ESTIMATING TURNS RATIO BASED ON WIRE SIZE AND RESISTANCE

[bob8907]

I am curious if this can be accurately done? Obviously we can determine the resistance in copper wire per diam, and determine over all resistance, BUT actually determining how many turns???

See, I think you can estimate how long the wire is but not how many turns. In sum, what I am trying to do is look at a small AC/DC PS transformer and determine what kind of resistance I should see on the input side. Output is low and I think there is high resistance on the input side..

 

[VEBill]

If you know ALL the relevant dimensions, then you can (in principle) estimate the number of turns. Old handbooks used to have tables, charts and/or nomograms to help with quick estimates. Rewinding transformers was not uncommon a few decades ago, and such information was needed.

If you're looking for the "turns ratio" (your subject line), then you can apply AC voltage, measure the output, and get an estimate of the ratio.

But it sounds like you're simply trying to troubleshoot a suspect power supply transformer the hard way. 99.44% of the time you just look for 'a few' ohms on the secondary, 'more' ohms on the primary, and check for short circuits every which way.

 

[Zogzog]

Not sure how accurate that would be, why not just use a TTR test set?