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Old 10-09-2013, 19:21   #1
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Stray 1.2v on mast?

I just finished wiring my masthead LED anchor / sail light. The only other electrical device next to the light is a masthead omni-TV / FM antenna (powered through the coax) and my VHF antenna. With all power isolated (incl. omni coax removed from amp panel) I now find that on the LED wiring coming off the mast I get 1.2V DC volts appearing at the patch panel. I disconnect the +ve and -ve run up the mast and I still get 1.2V from the LED run. Nowhere else in the system do I get any voltage appearing with the batteries disconnected and all breakers off. Any ideas or suggestions where this stray voltage could be coming from? I'm almost thinking my LED is acting as a solar panel!
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Old 10-09-2013, 22:06   #2
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Re: Stray 1.2v on mast?

An LED is after all, a diode.
It might be rectifiying light (which is electromagnetic radiation) or other nearby rf.
Are you measuring this in a marina or other space with a lot of other boats?
Try putting your meter across the same connections using the amps scale.
I'll bet there's no noticeable current available.
Maybe a few milliamps at best.
Maybe you could light up another LED?

Steve
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Old 11-09-2013, 21:47   #3
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Re: Stray 1.2v on mast?

Steve, this is out on a mooring so none of the other nearby boats would (or should) have any energized transmitters. Additionally I don't get any readings from either the side LED navigation lights or the stern LED light. Will put a load on and see if any current draw over the weekend. I was actually starting to think that there may have been a galvanic effect from different metals at the mast head at work.
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Old 13-09-2013, 22:12   #4
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Re: Stray 1.2v on mast?

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Originally Posted by rain View Post
I was actually starting to think that there may have been a galvanic effect from different metals at the mast head at work.
That would be my first guess.
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Old 14-09-2013, 15:36   #5
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Re: Stray 1.2v on mast?

To return to basics; galvanic corrosion require three components:
1. Two dissimilar metal objects;
2. electrically connected;
3. both metal objects immersed in an electrolyte.

I don't see #3 at the mast head.
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Old 14-09-2013, 16:29   #6
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Re: Stray 1.2v on mast?

Quote:
Originally Posted by CharlieJ View Post
To return to basics; galvanic corrosion require three components:
1. Two dissimilar metal objects;
2. electrically connected;
3. both metal objects immersed in an electrolyte.

I don't see #3 at the mast head.
Moisture in the air could be enough to get ion flow between metals. It does sound like a Galvanic issue. Is the mast keel stepped and is it bonded to through holes. BTW I would not recommend attaching an aluminum mast to a bonding system.
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Old 14-09-2013, 16:31   #7
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Re: Stray 1.2v on mast?

Quote:
Originally Posted by CharlieJ View Post
To return to basics; galvanic corrosion require three components:
1. Two dissimilar metal objects;
2. electrically connected;
3. both metal objects immersed in an electrolyte.

I don't see #3 at the mast head.
Salt air with a little humidity?

A meter usually has pretty high input impedance. You don't need much of a charge to register a voltage on them.

That small voltage could also be caused by inductive pick up if there is something nearby that generates a strong EM field. Again, modern meters tend to be pretty sensitive.
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Old 15-09-2013, 09:01   #8
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Re: Stray 1.2v on mast?

Sorry, still do not believe this is a galvanic current issue. Let's look at the Galvanic series; ABYC E-2, Table 1:

> Aluminum alloys have a corrosion potential of -980 to -1030 mVDC
> 18-8 Stainless Steel, Type 304 (passive) has a corrosion potential of -50mVDC to -100mVDC

With a solid electrical connection between the dissimilar metals and immersion in an electrolyte, the maximum potential that can be generated is:
Vmax = -1030mVDC - (-50mVDC) = -980mVDC

There is something else at work here.
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Old 15-09-2013, 09:43   #9
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Re: Stray 1.2v on mast?

A shot in the dark here.
Have you checked the polarities for all the grounds being to ground sides (even the diodes). Something may be back feeding. Aqua Signal Anchor/ tri-color lites do this if not wired correctly. How current flows to these consumers makes a difference. FWIW.
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Old 17-09-2013, 08:12   #10
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Re: Stray 1.2v on mast?

Quote:
Originally Posted by sailorchic34 View Post
Moisture in the air could be enough to get ion flow between metals. It does sound like a Galvanic issue. Is the mast keel stepped and is it bonded to through holes. BTW I would not recommend attaching an aluminum mast to a bonding system.
I've wondered about this myself. On the one hand I think I need to provide a lightning path for the mast to a ground plate on the hull. On the other hand, I don't want my mast base to start fizzing. What to do with two conflicting requirements. Maybe if the lightning ground plate is isolated from the rest of the boats ground, or perhaps connects to the boat's ground via spark-gap.
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Old 19-09-2013, 12:53   #11
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Re: Stray 1.2v on mast?

back in the old days we used led for both ends of a detector beam. so, yes some led could be solar. tape over it and check again.
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Old 19-09-2013, 20:16   #12
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Re: Stray 1.2v on mast?

An update, it's a deck stepped mast (fiberglass boat) so there is no grounding of the mast through the stays or via the mast itself, although I suppose the mast may get grounded through the VHF antenna ground which comes back down to the transmitter (will actually check that this weekend to see if the antenna ground does actually hit the 12v -ve ground)? In any case the 1.2v is just evident across the mast head light (single allround white, not tri) even when it's disconnected and just measured across the two wire feed up the mast - nothing else connected. So in theory I'm getting this 1.2v from nothing else than a LED light sitting atop a mast with no radars, transmitters or anything else nearby. Interestingly I don't get any such readings from either the LED stern or two LED side lights either when they're in the system or disconnected so they're back to their basic 2 wire configurations for each.
Just got a Top Climber delivered so will see if I can head up the mast this weekend and do some further searching and also cover the LED and see if that does make any difference. I'm now intrigued to find out what is happening.
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Old 22-10-2013, 08:36   #13
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Re: Stray 1.2v on mast?

Did you ever get to the bottom of this? or is that top
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Old 27-10-2013, 16:26   #14
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Re: Stray 1.2v on mast?

Looks like it's a photo-diode effect. Waited onboard until sunset and sure enough I can watch the voltage drop as the sun goes down. From 1.2v it drops to what I guess must be just reading error on the multimeter of some 50mV. My recollection of quantum physics for Uni is way too dim a memory so no idea on how or why a supposed LED is behaving this way (and why none of the other external LED's do) but it would appear to be what is happening.
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Old 27-10-2013, 16:41   #15
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Quote:
Originally Posted by rain View Post
Looks like it's a photo-diode effect. Waited onboard until sunset and sure enough I can watch the voltage drop as the sun goes down. From 1.2v it drops to what I guess must be just reading error on the multimeter of some 50mV. My recollection of quantum physics for Uni is way too dim a memory so no idea on how or why a supposed LED is behaving this way (and why none of the other external LED's do) but it would appear to be what is happening.
Hey you could use your mast to switch your anchor light on and off . Respect

Dave
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