Shielding a power cable

Let'sgoflying!

Let'sgoflying!

Touchdown! Greaser!
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I want to run a 24v pair of wires to a fan using a shielded tefzel 12awg cable.
The run would be:

Battery (+ & -) to an inline CB on the hot side, to a plug near the fan, then to the fan.

The shielding needs to go as close to the battery connections as possible, include the CB as much as possible, and the plug as much as possible.

(before I got involved, the fan was jury-rigged and unsafe; a much better connection to power was made as described above, using unshielded tefzel which caused a lot of noise on the radio.)
 
Let'sgoflying! said:
a much better connection to power was made as described above, using unshielded tefzel which caused a lot of noise on the radio.
Click to expand...
Are you sure the fan itself is not the item generating the radio noise? You may want to look at this a bit more as adding a shielded wire may not give you the result you are looking for based on what you've posted.
 
Bell206 said:
Are you sure the fan itself is not the item generating the radio noise? You may want to look at this a bit more as adding a shielded wire may not give you the result you are looking for based on what you've posted.
Click to expand...
I failed to note to all, in the last paragraph that there was no noise, before I changed the cable.
 
Let'sgoflying! said:
I have to look first at the change in cable; it was fine till I ‘fixed’ it.
Click to expand...
By "fixing it" you may have simply made the existing problem noticeable. Plus it is possible your noise may be coming in via the ground side. Personally I would troubleshoot a bit more before switching the wire to shielded wire. As a note, most wires are not shielded in general.
 
Bell206 said:
By "fixing it" you may have simply made the existing problem noticeable.
Click to expand...
Yes, I think the new cable is simply a better antenna for the motor noise than the previous cable.
It’s going to be difficult to troubleshoot without changing something, that’s why I’m thinking of trying shielding first, maybe a noise filter (on the power cable).
 
Capt. Geoffrey Thorpe said:
Brushed DC motors?
Small capacitors across the motor input should be considered.
Click to expand...
I googled this and did not see what I think you are saying. Any more details?
24v/20A max 12awg wires

Edit; maybe this?

Pololu - 9. Dealing with Motor Noise

Detailed information about the 3pi Robot, Orangutan SV-328/168 and LV-168, and Baby Orangutan B motor drivers, including truth tables and sample code.
www.pololu.com www.pololu.com
 
Last edited:
Let'sgoflying! said:
It’s going to be difficult to troubleshoot without changing something,
Click to expand...
There are ways to troubleshoot this issue without changing anything. To get you started....
Is the noise evident with just the master on, no engine run? Just the master and the fan? Pull CBs or fuses to isolate those circuits from any other circuit that is powered when master is turned on.
 
Let'sgoflying! said:
I googled this and did not see what I think you are saying. Any more details?
24v/20A max 12awg wires

Edit; maybe this?

Pololu - 9. Dealing with Motor Noise

Detailed information about the 3pi Robot, Orangutan SV-328/168 and LV-168, and Baby Orangutan B motor drivers, including truth tables and sample code.
www.pololu.com www.pololu.com
Click to expand...
Exactly.

20A - must be some hefty motors.
 
What could be happening is that the fan kinda sucks and is making RF. Without shielded cable the power supply wires are acting like an antenna and your radio is picking it up. Agree with others on the capacitor. Suggest maybe a .1uF X7R ceramic at 100V for a 24 motor AND you should probably have a 100V protection diode in reverse across the capacitor roughly equal to the motor current if it's more than a tiny motor. Combined the two parts should be less than $1, except for shipping, min quantity, etc.

I wouldn't use shielded DC cable. Instead of the capacitor you could also try a snap on ferrite bead, or looping the power cable a couple of times through a ferrite ring. The advantage of that is that there's nothing electrically to break or solder. The disadvantage of ferrite is weight and expense, with weight possibly being an issue if the ferrite can move around and damage something. For interference to aircraft radios, ceramic capacitor is probably better, cheaper, simpler.
 
Initial Fix said:
Agree with @Albany Tom I would use a ferrite RF choke - link below.
Click to expand...

Initial Fix said:
Just loop your wire through 3-4 times and you should be good.

RF choke.
Links to https://palomar-engineers.com/ferrite-products/FB102-43-1-2-ID-12-8mm-RFI-Range-25-300-MHz-p74532492
Click to expand...

This is 12 awg. To run the wire in, around then back into the choke the same as the first run, 4 times, might require a bit more than a 1/2" ID choke?
If I get a 3/4" ID choke, will it be physically too distant from the wires to have the desired effect?

I'm thinking of getting the split ring type which snaps together so I don't have to make new termini (end connectors).

Do I need to do both hot and ground wires?
Do the hot and ground wire chokes go as close to the motor as possible?

What about this one?

palomar-engineers.com

Ferrite Core Products - Ferrite Core Products - Palomar Engineers®

Ferrite Rings, Beads & Snap Ons Ferrite Core Products → Mix chooser and use-cases Review
palomar-engineers.com palomar-engineers.com
 
Let'sgoflying! said:
This is 12 awg. To run the wire in, around then back into the choke the same as the first run, 4 times, might require a bit more than a 1/2" ID choke?
If I get a 3/4" ID choke, will it be physically too distant from the wires to have the desired effect?

I'm thinking of getting the split ring type which snaps together so I don't have to make new termini (end connectors).

Do I need to do both hot and ground wires?
Do the hot and ground wire chokes go as close to the motor as possible?

