Electrolysis

[Ray Perry]

I have raised all of the negative cables above ground to the steel hull. I have a multi meter and a digital clamp meter. I have used the 2K and 20K ohms on the multi meter to check the grounding on the negative side. I rectified 4 problems and the multi meter on the two settings show no fault. On the 200K and the 2M settings it shows a fault.
How do I check the positive cables to see if I am getting any stray earth?
Advice would be appreciated.

[goboatingnow]

Originally Posted by Ray Perry

I have raised all of the negative cables above ground to the steel hull. I have a multi meter and a digital clamp meter. I have used the 2K and 20K ohms on the multi meter to check the grounding on the negative side. I rectified 4 problems and the multi meter on the two settings show no fault. On the 200K and the 2M settings it shows a fault.
How do I check the positive cables to see if I am getting any stray earth?
Advice would be appreciated.

You can do the same with the positive side , just disconnect the battery

Note resistance tests are problematic in determining cause as at higher ohms settings you can be injecting tiny currents. Equally you could have insulation breakdown at 12v that you mightn't see

What are you trying to find and fix ?

Dave

[Ray Perry]

Hi Dave,
My zinc blocks are not lasting and I am getting paint bubbles above and below waterline.

[surfmachine]

Hi Ray.
What I did was connect a 12v led, with resistor, from positive bus to the hull.
It glowed brightly, indicating a current leakage to the hull via the negative bus.

Then, disconnected each postive feed from the positive bus in turn until the led went out. Then checked the positive and negative wires to the item.. Found several faults.

Mainly on wiring to the sender units on the motor for temp guage. Also, vhf antenna braid was broken and touching inside of the mast. Tye this?

Cheers from Keith.

[Ray Perry]

Hi Keith,
Thanks very much for advice. Can you give me more info on the LED and size of resistor?

[surfmachine]

How to Wire LED Lights to 12-Volt Auto Wiring | eHow.com

Use a 470 ohm resistor in series on one leg of the led, drill a small hole in the fuse panel and leave the led poking through as a permanent fixture.

How to Wire LED Lights to 12-Volt Auto Wiring | eHow.com

Cheers from Keith.

[Andina Marie]

It is extremely unlikely that your zinc problem is related in any way to the 12 volt system inside the boat. You are tilting at windmills, fixing the wrong problem.

Your first line of defense is a Galvanic Isolator in the ground lead of your shore power connection. It is only a $100 expense and can pay for itself in one year of zinc savings.

Once it is installed, measure the AC voltage across it. The paint bubbles you describe are a symptom of AC leakage that forms bubbles of sodium hypochlorite under the paint. If the AC voltage is greater than about 0.5 volts you need to troubleshoot problems in your AC wiring and add a Galvanic Capacitor across the Galvanic Isolator to bypass the AC current if needed.

Rather than trying to isolate the battery system, there is less chance of DC electrolysis from the battery causing problems if ALL the negative connections are solidly bonded to the hull. That way they have to be at the same voltage as the hull and minimize introducing extra problems.

I lived aboard a steel boat for nearly 15 years, send me an email to tech@yandina.com if you have any questions.