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Trolling Motor Causes Sonar Problems

Old 10-02-2006, 06:49 PM
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Default Trolling Motor Causes Sonar Problems

New boat, new MinnKota trolling motor with copilot and autopilot, and new Lowrance 320c. Have engine on 1 battery. Have electronics and bait tank pumps, etc. on a house battery. Have 24volt trolling motor on 2 other batteries separate from all others. The trolling batteries and house battery are connected to a 3 bank on-board charger. When I turn on trolling motor via copilot remote I get heavy black interference on the sonar. When I turn off the trolling motor the black interference goes away and the the sonar screen is beautiful. I believe this is true whether or not the autopilot is on or off. Can't understand how the trolling motor interferes with sonar when they are on different batteries. Need help.
Old 10-02-2006, 09:03 PM
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Default RE: Trolling Motor Causes Sonar Problems

We assume the graph is on the bow with the TM? How is it powered, exactly where is the connection made? Some say its really best to go all the way to the battery directly to help this problem. Also, make sure the power wire and transducer cable are as far as possible from the TM power cables.

We assume the transducer is mounted on the TM? So the transducer cable would be in contact with the TM.

You can use ferrite beads / chokes, purchase at Radio Shack and wrap the power wire and transducer cable. although some people say its best not to have it on transducer wire - don't really know why.

MK TM's are know to cause a lot of interference. They do offer some models with transducers built in which may address this problem. On mine, before the chokes the interference was really bad anytime you first hit the TM button. It would clear up if you kept in on. With the chokes a lot of it went away.

Need to determine if its coming in through the power or transducer cable - usually power I'd guess.

Google search for "trolling motor interference" produces a lot of reading.
Old 10-04-2006, 11:25 AM
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Default Re: Trolling Motor Causes Sonar Problems

The sonar graph is on the center console and the transducer is on the transom. The batteries for the trolling motor and the house battery for the sonar are all under the center console. The EMI interference includes occasional heavy black bands I call telephone poles or complete screen blackout due to very heavy black interference. It goes away when I completely turn off the trolling motor. Sometimes it goes away for brief periods when the TM is on, but my joy doesn't last very long. I'm assuming this interference may be a grounding issue and that the sonar unit needs to be grounded somehow, but I am ignorant on just how to best do that.
Old 10-05-2006, 09:26 AM
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Default Re: Trolling Motor Causes Sonar Problems

OK, to clear up details about my situation. The sonar is mounted on the center console and powered by the house battery. The transducer is mounted on the transom. There is no other transducer mounted on the trolling motor up front. As stated above, I believe it's a grounding issue, but I wasn't sure how to fix it. I have since been told I can ground the sonar by running a wire from the negative terminal of the house battery all the way to the bolt that holds the transducer on the bracket in the water at the transom. Before I try that I am looking for confirmation here that this is correct and I won't screw something up. For example, the first time, a friend said run it from the "positive" terminal, and I'm pretty sure that is incorrect.
Old 10-05-2006, 10:52 AM
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Default Re: Trolling Motor Causes Sonar Problems

BassDaddy,

Perform your test again and disconnect the 3 bank charger from the house battery. I bet it clears up. Sounds like some noise is getting passed from the trolling motor to the charger and the charger is passing the noise on to your house circuit.

If this is the case, a filter installed on the positive charge lead on the house bank should fix it.

I have NEVER heard or running a ground wire to the xducer mounting bracket.

Old 10-06-2006, 09:23 AM
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Default Re: Trolling Motor Causes Sonar Problems

Hotspot,
Thanks for your suggestion. I had not thought about the battery charger possibly being the culprit. It's a simple test and I'll try it next time I get to go fishing. Meanwhile, where can I get such a "filter" and does it have a specific name or brand, etc.?
Old 10-06-2006, 09:31 AM
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Default Re: Trolling Motor Causes Sonar Problems

The link below was provided by THTer Hull Slap from an ealier post. He reported that this filter worked very well for him.

Any Power Line Noise Filter will work and most electronics stores should have them.

Link to previos thread: http://www.thehulltruth.com/forums/t...ighlightmode=1

Link to filter: http://www.crutchfield.com/S-1oy2DCd...lter&i=003S15A


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