Depth finder interference

Here’s my setup: 1990 Lund Predator, Minnkota Powerdrive V2, Vexilar FL-8 on the bow. I bought a “summer time kit” for the FL8, which included a transducer that mounts on the trolling motor. Everything works swell until I run the trolling motor. The interference fills the whole screen on the FL-8, rendering it useless. I thought perhaps the problem was the FL-8 was powered from the trolling motor battery. Today I tore the deck off and ran a twisted pair from the FL-8 back to the starting battery. That didn’t help at all. I tried clamp-on ferrite and a couple of other things but nothing helps. The noise is coming from the trolling motor’s motor, as the amount of noise changes with speed.

Am I missing something obvious?
Would more modern gear work better?
Would it help if I had at transom mounted transducer?

Thanks

SR

What has cured all my trolling motor interference is run a ground wire from the trolling motor skeg to the negative of the starting battery. Any ground under the front deck that goes to the starting battery will work. I have done this to 4 different trolling motors and each time it has worked, but as always your mileage may very.

The fl 8 is notorious for any other electronics to give it interference.

Does the trolling motor have a built in transducer? If so, that could be the cause.

Tom P, connect the skew to the negative of the starting battery or the trolling motor battery?

SR

Perhaps it could work if you run a fused wire from the trolling motor battery negative to a ground like the hull. Or since it is a transducer on the motor there is a loose magnet or something in the motor bell creating the bad juju. Either check the motor or try insulating the transducer from the motor housing with some rubber under the transducer and hose clamp.

My power drive had a built in transducer. Like some one stated above that could be a leading issue. Call vexilar and they are great to talk with

I tried connecting negative sides of the batteries to the hull, and also connecting the motor housing to various points. None of those measures had any effect on the problem. It occurred to me I had another transducer I could try, the ice fishing transducer that originally came with the unit. When I connect that transducer I see NO interference at all! So it,s either a mechanical problem like Greg suggested or a bad cable on the transducer. I’m going to do some continuity checks later today to see if I can find a break in the shield.

SR

I found a very bad spot on the transducer cable. That cable consists of a black and a white wire, a bare stranded “drain” wire, and foil shielding. The bad spot was missing most of the outer jacket as well as all the foil shielding. I cut out the bad spot and spliced it back together (along with a generous amount of water proofing) and it seems to be better. If I advance the gain on the FL8 I can see some interference, but hopefully I can see bottom at a lower gain setting than that. Long term solution here is to get a different depth finder for the bow and run the transducer on the transom, not the trolling motor.

SR

There is also a small fuse in the power head on the Minn-kota. I believe it is for interference, wiring diagram shows it running from power head to motor.

I looked under the hood, no fuse in my Minnkota. I must have an older model.