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Indulge my over thinking, shielding transducer cables...


immortl
Go to solution Solved by Bankc,

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Been working on rigging my kayak, mostly wrapped up the initial version 1 of the electrical wiring this weekend. Towards the end, I got to thinking.  What if they made a metal version of this PET plastic expandable braid sleeve I've been running all my wiring in? I looked, and sure enough, they do make a tinned copper version of it, it's even in convenient 25' lengths.

 

 So if I really want to make sure the transducer cables aren't picking up stray stuff from power wires, radio frequencies, etc...  If I put this tinned copper braid over the transducer cables and solder a wire to the sleeve, would I want to ground it to the battery ground or to an earth ground?  For a boat, I think I understand an earth ground goes to the water somehow? Would a single ground wire attached to the sleeve be enough, or would I want to attach one to each end?

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But... the parts are arriving later today...  Actually since I started typing this I think they were just delivered.

 

I do have a 125AH battery strictly for the trolling motor and then another 50AH for the sonar units, so they're separate.  I mostly have the wiring separated, as it gets to the front, they do come in close proximity But I've kept it as separate as I can.  I also have the excess transducer cable done up in the figure 8.

 

I was hesitant to power the finder and the FFS via the yakpower switch/power box so I put in a small fuse block and the sonar gear is powered 'directly' off the battery with the fuse block in between and the yakpower is for the other stuff (lights, power ports, etc...).

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20 minutes ago, immortl said:

But... the parts are arriving later today...  Actually since I started typing this I think they were just delivered.

 

I do have a 125AH battery strictly for the trolling motor and then another 50AH for the sonar units, so they're separate.  I mostly have the wiring separated, as it gets to the front, they do come in close proximity But I've kept it as separate as I can.  I also have the excess transducer cable done up in the figure 8.

 

I was hesitant to power the finder and the FFS via the yakpower switch/power box so I put in a small fuse block and the sonar gear is powered 'directly' off the battery with the fuse block in between and the yakpower is for the other stuff (lights, power ports, etc...).

MOST people don’t have issues with interference. You see it all over the place because content people don’t make noise.

 

I’d rig it up and see what your images look like then consider adding any interference mitigation if you end up having any

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56 minutes ago, immortl said:

But... the parts are arriving later today...  Actually since I started typing this I think they were just delivered.

 

I do have a 125AH battery strictly for the trolling motor and then another 50AH for the sonar units, so they're separate.  I mostly have the wiring separated, as it gets to the front, they do come in close proximity But I've kept it as separate as I can.  I also have the excess transducer cable done up in the figure 8.

 

I was hesitant to power the finder and the FFS via the yakpower switch/power box so I put in a small fuse block and the sonar gear is powered 'directly' off the battery with the fuse block in between and the yakpower is for the other stuff (lights, power ports, etc...).

 

That is the correct way to run it.  Power to a fuse block and then run everything to that.  You'll be fine.

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Well, lets propose that the sleeves arrived and I was bored while on a conference call and I bit by bit got them slipped over the transducer cables before reading the replies above.

 

If I was to ground the sleeves to the battery negative terminal, would I NOT want the metal sleeves to come in contact with the water or would it not matter?  I'm kind of thinking it wouldn't matter, kind of like in a car/truck, battery ground goes to the frame?  I don't know though.

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The problem is there's not a good ground on a boat.  Neither the negative battery terminal nor the water make for a good ground for getting rid of interference.  

 

However, interference is rarely a problem.  And when it is a problem, it's usually not something that grounded shielding will solve.  It's usually caused by signal noise in the power supply itself (battery in this case).  The problem is usually caused by the battery getting called on to provide pulses of high power on one circuit, and not having the capacity to provide steady power on a second circuit while keeping up with the pulses.  So residuals from the pulses bleed over to the other circuit and create noise which is interference.  Shielding it from outside noise won't help, because the problem is coming from within.  Hence why most people keep their trolling motor and sonar on separate batteries.

 

Plus, transducer cables are already shielded internally.  So you're shielding an already shielded cable, which means you won't gain much, if anything, from it.  It shouldn't hurt.  But it shouldn't help either.  

 

Now, there is the rare problem that you've got runs of wires or a transducer wire running right next to something like a trolling motor and picking up stray EMI.  However, like I said, it's already shielded, so more shielding usually won't help.  You usually need a better contact with ground, which you can't really do on a boat, or to physically move the wires so they pick up less interference.  The intensity of the radiation is inversely proportional to square of the distance.  In other words, if you double the distance between the wires, you cut the noise the wire picks up by 1/4th.  So moving a wire from 1/2 inch away to 4 inches away will cut the noise it picks to 1/16th the original amount.  Which is a huge amount of noise loss for just moving a wire over 3-1/2 inches.  

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Thanks guys for all the great feedback and explanations.  It's helped me gain a better understanding of possible interference causes and how it comes about overall.  I understand better why the additional shielding is way overkill and pretty much unnecessary.  I appreciate the education. 

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