Reverse polarity LED glowing dimly

[nigelmercier]

I should be using a Neon with virtually infinite resistance.

Until it strikes, at which point it becomes a low resistance, and curiously negative.

 

[VicS]

I installed the GI due to heavy wear of the anodes on the Hamble, a common problem I am advised. However, by installing an led rather than a neon indicator I may have defeated the whole point if fitting it, the led with its voltage dropping resistor effectively allowing a short circuit straight past the thing. The AC PD is virtually nil, but I am seeing nearly 3 vdc across the GI, designed to stop Galvanic DC voltages below 6v, so seems to me the GI is trying to do its job, just that LED short is allowing the upstream shoreside connection for neutral to earth to effectively completely bypass the GI, which would explain why I saw little benefit for having it last season.

You are suggesting that the "galvanic current" which the GI would normally block is flowing instead through the shorepower neutral and the LED ??

Question: The galvanic emf will be low, maybe only 0.4 volts, 0.7 ish at the most. That is presumably high enough to make the LED conduct ???

Since the galvanic current is DC if you reverse the LED wont it solve the problem, if its the LED that causing it because it will not then conduct. It wont affect its function as a reverse polarity detector because that will be AC.


it still does not explain why you can measure such a high DC potential difference across the GI

Watching with interest to see what you discover.

 

[nigelmercier]

it still does not explain why you can measure such a high DC potential difference across the GI.

Indeed...

... I would not remove the GI, just find out where the earth leakage is coming from. Do you have a RCD / ELCB?

 

[mjf107]

This is a very common problem and is probably caused by the shore supply cabling. A simple test is to get the boat next door, or on the same pontoon, to put a large load on their boat. If they run a kettle and fire and your Reverse Polarity LED lights gets brighter then the fault is the pontoon AC supply.

This may not be an actually fault, but the result of lots of boats on the pontoon using lots of amps and causing a voltage drop along the cables feeding the pontoon. If you've not noticed this before in your marina it could be caused by a lose connection somewhere on the neutral cable feeding your pontoon. It may take the marina a long time to admit to any fault!!!!!

At the marina transformer the Neutral and Earth are bonded together. With large currents down the cables there will be a voltage drop along the neutral wire which may get up to 5 volts or more by the time it gets to your boat. There will be no voltage drop on the earth cable as there is no current flowing, so there is now 5 volts between the Neutral and Earth which makes the LED glow. This can cause earth leakage breakers to trip so you will keep losing power.

You should measure the voltage between the neutral and the earth cable. It shouldn't go above 5 volts AC. When there is a full reverse polarity it will have 240 volts across it and shine brightly.

I can see where the potential difference is coming from and agree with some of the thinking. But what can also happen where the voltage drop is after the the neutral to earth bond point is that you can get a significant PD between this system earth and true earth causing all the CPCs on the system to have this PD on them. As an aside if you have bonding in place on your boat between shore CPC and stern gear, swimmer would be exposed to this PD as there would be a voltage gradient around the stern gear. It would be unlikely to experience such problems in the UK as marina systems would be TT and have there own local earth.

 

[sailinglegend420]

I can see where the potential difference is coming from and agree with some of the thinking. But what can also happen where the voltage drop is after the the neutral to earth bond point is that you can get a significant PD between this system earth and true earth causing all the CPCs on the system to have this PD on them. As an aside if you have bonding in place on your boat between shore CPC and stern gear, swimmer would be exposed to this PD as there would be a voltage gradient around the stern gear. It would be unlikely to experience such problems in the UK as marina systems would be TT and have there own local earth.

I didn't understand a word of your post. Please translate into English. I've googled CPC and TT and still don't understand! PD I get but others might not.

 

[nigelmercier]

I didn't understand a word of your post...

I had trouble too, and I understand electrics!

Bottom line is that earth wires are sometimes not as good as you would like them to be.

 

[mjf107]

I didn't understand a word of your post. Please translate into English. I've googled CPC and TT and still don't understand! PD I get but others might not.

