# Primary voltage is 220v and my secondary voltage is 12v

• bogoa

#### bogoa

how can I get the number of turns on my primary and the secondary transformer..if my primary voltage is 220v and my secondary voltage is 12v..

Not sure how you missed the electrical engineering section, but this is a VERY simple calculation. The ratio of turns from the primary side to the secondary side can be found by just dividing the primary side voltage by the desired secondary side voltage (in your case, 220v / 12v = 18.33).

From what you've given, you cannot determine the number of turns; only the ratio of the number of turns on each. Not quite the same thing...

You will want to have enough turns on the primary side so its XL is high enough that you don't draw significant current when the secondary is open.

To be safe, do not exceed 1 Tesla in the transformer core with no load. My experience is (without doing the math again) 1 volt per primary turn at 60 Hz if your core has a 4 square inch cross section, or 0.25 volts per square inch. This would mean 880 primary turns if your core is 1 square inch. This comes from Faraday's Law.

Bob S.