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 Electricians? Stray current- Conclusion

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T O P I C    R E V I E W
pdecat Posted - Jan 20 2007 : 13:50:30
I seem to have a stray current problem. New paint was removed in two months from props and shafts and the hull area near the shafts.
The problem could be on the boat or dock. How do I measure for stray current in the dock wires and boat? I realize that the 240V 4 wire system green wire should be earth ground but how would I measure for any voltage on a grounded wire??
I am particularly interested in positively identifying the cause before doing the usual clean everything routine.
44   L A T E S T    R E P L I E S    (Newest First)
GilligansIsland Posted - Jul 17 2014 : 16:18:02
I don't think I'm over zinked. I have the prop and transom zinc plus one on each tab. That's how my last one was and it was fine.

I took some more readings today and I'm within the recommended levels according to the chart. I will look into aluminum next year also.

Has anyone ever taken all the anodes off and then taken the readings? I may do that when I have time one day to see exactly what my zincs are doing.
foggysail Posted - Jul 17 2014 : 10:34:31
quote:
Originally posted by GilligansIsland

Thanks for the explanation. I understand the overprotected problem and think I found my leak. I'll do some more testing tomorrow just to verify consistent readings.

I am getting a reading of -1.00 on just the zinks but will verify that as well. Now, you bring up an interesting point... I'm assuming that the chart that came with the half cell is taking into account the -1.00 (or -1.05) reading produced by the cell and zinks when it says my safe range on a fiberglass boat with aluminum outdrive is -.850 to -1.100. Now, if I also have to add my base reading to that, I will be overprotected. But the kit does not say to do that. What do you think?

I bought this one...
http://boatzincs.com/corrosion-reference-electrode-specs.html



Could it be that you have too many zincs? Before I looked into galvanic corrosion I followed the herd, added zincs every where. Two each on each prop shaft, two on each rudder, two on each SS tab plus a diver's plate. What a waste of money!


Today I use ONLY ONE ANODE and it is NOT ZINC! I use a diver's plate aluminum anode mounted the transom AND THAT IS IT! I did install my self made shaft brushes to replace useless shaft anodes that seem to last about a month before falling off.

Now one is foolish to do what I did without taking the effort to measure the bonding voltages on the critical metals immersed in salt water. For that job I was lucky to find a silver silver chloride half cell, new-- never used on EBay delivered for $40 that was a part of some company's expensive equipment for taking commercial measurements.

All my measurements are in the -0.75v or so range which is just fine. The beauty of aluminum alloy (Mil-A-24779) is that it is about 1/2 the cost of zinc, has a slightly higher self voltage, -1.1v, lasts much longer than zinc because it has a higher electron capability and finally it can be used in either fresh or salt water. You should think about aluminum!
Billylll Posted - Jul 17 2014 : 05:07:01
Thanks Foggy for the link and explanation.
Bill
GilligansIsland Posted - Jul 16 2014 : 21:26:13
Thanks for the explanation. I understand the overprotected problem and think I found my leak. I'll do some more testing tomorrow just to verify consistent readings.

I am getting a reading of -1.00 on just the zinks but will verify that as well. Now, you bring up an interesting point... I'm assuming that the chart that came with the half cell is taking into account the -1.00 (or -1.05) reading produced by the cell and zinks when it says my safe range on a fiberglass boat with aluminum outdrive is -.850 to -1.100. Now, if I also have to add my base reading to that, I will be overprotected. But the kit does not say to do that. What do you think?

I bought this one...
http://boatzincs.com/corrosion-reference-electrode-specs.html
foggysail Posted - Jul 16 2014 : 20:48:43
A silver silver chloride half cell develops a -0.199 voltage when immersed in seawater. Zinc develops -0.76 volts when it is immersed in seawater. Both the zinc and the silver stuff function individually as half bridge.

Typically they are shown with each metal in a separate glass containers connected with a salt bridge. Now on a boat the zinc is in teh water along with the half cell. So placing a silver silver half cell or for that matter or other metals (but different voltages) and then measuring the voltage between them.........in this case it would be between the attached silver silver chloride half cell and the boat's bonding or any place that is attached to the bonding system that is also sharing the salt water.