Sorry I know exactly what you mean about abbreviations it can make it very hard to read if you don't know what they mean. CPC is circuit protective conductor, earth wire in old money. TT is an electrical system, with its own earth stake and usually with RCD protection, all the CPCs of this system are connected to this earth steak. It can be a stand alone system or part of a larger system that has an earth from the mains distribution system. But in all cases the earths from other systems should not overlap, otherwise one system can export fault voltages to another system. PD.... Potential difference, in this case the voltages which may be present on the CPCs, I hope this makes it clearer and easier to read.

 

[lw395]

Sorry I know exactly what you mean about abbreviations it can make it very hard to read if you dont know what they mean. CPC is circuit protective conductor, earth wire in old money. TT is an electrical system, with its own earth steak and usually with RCD protection, all the CPCs of this system are connected to this earth steak. It can be a stand alone system or part of a larger system that has an earth from the mains distribution system. But in all cases the earths from other systems should not overlap, otherwise one system can export fault voltages to another system

Make sure your earth steak is a meaty conductor would be my professional advice, as an IET member.

I would suggest the dim glowing LED is seeing an induced voltage.
Given that a fully bright red LED only needs 2V and 30mA or so, it would not take much to make it glimmer over part of the cycle.
Even with the fattest earth cable, you may see different 'earth' voltages between land and sea, or even different bits of land. I've even heard of (crackpot) schemes to extract energy from this.

 

[superheat6k]

Back on my home mooring now, so I will investigate the boat : shore earth PD further.

The boat suffers high anode wear on the port side, which is predominantly the side to the pontoon.

This is a potted history of the issues, and attempts to resolve same since I have owned OB ...

1 At purchase survey the surveyor got a minor tingle from an underwater fitting. The vendor informed me this was due to a faulty 240v socket, which was replaced. I took his word for this, but did not get a chance to verify his claim before the boat was re-floated.

2 Port side anode wear has always been high. Indeed having spent an extended period afloat prior to sale it was observed that the port prop retaining nut has heavily dezinced, and this was replaced along with the completely worn port anode. This was July 2011.

3 At haul out Feb 2012 the port anode had virtually gone again just 7 months later.

4 However, just prior to that I installed a 'power on' warning lamp at the distribution panel (wired neutral to live after the RCD) (I like to know when the AC supply is on). At that time I noted the reversed polarity indicator was missing, so I fitted the 240v LED which I now realise I should have used a neon indicator.

5 However when I put the power back on it immediately lit up brightly, which revealed the shore power was polarity reversed. This was due to incorrect connections of live and neutral at the shore end plug on the supply cable, so I corrected this and thought this may have been a contributory factor to both the anode problem and the tingle the surveyor had felt.

6 To reduce anode wear I then installed the Galvanic Isolator. However my choice to use an LED indicator providing a possible secondary earth pathway via the shoreside neutral to earth bonding may have obviated this device.

7 The yard where I keep OB advised high anode wear is very common, but it is still predominantly the port side.

8 However, at the Feb 12 haul out I found there was no continuity from the stbd anode to the bonding circuit, so put some of this wear imbalance down to this, and I replaced the anode studs and rewired the bonding connection.

9 At this years haul out in February again the port was mostly gone, albeit after 11 months this time, and I had good continuity from both anodes to the shafts / bonding circuit, although the stbd resistance was marginally higher (port 0.5 ohms, stbd 1.2 ohms (meter lead resistance probably 0.2 ohms)

10 I am now using a dangling anode, made from two part worn anodes bolted together and attached to a stainless wire strop, this in turn is linked directly to the earth bonding circuit boat side of the GI. I have been using this approx 5kg lump of zinc dangled level with the port prop between the boat and the pontoon for about 1 month. When I haul this in before I go out the wearing zinc on the surface as I handle it is obvious from the deposits on my hands.

My earth to earth PD across the GI earlier this week was just over 2vdc. Is this excessive or am I chasing ghosts here ?

 

[nigelmercier]

TT is an electrical system, with its own earth steak...

