Electrical current when circuit is off

[team karst]

Maybe the headaches will go away also…

[StoneCrab]

There are lots of stories about metal objects picking up RF. If the object resonates at the frequency it is picking up, I've heard that you can hear the transmission from the slight movement of the metal. I've never heard it myself but there are plenty of cases reported... Maybe hearing a radio station through your old metal fillings is urban myth, but the physics is there.

Maybe you've discovered a new way of charging you batteries...through induction

[Dieseldude]

This "phantom current" is most likely from background radio energy being received through the light circuit wiring that acts as an antenna. Suspect that it is reading as a negative voltage due to rectification caused by the LED lights. That means that only the negative half of the radio signal is passing through the LED's. Effectively, your lighting system may be acting as an old time crystal radio set, but over a very broad radio frequency spectrum which would make it receptive to a broad range of radio transmission sources that would sum up. Sources could also include the electromagnetic field of any close by AC wiring. It is quite surprising, as the PN junction barrier voltage for LED's is typically more than 1 volt, and it would take very intense radio signal to produce this in wiring. The fact that the phenomena disappeared after moving a distance of 30 miles supports this hypothesis. You simply sailed out of range of a strong radio transmitter that would have been the source.


"Most common LED’s require a forward operating voltage of between approximately 1.2 to 3.6 volts with a forward current rating of about 10 to 30 mA, with 12 to 20 mA being the most common range." https://www.electronics-tutorials.ws/diode/diode_8.html


It could be that your LED's are some newer type that has a lower barrier voltage. Or perhaps the light units have within them other semiconductor devices with a lower barrier voltage.


While in electronics college, my lab class had trouble getting basic diode circuits to work as expected due to background radio signals in the area. These were "signal diodes" with low barrier voltage, much lower than typical LED's though. So they were quite vulnerable to radio interference. Shielding our circuits with sheet metal objects would give a noticeable reduction in the stray voltages that we measured.


If you connect a typical digital volt meter to an AC circuit that is not live, you will often get readings if a few millivolts that generally fluctuate, though they could be stable. This is caused by current induced in the wiring from close by live wires, or possibly from more distant sources such as radio transmitters. The world is awash with countless invisible sources of electromagnetic radiation. Note that more expensive digital meters have a function to omit reading this stray low voltage noise. which is a distraction.


If you would like to test the theory, you might watch your lighting system while talking on your VHF radio. If this shows nothing, have an assistant hold a hand held VHF close to one of your lights and press transmit. If enough signal reached your light, the effect might be reproduced.

[donradcliffe]

There is a nice anchorage at the north end of City Island in Long Island Sound. Right next to a large radio transmitting tower. It lit the panel up.

[Cadence]

Originally Posted by crayiii

We moved about 30 miles to a new Anchorage yesterday. The panel and all the lights are now working as they should.

I'm glad you were chasing a non existing problem and it is resolved. I would hazard a guess you were anchored near a ham operator or someone had their radar on for an anchor watch. It might have been the aliens and their UFO?

[PaulvR]

What the hell it's all that is left :-)..

So what about the mast-head anamometer cable misbehaving in some way, leaking a little while bundled in the same harness or occasionally touching a conductive surface as it does the halyard dance?....only in the mast right? Minor wind generated currents?

I think I'm going to be flogged..SEND :-)

[Dieseldude]

Originally Posted by PaulvR

What the hell it's all that is left :-)..

So what about the mast-head anamometer cable misbehaving in some way, leaking a little while bundled in the same harness or occasionally touching a conductive surface as it does the halyard dance?....only in the mast right? Minor wind generated currents?

I think I'm going to be flogged..SEND :-)

Possible, but the anemometer does not produce much current to raise a strong electrical field. It probably is only in the tens or hundreds of milliamps, and less than 12 volts. This whole problem seems to be minor, so not worth a lot of bother. If it really is a concern, all lightig wires on the mast could be replaced with shielded cable, and the shields tied to the vessel's grounding system. Can't see it worth the bother and expense though. Wind ripping past wires will not generate currents unless the air is pushing tiny magnets. Maybe the boat was moored near soil with high iron content, so airborne magnetic iron dust was pushing by the wires. Was the wind direction offshore?

[GoodShipLolipop]

Originally Posted by senormechanico

Back in the '60's when I was in the US Navy and working in the Pearl Harbor Hobby Shop, we could always tell when the USS Enterprise came into dock. Even though the boat was tied up nearly a half mile from the hobby shop, the radar caused the PA system to make a zzzZZZzzz sound each time their radar antenna scanned past us.
Turning off the PA system made no difference, and this was in a completely metal building.

My dad was a pilot in the US Navy before he retired. His least favorite plane to fly of all time was the E-2C, thanks partially to the radar and insufficient/improper grounding. This is what he said to me in an e-mail about it once (and no, the doubled line is not a typo, he typed it twice).

Originally Posted by Lollipop's Dad

I hate the E-2C

I hate the E-2C.

Worst plane I’ve ever flown. 12’ diameter props made out of fiberglass with nickel leading edge wear strips. 4600 SHP engines each, same as the P-3. Radar on both the E-2 and the P-3AEW were identical, (APS 138) and cranked out 1 megawatt of energy with no shielding on the E-2. We had gold plated windows with grounding on all windows on the P-3 so we didn’t get zapped once every revolution. Six RPM.