What about this one?

palomar-engineers.com

Ferrite Core Products - Ferrite Core Products - Palomar Engineers®

Ferrite Rings, Beads & Snap Ons Ferrite Core Products → Mix chooser and use-cases Review
palomar-engineers.com palomar-engineers.com
Click to expand...
Ideally, both hot and ground go through, and as close to the motor as possible. If the ground connection is the case of the device, then don't worry about it and just do the hot. The snap devices do work, they're commonly used to fix RF issues in already installed equipment.

Filtering goes up with the square of the number of turns, but permeability (magnetic resistance roughly) isn't linear in most materials. That 43 mix is good, as Initial Fix posted. RF suppression is as much art as science, so you try things until it works.

Watch the weight of the filter, especially if the connection to the motor is soldered. Soldered can be brittle, and repetitive flexing will break the wire. For anything mobile it's common to secure the ferrite somehow so they don't break the wires.
 
I believe in resurrecting old threads when there is a valid purpose, and also I think it's important for those asking questions to check back in with the rest of the story so we can all learn (even if its so someone can say 'I told him so' lol)

The ferrite chokes/noise suppressors.
I bought a box full of the clip on I think 10-300mhz from palomarengineering around 100 bucks.
Someone else installed them as instructed with zipties or electric tape (no wire cutting, no soldering, no new connections; they just wrap around the outside of the cables/wires).
The airplane then flew 40 hours and the report from the pilot is that in those 40 hours there was no longer any emi/rfi/static/audio problems on the radio.

Ferrite; the new magic thing in my toolbox. I have a few other projects to try this on.
I think they are magnets? I wonder if they have a lifespan?
 
A very good thread to revitalize.

In an inductor, energy is transmitted to the core by CHANGING voltage, but not DC. The iron in the ferrite ring is magnetized and absorbs energy from the rising voltage of the high frequency noise, producing a very slight amount of heat. The falling voltage from after the peak also magnetizes the ferrite, producing heat. Thus, the spikes become heat, and do not go along the wire or radiate.

The rising and falling voltages produce opposite polarity magnetism, N or S, equal amount, so never much residual magnetism in them.

The ferrites last forever. :)
 
Let'sgoflying! said:
I think they are magnets?
Click to expand...
They're not magnets, but they're magnetic (or magnetizable) material. With a wire going through them they form an inductor. For a very crude analogy, they become an electromagnet absorbing energy as current though them increases, then return the energy as the current decreases, smoothing the current flow out.
 
geezer said:
A very good thread to revitalize.

In an inductor, energy is transmitted to the core by CHANGING voltage, but not DC.
Click to expand...
This is incorrect.

The inductor created by the wrapped ferrite blocks changes in CURRENT, not Voltage.

This, it will allow a steady DC current to flow without any issue, but will present an impedance to any AC signal, with the impedance increasing as frequency increases. Noise generally has a higher frequency than a power feed, so when the circuit is properly configured, the inductor blocks the noise and lets the power through.

electronicsphysics.com

Impedance of Inductor formula | Inductive reactance | Edumir-Physics

Electrical impedance of an inductor and its formula, unit, significance and numerical problems......Inductive reactance.... Inductance
electronicsphysics.com
 
I believe we are both right.

The change in voltage in the voltage spike results in a change in current. That change in current is what causes the magnetic changes that block the current in the wire. You cannot have one change without the other, the explanation would have been longer with the full story.

The goal is to stop the voltage spikes, or 'fuzz'.
 
geezer said:
I believe we are both right.
Click to expand...
No, what you posted is incorrect. Induction is only related to current. Voltage has nothing to do with it. Faraday's laws are quite clear.

geezer said:
The change in voltage in the voltage spike results in a change in current. That change in current is what causes the magnetic changes that block the current in the wire. You cannot have one change without the other,
Click to expand...
This is also incorrect. In a system with a very "stiff" low impedance power supply and a load with a variable impedance, the current will change with no significant change in Voltage. Conversely, with a very high load impedance relative to the source, the Voltage can swing all over the place without ever changing the load current.

Your statements here are based on a number of assumptions that may or may not be correct. The one thing we do know is that the system is inherently not a stable, linear DC circuit, else there would be no noise. Thus, thinking terms of Ohm's law with "r" being a fixed resistance value is tossed right out of the picture, and we need to start applying AC circuit principles.
 
Let'sgoflying! said:
I believe in resurrecting old threads when there is a valid purpose, and also I think it's important for those asking questions to check back in with the rest of the story so we can all learn (even if its so someone can say 'I told him so' lol)

The ferrite chokes/noise suppressors.
I bought a box full of the clip on I think 10-300mhz from palomarengineering around 100 bucks.
Someone else installed them as instructed with zipties or electric tape (no wire cutting, no soldering, no new connections; they just wrap around the outside of the cables/wires).
The airplane then flew 40 hours and the report from the pilot is that in those 40 hours there was no longer any emi/rfi/static/audio problems on the radio.

Ferrite; the new magic thing in my toolbox. I have a few other projects to try this on.
I think they are magnets? I wonder if they have a lifespan?
Click to expand...
Happy it worked, and appreciate you posting back the info!

As others have mentioned, ferrite is a magnetic material, similar to iron, but generally has a much higher permeability (more or less meaning it easily allows a magnetic field to flow through it). At some frequencies, some ferrite mixes can be very efficient, so they can be used for RF transformers, at other frequencies, they are inefficient, meaning they turn the magnetic field into heat, kinda like a resistor. So you get the right mix and size for what you're trying to block, and it acts as an RF choke. They're used all the time for RF noise reduction, you'll see the lumps on different types of cables that are used around computers and other noise making devices. They aren't affected at all by DC current, except the minor current spike that can happen during power on or off, and used as a filter like that they'll last forever.
 
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