But these are quite rare

My earth to earth PD across the GI earlier this week was just over 2vdc. Is this excessive or am I chasing ghosts here ?

It is excessive, there should only be a voltage here under fault conditions. As I've said twice in this thread, you have an earth leakage problem that you need to sort out.

 

[superheat6k]

Investigations this weekend on my home mooring reveal a more promising picture and at least one significant likely galvanic leak has been traced.

The PD across the GI was much reduced from the 2.4v at Weymouth down to a more acceptable 0.15v. So I suspect the shore earth may have been dodgy.

The glow was obviously due to high current flow in the neutral wire when the power is loaded up to around 12 amps, and I was able to duplcate this this morning, but the GI PD remained at 0.15v. Anyway I have removed the offending LED, and will install a neon instead for reverse connection alarm.

I then disconnected the stbd battery set feed, which also serve the permanently connected automatic bilge pumps. This revealed a voltage of approx 5v to otherwise 'off' circuits. I then removed the auto bilge pp fuses one at a time, to find the specific feed showing the 5v, which was the feed to the engine bay float switch. This voltage persisted even when the switch feed to the pump was disconnected. Indeed the float switch itself was still working because when manually raised whilst still wired to the pump the voltage went to a full 13v via the pump circuit to normal negative.

This was a Rule 14amp flapper type switch, which is now consigned to the bin. The new replacement is a Whale Electric field type switch. Not used these before so any pros or cons for these would be appreciated. Although this seems to have solved the galvanic leakage, I shall in due course replace the other three Rule flapper style switches.

The other bilge pumps (fed 2 per fuse) showed a voltage of 0.05 - 0.12 so I need to consult Calder's bible further, but I seem to have resolved the big one.

I will now be making this disconnected voltage check an annual maintenance item for both battery banks.

 

[nigelmercier]

Anyway I have removed the offending LED, and will install a neon instead for reverse connection alarm...

Why do you think a neon will be any better?

 

[superheat6k]

A neon will only light up at the designated voltage i.e 240, so will not show a false glow due to a few volts PD occurring from a loaded neutral, and would have been what Fairline originally installed in the power panel. However, I might imply opt for the plug in tester, and do a simple check each time a attach shore power.

 

[sailinglegend420]

A neon will only light up at the designated voltage i.e 240, so will not show a false glow due to a few volts PD occurring from a loaded neutral,......

The whole point of this post was that a false glow warns you that there is a problem with the shore power. Our Legend has LEDs. The LED was not your problem!

 

[nigelmercier]

A neon will only light up at the designated voltage i.e 240... I might imply opt for the plug in tester, and do a simple check each time a attach shore power.

There are a lot of myths about neons: two have now cropped up in this thread. The first myth is that they are high impedance.

Go for the plug-in, as it also tests other fault conditions.

 

[mjf107]

Superheat6k I keep coming back to this thread trying to fit your observations with plausible explanations, I don’t think there’s going to be one answer. But at least your making progress well done

You might consider the following.

Investigations this weekend on my home mooring reveal a more promising picture and at least one significant likely galvanic leak has been traced.

The PD across the GI was much reduced from the 2.4v at Weymouth down to a more acceptable 0.15v. So I suspect the shore earth may have been dodgy

Views please !

It could also be that the GI has failed open circuit, leaving the boats earth “floating”, in this condition it would be quite possible for the earth wire to have a few volts on it due to naturally “leaky” equipment. This would also explain why the surveyor felt the “tingle”. As others have said 2.4 volts is on the upper limit for the GI to start conducting, they normally operate in the range of 1.2-2.4 volts. The difference in voltage across the GI from Weymouth to home could be because you have removed the polarity LED, or that N-E potential is less.

If the GI is indeed open circuit, it could have happened when the socket developed a fault causing large short circuit currents to flow, hence the former owner reporting a “dodgy” socket. I would be inclined to check the GI in any case for peace of mind.

A further question for you about the MCB that reduces the “glow” when turned off, is there a switch mode battery charger on this circuit?