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Old 19-09-2016, 13:31   #1
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Stray Current Isolation Testing?

I am now sure my boat is bleeding stray current and I need to isolate and fix the issue. When I bought the boat my single shaft zinc lasted a 6mo season, but the following season the zincs lasted only 3mo and I had to refair my keel due to it corroding. I blamed the marina and installed a galvanic isolator, which didn't help. This year I'm on a mooring and still loosing a pair of shaft zincs in 3 mo. The only electrical changes I've done are a Victron energy battery monitor, and a bilge pump replacement. All the wires are out of the bilge water, save the lead where it enters the pump itself.

Can anyone point me to a procedure that I can use to help isolate where the source of my current leakage is using a multimeter?

BTW, I've lifted the 'ground' wire from the battery negative circuit and tested current/voltage that is 'leaking' into the ground/bonding wire for all DC circuits. all readings in milliamps, a few dozen at most and max 0.15 volt. I was expecting a bigger issue/smoking gun. nope. The PO did a lot half A$$ wiring. so could be a witch hunt. Please point me to salvation or a procedure would do.

thanks
Zach
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Old 19-09-2016, 17:11   #2
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Re: stray current isolation testing?

Is the keel lead? I've seen issues with exposed lead keels causing corrosion issues when bonded to other underwater metals (sail drives for example). The way to approach your problem is to obtain a hull potential meter and start taking readings to see what voltages exist underwater. Turn appliances on/off to see if the measurement changes.
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Old 19-09-2016, 17:47   #3
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Re: stray current isolation testing?

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Originally Posted by boatbod View Post
Is the keel lead? I've seen issues with exposed lead keels causing corrosion issues when bonded to other underwater metals (sail drives for example). The way to approach your problem is to obtain a hull potential meter and start taking readings to see what voltages exist underwater. Turn appliances on/off to see if the measurement changes.
Thanks boatbod. Yes, it is a lead keel, which is bonded to the engine and mast. My through hulls and rudder float. Is this 'hull potential meter' the same as a silver/silver chloride reference probe? Where can I find one at a reasonable price, preferably with a good instruction manual? Is there no way to start from the inside out to see if I'm dumping current into the bilge, prop shaft, etc.?

thanks again
zach
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Old 19-09-2016, 22:02   #4
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Re: stray current isolation testing?

You might disconnect the bonding wires one point at a time and reconnect through a multimeter on the milliamps range to see if you can identify where the current loop is and go from there.
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Old 20-09-2016, 06:52   #5
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Re: stray current isolation testing?

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You might disconnect the bonding wires one point at a time and reconnect through a multimeter on the milliamps range to see if you can identify where the current loop is and go from there.
Thanks RaymondR, let me ensure I understand... My boat has 3 bonding wires. 1 from the negative battery term to engine, 2nd is engine to keel bolt, 3rd keel bolt to mast step. I have disconnected the negative battery lead from the bonding wire and found only a max of ~30 milliamps. I believe you are suggesting I repeat that test at the other 2 connections..? I'm not sure why there would be current in the other 2 if not at the battery, but this electrolysis stuff is like black magic, so I can certainly do that.

Question, I assumed the stray current causing my zinc loss was relatively slow and therefor a constant happening the whole time the boat sits at the mooring. Is it possible that this is a quick thing that is occurring only when a certain item is running, like the engine or a pump? if so, that would change my search strategy.

thanks,
zach
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Old 20-09-2016, 08:48   #6
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Re: stray current isolation testing?

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Old 20-09-2016, 08:51   #7
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Re: stray current isolation testing?

multimeter and a silver silver chloride half cell.


you turn systems on and off and watch the meter
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Old 20-09-2016, 11:54   #8
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Re: stray current isolation testing?

Quote:
Originally Posted by zstine View Post
Thanks RaymondR, let me ensure I understand... My boat has 3 bonding wires. 1 from the negative battery term to engine, 2nd is engine to keel bolt, 3rd keel bolt to mast step. I have disconnected the negative battery lead from the bonding wire and found only a max of ~30 milliamps. I believe you are suggesting I repeat that test at the other 2 connections..? I'm not sure why there would be current in the other 2 if not at the battery, but this electrolysis stuff is like black magic, so I can certainly do that.

Question, I assumed the stray current causing my zinc loss was relatively slow and therefor a constant happening the whole time the boat sits at the mooring. Is it possible that this is a quick thing that is occurring only when a certain item is running, like the engine or a pump? if so, that would change my search strategy.

thanks,
zach
30ma is a fairly hefty amount of current. That's about .75 amp hours each day leaking out. Time to start tracing the wiring.

Boatzincs.com sells a reference electrode for $125, not sure what your budget is and whether it fits the definition of inexpensive.
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Old 20-09-2016, 15:19   #9
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Re: stray current isolation testing?

I would suggest using an analogue test meter only for this job. I would also check alternative sources for stray currents like steel objects under the boat near your shaft anodes.
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Old 20-09-2016, 15:37   #10
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Re: stray current isolation testing?

