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Positive Charge
11-03-2005, 11:55 AM
I am new to electric flight and have just finished a park jet pusher where the instructions say to wrap the long power cables in cooking foil for shielding.
Many years ago I was shown a method of shielding long servo cables and wondered if our experts would let me know if it would work on high power battery or ECU cables.
If you remove the outer plastic sheath from TV co-ax cable the braided "tube" can be removed by lightly pushing the ends together. You can then feed this over your cables, pull tight, tape one end, cut to length, tape cut end to prevent loose strands and finally solder an insulated wire from this shielding to the NEGATIVE side of the battery.
I hope someone can comment on this method or even tell me it is common practice, but as I say I am new to electrics.

Alan

Geoff_Gino
11-03-2005, 01:58 PM
Hi Alan

Yes that would work, although to have it completely shield the cable you would have to earth the sleeve at both ends.

Geoff

flyranger
11-03-2005, 02:47 PM
Sorry Gino, I disagree. There are three ways to shield cables.

1. A floating shield, not tied to "earth" at either end. Will give some shielding, but works as an antenna. Not what I want in my models.

2. Tie one end to shielding to "earth" and the other end floats. This is how cables are shielding in most industrial environments. Probably the best arrangement, but I would be concerned about accidental shorts to the power system. Since our models are DC and have only plus and minus leads, one of them becomes the "earth" connection (for example: minus or black). If the red plus lead contacts the black lead or the shield lead, smoke and flame will result - not what I want in my models.

3. "Earth" the shield at both ends. In industry, this creates what is known as a "ground loop" - very unpredictable results in long leads, causing lots of problems with EMF.

With all that said, the leads inside a model are so short, there may not be any bad effects at all. Based on my own experience, I would not want to tie an extra "earth" to the plus or minus power leads inside my models. If a range check shows interference, I would move components around inside the model to get rid of it.

Geoff_Gino
11-03-2005, 02:56 PM
Hi Flyranger

I agree - you are quite right, but Being a Radio Tech I was looking at RF shielding and to prevent the control leads radiating noise.

EMF should not and would not radiate in the RF bands.

Please correct me if I am wrong as I am sitting with this very problem and have just had my Tx and Rx's returned to me from the dealer with a "no fault found" remark which has me worried.

Geoff