Now lets get to measuring zinc! The voltage between the zinc and the half cell will be zinc's -0.76 volts and the half cell's -0.199 volts. Voltage measured is |0.199| + |0.76| = |1.059| volts. In my above post I simply took the first three digits, 1.05 volts.

This should not be complicated. Take the reading, record them. Check the self voltages for the various metals your boat has in the water. Add the half cell's voltage to those of the concerned metals. As long as the readings are LESS positive than the sum of the half cell's voltage plus that of the concerned metals, you should be OK.

Now this even gets easier if you instead use the tables that show the metal voltages that were read using YOUR particular type of half cell. Your readings then just need to be less positive than those shown in the tables. And for the questions about over protection..... take the effort to read the attached paragraph or even better, check out the URL

The paragraph below PERTAINING TO OVER PROTECTION is copied from Crawley Advisor

http://crowleysyachtyard.blogspot.com/2013/05/marine-corrosion-part-2.html

"You may think that over protected is ok, but unfortunately, being over protected has its own set of problems. Under water coatings can be literarily blown off the bottom by gas bubbles forming on the surface of the metal. Also, an alkali solution can form on aluminum which will eat into the metal. Neither of these issues are good and their symptoms can look like galvanic corrosion. The reason we use precise alloys for our reference cell and a volt meter that is accurate measuring 10s of millivolts is so that we can know what is going on with the boat, not make guesses, nor assume that the dock chat about corrosion is correct."
GilligansIsland Posted - Jul 16 2014 : 18:06:39
Thanks. I have a fiberglass hull with aluminum outdrive and Zinc anodes.

According to the chart the reference anode (silver-silver/chloride) came with a proper reading should be between -.850 and -1.100. A more positive reading indicates under protected and a more negative one indicates over protection.

I'm not showing a more neg reading with the charger on by 7mv more negative - not sure what that means.

I did find a loose wire on the charger which helped my readings.

...still trying to learn


***apparently having to much sacrificial anode cause other problems, like paint be blown off the drive and exposing the aluminum.
Billylll Posted - Jul 16 2014 : 17:51:14
Can you explain over protection?
Thanks,
Bill
foggysail Posted - Jul 16 2014 : 05:26:02
quote:
Originally posted by GilligansIsland

This thread may be dead, but I'll post anyway and hope it comes alive.

I picked up the Silver Silver/Chloride reference unit from Boatzincs.com and did some testing. In testing the Bonding strip and Engine Block, It appears that my battery charger may be the culprit but I'm a little confused... when the charger is charging I'm getting a reading of just over 30 millivolts more negative. That is, if my base reading is -1.036 with the charger off, it is reading -1.060 with the charger on. Does that make sense in terms of creating a corrosion issue?




You have two issues. The first is why there is a change when the battery charger is energized and the second is that you may be over protected. Zinc by itself read with a silver-silver half cell should read -1.05 and I am presuming you are using zinc and not magnesium.

Be careful about over protecting, it can cause problems.

I would expect readings around -0.75 volts maximum. For example, if you are reading over -0.8 on your shafts with bronze props attached, those props are over protected. JMHO!


GilligansIsland Posted - Jul 14 2014 : 18:40:29
This thread may be dead, but I'll post anyway and hope it comes alive.

I picked up the Silver Silver/Chloride reference unit from Boatzincs.com and did some testing. In testing the Bonding strip and Engine Block, It appears that my battery charger may be the culprit but I'm a little confused... when the charger is charging I'm getting a reading of just over 30 millivolts more negative. That is, if my base reading is -1.036 with the charger off, it is reading -1.060 with the charger on. Does that make sense in terms of creating a corrosion issue?
Capt. Bill1 Posted - Jul 06 2014 : 10:39:49
quote:
Originally posted by pdecat

Extra bond wires were simple. 14GA tinned stranded green wire from HD. they didnít have 10GA which the boat maker used, oh well. HD also had marine quality ( silver or tinned ?) crimp on eye connectors. I used those twisted edge washers instead of split lock washers for better electrical contact. Bolted new wire to the new brushes and tomorrow Iíll ad another wire to the engine direct to the buss bar.



