: How to Find the Primary and the Secondary Coils of a FlyBack Transformer

The main problem, in most cases, is that you don't know the pinout diagram of a flyback transformer. So, I shall try to give you a simple method to find the primary coil input pins and also the 0 V output pin of the HV secondary coil.

-=I do not take full credit for this=-

Step 1: How to Find the 0 V Pin Connection of the Secundary Coil?

With a common digital ohmeter it is impossible to find the secondary coil pinout because its resistance is much too high. The main HV output is simple to find : this is the big red cable with the suction cup, but you need to find the 0 V pin of the secondary coil on the flyback transformer. So, I give you a simple method to find this 0v pin :

a) You need a 24 V DC power supply and a digital voltmeter set in 20 V range. Connect the + input of your voltmeter to the THT ouput plug ( in the suction cup ) and the (-) to the 0V of your power supply. Then, with the +24V output from your power supply, test each pin of your flyback transformer. When you measure a voltage between 5 and 10 V you have found the 0 V pin of your secondary coil. This is very simple... Look at the diagram and the photo below :

Step 2: How to Find the Pins Location of the Primary Coil?

With a simple ohmeter this is very simple, you will find easily the primary inputs because the coil resistance is about 1 ohm 

Step 3: How to Find the Polarity of the Primary Coil?

The purpose is to find the polarity of your primary coil. You need a simple 9 V battery. Connect a digital voltmeter set in 100 V range between the main THT output and the 0 V pin of the secondary that you have indentified in test #1. With the 9 V battery send a short pulse on the primary input, measure the spike of the voltage, then reverse the polarity of your 9 V battery. When you get the max voltage ( about a 30 V spike ) you have found the correct polarity of your primary coil. The (+) is the pin number 2 and the (-) is the pin number 1 in the main diagram.

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    26 Comments

    don't forget guys. ac from wall socket will not work. frequency is too low.

    using a fluorescent ballast as a driver into the primary puts out some serious voltage. i would suggest submerging the whole thing in mineral oil so as to prevent any shorts before using it to create any really high voltage (10k - 50k volts)

    you can even use a driver from a CFL. plenty of videos out there on youtube and such about it.

    thanks for the late reply but i've learnt much more in the past six years. thanks anyway

    so i know what the main THT out put is but i have 3 other wires hanging about what are they 4

    probably primary in and a ground. primary in is usually red and white ground is green or grey. i'm just going off the flybacks i salvaged from old crt monitors though.

    I am replacing the volt meter with led and also woks, led is on even only a small light ( I use red one for easy to look at)

    i tried to find primary and secondary for 4 different flybacks . First of all there are many combinations of pins which have resistance of around 1 ohm and for the secondary i got at most 0.6 volts with 18 volts supply.

    @ dudes, that's a good question, and if you could use both, could each one be "tuned" to different frequency so that a harmonic resonance is reached, causing the flyback, with the HV return pin earth grounded, to become an actual "Tesla coil"?
    the possibilities intrigue me, lol.

    i don't have 24 volts dc power supply but i've 12 volts dc power supply
    please give me a advice