Author Topic: Interference from outboard  (Read 5949 times)

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Offline johnmr12

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Interference from outboard
« on: November 08, 2015, 07:51:13 PM »
My 898 is on the console with two transducers. The SI is on the back of the boat and the DI is a thru the hull type. When the engine is off or idling I have a good clean image on both transducers, but as soon as I push the throttle I get noise all over the screen from top to bottom.  I unplugged each transducer one at a time and it had no effect. I have been researching different possibilities, and I have ordered some ferrite cores to attach to the transducer cables. Has anyone tried this and is more better, or does 1 core per cable work as well as 4 or 5? Does anyone know why the increase in RPMs would cause this problem?


Offline bobcoy

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Re: Interference from outboard
« Reply #1 on: November 09, 2015, 04:28:45 PM »
1 core per cable. If still with problems make sure you turn the filter setting higher. It could be your spark plugs or plug wires on the engine causing the interference.(with time the wires break down inside) Try one thing at a time till you get it fixed. Bob
Under the sonar tab you will find the noise filter(off to high 3) Default is low.
« Last Edit: November 09, 2015, 04:37:20 PM by bobcoy »

Offline johnmr12

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Re: Interference from outboard
« Reply #2 on: November 09, 2015, 04:35:07 PM »
Bob, should I place the core close to the transducer or close to the 898?

Offline bobcoy

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Re: Interference from outboard
« Reply #3 on: November 09, 2015, 04:40:24 PM »
close to the 898. There is a you tube video by Doug Vahrenberg for ferrite ring install. Don't hold me to the spelling of Dougs last name.(most of the letters are correct.
« Last Edit: November 09, 2015, 04:43:00 PM by bobcoy »

Offline rnvinc

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Re: Interference from outboard
« Reply #4 on: November 09, 2015, 11:31:30 PM »

Offline johnmr12

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Re: Interference from outboard
« Reply #5 on: November 10, 2015, 09:34:24 AM »
The devices that I bought actually open so you can put the cable inside and then snap them closed. From what I saw in the video the ones I ordered are much easier to install and eliminate all the cable crimping in the line but I'm not sure if they are as effective as the one in the video.

Offline bobcoy

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Re: Interference from outboard
« Reply #6 on: November 12, 2015, 10:55:38 AM »
The number of wraps is key in reducing the noise. If you are talking the Radio shack chokes I did see some reduction but nowhere as much a difference as the HB supplied rings gave. Bob

Offline johnmr12

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Re: Interference from outboard
« Reply #7 on: November 12, 2015, 11:10:44 AM »
I bought these cores online and got 10 of them for 10 bucks. I'm still waiting to get them. I will see if they fix my problem, and if they don't I will get the HB ones and try them.  On a slightly different topic, I was always under the impression that the trolling motor electrical system should be totally isolated from the rest of the boat's electrical system. My boat is wired so the starter battery supplies power to everything on the boat except the trolling motor, and the 3 batteries that run my trolling motor are totally dedicated to just the trolling motor. Then I came across an article about sonar unit interference, and here is what it said.

"If you disconnect your transducer from your depth finder and you continue to see noise when the trolling motor is running, then you are dealing with conducted interference coming in through the power connection. This can happen when the boat's electrical system does not have one common ground that connects to the water. Using a multi-meter, available at places like Radio Shack, check for proper grounding in your boat's electrical system. Set the meter to measure resistance or continuity. Then connect one lead to the negative battery post that connects to the trolling motor and the other lead to the negative post on your starting battery. The reading should show zero and the meter may beep. Also, check between the negative starting battery post and an unpainted portion of the outboard motor, like the prop shaft or trim tab. You should also measure a complete circuit here as well. If the ground connection is missing between the trolling motor battery and the starting battery, add a small gauge wire, about 18 AWG, with a 1 amp fuse. This will complete the ground connection here."

In my case, I had continuity between the starter battery ground and the trim tab, but because my trolling motor batteries were isolated, I had no continuity between the trolling motor negative and starter negative. So I added the wire that was suggested in the article. I am waiting for my ferrite cores to arrive before I take the boat out and test everything. I'm curious what others think about this article.

Offline bobcoy

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Re: Interference from outboard
« Reply #8 on: November 12, 2015, 11:28:30 AM »
I did the common ground thing. I did not help my situation. I disconnected it and with the HB ferrite rings I am noise free. One thing at a time is the way to go. If you do multiple things it can get very tricky and even get new and improved problems. Make sure you note which things showed improvement. Maybe add those one at a time to see if the combination works. Bob

Offline rnvinc

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Re: Interference from outboard
« Reply #9 on: November 12, 2015, 08:31:04 PM »
The article scenario is just 1 of many possible fixes for RFI ...every boat is different ...and scenarios must be tried one at a time until the interference is eliminated ...

Read this ...
http://www.humminbird.com/Category/Support/FAQ/Trolling-Motor-Interference/

HB deals with these issues every day ... They are a great resource for tracking down and eliminating RFI ...

1-800-633-1468

Rickie





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