I hate to say it it those bonding wires should have been at least #8 wire.

GilligansIsland Posted - Jul 06 2014 : 09:09:04
I know this is an old thread, but it's a great one - I'm fighting massive corrosion right now so hopefully you guys won't mind helping a newb...

When checking the reading at the block, what probes your you holding where?... yes, I'm electrically challenged but am very mechanical and hope I can learn this process.

Thanks in advance.


quote:
Originally posted by divedaddy

Okay, maybe I am confused. If I understand (not sure I do) the engine block which should be at ground is reading +0.2V above ground and the shaft is reading +0.6V ? If that's right it sure sounds to me like you have a faulty ground connection somewhere on that engine/shaft side. If the connections were sound it should be at zero volts. There is a 0.4 V difference between engine and shaft, and shaft brushes may help that, but that doesn't explain the +0.2V on the engine.

I am guessing you have more than one grounding bus or bonding strip that tie back to a main or central bonding strip. Have you tried that measurement at different reference points - like a negative battery terminal? Have you checked for voltage differences between the various grounding points / bonding strips?

Check you PM's.

Babyboomer02 Posted - Feb 01 2007 : 16:04:01
GOOD READ
http://www.boatus.com/seaworthy/galvanic/default.asp
pdecat Posted - Feb 01 2007 : 09:01:05
I think I am finished, after receiving a lot of information and advice from several folks but especially Divedaddy and GVP and Wayne Alexander I will have to wait for the divers reports on new paint after a few months. The only problems I found were four unbounded sea strainers and no brushes on the shafts. GVP explained that shaft flange couplings can build up resistance where none was previously through rust.
The mystery voltage at the dock power ground is probably the result of using the alligator clamps I was using to hold the test metals in the water. A careful look at the silver chloride cells shows that everything is well insulated except for the test metal. The voltage varied up to .5V but I discovered that by keeping the clip out of the water and trying Zinc, SS and copper as the electrode that the readings did were different for each metal. My conclusion is that the clip was overpowering the metals when everything g was submerged and creating a couple with the copper house ground rod.

The other interesting point is that CorrosionPro stuff that I spray on everything is an excellent insulator. I was puzzled over poor conduction readings on the newly bonded strainers until I filed down the surfaces to bright metal. The CorrosionPro actually prevented the meter probe from making electrical contact despite scraping and heavy pressure. Perhaps a sharper probe would have worked but Corrosion Pro is impressive. Sure wish I could find it again around here but now I have some CRC stuff and Boshield. I hope they are as good.

After all was done I measured .6V across the zinc saver so it must be doing its job of blocking the DC. Today the boat gets hauled and paint repaired then weíll see.
Ed Dippel Posted - Jan 24 2007 : 08:22:40
Good work.

I disconnected and sandpapered all of my engine and battery connections. I also coated them with dielectric grease from an automotive store to slow future corrosion. This got my disappearing zincs under control. I highly recommend the Nigel Calder book.....that Dive Daddy mentions. He talks about measuring the voltage between the negative battery post and the disconnected negative cable. Remove direct wired bilge pumps one at a time looking for voltage changes. Then disconnect one terminal at a time on the negative buss until the offending circuit is found. Disconnect shore power and make sure genrator is off before starting.

If you are baffled by a stray current problem also consider taking a measurement away from your slip. Sometimes your neighbor's boat is helping the problem!

Good hunting.
pdecat Posted - Jan 23 2007 : 18:06:52
Extra bond wires were simple. 14GA tinned stranded green wire from HD. they didnít have 10GA which the boat maker used, oh well. HD also had marine quality ( silver or tinned ?) crimp on eye connectors. I used those twisted edge washers instead of split lock washers for better electrical contact. Bolted new wire to the new brushes and tomorrow Iíll ad another wire to the engine direct to the buss bar.
navman Posted - Jan 23 2007 : 17:54:34
pdecat, Nice.
When ya get the time can you explain more about adding more bond wires. I would not mind seeing zero myself.
Thanks
divedaddy Posted - Jan 23 2007 : 17:50:19
Cool! Nice work.
pdecat Posted - Jan 23 2007 : 17:46:33
Installed shaft brushes and more bond wires today everything measures zero. Tomorrow I'll start from scratch, measure everything everywhere again, and see what's up but since the problem was props etc I am a bit more confidant.
pogybait Posted - Jan 23 2007 : 17:17:02
Thankyou Navman,Pogybait
pdecat Posted - Jan 23 2007 : 13:26:36
right, so the connection must be bad. I am just going to add a new connection as the original is in a very difficult location.
divedaddy Posted - Jan 23 2007 : 09:07:19
quote:
Originally posted by pdecat

