Anyone know how to suppress EMI?

My 20 ft boat has a sonar unit on the front deck which gives a "picture" of the bottom as well as depth information. The power wires to it run parallel to the power wires to my electric trolling motor that is mounted to the front of the boat. The batteries are in the back. Separate battery for the electronics, two 12 volt batteries for the motor. When I activate the trolling motor the picture on the graph lights up with lines that obscure the picture. I suspect EMI from the large gauge (24 volt) power to the motor. My questions. If I buy some wire shielding do I place it over the wires to the motor or over the wires to the graph? 2nd question, do I shield the Pos and Neg wires separately? This might be coincidence, but the problem didn't surface until after I switched from AGM batteries to lithium. For those who aren't familiar, this is the type graph I have.
Humminbird HELIX 12 CHIRP GPS G4N Fish Finder/Chartplotter | Bass Pro Shops

 

A shielded wire/cable for the fish finder should do the job.
Hope they don't use proprietary connectors on it.

 

My plan was to cover the existing wires with shielding. Something like this. It comes in various diameters.

Amazon.com: Tinned Copper Braid Metal Cable Shielding Sleeve Ground Straps EMI RFI ESD EMF Interference Wire Sheathing Flat Mesh (5/16 in Wide(0.20 in Dia)-28ft) : Electronics

 

The CCD wiring for communication between computer modules in my era of trucks use a twisted pair of wires for each wiring run between modules. Those wires are not shielded. I wonder if that would work for the power supply to your sonar.

- John

 

It came with 18 or 20 gauge wires that were too short for the installation. I've used 14 gauge to eliminate voltage drop for the 20 ft run. There is only one conduit from the rear to the front of the boat so there isn't any other way to route the wires. This graph, along with a similar graph in the back draw a 100 amp battery down to about 75% in a day of fishing. I think shielding what I have would be easier than experimenting with twisted wires.

 

Wrap the power wires through a torrid. Usually just need to do the positive cables. On a boat, you may need to do both + and - cables. Adding capacitors on the positive also can help filter out the noise. Look up filtering power for 2-way radio installs. This is about the same as a radio install with noise affecting reception. Good luck.

 

I'm guessing you mean a toroid? (I googled electrical torrid). After reading a little I'm not sure how I would go about doing that. The toroid is circular and my power lines are linear. I already have a filter on the graph. I'm interested in the proper way to install shielding which is readily available and not very expensive.

 

I'd give ut a shot at that price. If it won't work you can still buy a more expensive cable.

 

So, is it better to shield the 24 volt wires to the motor or the 12 volt wires to the graph? I have two sets of wires going forward. The other pair powers a transducer that is mounted to the motor.

 

Correction. The transducer is mounted about 10 inches from the motor.

 

A lead acid battery has some effect as a capacitor and filters out some AC signals. I am not sure the Lithium Ion batteries work quite the same. This article, while having lost a little understanding in the interpretation process, does refer to the "bare" LI batteries not having a good EMI suppression.
Assuming both systems are isolated - not hooked to the electrical charging system - when the boat main power is operating:
I would start with the assumed source, shielding the motor wires and connect the shield to the electric trolling motor's ground connection at the battery.
Topzide's capacitor suggestion is another economical way to try to filter the noise. Not sure on the capacitor's spec needed in your case. Amazon has some EMI/RFI filters for a reasonable cost, too. Apply to the sonar set.
On edit: Then John's twisted wire suggestion has merit, too. Not sure on the effect as the interference from the trolling motor is large vs. CCD signals. It helps to reduce the induction caused by parallel run wires.