With regard to the E-2C. Sometimes when you were flying you might notice, in your rear view mirror, that one of the landing gear started to extend all by themselves. Doors would open…Yup, here comes a tire, Dang! After takeoff you would isolate the hydraulic non flying systems like brakes and landing gear from actual flying stuff like flight controls, but after awhile here comes Mr. Tire.

To get Mr. tire to go back into its house you would tell the hydraulic system that you wanted to land by selecting “Combined”. The problem was that by now the hydraulic fluid was now very cold and not very viscous and made a large bang when when you hit the switch. Woke up all three crew members in the back.

If for any reason you lost generators or hydraulic power you got to bail out. Happened more than once.

I could go on for hours on how bad the E-2 was.

Not sure what he meant by "bail out", I really don't think he means that he ditched multiple E-2s. I'll have to follow up with him on that one day.

[Dieseldude]

GoodShipLolipop's story about grounding on aircraft brings up a point which I'd not bothered to mention. Assuming that crayiii's mast is aluminum. I had also just assumed that it is well grounded the vessel's grounding system. But is it? Would be good to check on that. A large vertical ungrounded conductor could certainly attract strong radio signal which might induce signal into attached wires. Recalling the old TV VHF antennae, if you looked closely at the elements, some were not connected to the cable that led to the TV. They were made to a length to resonate with TV signal frequencies, and they were positioned at optimum distance from the "driven elements" to direct signal to them. This resulted in extra signal being applied to the driven elements, giving the signal some gain. These were quite an ingenious design that made longer distance reception possible. An ungrounded mast could possibly have a similar effect on any radio signal that might intercept it. OK, a long shot of a possibility, but making certain of grounding is a worthwhile check. A bit of corrosion on fasteners can interrupt ground connection.

[team karst]

A shield, such as a Al mast, will have degradation due to unprotected cables at both ends. Grounding one end of a shield is likely to have no effect on high frequency signals, like radar. Shields work because RF has a difficult time propagating through a conductive medium. Nothing to do with grounding.

[Dieseldude]

Originally Posted by team karst

A shield, such as a Al mast, will have degradation due to unprotected cables at both ends. Grounding one end of a shield is likely to have no effect on high frequency signals, like radar. Shields work because RF has a difficult time propagating through a conductive medium. Nothing to do with grounding.

True, shields can work without grounding. However, an electromagnet field can induce a current in a shield that may re-radiate to a conductor within. Grounding the shield can cause an induced signal to be shorted to ground. It is generally little effort and expense to ground a cable shield, so no point in not doing it. Grounding both ends of a shield can cause a ground loop which may induce noise in the conductor within and defeat the purpose of grounding. It is generally advisable to ground only one end of a shielded cable. RF noise can be a difficult to abate phantom, and application of strict rules may not succeed in all cases. Sometimes a bit of trial and error and black magic will help.

[Wotname]

^^

Yep, there is no silver bullet when it comes to shielding. There are times when the shielding is there to contain RFI / EMI from radiating from within the cable and there are times when the shielding is to prevent external interference from getting into the cable and then there are times when you want to do both. On top of this, one has to consider the intensity of the expected interference. High Intensity RFI often needs the shield to be grounded both ends but as DD says, this can cause other problems which then have to be migrated.

I recall using some radar cable that had (IIRC) 3 levels of shielding and it was pretty expensive - maybe $10+ an inch and that was 20+ years ago. Each pair of twisted conductors were shielded, the cable then had an inner shield and an insulated outer shield. The outer shield had to be grounded at both ends, the inner cable shield grounded at one end and the shields around each twisted pair was left open circuit at both ends. Even with all that, the cable had to be routed away from strong EM fields.

[Dieseldude]

Originally Posted by Wotname

^^

Yep, there is no silver bullet when it comes to shielding. There are times when the shielding is there to contain RFI / EMI from radiating from within the cable and there are times when the shielding is to prevent external interference from getting into the cable and then there are times when you want to do both. On top of this, one has to consider the intensity of the expected interference. High Intensity RFI often needs the shield to be grounded both ends but as DD says, this can cause other problems which then have to be migrated.

I recall using some radar cable that had (IIRC) 3 levels of shielding and it was pretty expensive - maybe $10+ an inch and that was 20+ years ago. Each pair of twisted conductors were shielded, the cable then had an inner shield and an insulated outer shield. The outer shield had to be grounded at both ends, the inner cable shield grounded at one end and the shields around each twisted pair was left open circuit at both ends. Even with all that, the cable had to be routed away from strong EM fields.

Hmmmn... $20 per inch for cable 20 years ago. Seems like something for a military budget. Just shows the extreme measures that may sometimes be required to combat electrical noise. Lots of effort and money can be expended. It is invisible to the eye. It can drive you around the bend. It can be difficult to measure and trace with instruments. Equipment such as an RF voltmeter is expensive for casual use. Even paying experts and using expensive cabling can be fruitless at times. Sometimes simpler less costly approaches such as keeping cables and devices as physically distant as possible will help.

[RaymondR]

Conductors inside a metal mast should be within a Faraday cage?

[GoodShipLolipop]

The mast itself should act as a Faraday cage so long as it's grounded. Mesh is typically used because it's much cheaper than solid metal. Solid metal does the same thing, and works on a broader range of frequencies.