Well, I know couple of things. The voltage is not supposed to be there, and there is some resistance between the other stuff and the engines, also the voltage is in the range of what would be produced by freely eroding stuff relative to the zinc bonding system. Shaft brushes will eliminate that voltage and since everything is supposed to be wired together that is a start. Since the paint problem is associated with the parts that have this voltage thatís where I am going to start.



I would encourage you to find the reason for the errant ground connection first. If the engine block that reads +0.2V is well connected to the bonding strip you used as a reference, then there should be no voltage difference even if you have a galvanic problem.
divedaddy Posted - Jan 23 2007 : 09:00:34
nav,

That's pretty much why the reference half cell is used. It provides a fixed point of reference (if it's a good half cell)independent of the boats ground point. With that, you can do exactly as you say - test for potential differences relative to the half cell potential.

One of the better ways to use it when probing for a galvanic corrosion problem is to disconnect everything from a bonding strip with all switches off, measure the potential, then systematically reconnect each bonding wire one at a time and remeasure. The change should be no more than a few millivolts - about 10.

Looking for a stray current is a bit of a different beast. Finding a voltage difference from ground when it should be at ground tells you there is a problem in a connection or a broken ground path somehwere, but it doesn't tell you what the path is. For that you need to start looking for currents. If there is a stray DC current you should be able to find the arm by using a multimeter in current mode placed between the positive of a battery and the battery cable - all breakers and switches off. Current should be zero, unless a bilge pump or stereo or something running on the battery side. If that's okay, then turn breakers on one at a time, so long as there is nothing on that circuit turned on current should remain zero. If it doesn't then you go looking on that circuit for a problem.

The brushes are intended to assure that the shaft has a good ground connection, which is typically difficult to achieve through the transmission. An additional element is a simple grounding strap connected to both sides of the coupler - it doesn't even need to be insulated - just a good copper strap across the coupler.
pdecat Posted - Jan 23 2007 : 08:39:31
Well, I know couple of things. The voltage is not supposed to be there, and there is some resistance between the other stuff and the engines, also the voltage is in the range of what would be produced by freely eroding stuff relative to the zinc bonding system. Shaft brushes will eliminate that voltage and since everything is supposed to be wired together that is a start. Since the paint problem is associated with the parts that have this voltage thatís where I am going to start.
navman Posted - Jan 23 2007 : 08:02:13
I believe that is why the marine electrician uses the half cell to water to use as a ground reference, a starting point since the boat no longer has a reliable ground(if that makes since).
Cause he is then also probing ground wiring in engine bay along with block , shafts etc to find current.
Here is a pic of the shaft brushes I installed before the first of the year. They were relatively cheap, I did both shafts for 80 bucks, again this was an electroguard product I bought locally.
Not sure what the brushes are really gonna do for ya if ya have a half volt floating around in your system. The brushes may just be another transfer point to carry the current. The brushes are either connected to your bonding wires, or engine block.
Just for Grins Bruce, disconnect the bonding wire from you engine block and then test your bonding wires somewhere, do a before and after.
Also, if you are running with twin engines-Are they grounded together, say like with a # 2 battery type cable? if not for another test just take a jump cable that you would use to jumper a battery and connect your two engines so you have them grounded together, then test again.
Try a couple different grounds like DD mentioned also, since you do not know for certain where this stray is comming from. Good Luck

divedaddy Posted - Jan 23 2007 : 00:02:32
Okay, maybe I am confused. If I understand (not sure I do) the engine block which should be at ground is reading +0.2V above ground and the shaft is reading +0.6V ? If that's right it sure sounds to me like you have a faulty ground connection somewhere on that engine/shaft side. If the connections were sound it should be at zero volts. There is a 0.4 V difference between engine and shaft, and shaft brushes may help that, but that doesn't explain the +0.2V on the engine.

