Shielding a power cable

[Let'sgoflying!]

(all exp, no legal concerns.)

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.)

 

[Bell206]

a much better connection to power was made as described above, using unshielded tefzel which caused a lot of noise on the radio.

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.

 

[Capt. Geoffrey Thorpe]

Brushed DC motors?
Small capacitors across the motor input should be considered.

 

[Let'sgoflying!]

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.

I failed to note to all, in the last paragraph that there was no noise, before I changed the cable.

 

[Let'sgoflying!]

Brushed DC motors?
Small capacitors across the motor input should be considered.

I have to look first at the change in cable; it was fine till I ‘fixed’ it.

 

[Bell206]

I have to look first at the change in cable; it was fine till I ‘fixed’ it.

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.

 

[Let'sgoflying!]

By "fixing it" you may have simply made the existing problem noticeable.

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).

 

[Let'sgoflying!]

Brushed DC motors?
Small capacitors across the motor input should be considered.

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

 

[Bell206]

It’s going to be difficult to troubleshoot without changing something,

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.

 

[Capt. Geoffrey Thorpe]

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

Exactly.

20A - must be some hefty motors.

 

[Half Fast]

It’s going to be difficult to troubleshoot without changing something,

Do you have an oscilloscope, or access to one? You can make a simple RF sniffer and use it to see where the RF is coming from.

See post 19 and following, https://pilotsofamerica.com/community/threads/antennae-appearance-database.145886/#post-3481341 .

 

[Let'sgoflying!]

Do you have an oscilloscope, or access to one? You can make a simple RF sniffer and use it to see where the RF is coming from.

See post 19 and following, https://pilotsofamerica.com/community/threads/antennae-appearance-database.145886/#post-3481341 .

Sorry nope, don’t have O’scope, nor the time to learn to use anyway. Appreciate the idea.

Ref “20A max” motors, its 12awg so 20A max.
Probably close to a10A draw.

 

[Albany Tom]

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]

Agree with @Albany Tom I would use a ferrite RF choke - link below. I use these all the time in amateur radio as all kinds of stuff makes RF noise. 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

 

[Let'sgoflying!]

Agree with @Albany Tom I would use a ferrite RF choke - link below.

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

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?

FSB Mix 43 - RFI Range: 20-300 MHz - Ferrite Core Products - Palomar Engineers®

palomar-engineers.com

 

[Albany Tom]

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?

FSB Mix 43 - RFI Range: 20-300 MHz - Ferrite Core Products - Palomar Engineers®

palomar-engineers.com

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.