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Old 24-11-2020, 14:39   #1
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DC leak to aluminum hull

Iím curious as to methods and instruments to detect wiring faults where current is carried by the hull rather than the wire.
I prowl around with my multimeter and dive on my hull to check the zincs.
My house is 24 V DC 700 amp hours and not connected to either my main or gen set motors which are 12 volt.
I donít think I have any faults but maybe Iím not using the best method.
I think i understand most of the places one can have issues in the 12 volt system which I plan to redo but Iíd like to hear from the collective expertise on the 24 volt system.
Thanks to all who respond in advance.
Happy trails to you
Mark and his happy manatees
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Old 24-11-2020, 15:02   #2
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Re: DC leak to aluminum hull

Ah, one of the more interesting subjects

This is what you need; it comes with a complete manual: https://www.boatzincs.com/corrosion-...RoCgmsQAvD_BwE
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Old 24-11-2020, 17:35   #3
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Re: DC leak to aluminum hull

Some free information, for pre-purchase study.

ABYC E-2 CATHODIC PROTECTION
http://www.pcmarinesurveys.com/E-2%2...protection.pdf

Corrosion Protection, What Are the Numbers? ~ by Ed Sherman (ABYC Blog)
https://abycinc.org/blogpost/1678504...ion+Protection

A Guide to Understanding Reference Electrode Readings
Readings taken with different reference electrodes can be adjusted to the copper/copper sulfate (Cu/CuSO4), or CSE potential.
https://www.farwestcorrosion.com/med...E-readings.pdf

INSTRUCTIONS FOR ‘SALTY DOGGS’ SILVER-SILVER CHLORIDE REFERENCE ELECTRODE
http://www.shop.saltydoggs.com/media...-Electrode.pdf
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Old 24-11-2020, 19:33   #4
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Re: DC leak to aluminum hull

I guess I need to clarify what Iím trying to find. GordMay post from the ABYC was great (thank you very much!) as I had never seen this discussion before. We are anchored in a fast running river and itís salinity is wide so Iíve seen interesting readings when I borrowed a silver reference cell. Maybe I need a new or better meter and maybe I should buy my own silver cell. Any recommendations for a reasonably priced meter and cell?
Iím pretty sure we have the hull protected.
Itís slathered in epoxy and I donít see any problems with the zincs.
Is there any better way of checking for an electrical leak inside the hull.
Any kind of meter that will check that can be installed.
Or is there something that can be added to the electrical system.
Something like the new battery meters.
Happy trails to you
Mark and his overprotected manatees
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Old 24-11-2020, 20:53   #5
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Re: DC leak to aluminum hull

An electrical leak should register in measurements with the silver chloride cell. The link I supplied has a good one that is reasonably priced.

To check if the hull is isolated from DC negative you can simply use the resistance settings of a multimeter.

So a good multimeter... gets expensive. If you donít need milliAmpere or even microAmpere features you can get a Fluke 117 but Fluke gets very expensive if you want accurate measurements of small currents, which I would get if I were you.

I have chosen the EEVblog meter but that is so hard to find so you can get one without the eevblogbranding because itís now sold as a GreenLee in the US. This meter is the same price as the Fluke 117 but it has much more features like mA and uA and is very high quality as well.

Here is a link: https://www.amazon.com/Greenlee-DM-5...s%2C180&sr=8-7
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Old 24-11-2020, 21:41   #6
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Re: DC leak to aluminum hull

Here are various sources for corrosion reference electrodes

https://www.google.com/search?q=recr...&client=safari

And hereís just one example of an installed type of corrosion monitor

https://www.boatcorrosion.com/product-catalog.php
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Old 24-11-2020, 22:27   #7
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Re: DC leak to aluminum hull

In the industrial space we us an Insulation Resistance Monitor to detect tiny ground faults in ungrounded AC and DC systems. Something like the Bender Iso685. This thing will find tiny leaks in insulation before they actually become faults. It will also set you back several boat bucks, don't know if a cheaper consumer option is available. Would take a little thought as to how it would get installed in a boat system.

Might also investigate the solar space, detecting leaks on high voltage DC systems is required by code, don't know capabilities or whether they are available down at 24V.

Option C is to install a differential current sensor on your positive/negative cable. This is basically a GFCI/RCD/ELCI without the "interrupter" function. They can be done in DC circuits but I haven't played with any so no idea as to cost/accuracy/complications.
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Old 25-11-2020, 02:32   #8
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Re: DC leak to aluminum hull

I presume that your electrical system is isolated from the hull - both positive and negative? If so, you can measure the voltage between the hull and positive, and negative using a low impedance volt meter. your reading should be (for the scientists amongst us) approaching zero.