I am guessing you have more than one grounding bus or bonding strip that tie back to a main or central bonding strip. Have you tried that measurement at different reference points - like a negative battery terminal? Have you checked for voltage differences between the various grounding points / bonding strips?

Check you PM's.
pdecat Posted - Jan 22 2007 : 23:25:52
to the bonding system
divedaddy Posted - Jan 22 2007 : 23:00:52
What's the reference point for those voltages ? You found 0.20V on the engine - relative to what?
pdecat Posted - Jan 22 2007 : 22:47:30
After checking every socket and wire for improper continuity and voltages, I started checking the DC connections as navman suggested. I found a voltage 0.6 on the shafts with everything off. It seems that I have a galvanic problem not stray current as a resistance has developed in the shaft coupling. The engine measures 0.2V while the shaft is higher. This does explain the sudden increase in shaft zinc action. I am going to install shaft brushes.
divedaddy Posted - Jan 22 2007 : 22:43:31
Marinco also has a reference cell - part number 2435, listed for $84 at West. As an electrochemist, I would prefer a silver/silver chloride ref to zinc. If you're in salt water you could also use a clean silver wire.

Calder has a good, systematic "Comprehensive Grounding and Test Procedure" in his Boatowners Mechanical and Electrical Manual. Parts of the test make use of a reference electrode in the water.

Just like troubleshooting a short in a car, it takes time and patience -- much more so far a boat.
navman Posted - Jan 22 2007 : 22:18:55
yup , he found the current path with this set up (except he had a fluke meter) . It worked , he solved my problem. Of course he did not flip it in the water and say there it is, he had to go through all the motions with AC and DC trouble shooting methods. The reference cell is made by electroguard.
divedaddy Posted - Jan 22 2007 : 19:14:43
The voltmeter with a half-cell is a standard electrochemical set-up, just like a pH meter (I'm an electrochemist). The challenge is that if there is continuity, there will always be a reading. The problem is what the reading should be. There are some general reference numbers, but the actual reading will depend upon where you put it in the water, the conductivity of the water, etc. Even a zero reading doesn't mean zero current. If you change the reference half-cell, the reading will change.

The challenge is to find the current path. Basically, it is just like looking for a short circuit in an automobile, except you need to include the AC system and shore power connections.
navman Posted - Jan 22 2007 : 18:43:28
pogybait
Here is the unit for testing, see pic of the zinc that you lower into water. Then use the positive to probe metal components The leads are now long enough to reach about anywhere on the boat.
a close up pix of the zinc half cell that is put into water
divedaddy Posted - Jan 22 2007 : 17:33:00
Bruce,

How are you measuring or determining that you have a leak now?

A suggestion - if you have one it needs to through either the AC circuits, the DC circuits or possibly both. I suggest start simple -- shut down the AC and disconnect all shore power cords, and disconnect all battery negatives. There should now be no leak. Then add back the DC and check again. If no leak, add the AC and check. This will narrow the hunt in the minimum amount of time. If you are clean on DC only but adding AC returns the stray leak, test again with AC connected but All DC disconnected - watch out for battery chargers and the like.

Once you know which side to isolate it should be a matter of isolating the circuit or ground path. An ammeter in line might also be helpful.
navman Posted - Jan 22 2007 : 16:57:05
pogybait

I did not make the DVM, I made up a longer positive test lead cord.
I bought the negative half cell test lead cord along with the DVM at last years Seattle boat show.
The reason I went with a DVM is I can can now use it for multiple problems. If you still would like a pix for a visual of the cord i use and the DVM i can certainly take one and post it here. I just need to make a run to the boat with my camera.
pogybait Posted - Jan 22 2007 : 16:04:00
Navman, could you show a picture of the DVM you made.Pogybait
abdiver Posted - Jan 22 2007 : 14:37:06
Some years back I was vacationing in Tahiti, the island of Moorea. I flew there, but I was staying on Cook's bay which is the popular hangout spot for the cruisers, most of whom are waiting for repair parts to be shipped from where ever they called home.

