Flyback EMF diodes

Maker, DIY
1

Hello, I am looking for a directional diode to install across the +/- terminals inside of my Motorguide xi3 trolling motor where the wires connect to the brushes plate. My purpose for this is to hopefully help decrease flyback EMI created by the rapid PWM switching of the motor speed controller. The flyback EMI is creating excessive screen interference on my sonar units. The trolling motor is a 24v dc. The PWM is operating in the 22-44 khz range. The motor does require a 50 amp breaker for the main power. However, in the case of this particular diode SB560 it indicates 5.0A IF(AV) and 220A IF(SM). I do have not an electronics background so I am hoping you can help me with this. Thanks for your help, Ronnie Wetherington

Chosen category: MakerDiy

Part number(s): SB560

2

Hi ronnie3945,

Welcome to the TechForum.

Before one tries to get inside the unit to mitigate EMI, it’s important to consider some external issues that could affect the interaction between your motor and the sonar system.

Have you checked out their interference trouble shooting info at this URL?

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Here is what they post there:

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Regarding point number 6:

Here’s a link to some of our clamp-on ferrites to help mitigate EMI issues. Passing a cable through one of these will help reduce EMI from conducting down the line, and if you can loop the cable through the ferrite twice, it will reduce the EMI even more.

I would suggest following their recommendations regarding adjusting sonar sensitivity, routing of cables, and possibly separating power sources before anything else, as these are non-invasive and have minimal cost associated with them. Then, one might consider other measures such as adding ferrites or other measures.

1 Like
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I have tried everything you suggested, anyone on the internet has suggested, contacted Motorguide and two of their certified service members. I have a well documented list of trial suggestions and their results.

Things tried to clear front and rear echomaps 2D Sonar interference:

