|27th November 2003, 07:37 AM||#11|
Join Date: Apr 2003
you must ensure that those chokes are really meant for common mode filtering Check the winding directions on both coils on that torroid. If they are not wound for common mode use, then the flux in the ferrite core would cause huge currents to flow in the core, heating it up and cracking it. The heat could burn the insulation off the windings as well, and cause a mains short. I know because this is exactly what happened to me! I wound the coils for a common mode choke the wrong way and had some nice fireworks
As I understand it, a common mode choke must have negligible flux in the core during normal operation (i.e. the fluxes from the two windings must cancel each other). Only in the presence of common mode noise is some net flux generated in the core. What this means essentially is that the choke acts as a short for differential mode AC, and a high inductance for common mode AC line noise, thus allowing it to pass the normal (diff-mode) AC and block the common mode noise.
|27th November 2003, 02:59 PM||#12|
Join Date: Mar 2003
thanks for the insight. I myself am very careful especially when tinkering with mains wiring.
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