Humminbird 788ci /MinnKota Universal Sonar Trouble

I just installed a Humminbird 798c SI on the console and a 788 ci on the bow of my 2002 Lund Explorer 1650 SS. I have a MinnKota Terrova trolling motor with the universal sonar 2. I put it in the water today for the first time. No problems with the 798c SI. I idled around until I located a school of fish in 30 FOW. Dropped in the Terrrova and powered up the 788ci the interlink synched up fine. I went trough the menu and set the sonar to Universal Sonar 2. Console graph was showing fish, the bow was not. Temp, speed, depth all read the same on both units. As soon as I turned on the trolling motor the front unit jumped to 500+ FOW and showed a screen full of interference. All sensitivity levels are still at the default levels. As soon as I shut the trolling motor off or run it at extremely low speeds it reads the correct depth, but still is not showing the same arches that the console unit shows. Both units are wired to individual 3 amp accessory fuses on the console that are provided by Lund. The GPS works great on both units. I did swap the units back an forth, they seem to exhibit similar problems when attached to the Terrrova/US2 in regards to loosing their mind when the motor is ran. ? I am still learning how to use these so my knowledge is pretty limited at this point. I have not messed with any of the default sttings that I can think of. I have only had my Vexilar FL-20 attached to the Terrrova in the past and that seemed to work just fine. Any recommendations?

Ok, silly question #1. You said you’ve used the US with your FL-20. Do you have the correct US adapter for the ‘bird (different from the Vex)?

I do have a Humminbird cable installed, not the Vex cable.

Where is the power for the locators comming from? The batteries for the locator and the trolling motor need to be seperate. The locators should be hooked up to the outboard battery. If you use a seperate battery for your electronics (like me)the ground for the electronics battery and the ground for the OB starting battery need to be connected (common). The Instructions for the minn kota discribes this. I talked to a tech at minn kota and he told me about the common ground between my electronics and starting batt. The system uses some kind of grounding plane using the water between the OB and the Minn kota. I just hooked mine up but havent been able to test it out yet. Let me know if this helped.

Sounds like Trolling Motor Interference. Call HB Customer Service 800-633-1468 they can help you and have kits to resolve.

Finally had a chance to call Humminbird. They are sending me some sort of choke kit for the finder and for the trolling motor. Hopefully it helps.

I have a 80 pound Maxxim with US2 on my Nitro. I was getting eratic depth readings. I talked to one of the guys at Cabelas last month when I was picking up the motor for my other boat. I told him it did the same no matter which one of my Humminbirds I had hooked up. All of the Humminbirds worked properly until hooked to my Maxxims US2. With mine the trilling motor just needed to be turned one way or the other to produce the symtems. I removed the Maxxim from my boat and took it to Cabelas, 10 days later they called said it was ready. I reinstall it on my Nitro, went fishing and the damn motor still does the same. They put a new transducer in it. I didn’t start having this problem intil Cabelas put a new board in the foot pedal last year. I wonder if the board could be causing this problem…

Any thoughts?

H-Bird Customer Service.

Let us know how the choke works.

I posted this under the other US issue but I will post it here.

When I was talking to Vexilar it seem that it is a shelding issue with the US cable by the motor. I think it needs some extra shelding as the issue your seeing is radiated noise.

Please read below as the issue would be with any locater you use with your minn kota.

There are two possible sources of the interference. One is conducted interference, caused by the Pulse Width Modulation speed control in the motor sending pulses into the power circuitry. The other is radiated interference, electromagnetic interference (EMI) from the motor’s lower unit and brush leads. Before you can solve the problem, you’ll need to determine the source of the interference. Here’s how to tell, unplug the transducer from the back of the depth finder. Now run the motor. If you no longer see interference, the problem is radiated noise. If you do, the source is conducted interference from the power line.

To solve conducted interference, you’ll need to connect the main negative trolling motor battery post (where the negative trolling motor power wire connects) to an effective earth ground. This can be the negative post on your cranking battery or the hull of the boat, if it’s an aluminum hull. Use a small wire, 18 gauge wire will do, with a 1 amp fuse. If you have an on-board charging system, you need to be careful. If the trolling motor power wires connect to the charger, and do not connect directly to the batteries, you’ll need to contact the charger manufacturer for further instructions.

If the source of your interference turns out to be radiated noise, you’ll need to add a Ferrite Core, a simple piece that attaches to the transducer wire, or replace your transducer, or possibly both. We have been experiencing this issue mostly with the high-thrust motors. The 36 volt motors are the worst. Last year we developed a new Puck that greatly reduces this noise. A new style transducer along with the Ferrite Core should completely eliminate the noise, even in severe cases.

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Minn Kota / Vexilar Interference Solutions

Our testing regarding interference from the Minn Kota motors on our FL-8 and FL-18 depth sounders have found some ways to help eliminate the problem of electromagnetic interference being displayed.

Common Ground – Some boats have a common ground where the negative of the trolling motor battery is connected to the negative of the starting battery. Although this wire has been helpful in the past to eliminate conducted interference from the trolling motor speed control (Pulse Width Modulation) circuitry, we have found that this connection introduces EMI noise into the rest of the boats electrical system. Removing this connection can significantly reduce the interference.

Cable Locations – Making sure that any and all power and transducer cables are as far away from the trolling motor power cables will help reduce interference. Simply neatening up wiring jumbles into neat bundles, separated between deep-cycle and cranking battery sources will help.

Universal Sonar Grounding – The Vexilar trolling motor transducers have a small metal tab that protrudes from the top of the puck. This ensures a good shield ground at the point of the interference, which significantly reduces noise on the display. The Minn Kota U.S. system does not have this ground. The motors transducer cable is shielded, and this shield is only connected through the depth sounder to the cranking battery negative. However, the final ground to earth (the water) is far away from the motor, usually ending at the outboard. Connecting the transducer shield inside the lower unit to the metal motor housing would be the best way to get a good ground, but achieving this after the motor is built is difficult. For aluminum hulls, connecting the negative of the cranking battery to the hull and then connecting the bow mounted depth sounders negative to the hull in front should help interference problems. This is similar to automotive systems where the chassis is the ground current path. For fiberglass hulls, the easiest solution may be simply to use an external transducer that has the ground tab. Another, more invasive, solution may be to tap into the shield within the U.S. adaptor and connect this to a ground point as close to the motor as possible.

Defective Parts – The transducer cable shield is extremely important to clear sonar reading in all marine situations. If the shield is not continuous, the “drain path” for the interference is not complete. Defective transducer cables and adaptors, as well as bad connections within connectors and jacks can cause problems. A simple continuity check to ensure a complete circuit from the earth ground point (outboard lower unit or aluminum boat hull) to the grounding tab on the transducer will tell if there is a problem. For Universal Sonar systems, check from earth ground point to the end of the adaptor plug that connects to the motors transducer cable. Further checking would require a service center visit.

Ferrite Core – A ferrite core is a part that attached to the exterior of a cable that has interference noise within. We found that ferrite cores had little effect on severe interference from the Minn Kota motors. However, mild noise (green color with some orange) was controllable with this solution.