Outboard Grounding

[Capt No Fish]

Hello, I have a few questions about outboard grounding.  I am having an issue with my electronics and interference when the motor is running, as seen on my previous post.  I am working with Garmin and they sent me new power wires, and a transducer to rule those out. In addition I hand held and moved the transducer all over the stern of the boat on both sides of the motor and nothing worked till I held the transducer next to the drivers seat in my aluminum tracker. Replaced the plug which are resistor plugs.  The one thing that everyone keeps mentioning is to check the grounds. So here are my questions.

 

1.  I have a 2019 20 HP Mercury EFI  Model F20ELPT.  I have looked all over the internet and downloaded the manuals. I didn't see anything in the installation section on where the motor ground may be, nor could I find it on the internet.  I can see that there are bonding wires connecting all the metal items together on the motor.  They connect the mounting bracket to the tilt bracket and then mounting bracket to the hydraulic tilt cylinder.  At the lowest point of the mounting bracket it ends up bonded to a bare aluminum anode, which is clean but I took off and sanded everything down anyway to make sure there was a good connection.   Where would the ground wire be?  Is it simply that the block is the bonding buss and by virtue of the block being bolted to the outboard housing and drive shaft be the ground?

 

2.  If I wanted to test or even create my own grounding system to the water. 

---Is it safe to take the negative of the battery and run a wire to a bolt below the water level? 

---If I did something like that would I be creating undo electrolysis  causing my motor to get eating up?

--- Would this cause the battery to discharge while the boat was just sitting in the water.

 

I know there are some good electrical people here and I thank you for your input during my troubleshooting!

[WRB]

Your OB engine is grounded via water.

Your negative cranking battery ground is connected to the OB engine ground directly, use that battery post for your electronics ground.

Tom

PS, the bare metal plate on the OB lower unit is zinc a sacrificial metal to prevent electrolysis attacking the aluminum OB parts.

[TnRiver46]

I’ve got a merc EFI

 

the black ignition wire is grounded to the starter

 

then you have ground straps going from top to middle, middle to lower unit, and then to the trim cylinder like you mentioned. One of my ground straps caught on fire and burned thru while the boat was in the parking lot. 

 

@galyonj isolated the problem and found a little nick in my depth finder wire that was touching the hull and causing the ground strap to glow hot, it’s a sacrificial lamb so the motor doesn’t catch fire . I just replaced it with stainless steel picture hanging wire

 

 

[WRB]

Stainless steel wire is a poor choice it’s about 40X less conductive as copper wire.  Use insulated 16 gage stranded copper wire.

Tom

[TnRiver46]

1 hour ago, WRB said:

Stainless steel wire is a poor choice it’s about 40X less conductive as copper wire.  Use insulated 16 gage stranded copper wire.

Tom

It’s what came on there , it stays underwater is why I’m guessing they don’t use copper 

 

the ground straps aren’t designed to carry current the way I understood it, just divert shorts and are a sacrificial lamb so the motor doesn’t catch fire 

 

the negative wire under the cowl that stays dry is thick

copper and grounded to the starter . The straps from upper to middle to lower get wet and are stainless by design. They don’t want to be conductive, they want to stop the energy 

[WRB]

2 different situations. Lower unit Bond strap vs Sonar interference. If your lower unit bond wire burned it wasn’t caused by a sonar ground wire shorting to the aluminum hull. More then likely a loose bond wire connection, the 2 grounds are not directly connected.

Peace,

Tom

[TnRiver46]

Yes two different scenarios, I was just trying to answer the question of where is it grounded since I have a similar model. 

[Capt No Fish]

10 hours ago, TnRiver46 said:

I’ve got a merc EFI

 

the black ignition wire is grounded to the starter

 

then you have ground straps going from top to middle, middle to lower unit, and then to the trim cylinder like you mentioned. One of my ground straps caught on fire and burned thru while the boat was in the parking lot. 

 

@galyonj isolated the problem and found a little nick in my depth finder wire that was touching the hull and causing the ground strap to glow hot, it’s a sacrificial lamb so the motor doesn’t catch fire . I just replaced it with stainless steel picture hanging wire

 

 

Thank TnRiver46.  So this is set up like mine with all what I am calling bonding wires.  I am assuming that if my electronics are using the cranking battery then I have a common ground and shouldn't be getting the interference.

 

23 hours ago, WRB said:

Your OB engine is grounded via water.

Your negative cranking battery ground is connected to the OB engine ground directly, use that battery post for your electronics ground.

Tom

PS, the bare metal plate on the OB lower unit is zinc a sacrificial metal to prevent electrolysis attacking the aluminum OB parts.

Thanks for the input Tom. Since my motor is hooked up to the batteries negative then I am properly grounded.  I am assuming that if my electronics are using the cranking battery then I have a common ground and shouldn't be getting the interference.

 

What about the second question of taking a ground from my battery and running a wire to the same anode to rule out a bad ground.  Would that work for that test or would I be doing harm to my equipment?

[BucksBasser]

On 3/23/2024 at 4:57 PM, Capt No Fish said:

Thank TnRiver46.  So this is set up like mine with all what I am calling bonding wires.  I am assuming that if my electronics are using the cranking battery then I have a common ground and shouldn't be getting the interference.

 

Thanks for the input Tom. Since my motor is hooked up to the batteries negative then I am properly grounded.  I am assuming that if my electronics are using the cranking battery then I have a common ground and shouldn't be getting the interference.

 

What about the second question of taking a ground from my battery and running a wire to the same anode to rule out a bad ground.  Would that work for that test or would I be doing harm to my equipment?

Are there any ferrites on the power cord to the sonar unit?

[Capt No Fish]

On 3/25/2024 at 3:55 PM, BucksBasser said:

Are there any ferrites on the power cord to the sonar unit?

Not on the power cord.  They are on the Transducer cable as provided by Garmin's instructions.

 

I have 100% narrowed it down to something from the motor because I tried a Lawrence unit and it's own battery and still happening.  Below is the image of just when I give throttle.  I have replace the plugs as Tom suggested.  With weather we have been having here in the mid-atlantic over the past week or so I haven't had the opportunity to get out and try that.

 

[BucksBasser]

I'd put one one the power cord of the sonar and another one on the power cable to the motor towards the motor end of the cable.

In fact I'd make sure there was two one the transducer cable.  One towards the transducer and one towards the sonar unit.

 

It's obviously being radiated into the sonar system.

 

As Tom suggested, it's better to identify the source and fix it there.  But sometimes that's elusive and you have to attack where it's getting into the sonar system.

 

 

[TnRiver46]

Seems like mine goes slightly fuzzy when you accelerate, but I get a very clear picture at scanning speed (3-4 mph). I can still see the river bottom at top end but its blurry