 

@GAmes, Spelling is not my best and forget to use spell check a lot of times. Passing the power wire through a toroid will keep the stray electrical noise off the wires. You'll see them on the USB cords and computer power supplies to help with noise. If you have some slack in the cables, you could find a toroid large enough to get connector end to go through and then a wrap or two would be good. I know that way back in the day, set up a CB radio rig and used a LARGE can capacitor to suppress the noise on the system. Had a guy that got them from elevator systems, so they had some size to them, don't remember there ratings. Talk to a local HAM radio club about noise isolation. You might just be able to wrap a wire around them and connect to ground. Do you have an external zinc ground through hull? This might be the grounding needed to get rid of the noise. Ground isolation wire here instead of the negative of power system. Boating brings its own set of issues to the table. I've wrapped cables with the with from CAT cable to act as shielding. It sounds more like the transducer cable is picking up most of the noise and effects would be better focused there. Good luck with tracking down best solution.

 

The power wire into the unit has a round gizmo that I believe to be pertinent. I have also discovered it has a noise setting in the setup menu. I'm going to experiment with that and if there isn't an acceptable result I'll order the shield material. I'm thinking I might as well wrap both the pos and neg wires to the trolling motor while I'm in there. #ad

 

That's a built in toroid on that cable. What about the other end? Add one there if possible. If it has a noise menu, worth checking those settings out as they're put in there for a reason. Here's some interesting reading:
https://humminbird-help.johnsonoutd...les/4412819927063-Trolling-Motor-Interference
https://humminbird-help.johnsonoutd...3243658391-Main-Motor-Electrical-Interference

 

Those links are excellent. Thankyou. Of note " Most models will have four to six numerical settings that are not to be considered as low to high. They are instead each calibrated to address a particular frequency range." I assumed that cranking the digits up was like a volume knob. I'd be interested in this item also, if they would have been nice enough to say how and where to install it. Maybe instructions are included. A lot less cost than the shielding I was contemplating. Ferrite Steward - Humminbird (johnsonoutdoors.com)
I'm going to spend part of the day looking for a ground wire fuse too. Thanks again.

 

In Topzide's first link in Post 14 the #5 Check wiring suggestions of keeping the motor and depth finder wiring runs apart for both motor types reducing the effects of extraneous signal induction may be a factor for the noise along with the recent addition of the LI batteries. Is it possible to run each power source cable on opposite sides of the boat?

5. Check wiring: Make sure the deep cycle/trolling motor batteries are not linked to the Cranking Battery. Disconnect chargers, Perko switches, and anything else that may link the two sets of batteries. Try to keep the depth finder power cable away from the trolling motor power cable when rigging. It is also recommended that the excess length of power and transducer cables not be coiled. If you find that interference is still present then you might try using a separate small 12-volt battery to power the depth finder and retest.​

 

As I said earlier there is only one conduit from the rear to the front. Between the outer hull and inner structure of the boat the empty space is filled with floatation foam. The intent was to separate the two sets of wires using the shielding. My original question was which wires do I wrap in shielding. I already have the graph connected to it's own battery.

 

@GAmes, You don't even have the small gap under the gunnels the you could run some wires? I've helped fish wires that way a few times. A friend of mine even forced some of the flexible conduit through both sides to separate wires and run speakers from bow to stern! He like that the liquid type conduit allowed him to keep water out with all the fittings available! Maybe a possibility in your case. If you have only the one option, shielding the Hummingbird wires would be the most effective option. Good luck, fishing season is closing in fast, "gettr' done"!

 

Since separating the runs is not an option, shielding, filters (which includes the sonar equipment's settings) and running a twisted wire line are all options to try.
Here is an article giving insight to the twisted wire use. https://www.mercurywire.com/twisting-and-cabling/#:~:text=In order to help eliminate this electromagnetic interference,,canceled by the interference/noise produced by the other.
Best of luck in resolving the "fish search" feature and enhanced fishing enjoyment.

 

It's a Ranger bass boat. No gaps under the gunnels. Here in TX it is always "fishing season". Spring is best but there have been Decembers and Januarys that have been awesome. I'm off for a week long trip on Tuesday. For the time being I can only experiment with the filter settings on the graph. If there is no joy I'll be ordering the shielding. I'm also going to look into 14 gauge wire that comes as twisted and shielded. That sounds to me like a winning combination.