Help needed. Transformer tester (Low voltage DC - AC inverter)

[DaddyLancer]

Hey guys, I did a quick google search for ways to convert DC to AC as I have a bunch of different unidentifiable transformers that I would love to be able to use.
The results usually gave me either how to make a spot welder, or use a car battery to power household appliances. Neither of which is anything near the results I wanted.

I can see from a majority of diagrams that most people use a 555 timer, to make the oscillations.
However, I don't have any IC-Chips that could do that.
But I do have some transistors, mosfets, etc.
I also have an Arduino which could be implemented if that would make things easier.

So what I'm basically asking for, is help in creating a simple low-voltage transformer tester.
The testing voltage doesn't have to be high, as i just need to see the conversion ratio on the transformers.

Is there a simple method that I'm just missing all together, or is there a way to make this happen without having to purchase extra components?

Also, I've tried figuring out what would happen if I simply connected a transformer without any load, to my mains (230v) but I couldn't really figure out the answer from google (may just be my search terms that weren't the ones I should have used.), so in fear of blowing my fuses, I haven't done it.


Thanks in advance for any and all help

[Benta]

Do you have an oscilloscope? Then it's just using the calibration 1 kHz out to drive the transformer primary and see what you get on the other side. That should at least tell you the winding ratio.

[HB9EVI]

Simple solution: get a known small mains transformer 220/110 -> 12V - like that you can check by DMM which side of the dut transformer is primary or secondary.

Do not use mains; connecting the low voltage secondary will certainly burn the transformer and maybe fuses too.

more complex solution is a phase-shift or 'wien-bridge' oscillator, either with a transistor or an opamp; with bigger caps you can reach a rather clean 50 or 60Hz sine.

[DaddyLancer]

Do you have an oscilloscope? Then it's just using the calibration 1 kHz out to drive the transformer primary and see what you get on the other side. That should at least tell you the winding ratio.

Unfortunately i don't have an oscilloscope.. It's on my wishlist tho

Simple solution: get a known small mains transformer 220/110 -> 12V - like that you can check by DMM which side of the dut transformer is primary or secondary.

Do not use mains; connecting the low voltage secondary will certainly burn the transformer and maybe fuses too.

more complex solution is a phase-shift or 'wien-bridge' oscillator, either with a transistor or an opamp; with bigger caps you can reach a rather clean 50 or 60Hz sine.

Some of the transformers were from old DVD players, so one of them is certainly from mains to something I've long forgotten.
What is DMM?

Some of the transformers has several different input and output wires (multiphase?), so knowing the primary isn't always easy for me.

[HB9EVI]

Multiple primaries/secondaries allow to run the transformer with different voltages e.g. 115V (2 primaries parallel) or 230V (2 primaries in series); on secondary you can run either double voltage (2 secondaries in series) or double current (2 secondaries parallel). There are transformers with multiple secondaries for different voltages.
Just measuring will tell you the facts, unless you have a wiring scheme on the transformer (at least on most toroid common)

DMM = digital multimeter

[DaddyLancer]

Multiple primaries/secondaries allow to run the transformer with different voltages e.g. 115V (2 primaries parallel) or 230V (2 primaries in series); on secondary you can run either double voltage (2 secondaries in series) or double current (2 secondaries parallel). There are transformers with multiple secondaries for different voltages.
Just measuring will tell you the facts, unless you have a wiring scheme on the transformer (at least on most toroid common)

DMM = digital multimeter

Digital Multimeter, of course!

So would I be able to connect a 230v/XXv transformer to mains without any load to measure it?
Or what can I do to measure a transformer connected to mains? Can I use a dummy load such as a 1Mohm resistor?

Also, some of them are torroids and some are those 3core "brick" transformers.

[HB9EVI]

Like I said: don't work with unknown transformer on mains.

Get a well known and labeled transformer to get a low AC voltage to test your transformers in the range of 5-12V secondary voltage with a 5VA rating.

[DaddyLancer]

Like I said: don't work with unknown transformer on mains.

Get a well known and labeled transformer to get a low AC voltage to test your transformers in the range of 5-12V secondary voltage with a 5VA rating.

Alright, thanks for the help

I am a bit confused tho. If i plugged in that transformer you mentioned, and just measured it, wouldn't that also be dangerous? Even with another transformer connected?


Edit:
Actually, would it be possible and safe to use a transformer from a LED light bulb or from a cellphone charger, and connect the unknown transformers to the output of the bulb/phone transformer?