Topic: Motorguide Tour 82 Trolling motor PWM (Pulse Width Modulation) interference

[RBrad]

After many hours of starting out to add a second SI transducer to my trolling motor, I finally determined that the problem existed all along. I just never had used or looked at my transom transducer output while on the trolling motor since I had a smaller 2D unit up there.  Boat is a Skeeter TZX190.

I have the 898 SI unit powered directly to the cranking battery now.  I tried all the numerous grounding tips, ferrite rings, etc.  With just the head unit powered up, with and without a transducer in it, no transducer on the trolling motor (just put it over the side by drives seat), I get interference on the unit display.  For instance even without the transducer, there are interference lines.  I am trying to run at 800 mhz.

From what I have read, this should mean that it is electrical and not RF.  With just the head unit powered, no other inputs.  If I run the trolling motor on full speed, effectively eliminating the PWM, there is slight line of interference at first but then it is clear.  If I run the motor at any other slower speed, effectively now using PWM, the interference stays on.

I am not sure how the PWM interference gets over to the power input on the head unit since everything is separated?  Is there a method to eliminate the PWM?

[rnvinc]

Are your TM batteries and your electronics battery connected with a common onboard charger ... ??

Rickie

[RBrad]

Yes, I have a common 3 battery charger.  Yesterday I tried disconnecting the negative lead on the cranking battery from everything except the head unit but not the positive lead.  I will try to disconnect everything today, that is, just only have the hummingbird head connected to the battery to see if dedicated battery helps.

[bobcoy]

RBRAD, You said you installed ferrite rings. Did you put one Humminbird supplies for free on your transducer cable right next to the connector on the unit? 7 wraps in the ring? RFI in definitely a possibility. Bob
Forgot to mention. Do all your testing while on the water with you trolling motor deployed. Having it in the water kills most of the RFI. Also the 800khz frequency seems to be the most affected frequency.

[RBrad]

I have tried that.  I get the interference without a transducer even being connected into the head.  Power cable only, still can see interference lines on display even without a transducer picture, when operating the trolling motor.

[bobcoy]

rfi induced noise does not need anything attatched. In fact an open input may be more susceptible. I don't know how old your trolling motor is but if it has seen a lot of use the brushes could be worn to the point of creating RFI. Bob

[RBrad]

The trolling motor is around 2 years old, I replaced older Tour 82 analog with newer Tour 82 digital model.

[RBrad]

More info.  I removed all other electrical components from cranking battery, except the head unit.  I had tried a dedicated separate battery earlier in testing with same results.

Still get interference, with and without a transducer attached.  Lines across the display when trolling motor is activated at lower speeds.  Pictures attached, show head unit completely out of the boat, power cord only attached, around twenty feet from trolling motor.  Motor is deployed into the water but boat is on the lift.

Does RFI go thru the airway or follow an electric cord (like an antenna) into the head unit?

I have also tried grounding wire from trolling motor to cranking ground, with and without a grounding cable from trolling motor batteries to cranking battery.

I saw a post on a Basscat forum where the boat manufacturer tried everything, even what I have done here, and never were successful with a boat.

I'm pretty much resigned to there is no solution?

[bobcoy]

RFI is radio frequency interference. It goes through the air. An inducted signal can go short distances (cable to close by cable) power or communication. With the boat on a hoist, unless your big motor is also in the water. Otherwise your grounding system in your boat is not functioning. I did have one more thought, I am sure you have messed with your filter settings, but if not try setting it on high2 or 3 whatever the highest setting is and see what that does for you. I went through a similar situation and was chasing my tail because I had my boat on a hoist while troubleshooting. Gave up and went fishing and my problem was gone. I backtracked and found out it has to be on the water. Good luck in your quest. Bob

[RBrad]

Thanks for the feedback.  When my trolling motor is in the water on hoist, a portion of engine and prop is in the water.  The boat itself does not rest on the water.  Early on in my troubleshooting, when I had everything hooked up (transducer on trolling motor, etc.) I did go out on water and had problems.  I can float the boat out and see if that would help, lot of metal in hoist if that makes any difference.

I have tried all the interference settings from none to high 3, no help.  If you had any other particular implementations of "fixes" that seemed to help, I would like to know what they were.

I see where HB has a TCM-1 choke, that installs on power input to the trolling motor.  Wondering if anyone has tried this and if it would be useful to my situation.

I also have read (dangerous probably) about most larger boats have a RF ground (lead to metal plate on boat in water) that is typically used to help eliminate/prevent/drain  sensitive equipment interference, by providing an earth ground thru water.  I think that is supposed to be accomplished in bass boats thru cranking battery negative to motor in water.  Don't know if that has any usefulness here.

[bobcoy]

I went through humminbird with my initial battle. They started with the TMC-1. It helped some. I then started using my knowledge of electronics(37 years a an electronic tech) did shielding(adhesive backed aluminum for duck work) and separating the motor leads from everything. Some progress then back with HB they sent me stuff. New power cable,transducer. No help. I tried radio shack chokes on the transducer cable. Small improvement. Then requested The HB ferrite ring. It made a big difference. 455khz was almost free of noise. 800khz was still bad. At that point I was going to call it good as 800 has very little use in my deep water anyway. Like I said went fishing and my problem disappeared. Bob

[RBrad]

Update.
I saw a lot of pictures of grounding a trolling motor of wires attached to the clamp holding the transducer.  The actual fix usually says to drill a small hole in like the fin of the trolling motor and use a self tapping screw.  I saw a post on another site that mentioned to make sure the trolling motor attachment area is free of paint and down to bare metal.  That sort of made the "light bulb go off", as drilling and using a screw gets you inside to bare metal.  The WHY is usually missing from explanations of using the screw into drilled hole but some, like me, try testing other attachments before actually drilling the motor. 
So I did the drilling and also scrapped paint off around the hole to get to bare metal, used a self tapping screw and a round terminal end on the attachment wire.  Then I attached the other end to the negative trolling motor lead inside the bow of the boat.  This helped reduce the RFI from the motor.
Then I tested moving the transducer, not attached, moving it close to and then away from the trolling motor.  I was seeing conductive interference the closer I got to the motor.  HB had sent the ferrite ring so I was able to get 4 or 5 wraps of the transducer cable in it.  That helped reduce the transducer interference.

Where I ended up is that I run SI on the trolling motor at 455mhz OK, but still get interference on the higher 800mhz.  This is evidently the hardest to ever get clear based on a lot of posts I have read.

That's where I think I will leave it for now.  So now I have a transom and trolling motor transducer connected thru a HB TS3 switch, so I can switch.  I put a small LCD monitor fed by video out from the head unit up by the trolling motor.  I have to set the head unit to the display I want before going to the trolling motor, but saves a lot of money from buying two head units.

[bobcoy]

Way to go!

[rnvinc]

RFI is a beast sometimes ...

I finally cleared the rest of mine up by changing my TM power wires all the way to the TM batteries with tinned multistrand marine grade wire ... 

The cheap wire I installed to power my TM was allowing excessive amounts of RFI out of the TM power circuit evidently ...

Go figure ...

Rickie