# Speccing Transformator help?

#### Eirikki

Joined Apr 30, 2016
12
I have salvaged a transformator and want to know the coil ratio and current rating of it, but i cant fin anything by googling the letters on top.
Help?
I included a "map" of resistance on the pins
Pics:

#### Lestraveled

Joined May 19, 2014
1,946
@Eirikki
Hello and Welcome to the forum.

There is no good way to determine the turns ratio from the resistance. You can use a signal generator and a scope to determine the voltage ratio which is the turns ratio. You can also determine the turns ration from the inductance but, that is a little difficult if you don't have an inductance meter.

#### Eirikki

Joined Apr 30, 2016
12
At my school i have access to an oscilliscope, a signal generator, bench powersupplies and more
At home i only have basic tools :/

But what you mean is to put an 23v or higher 50hz signal onto the trafo and measure the output?
and How do i determine current rating?

#### Eirikki

Joined Apr 30, 2016
12

#### Lestraveled

Joined May 19, 2014
1,946
@Eirikki
I would use a signal generator and a oscilloscope to determine ratios and if the transformer is for 50Hz before I connected it up to the mains. The terminals on the black plastic appear to be the primary.

To determine the current capacity, I would look at the Gage of the wire on each of the secondary windings and the expected voltage out. The transformer has a max total output (watts). This can be determined by comparing the size and weight to a known transformer. The secondaries that are large Gage wire will produce the majority of the power.

This is a unknown transformer. Understand it at low power/voltage on the bench before you plug it in. Once you get the turns ratio, determine which taps to apply the line voltage to that makes sense.

#### Eirikki

Joined Apr 30, 2016
12
@Lestraveled
I did the measurements safely at 230v without any difficulties, i will soon get the diameter of the coil wires and calculate the rated current...
Heres a image:

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#### Eirikki

Joined Apr 30, 2016
12

#### Lestraveled

Joined May 19, 2014
1,946
@Eirikki yes I see

You will need to estimate the gauge of the wire for the windings and look it up on a standard wire gauge chart for the amount of current it will carry. 50% of that value would be a good estimate the current. When you load the transformer at that current value, notice how hot the transformer becomes after 5 minutes. If it is hot to the touch, you are drawing too much current. The current drawn by the thicker gauge windings will be the major factor for the temperature.

Since the transformer is unknown, all of the above is to make a "educated guess" as to what the transformer will do.