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.


ARJOON (author)2011-02-01

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

vreeland (author)ARJOON2017-06-24

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)

vreeland (author)vreeland2017-06-24

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

ARJOON (author)vreeland2017-06-24

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

R.A.T.M (author)2012-02-07

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

vreeland (author)R.A.T.M2017-06-24

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.

delokaver (author)2015-06-30

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)

ShubhamR3 (author)2015-04-21

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.

Doctor90250 (author)2015-04-20

@ 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.

Bumba Lodh (author)2011-09-07

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

Jimmy Proton (author)Bumba Lodh2011-09-07

That might work, if it does then you should see around 3 volts on your meter.

cupsster (author)Jimmy Proton2014-12-16

I can confirm that reading.

crazy-blender (author)2013-03-30

What multimeter is that it seems that everybody has that multimeter

cupsster (author)crazy-blender2014-12-16

If you can read it is NG60... :)

trekman (author)2010-12-28

The fly back transformer I have came from a 19” TV. I followed the instructions and found the 0 V pin and tested for the 2 primary pins. I got very low reading using a 9 volt battery. I happened to have a 9 volt A/C adaptor but the output was 9 volt A/C so I used that to find the primary coil pins. The thing is I found 2 sets of 2 pins that give me 35.5 and 34.7 volts output. Pines 9 and 10 also pins 10 and 1 give almost the same output. Which 2 should I use? This reading is on the A/C scale on my VOM. Using a 9 volt battery I was only able to get 3 to 4 volt reading.

Thanks for any help.

Jimmy Proton (author)trekman2010-12-28

flybacks often have more than one primary, use whichever one you like.

dudes (author)Jimmy Proton2013-10-31

what if you use multiple primaries?

abhilash476 (author)2013-05-21

i could not find the primary and secondary pins/.........

a226263 (author)2012-07-04

I'm trying to find the pins to the primary coil. I bought a new flyback a couple of weeks ago. My flyback has 10 pins. I got these results:

Pins ..... Resistance
1 + 5 .... 2 ohms
1 + 9 .... 1.8 ohms
5 + 9 .... 0.9 ohms

2 + 8 .... 0.9 ohms

3 + 4 .... 0.8 ohms
3 + 6 .... 0.8 ohms
4 + 6 .... 0.6 ohms
All the other combinations (i.e; pins 1 + 3) produced no resistance, so that means that pins 1 + 3 are not connected. Conversely, this means that pins 1+5+9 are connected; pins 2+8 are connected; pins 3+4+6 are connected; and pin 7 and pin 10 are not connected to any other pins.

The first problem is that many of these gave me a resistance close to 1 ohm, so I still don't know which pins to use for the primary coil.
The second problem is that a flyback should have two sets of connected pins; pins that connect to the primary coil, and pins the connect to the secondary coil. However, I seem to have 3 sets of connected pins (or five sets, depending on how you count). Does this mean something is disconnected inside my flyback?

I didn't know what to do, so I just went ahead and connected it to the CFL circuit. I tried pins 5+9, 2+8, and 3+4 as the pins to the primary coil, along with every combination of the 4 pins on the CFL circuit, but did not get a single arc for any of them. Does this mean that my brand-new flyback is bad?

crazy-blender (author)a2262632012-07-17

it might be bad double check with each set of pins and if it still does not work buy another flyback and see if it works

a226263 (author)crazy-blender2012-07-17

Alrighty. Will do. Thanks!

crazy-blender (author)a2262632012-07-18

your welcome

crazy-blender (author)2012-07-17

will a 9 volt battery work for finding the primary and secondary coils ?

geckomage (author)2011-10-25

hey man, ive been searching and searching on how to find these and everyone always gave some far out crazy ways that i could not get to work. but yours has. so i would like to thank you! :) with a continuity meter i found that there were 2 pins with no matches (one turned out to be hv ground) then 3 pins with matches. 2 of those made the 1 ohm resistance thing for the primary coil. and then 7 pins all seemingly connected together with about a half ohm of resistance between them all. if you could explain what that is it'd be appreciated. also i couldnt get my slow volt meter to read a spike of 30ish v. but i did get it to read about 13-15 with a 9 volt battery pulsing it. and the other polarity got like .3v or somethin. so i'd say i found a winner ;) ima make a driver now and hope i dont blow up my transistors. haha. thanks so much! :) i wish you the best of luck in all your endeavors.

Rbwood (author)2011-08-16

I have to say thank you so much! Your instructions are the one and only set of directions that actually worked for me. Thank You.

Jimmy Proton (author)Rbwood2011-08-16

Your welcome but i do not take full credit for these.

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