# Can the resistance ratio of a transformer be used to calculate the turns ratio?

Joined Aug 29, 2013
19
I have several transformers I don't know the values of.
Could I compare the ratios of the resistance of each coil and use this to calculate the turns ratio (if the wires are different gauges, does this make a difference)?

#### Brownout

Joined Jan 10, 2012
2,390
No, because the guage of wire is typically different for the primary and secondary. You can use the ratio of inductance.

#### Papabravo

Joined Feb 24, 2006
18,138
You can also apply an AC source to the primary and measure the secondary voltage. The safest way to do this would be starting with a known transformer to isolate the experimental unit from the mains.

• atferrari

#### alfacliff

Joined Dec 13, 2013
2,458
use a low voltage ac for one winding, and measure the other, the voltage ratio will give you the turns ratio. if you use a higher voltage supply, the other winding, if a step up ratio might make a hazardous voltage.

• RichardO