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Basscatp4.
I have a Motor Guide Tour 81 trolling motor with a Humminbird 998c si transducer mounted on it. Whenever the motor speed is anything but wide open, the screen is covered up with hf noise. I know there were some threads on the subject but I am having difficulty locating. Currently, power comes from the front panel with the trim switches. The unit has the inline choke. Per Rockwall Marine suggestion, I wired the cranking battery (-) to the TM battery (-) with AWG # 6 wire with no improvement. My next thought is to run AWG # 20 ga twisted-shielded-pair wire the length of the boat and connect direct to the cranking battery (with an inline fuse). The trolling motor is also making a high pitch noise when running at any speed except wide open (maby the pwm circuit is bad??) Suggestions pleaseI also included a pix of the dash mounted instrument, still having dificulty seeing, the lighting is noticeably less than the bow unitthanksjwthttp://s983.photobucket.com/albums/ae318/thomasbetty/
I had a similar problem a few years ago with interference. I was able to run a 16 gauge ground wire to the bottom of the trolling motor pedal.
Run a seperate positive and negative wire from your starting battery. Put chokes on each wire (get them at radio shack). This should eliminate any and all interference. Not a fun job, but worth the time and effort.
Chokes help and they may eliminate it. Though when you mess with the ping speed and resistance you will still have noise on some. There is no simple answer and 20 gauge AWG is not enough for your 997 to the bow unit from our experience. We would go with at least #14 and probably #12. We know this exists on some rigs, though we have never seen an easy answer. Even with separate batteries we have seen the RF noise, so a choke close to the unit is also a good idea. Also the positive should be the only wire you require a choke as the system does not flow voltage to the unit from both leads, the positive flows. BCB
It will be this weekend before I can try it, but:I believe that the interferrence is electro-magnetic comming directly from the motor case to the transducer. All of the filters, ground wires and chokes will not protect from this instance. In the aircraft industry, we have something called mu metal, it is a highly permable metal used for protection from magnetic interferrence. If one were to take some ferrus metal (a magnet sticks to it) and place it between the motor case and the transducer, the magnetic pulses from the motor should be shunted through the metal and circulate within the metal and not make it to the transducer. Perhaps something as simple as a steel soup can would work.Might be worth a tryjwt
It may work, though we usually dont see that help enough.
It is called ferral resinance. As stated a couple of replies up, a different metal makeup put between the transducer and the housing should cancel out the RF noise. The noise is coming from the magnetic field put off by the armature in the motor. We deal with this alot in the electric industry. It depends on the application of how we counteract it. Lightening arrestors on some applications and even something as simple as penatrux inhibitor can stop this. If the the metal doesnt stop it, find someone that works for an electric company and ask for some of this inhibitor and place it on the metal between the transducer also. Watch out for this because is a messy substance. Maybe this will help. Another product to stop it, is add a capacitor parallel on the positive side. A capacitor acts as a noise filter and will remove any unwanted noise on the DC circuit. Just skin back the wire in two places that are same length as the athode and cathode ends of the capacitor. Wrap the legs of the capacitor around each part of the bare wire and solder it. This will remove any noise if it is in the power supply.
Ive never dealt with as much interference as you state but I saw one guy had a wire clamped to the trolling motor housing and the other end connected to the trolling motor ground. He said it stopped the interference. He ran the wire along side the transducer wire on the shaft.
Clamping a ground to the housing could cause bad problems. If the paint wears off, and the armature in the motor starts to get corrison or dirt across an armature field. The ground on the housing will cause a major short in the trolling motor frying it severly.
Looking at your photos,I see that you have ran the transducer cable along with the TM Power and foot control cable. In your Humminbird manual, they state that this will increase your interfearance. I would take a differane path. I can snap a picture of mine of how I ran mine. Also Did you get the interferance kit from humminbird? I had to put one on my 1157 unit also. Its free, and it did take care of any problems I had. Do not run the humminbird power wires on the same side of the boat as the TM power wire. This will induce noise also. With DC power you have to calculate your power drop twice your distance. If your wire run is 25 feet long you have a 50 foot voltage drop. I would run #12 awg with a very high strand count. Eric
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