Help with unknown scrap Transformer

Hello,

I have one big scrap transformer (from 1200VA UPS) which I want to utilize it as Bench Power supply. I think it is minimum 5A but how can I define this exactly ?

Transformer seems pretty simple but there are 3 input red, blue, black where blue and black shorted and 3 output wires. Do black wire is ground or what is the purpose of it?

Coming to output, as you can see from the picture the marked wires are thick coppers and 2 red wire are shorted all together and negative is two green wires. Question what is the purpose of these copper output wires ? As they are all shorted can I cut off copper ones as I don`t see any use of them?

BTW my old forum account (trecords) is closed for some reason, so this is my new account.

Regards,
Turkel.

1transformer.jpg

2transformer.jpg

1transformer.jpg

2transformer.jpg

Need to take pictures outside in full daylight but not sun, perfectly focused and with a lot more detail.

Referring to cutting off wires indicates this is not a project within your current level of competence. :roll_eyes:

Using the multimeter as a scale factor suggests this transformer is either not rated within a tenth of 1200 VA, or not operating at mains frequency. :astonished:

Since the transformer is laminated iron core, it probably does work at mains frequency, and might just be used to charge the UPS batteries (usually lead-acid gel cells).

So, it might have a 120 or 240 VAC primary, and put out around 12-15VAC (or twice that if center tapped) at a couple of amps.

The 1200VA figure is probably the UPS output when activated, and then only for tens of minutes.

Just get an old PC and use the power supply as an inexpensive benchtop supply. I agree with Paul's assessment. Throw in your junk pile. I save old transformers and take them to the local junkyard. I doubt it's center tapped that costs money :slight_smile:

I agree, that transformer looks too small for a 1200VA rating.
Here are my guesses:
The black, blue and red wires to one connector are probably the
AC outputs, a common wire, a full secondary connection and
a lower voltage tap. The heavy red wire is probably the battery
positive connection. The red and two green wires to a connector
are probably low voltage for AC input for the PCB power supply. The two black
wires with ring terminals probably connected to heat sinks for the
transformer driver FETs. Don't cut off any wires! The primary winding
is quite low in resistance since the battery must supply a high current.
Good luck and be safe.
Herb

Many Thanks for all of you for directing me!

@Paul__B Pictures are just diagrams so at night time this was only choice for me. Yes I am not good at electronics but I am OK with soldering and understanding things wiring, debugging etc. Mainly I want to build Bench power supply with this tutorial and I have all parts and this transformer as replacement of switching on on video:

@jremington yes it is 13-14 volt transformer to charge one 12V 12A battery

@wolframore I need linear quality power supply :slight_smile: It will supply this board LTC3780: https://www.aliexpress.com/item/32834139255.html

@herbschwarz you guessed all as it is :), but I will not use it for charging battery, and board like LTC3780 don`t have much resistance, I hope so. I think just connect input to AC output to rectifier, capacitor then to LTC3780. Connection

You could probably measure the winding resistance and assume some typical loss. However as odd as it might sound you should measure the lamination size and look for a commercial transformer that has similar dimensions.

Transformer size is a combination of lamination size, and the space for primary and secondary windings (aka window size). At 60Hz and standard lamination material you will find the most cost efficient design doesn't have many size choices. Unless you can do something with the numbers printed on the transformer or get a service manual for your dead UPS I think this is the best you can do.

In the video you cite, he uses a pre-made switchmode power supply.

That is the part you need. Not the transformer you have. It is simply "old school".

Get the proper part to do the job properly. :roll_eyes:

turkelali:
Many Thanks for all of you for directing me!

@Paul__B Pictures are just diagrams so at night time this was only choice for me. Yes I am not good at electronics but I am OK with soldering and understanding things wiring, debugging etc. Mainly I want to build Bench power supply with this tutorial and I have all parts and this transformer as replacement of switching on on video:
Build your own Variable Lab Bench Power Supply - YouTube

@jremington yes it is 13-14 volt transformer to charge one 12V 12A battery

@wolframore I need linear quality power supply :slight_smile: It will supply this board LTC3780: https://www.aliexpress.com/item/32834139255.html

@herbschwarz you guessed all as it is :), but I will not use it for charging battery, and board like LTC3780 don`t have much resistance, I hope so. I think just connect input to AC output to rectifier, capacitor then to LTC3780. Connection

That transformer will disappoint you if used in a linear regulated power supply. You need at least 16 volts or more. That transformer works perfect for battery charging.

Paul