EMI radiation from cables

[jophuds]

Hi Guys,

I have am trying to minimise the EMI radiation from cables carrying power to magnetic coils.

I have read that shielded twisted pair cables with a drain wire where both the drain and the shield are connected to ground is the best approach - is this the case?

What types of connectors are best to use?

This voltage will be up to 25V and the current as high as 10A.

Thanks in advance,

Joe

 

[VEBill]

Best would be a military circular connector with 360-degree shielding continuity through the connector. But you can probably get away with a lot less depending on the frequencies involved.

Especially if the load is a set of coils anyway...

 

[Henneshoe]

Correct me if I am wrong, but it may be tough to find twisted pair in a large enough gauge to handle 10A. Have you tried Ferrite "Magic" beads?

 

[VEBill]

Heavy gauge twisted pair wire is available. For example, Belden 1860A is 12AWG twisted pair. This doesn't mean that this part number is suitable in all respects.

So long as the frequency is low, then the tightness of the twist isn't critical.

 

[VEBill]

The ferrite beads or common mode coils can help (again, depends on the frequency). A common EMI issue is when the antenna (or perhaps coils in this case) radiate RF that gets onto the feedline in common mode. For antennas on towers it is a common trick to loop up some feedline in an attempt to choke-off such paths. But if the frequency is low, you need to consider other methods of choking such common mode current paths. A few turns wouldn't help at low frequencies.

 

[itsmoked]

Just get the twisted pair that VE1BLL suggested or twist it yourself depending on the installation. If you want to go way overboard run it in steel conduit.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[analogkid2digitalman]

If you decide to 'twist' your own, chuck up one end of the pair in a drill, tie off the other end to something solid, and turn on the drill at a slow to moderate speed
and do not overtwist. I just made some this morning.

Run drill CW for use in the Northern hemisphere, CCW for the Southern.

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"It's the questions that drive us"
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[itsmoked]

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

If you twist it yourself, then start with wires that are quite a bit longer than you think you need. And don't twist them too tight or you'll find the finished cable getting shorter and shorter and shorter...

 

[GonzaloEE]

analogkid2digitalman:
Can I use your cable in the Equator? Do I need an 'Equator interface'? ;-)