One of the more interesting situations was a ~45 sail boat that had lost its rudder a couple hundred miles from Tahiti. They were sailing along fine and all of the sudden the rudder just falls off!

They made it to Tahiti using drouges to steer then got a tow into the bay.

Turns out that the problem was an electrical failure in their compass! The compass light essentially lost ground, so the current was seeking an alternate path. That path was down through the steering, through the rudder, across the wet joint to the stuffing box to the ground bonding system.

The 12 volt current slowly ate away at the rudder shaft until it broke.

D. Andrews Posted - Jan 22 2007 : 10:14:43
A while back there was a post from a guy with jet drives that were pretty much ruined by stray current from somewhere, there was a lot of usefull info in that post on how to find and detect strays, might be worth looking at it again, there was a lot of info on meter usage as well.....D.......
GSENT Posted - Jan 21 2007 : 18:28:13
Pdecat,
Remember to disconnect and clean your engine ground wire, (battery cable) from the block. Even if there is no evidence of corrosion from looking at it, there is alot less voltage drop once cleaned. I like to secure the connection, than paint it with black paint to seal from moisture.
navman Posted - Jan 21 2007 : 11:25:26
AC setting will detect either the 12v or 110v where as the 12 v setting will not detect the AC. Sorry I forgot to mention this.

You might pick this book up at some time also, very good one . Easy read , has diagrams.
Also a section on corrosion /bonding/grounds
It is called:
Boatowners Illustrated Handbook of Wiring
by Charlie Wing
pdecat Posted - Jan 21 2007 : 09:59:54
Thanks Joe, there is at least a clue with the meter instructions. Since the engine block is connected to the bonding system i didnít think there would be any voltage but it wont hurt to check.
JoeBTB Posted - Jan 21 2007 : 08:57:13
Bruce,
From this month's Boating magazine, page 80. Like most Boating articles, the actual helpful part is very minimal, but maybe it will be some help.



navman Posted - Jan 20 2007 : 20:12:15
I was stuck on AC also, I ended up hiring a marine electrician who found it after going through a process of elimination.
He also had a DVM with about a 20 foot neg cord with a zinc half cell that was lowered about a foot into the water. He then took the pos side and placed it on my thru hulls, shafts, engine block, bond wire etc and measured. After checking the AC by shutting it all down , plus removing the cord from the Shore power Kiosk we still had voltage.
That told him to look at 12volt side. We then shut down the 12v stuff one at a time including main breaker and it was still there. So he began to take the neg cable off the batteries, it was then found.
I have since purchased a good DVM and the 20 foot or so Neg half cell cord and have made up a longer pos cord for doing my own testing. I probably test about every three months , just for the sake of it. I am stll paranoid I guess.
His bill was relatively cheap, 2 hours labor. I think I paid him less then 2 hundred bucks if I recall.

PS, I have heard of bilge pump wiring running direct to batteries can cause issues if water is left in bilge and a break in the wiring also.

Original reason for concern:
I could probably ratlle on for another 15 minutes on this because I was PO'd my diver was not checking things closer when I belly ached about my zincs eating up so fast.
I finally talked to him one on one and told him of my concerns to look closer at why my zincs were not lasting.
I think the damage you see to my prop took about 6 months or so. I believe I had around 2.5 volts at the time going thru my engine block and bond wire.
If you recall many of my posts have to do with the problems on my port motor.
Boost/gauge-Stop solonoid etc. Just possible it all started with the stray current?
pdecat Posted - Jan 20 2007 : 19:20:41
Thanks I;ll check those too. How did you find it?? And how can you be certain it is fixed? I have been thinking AC but..........
navman Posted - Jan 20 2007 : 17:57:58
Bruce, a pic of my stray current problem I had a year ago. Had to replace all my thru hulls.
Turned out to be on the 12v side of my boat, just a bad 12v ground.
Since not making the electrical loop , the current went looking for ground. Which it found going thru my engine block and into the bonding wires and out the thru hulls ,down the shaft etc. I now have a good size ground cable connected to both engines, if I ever have a bad ground connection again on a battery it will ground off the other side, I hope.




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