How to measure a unknown Transformer? - Page 1
Forum section: electronics / beginners

author: Nirbug
author_rank: Newbie
timestamp: February 08, 2016, 05:19:08 pm
content: Hi,i have a question about how i can figure out the properties of a unknown transformer:I try to understand a circuit for powering my old Russian night vision device in order to find a smaller replacement later on. The last unknown part is the Transformer, circuit diagram is attached.I started by measuring the dc resistances to get a feeling for what is going on:Primary Side: Flyback Coil: Pin 4->5: 800mOhm, 4->2 & 2->5 400mOhm as expectedPrimary Coil: Pin 3 -> 6: 1.9Ohm; Pin 1->6 & 1-3: 1,8OhmSec. Coil: 7,7kOhmFurther Information: The voltage behind the Cockcorft-Walton Component should be around 14-19kv, the Transformer uses a iron core and is complitly embedded in Bakelite. The whole circuit consumes about 250mA @ 12V DC under load.Is there any good and beginner friendly method of how to find the missing Properties of my Transformer? (I have only a DSO and a cheap DC bench power supply.)

author: station240
author_rank: Unknown
timestamp: February 08, 2016, 06:16:34 pm
content: You also need to know the frequency the transformer is operating at, should be possible to do that with the scope.That frequency is then used to determine what core type the transformer needs.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 08, 2016, 07:57:17 pm
content: Since you know the input (12V) and the output (14-19KV) why not get a suitable modern replacement? For instance EMCO makes a lot of these modules, and you can find them on EBay regularly.

author: Nirbug
author_rank: Newbie
timestamp: February 08, 2016, 08:22:17 pm
content: Quote from: PA0PBZ on February 08, 2016, 07:57:17 pmMay i ask you to link such a component? I can't figure out which one you meanI'm reassembling the transformer now and try to get the input frequency. I don't want to blow anything up so it will take a while.The ultimate goal is to find a small replacement that can be powered by a LiPo Battery, there are a few, "solutions" out there: hacked diy stun gun or "ccfl inverter + multiplier stages" circuits, but nothing like ,,This is it!" yet. I thought first i need to kown what i have, then i can search for it - without getting me and my equipment stunned or killed

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 08, 2016, 09:47:07 pm
content: Quote from: Nirbug on February 08, 2016, 08:22:17 pmSome examples:http://www.ebay.de/itm/271393108051http://www.ebay.de/itm/281723039651http://www.ebay.de/itm/281260036979Of course you have to find the right voltage and current for your application.

author: Nirbug
author_rank: Newbie
timestamp: February 08, 2016, 10:03:49 pm
content: I managed to get the frequencies.The primary Coil: I used Pin 1 for reference and on the flyback coil Pin 2 using the PNW-transformer.jpg in my first post.The system seems to oscillate at about 1.35 kHz.Thanks for linking these devices, i will get one to have a look inside.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: February 09, 2016, 06:56:42 am
content: DSO and supply not really enough IMHO. It is good to have an LCR meter and Function Gen if you want to characterize a transformer, find its coupling coefficient, inductance of windings etc. Knowing DC resistance of coils helps to estimate current handling. You need DC supply if you want to find out about core saturation. There are lot of things to measure in a transformer if you know nothing about it to start with. HAM radio people's book, ARRL something has good chapter on the procedure.

author: Nirbug
author_rank: Newbie
timestamp: February 10, 2016, 02:36:27 pm
content: My main Problem is that the Voltage Output is wide over my measurement range: 14-19KV behind the Multiplier should be equal to an Transformer Output of 3.5 to 4.8Kv Output on the Transformer.How about getting a signal generator and hooking up the transformer with a significant smaller voltage input of around 100mV, the output should be around 25V and the within the measurement range of my scope? My local Electronics store has cheap 1khz 100mV to 2V function generator kit - it should do the job for this?!I ordered the parts for a diy LC Meter which i found nicely documented by some HAM Radio amateurs, but i still don't see a way to calculate the transformer ratio blind from the inductance of the winding. With the Inductance and series resistance i will most likely get my LTSpice Simulation to run - but i'm still not sure if i have all the Parts together.

author: Zero999
author_rank: Super Contributor
timestamp: February 10, 2016, 05:59:51 pm
content: I don't see why you need to know the frequency. It's a Royer oscillator. As long as the turn ratio is correct, the output voltage will be right and the circuit will oscillate at the optimum frequency for the transformer.http://www.smps.us/inverters.html