Audio Transformer Primary Wire Gauge Design Reference? - Page 1
Forum section: electronics / projects

author: bklein
author_rank: Contributor
timestamp: February 02, 2018, 06:56:15 pm
content: I looked for a table that shows AWG vs current capability and got confused quick.I am trying to determine what I should set as a current limit for an audio transformer primary.I found three different type charts: one that gives chassis wire and power carry numbers, and another that gives 500/750kcmil/A numbers.What do I use? #37 and #46 is of interest BTW.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 02, 2018, 07:05:59 pm
content: "Audio transformer" covers a huge range of applications.Your question is impossible to answer in its present state.Do you mean a microphone input transformer? Current is probably measured in mA or pA.Mechanical stability of the wire will probably be more important than current rating.Do you mean an output transformer in a 1000W power amp?Firebottle (high voltage low current)? Solid-state (low voltage high current)?Should be easy enough to calculate from the voltage and power rating.

author: bklein
author_rank: Contributor
timestamp: February 02, 2018, 10:17:31 pm
content: Trying to do root cause FA of 600 ohm 1:1 transformer, I have a sample with open primary.Driven differentially by op amps with +/-120mA capability.

author: bklein
author_rank: Contributor
timestamp: February 02, 2018, 10:26:30 pm
content: I am not suspecting overdriving with an AC signal.I am suspecting a DC offset caused by unexpected DC input to preamp or op amp power sequencing.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 03, 2018, 01:23:55 am
content: Did the driving devices (the op-amps) fail? Like output short to power supply rail? Did BOTH of them fail? Else it is hard to imagine that even the DC power supply could fry the primary. I supposed since it is failed, you don't know what the DC resistance of the primary was?Agree it is unlikely to have been fried by the audio signal. But seems also unlikely that it could have been fried by the supply rails, either (although we don't know the DC resistance).Perhaps the next most likely failure would be a termination failure. PC board pins, or solder lugs, or flying leads (you don't provide any details). Or just some other random failure. Mass-produced items are not perfect.

author: bklein
author_rank: Contributor
timestamp: February 03, 2018, 05:30:19 am
content: Take a look at AWG/current charts on the net though.https://www.powerstream.com/Wire_Size.htm#37 = 28.9mAhttps://learn.adafruit.com/wires-and-connections/wire-guages#37 = 170mAhttps://www.powerstream.com/Wire_Size.htm#37 = gives both above...

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 03, 2018, 05:57:58 am
content: I think you are approaching this backwards. Unless you are talking about high-power (like an output transformer for a power amplifier), the "power handling" of small-signal audio transformers is typically not even a factor.I would much more suspect failure of some other component(s) in the circuit before assuming that the transformer was externally "fried" (vs. a simple random internal fault). Even if you accurately established the gauge of the transformer winding, and determined what was the appropriate current-handling was, where does that get you in your failure analysis?