  1. Ran 18’ dedicated shielded 14 gauge wire from starting battery terminals directly to bow fish finder.
  2. Soldered connections of new shielded wire and factory power cable.
  3. Sealed with heat shrink.
  4. Attached wire shield to negative starting battery terminal as recommended.
  5. Installed ferrite choke on front unit transducer cable with loop in cable.
  6. Installed ferrite choke on front unit power cable.
  7. Installed ferrite choke on rear unit transducer cable with loop in cable.
  8. Installed ferrite choke on rear unit power cable.
  9. Installed ferrite choke on network cable at rear unit.
  10. Added a plastic spacer between transducer and motor housing to increase gap by about 1/2" hoping to reduce interference.
  11. ITEMS 1-10 ONLY HELPED MINIMALLY IF AT ALL!
  12. Increased spacer to 1" to further increase gap.
  13. Wrapped trolling motor lower unit with copper foil tape to hopefully help shield interference.
  14. Foil tape did not help with transducer mounted on motor.
  15. Removing transducer from motor unit, increasing distance between motor and transducer 24 inches or more did help during brief out of water testing. Screen interference was somewhat clearer at 80+ gain. Seemed this was a positive sign.
  16. Reinstalled transducer on motor to conduct water test. Interference was still highly visible during water testing. (Was this an indication of a common ground connection) Disconnected network cable from rear unit to verify if interference was only coming through front fish finder. Interference was visible with units separated from each other!
  17. Removed transducer from trolling motor and mounted on a temporary bracket approximately 4 ft from motor. Interference was still visible especially on 2D at above 70% gain! Water seemed to increase problem. Why? Conductive interference?
  18. Removed 6 awg marine grade trolling motor battery cables. Cut off excess 24" of unnecessary leads. Twisted wires together about 6 times per foot as was suggested online to help EMI by making one line cancel the others signal. Sealed leads in conductive copper and aluminum foil tape. Attached copper shielding to negative battery terminal on first battery of 24 Volt system.
  19. Ran a dedicated ground wire from trolling motor skeg to negative battery terminal on starting motor/fish finders battery. Also ran a ground wire from starting battery negative terminal to same negative battery terminal of first battery in 24 Volt system that power cables shielding is grounded to. No improvement! REMOVED!
  20. Removed front transducer cable and arranged excess wire in a figure 8 instead of looping as recommended online to help reduce EMI. No improvement
  21. Removed foil tape shielding from trolling motor lower unit housing. Reinstalled transducer back onto motor without foil shielding or pvc spacer.
  22. Conducted out of water testing to verify any improvements. 2D still has significant interference when gain is increased above 80% even with Interference and TVG adjusted to High settings.
  23. Rearranged transducer and power cable wires to rear fish finder to increase distance between transducer cable and power cable. (Pulled transducer cable out of boat. Ran cable through 5/8" section of water hose. Inserted hose and cable back through upper gunnel area to increase space between power and transducer cable. Rearranged wires from gunnel out to fish finder to increase space between wires going to fish finder power cradle.) No Noticeable improvement in 2D.
  24. Rearranged transducer, data, and power cables to front fish finder. (Increased distance between where wires exited bow under switch panel to approximately 2.5" between each wire. Separated wires going to front power cradle.)
  25. Ran out of water interference test. Scanned wiring, trolling motor head, shaft and lower unit with EMF meter. Wiring from 24 Volt batteries to trolling motor receptacle, plug and motor head were good.
  26. NOTE: There were high EMF readings, (possibly from PWM) at top of head unit, along shaft and at lower unit barrel out to a distance of 30-48". Readings also high along transducer cable through bow mount to fish finder. +1500uT
  27. Scanned starting battery, wiring up to rear fish finder. Readings were much lower! -10uT
  28. Ran another on water test. Rear unit was clearer on 2D sonar at/above 90% gain. Front unit still showed same levels of interference as before with gain at 68-70% and above which do coincide with high EMF readings at PWM controller.
  29. After returning home rescanned trolling motor wires and all of motor, readings still high as before in in all places.
  30. Removed transducer and cable from trolling motor. Ran EMF scan on transducer while holding TD and extending out approximately 30". EMF readings steadily decreased as transducer was moved away from motor down to under 20uT
  31. Moved transducer back towards motor and readings increased proportionately. 1500uT
  32. Moved transducer around to starboard side and monitored EMF on transducer while relocating. Readings remained low during and after relocating. -20uT
  33. Completed relocation of transducer onto portable/removable mount on starboard side. Distance between transducer and trolling motor approximately 48"+. Readings remained very low on meter during out of water testing. -10uT
  34. Conducted on water testing. Rear fish finder 2D Sonar screen showed minimal interference with gain at/above 90%. Front fish finder still showing interference at/above 65-75% gain.
  35. Called Motorguide and talked to Jerry in customer service. He indicated there were usually a couple of primary causes with the main issue being some form of common ground connection in the wiring systems. After some discussions about this, I did indicate I had run a ground wire from trolling motor skeg back to negative starting battery terminal and also connected to the negative terminal of the first battery in the 24v pair. I also mentioned having tried disconnecting this extra ground wire from the batteries while testing without seeing any noticeable changes either way. Based on past experiences, Jerry felt like there must still be a common ground connection in the system somewhere? I wasn’t aware of any other grounds linking the two systems but couldn’t rule out the possibilities without digging deeper into the wiring since the previous owner had wired the live well aerator, bilge pump and radio to the first 12v battery of the 24v pair. After our conversation , I began dissecting the dash wiring to look for issues. Initially found radio connected to positive wire of original boat harness accessories switch. Radio negative wire was connected to original ignition system ground wire from dash panel to outboardmotor battery negative terminal. Upon further investigation, a negative wire from the first battery of the 24v system was also connected with the negative wire of the ignition switch harness for the outboard motor. The wiring was very confusing. To resolve some of potential common grounding issues, I disconnected the joint connection between first 12v battery of 24v system and starting battery. Next, I reconnected the original harness negative wire to the starting battery - terminal.
