Voltage between batteries and aluminum hull

[Riley1840]

Was putting cover caps on batt terminals when I discovered there is voltage between batt pos and hull. See pictures. I don’t feel a shock if I touch POs terminal and hull but ohm meter shows batt voltage. Maybe since motor is grounded and is bolted thru hull this could explain. Or do I have a problem?

 

[dingbat]

Was putting cover caps on batt terminals when I discovered there is voltage between batt pos and hull. See pictures. I don’t feel a shock if I touch POs terminal and hull but ohm meter shows batt voltage. Maybe since motor is grounded and is bolted thru hull this could explain. Or do I have a problem?

You have a problem......

The hull should not be tied to ground

 

[Riley1840]

Kinda of what I thought, but so far have not found a ground to hull. Except for OB which ic grounded and then thru bolted to transom.

 

[airshot]

Have the same issue, been thru everything, only ground is thru the outboard motor. I added a cutoff switch for piece of mind on both battery terminals. It has not caused an issue for me, no sign of any corrosion at all. My boat is a 1992, all aluminum transom, no wood, not sure if that has anything to do with this or not.

 

[cyclops222]

The METAL frame of the starter motor is battery minus voltage.
Evinrude uses the motor frame as the _ negative part of the charging rectifier circuit to the battery - minus.

 

[airshot]

The METAL frame of the starter motor is battery minus voltage.
Evinrude uses the motor frame as the _ negative part of the charging rectifier circuit to the battery - minus.

What about Mercs? I have been thru all the wiring, nothing is grounded to the hull ! Has to be the motor. Not sure anything can be done about it and no issues, appears to have been that way since 1992....

 

[dingbat]

You need to find the ground path….

Disconnect the “boat” ground cable from the battery and test again. If you still have continuity, the motor is grounded to the hull.

If this is the case, it’s not ideal but whatever you do don’t use the hull as a grounding point. All circuit grounds must be tied back to the negative post on the battery. Otherwise you’ll end up with different ground potentials and set yourself up for electrolysis

If you don’t have continuity with the motor, the “boat” ground is grounded to the hull somewhere. It needs located and removed to prevent electrolysis

 

[Riley1840]

Update spend two days tracing grounds none are grounded to hull. Only way to get o volts between batt. POs and hull is by disconnecting batt neg from motor. So as airshot and cyclops222 say must be the motor grounding to hull. As I said earlier can’t feel any power when touching batt POs and hull at same time.

 

[Alumarine]

Update spend two days tracing grounds none are grounded to hull. Only way to get o volts between batt. POs and hull is by disconnecting batt neg from motor. So as airshot and cyclops222 say must be the motor grounding to hull. As I said earlier can’t feel any power when touching batt POs and hull at same time.

You won't feel power touching battery + and hull.
Just like you won't if you touched the + and - terminals on the battery.
It has to overcome the resistance in your skin.
In theory it's possible, but unlikely.

 

[airshot]

On my boat, it is the house battery where you get voltage between the battery and hull, nothing from the start battery nor the trolling motor batteries.

 

[dingbat]

Update spend two days tracing grounds none are grounded to hull.

For future reference, you could have quickly eliminated the electrical harness as the source of the problem. Remove the ground cable from battery then check for continuity between the cable and the hull. No continuity, no ground leak.

 

[Riley1840]

But only when engine cable was removed. Removing any other had no effect.

 

[cyclops222]

You do sound safe enough.