What kind of AC line transformer is this?

Can you tell me what kind of AC line transformer is this and what is its function? What should the winding DC resistance?

Input: 110VAC Output: 110VAC

Winding inductance: 18mH Input and output windings are side by side, but do not over-lap, Schametic:

o----WWWWWW------o ========== in ========== out 110VAC for 160 watts o----WWWWWW------o

I am unable to measure the winding DC resistance? My VOM meter shows 0.1 Ohm and moving around? What is the winding DC resistance should be?

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It looks like a common mode choke. They are used as a line filters to reduce noise, switching transients and the like. There is 18mH of inductance from the input to the output but it is wound so that the normal mode, across the line inductance cancels out. The input side goes to the line, the output side to the load, up to 160 Watts.

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Bob Eld

Do you this noise filter purpose to reduce noise going back return on the AC line from the output motor load? How does this choke wound any differently? How does the line inductance cancel out works in the AC line? How do you determine how much inductance do I need in this Common Mode Choke? What is maximum DC resistance should I specified for this 160watt load?

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Assuming this device is a common mode choke based on your description, it is used to reduce motor switching noise from being conducted back into the power line. Such noise is caused by switching transients in inverters and various switching circuits used for motor speed control.

This type of choke is really a larger, higher inductance version of placing a ferrite bead on a power cord. Of course, it has many turns on an iron core to get the required inductance. As with the ferrite bead, it is wound the same way with both wires in parallel (not connected) wound together on the core.

There are two windings, A and B forming four terminals, Ain, Bin, Aout, Bout. If you measure the inductance on A from Ain, to Aout, you will see the

18mH. Likewise if you measure B you will also see 18mH. Now, if you short the output, Aout to Bout and measure the inductance on the input, Ain to Bin you will see nearly zero inductance. because the two windings cancel each other in this mode. This is the normal mode.

The amount of inductace is determined by the impedances involved, the frequencies to be attenuated and the amount of attenuation required. It is not possibe to calculate or estimate this without the specifices of the devices involved as well as the attenuation reqirements.

The DC resistances should be very low, a few tenths of an ohm on each of the windings. The lower the better.

Reply to
Bob Eld

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