Determining transformer terminal functions

Mr.Sunshine's picture


Joined: Mar 24, 2020

Replies: 1
Determining transformer terminal functions
March 24, 2020 - 4:30pm


I'm an absolute novice with elextronics but regardless i'm trying to build something that needs a 12V transformer. A colleague of mine once gave a whole bunch of 12V transformers (harvested from extractor hoods) to play around with. I've never needed one before today and the colleague doesn't work at my company anymore. For the life of me i can't figure out how this thing is supposed to work. I've tried all the connections and checked with a multimeter but i cant get 12V out of this.

I reckon i am missing something like a kind of "on switch" on one of the terminals which needs to be powered before giving 12V on the other terminals?

I was hoping one of you fine folks would reckognize what this is and what the function for each terminal is.

In the included photo the one with the black cap on it is in "new" state and the one with the wires from it is one that got salvaged but should still work regardless, those wires are the wires that were still attached to it in the extractor hood.





Kind regards, Stefan

John_Kripto's picture


Joined: Aug 11, 2018

Replies: 35
It is a SMPS circuit
March 25, 2020 - 10:01am

Hi Stefan, what you have shown in the picture is called is not a 12V transformer. It is an SMPS (Switching Mode Power Supply) circuit. It is not possible to tell if it is rated for 12V just from the picture. But what I can tell is that

1. The white and Grey wire is for AC input, so you should connect these two to your AC mains

2. The blue, brown, green, black and yellow should be DC outptu but it hard to say which wire is what just from the picture.

May be your SMPS id rated for more than one voltage that is it can provide 12V and 5V at the same time. I would suggest you to power down your SMPS and use a multimeter in SMPS mode to check if there is any continuity within all 5 wires. If yes we can assume them as ground and further measure the voltage acros each other wire.

Be advised working with AC mains is dangerous. do not try things if you are not sure what you are doing