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

Picture of 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?

Picture of 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?

Picture of 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?

Picture of 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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