Yes you need a silver-silver half cell and the corrosion reference work book. Basically measure from the half cell h immersed over the side) to various bonded metals in the boat. 750-950mV is good. Anything less is suspect.
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Old 20-09-2016, 16:11   #11
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Re: Stray Current Isolation Testing?

Does anyone have any experience with this:

Electrolysis

Looks interesting
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Old 20-09-2016, 16:53   #12
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Re: Stray Current Isolation Testing?

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Originally Posted by Yachtmasteroz View Post
Does anyone have any experience with this:

Electrolysis

Looks interesting
Yes.

The purpose of a Galvanic Isolator is to prevent stray DC current from connecting with other boats connected to shore power through the green ground wire on the AC system.

There are 2 ways to do this.

The best way is through an isolation transformer. With a transformer there is no physical connection between the boat's AC system and shore power. DC currents are completely blocked.

The other way is with diodes and there are 2 types, fail safe and not fail safe. The diode method blocks DC current but allows AC current to pass in the case of a fault to ground.

Fail safe systems will connect the AC ground to the shore power ground if the diodes fail.

The other systems do not connect the AC ground when/if the diodes fail. This protects the DC system, but does not protect the AC system if something shorts out.

There are ways around this as Yandina will point out. It is necessary to have an indicator to show that the GI has failed.

The fail safe GIs will be more expensive because it is more expensive to make them.

The Yandina product is better than no GI protection but it needs to be routinely tested to see that it it still allows and AC fault to go to ground.

That's the simple answer.
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Old 20-09-2016, 19:16   #13
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Re: stray current isolation testing?

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Originally Posted by Dave Lochner View Post
30ma is a fairly hefty amount of current. That's about .75 amp hours each day leaking out. Time to start tracing the wiring.

Boatzincs.com sells a reference electrode for $125, not sure what your budget is and whether it fits the definition of inexpensive.
Thanks Dave, I tested the current between the neg batt term and bonding/ground with batteries off, on and each of the DC switches on. The leakage was essentially a percent of the load and was not specific to any system. example, 1.2mA switches off, 3.4mA stereo On, 10mA cabin lights, 29mA Water pressure pump running, everything! running max was 45mA... how do you trace the wiring when all systems leak? BTW, the boat is normally left with only the bilge pump on which reads 1.3mA. I wouldn't think that 0.001amp would cause this... But maybe my issue is a quick depletion while I'm running gear on board and I've been barking up the wrong tree...? I haven't done any testing with the engine on and really have no idea what to look for or where.. any help?

I'm not stoked about $125 test gear, but I think I have to bit the bullet. thanks for the vendor name. I'm just not sure how it will trace the problem to a specific wire or system. I get that it will show what metal parts are protected or not or energized, but I don't see how that gets me to the root cause... anyway, I need a fix so I'm willing to try it.

Quote:
Originally Posted by Yachtmasteroz View Post
Does anyone have any experience with this:

Electrolysis

Looks interesting
I've been through the yandia / galvanic isolator thing. I installed one last year b/c it wasn't too much $$. But this year I'm at a mooring and haven't touched shore power all year. still loosing zinc
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Old 20-09-2016, 20:50   #14
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Re: Stray Current Isolation Testing?

hi Zach!

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Old 20-09-2016, 23:32   #15
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Re: stray current isolation testing?

Quote:
Originally Posted by zstine View Post
Thanks RaymondR, let me ensure I understand... My boat has 3 bonding wires. 1 from the negative battery term to engine, 2nd is engine to keel bolt, 3rd keel bolt to mast step. I have disconnected the negative battery lead from the bonding wire and found only a max of ~30 milliamps. I believe you are suggesting I repeat that test at the other 2 connections..? I'm not sure why there would be current in the other 2 if not at the battery, but this electrolysis stuff is like black magic, so I can certainly do that.

Question, I assumed the stray current causing my zinc loss was relatively slow and therefor a constant happening the whole time the boat sits at the mooring. Is it possible that this is a quick thing that is occurring only when a certain item is running, like the engine or a pump? if so, that would change my search strategy.

thanks,
zach
You are trying to find the source of the electrical current consuming your shaft anode. It could be coming from a source external to the electrical circuit made up of the bonding wiring, the submerged metals bonded and the sea water electrolyte.

The bonding wire from the mast step to the keel bolt is there for lightning protection and should not be the source of any stray current(until you get a lightning strike anyway)

If you have disconnected the battery from the engine and have 30ma flowing through the bonding wire and there are no other connections to the bonding wire and you do not have a flexible coupling between your gear box and the prop shaft you have 30ma current flow through the water between your prop shaft and keel.

This may or may not be excessive depending upon the surface area of the keel exposed to the electrolyte you are floating in, and the metals the keel is constructed from and the nature of the immersion water. Sea water is generally more conductive than fresh.

According to a paper on cathodic protection the current producing potential for zinc is 780 Amp hours/kg of zinc consumed. 780Amphours /.03Amps = 26,000 hours or about 3 years if your shaft anode weighed a kilogram.

Lot of variables.

If you want to ensure the submerged metal parts don't corrode and try to reduce the consumption of your shaft anode I'd go the external anode connected to the bonding route. Go buy a big anode and hang it over the side on a wire which is connected to the bonding system.
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