The 110volt control circuits on the locomotives I worked on had both the positive and negative isolated from the chassis. To check that the system was still isolated from the chassis, we had a switch in series with a lamp connected between the chassis and the positive, and another connected between the chassis and the negative. If the lamp burned with the positive switch closed, then you had a negative to chassis issue. If the lamp burned with the negative switch closed, then you had a positive to chassis issue.

Not sure if this helps you, or not. It is how I understand your query.
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Old 25-11-2020, 05:28   #9
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Re: DC leak to aluminum hull

Quote:
Originally Posted by Manateeman View Post
... I’m pretty sure we have the hull protected.
It’s slathered in epoxy and I don’t see any problems with the zincs...
Paint (epoxy) is not usually considered a reliable electrical insulator, especially under bolt heads, or nuts or washers, or near edges of sheets of metal. The paint is usually damaged on installation, or by subsequent movement (chips, holidays, etc).
Note that the chromium oxide film layer, on stainless steel, is very thin, and not an electrical insulator. Therefore the chromium oxide film will not prevent galvanic corrosion.

FWIW: As a rule of thumb, if the potential difference is less than 0.1 volt (100 mV/uV), then it is unlikely that galvanic corrosion will be significant.
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Old 25-11-2020, 07:57   #10
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Re: DC leak to aluminum hull

Desanduril. Thank you for your post. I sure learning about differential current sensors will keep my ever diminishing brain cells working for a few more days.
So I’m looking at the sensors and find amplifiers. Texas Instruments makes something called a Precision E Fuse which is for automotive but I’ll look into it.
This is a difficult science to grasp if you have limited electrical engineering exposure in college.
Jedi gave me excellent advice. A better meter and my own silver cell.
The manatee crew keeps stealing my credit card for beer.
Thanks to all who have replied.
Happy trails to you
Mark and his not so innocent crew
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Old 25-11-2020, 10:48   #11
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Re: DC leak to aluminum hull

Question- do you suspect a leak or you want to avoid having one?
if just checking for one-and verify your present meter- short a ground to the hull and then measure- if it is registering then it gives a reference
you should have zinc grounding plates someplace. be sure they are clean connected and maintained. As well, consistently check them and note condition. If white crusted (not working) check you connections and clean. If corroded heavy, begin looking at what is operating (not that simple)
BTW, a bigger issue is metallic trash in bilge. A coin can burn a whole thru the hull if given time.
And on the subject of bottom paint- be sure the zincs are connected clean. The number of commercial vessels that are bottom painted and zincs installed without cleaning the threads/connection surfaces is more common than expected. To the detriment of the owners because the damage is not noticed until obvious.
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Old 25-11-2020, 13:08   #12
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Re: DC leak to aluminum hull

I made a simple indicator of a potential leak between the hull and negative, and the hull and positive. It consists of two LEDs connected accordingly. Plus the third one connected to a battery for reference. The reference diode gives bright light at 20mA. Two other diodes give much weaker light for tiny leaks. I flick a switch from time to time to see if I have a short circuit. This switch connect test LEDs connected as above.
I found that 1. The bilge pump was sending current to the hull through bilge water. 2. Windlass motor through the copper powder from the motor brushes. 3. Autopilot motor leaked current too.

This little device cost less than $10 to make. My boat is 35 years old and seems to be corrosion free.
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Old 25-11-2020, 14:11   #13
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Re: DC leak to aluminum hull

Mr.,Captain? Deseroseii. Thank you for your post and welcome.
What kind of boat and where do you sail.

Itís the tiny leaks Iím trying to avoid. I donít have them but I need a new meter as suggested by Jedi.
I like the led idea. One of the big boats had two lights that the engineer would watch for even a slight glow. He had a cup with a pin hole to look ar them in the dark. Long before led. I have a Midnight Solar lightning protector on the DIN rail after the fuses but before the controller. It has two blue led lights to tell you itís ok. That would be my ideal for knowing I had a bad wire or some carbon dust.
My electrical knowledge is very limited.
We have some very talented people reading and I hope they will comment.
Happy trails to you
Captain Mark and his vegetarian manatees.
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Old 25-11-2020, 15:49   #14
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Re: DC leak to aluminum hull

Hi Manateeman. Might this device help? I donít have one yet but am considering it for my aluminium hull.

https://www.seabis.com/

Cheers
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Old 25-11-2020, 15:56   #15
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Re: DC leak to aluminum hull

#14
Wideocean7

I just took a quick look at seabis.com. What they are selling is pure snake oil. None of their "explanations" are technically correct and they have conflated stray current corrosion and galvanic corrosion. Good grief.
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