Dff3d Grounding - *UPDATE* Interference with Engine Running

[ToddF]

I started getting some interference in the cross section and history screens of my dff3d but mostly in very deep water (over 400 ft). I read up on the torchlight interference and the most common cause being improperly grounded transducer cable. Here are some pictures of how mine is done. Any feedback?

I did not install this so I'm not 100% sure what's under the tape. It feels like the grounding shield is wrapped around the sheath as guide suggests.
It also seems like the electrical tape is over the grounding shield and then the copper tape is over the vinyl tape (not how the install guide suggests).

Side note: The dff3d isn't on its side like picture suggests. I just rotated it to fit as an attachment

 

[jp498]

Electrical tape is not part of the instructions. I would carefully remove the copper wrap hoping to re-use it. Then remove the tape. The braided shield should be under the yellow tape. If it's not, it should be showing. Wrap the braided shield with the copper wrap, and there should also be some drain wire that can wrap under one of the screws.
The only thing I do different than the instructions is to peel back another 1.5" of insulation as it seems the wires a bit short coming out of the transducer cable.

 

[ToddF]

Thanks!

I typed electrical tape but for all I know that yellow tape could be vinyl tape. I thought they were the same thing.

Good idea. I'll try to preserve that copper tape but will bring some extra just in case

When you say the wires a bit short (peel back 1.5" insulation), I'm assuming your talking about the shielding wire? or maybe all the wires?

Also, when you say there should be some drain wire to wrap around one of the screws, can you elaborate any more? Is the drain wire the same as the shield wire below? Are you making it longer to wrap the screws that tighen the clamp?

 

[Titanic II]

The end game is to have the clamping plate in direct contact with the conductive tape which is in direct contact with the shield wire you wrapped around the sheath.

 

[ToddF]

Thank you. that makes sense aad I appreciate the pictures.

 

[ToddF]

Update:

Pulled back the copper tape and then the vinyl tape. The shield wire was under the yellow vinyl tape with zero contact to copper. I'm surprised the unit worked as well as it did with no contact direct metal to metal contact. Rewrapped the shielding wire properly in copper tape and reconnected. Didn't get a chance to use it but at least now I know its done correctly.....I think!
Thanks

 

[Deep Blue]

ToddF,

This is a common installation mistake. When it comes any sensitive multibeam systems, it's very important to have the transducer cabling properly grounded, as to combat any potential noise issues.

I'm glad that you were able to solve it, good luck out there fishing..!

- Deep Blue

 

[ToddF]

Wanted to update this. Got a chance to visit some deep water and check on the DFF3D re grounding work I've done. Bad news is I'm still getting some interference. Good news is I think I can confirm its related to engine interference.

When I'd sit still with engine cut, there was zero interference. It would return when motor was restarted, and as I increased RPM it would get worse.
I really don't see this type of interference in normal fishing depths but only at the out past 400', even with Gain set the same in shallow and deep.

It seems like all signs are pointing to the transducer cable being too close to engine/alternator cables. Does this seem like I'm on the right track?


These are some screen captures showing me going from static boat to 7 knots and the increasing interference.
Rejection levels on TZ and DFF3D both set to High.

 

[Deep Blue]

ToddF,

Yes, that could be one issue. There still could be an issue with the engine's alternator when it's charging the vessel's electrical system as well. I would try to power on your DFF3D completely separated from the vessel's voltage system. Any possibility of powering the DFF3D from an isolated battery..?

- Deep Blue.

 

[jp498]

What kind of engine? If it a diesel, it's probably the alternator. If it's a gasoline engine, I could not narrow it down so fast.
If the alternator is on a belt of it's own, you could pop that belt off see if there is noise with the alternator out of service.

 

[ToddF]

ToddF,

Yes, that could be one issue. There still could be an issue with the engine's alternator when it's charging the vessel's electrical system as well. I would try to power on your DFF3D completely separated from the vessel's voltage system. Any possibility of powering the DFF3D from an isolated battery..?

- Deep Blue.

This might be tricky only because most of the interference is showing only in deeper water. Maybe I can crank up the gain to see if it shows at the dock, separating from the system would be easy there. If not, I'll have to probably find a battery to take with me to deeper water.

 

[ToddF]

What kind of engine? If it a diesel, it's probably the alternator. If it's a gasoline engine, I could not narrow it down so fast.
If the alternator is on a belt of it's own, you could pop that belt off see if there is noise with the alternator out of service.

Single diesel, Yanmar 6lp. Unfortunately the alternator is not on an independent belt. The transducer cable does pass by the side of the engine where the alternator is (stbd side ) and may even share a hole through a bulkhead with the cable coming off the alternator. I'll take some pics and post.

 

[C-Bass]

You can set the range manually at the dock. 600' and crank the gain. If you are on the section view you will see the torch beam. Then its just a matter of finding the source and eliminating. Example below showing noise at the dock.

 

[jp498]

That looks really bad...
Another source of noise related to engines is if you have engine run hydraulics. I've seen the electric clutches get wet & corroded turning their electromagnets into pulsing ignition coils creating pulses of voltage all through everything connected to hydraulics.