  36. Tested for ohms readings between 12 and 24v systems. No readings found.
  37. Performed on water test. Rear unit was clear on 2D sonar at 90% gain on Chirp. Front unit still showing high level interference. Tried adjusting gain between 65%-90%. Less interference lower range 65-70% Tried adjusting cone angle from 16°-24°. Least interference at 18° around #5 speed.
  38. Performed another on water test using the UHD head unit trying to see if UHD could provide a clearer 2D Sonar image using lower or no Interference and TVG settings. Results were still the same. High screen interference unless the gain was reduced below 70%. This low gain setting won’t allow visually sèeing a bait vertical jigging over a school of fish or structure.
  39. Ran a frequency test on PWM CONTROLLER. Frequencies ran from 25.4 to 42.19 khz. On speed 10 frequency dropped to 0 khz and interference clears up tremendously.
  40. Talked to Jerry at motorguide. He suggested checking wiring under head cover for proper routing and spacing of +&- wires (to/from motor control module) and GPS module cable. There had been some interference issues associated with this in past.
  41. Checked head unit wiring. Made some spacing adjustments.
  42. Removed motor control module cover. Added a ferrite choke around +/- cables from PWM to head unit that has been implemented on Minnkota Terrova to help reduce EMI on Humminbird fish finders. No improvement!
  43. Found another potential common ground while reconnecting power to radio. To gain access to radio wires I removed bilge pump switch from dash. It was powered by the first 12v battery in the 24v trolling motor pair. There was a wire connected to positive side of switch supplying power to cigarette lighter. The lighter ground wire was connected to ignition switch harness. I removed lighter wiring and attached + radio wire to the + wire from trolling motor battery side.
  44. Did on water test. Interference was bad on both units on 2D sonar and some visible Interference on Clearvu and Sidevu. Removed ferrite from PWM controller wires to motor head unit. Added a toroidal ferrite choke to front transducer cable. Wrapped the cable 4 times in one direction then up over around 4 times in opposite direction. Did another ground and voltage check between starting battery + terminal and all four terminals of 24v batteries. Initial readings were 12.4 volts. Disconnected/removed +/- battery leads from first 12v battery in 24v system used to create auxiliary power on starboard side. Added new +/- wires from starting battery to old auxiliary terminal strips to power bilge pump, radio and dash. Rechecked voltage between starting and trolling battery terminals. Readings less than .5v initially. Turned on radio and voltage increased to around 6v. Not sure what’s still connected?
  45. Removed radio & found there was no direct ground wire connected from the starting battery. Radio was grounded through the metal dash plate. Not sure how/why or if anything else is connected to dash plate supplying the ground circuit. (Metal dash plate was found to be grounded to the outboard motor via the steering cable and the helm mounting base. Isolated the helm from dash plate using nylon washers and rubber electrical tape on any contact points.)Insulated radio mount bracket with rubber electrical tape. Ran new dedicated +/- wires from starting battery auxiliary strips to radio, reinstalled radio and tested. Checked voltage again between 12v battery + & - terminals and all 24v system terminals. There is still a low voltage of 0.3 to 0.38 present between trolling and starting battery. Checked ohms between both battery sets. No ohms readings were found.
  46. Need to check ohms between dash plate and both sets of batteries for continuity to see if there may be a source of common ground .
  47. Checked ohms between dash plate and 12v starting battery terminals. Very low to 0 ohms. Checked ohms between dash plate and 24v battery terminals. Very low to 0 of 24v batteries still reading less than 0.3 voltage???
  48. Reconnected cigarette lighter to radio supply wire. Main supply wire has 10 amp fuse. Radio has 3 amp.
  49. Made a toroidal ferrite choke with 8 wraps total. Four wraps in opposite direction. Installed on transducer cable. Questionable improvements?
  50. Made a second toroidal ferrite choke with 12 wraps for power cable. Did on water test. Interference was still visible at above 70% gain.
  51. Disconnected all wires from starting battery that also supply power to fish finders. Reconnected fish finders to battery. Conducted another in water test. NO IMPROVEMENTS OR CHANGES SEEN ON 2D SONAR ABOVE 70%.
  52. Relocated ground and hot wires from starting battery terminals for all 12v gauges, accessories and fish finders to individual + & - buss barrs to reduce stacking of wire rings on battery terminals in hopes of creating better quality current flows.
  53. Added 4 ferrite chokes onto motor leads inside of motor shaft approximately 2 inches above brush plate.
  54. Installed a section of 1/2" EMT electrical conduit from top of ferrite chokes at bottom of shaft joint to motor housing.
  55. Rescanned EMF readings on every part of trolling motor starting at batteries, traced along +/- cables to plug, through along trolling motor PWM circuit, cables from PWM to head unit, along shaft to lower unit and all sides of lower unit. Readings of 35-45 uT micro Tesla range were present and common up to the trolling motor lower unit. The readings increased from the previous averages up to a maximum of 450 uT on the bottom side of stator housing. These readings were checked with the motor both connected to 24v power and running at various speeds as well as disconnected from power completely.
  56. Scanned all power, transducer cables, Garmin Echomap mounting bases, network cable front to rear fish finder and power cables from main starting battery to Garmin units. All parts and pieces scanned in the 30-55 uT micro Tesla range well below the Motorguide XI3 stator housing.

Trolling motor can be heard running through the boats AM radio at various frequencies:
AM 580 khz sounds very clear
AM 1160 khz can hear but not as clear.

So, I believe I have tried every viable option with exception of trying to install a second flyback diode across the main +/- terminals connected to brush plate inside of the motor housing.

Please share your ideas. Please do not share sarcastic comments.

Thanks