GI and AC leakage

[RadiumRob]

Today I fitted a Safeshore galvanic isolator to my shore power earth. I tested it with the multimeter and the bias voltages are ok, and the 9v battery test across the terminals lit the LEDs as it should.

When I connected to the power supply both LEDs lit faintly, which apparently indicates AC leakage to earth. The manual recommends isolating AC systems until the LEDs go out to identify the faulty item, but at this point the main isolator was OFF and no circuits were live. The BM1 battery monitor was showing a current of 0.5mA flowing, presumably straight to ground.

Presumably there is some leakage in the battery charging circuit. The previous owner ran shore wer occasionally with no GI fitted ANSI presume he was unaware and unaffected by the leakage. Should I be worried about it?

Thanks in advance,

Rob

 

[dt4134]

Today I fitted a Safeshore galvanic isolator to my shore power earth. I tested it with the multimeter and the bias voltages are ok, and the 9v battery test across the terminals lit the LEDs as it should.

When I connected to the power supply both LEDs lit faintly, which apparently indicates AC leakage to earth. The manual recommends isolating AC systems until the LEDs go out to identify the faulty item, but at this point the main isolator was OFF and no circuits were live. The BM1 battery monitor was showing a current of 0.5mA flowing, presumably straight to ground.

Presumably there is some leakage in the battery charging circuit. The previous owner ran shore wer occasionally with no GI fitted ANSI presume he was unaware and unaffected by the leakage. Should I be worried about it?

Thanks in advance,

Rob

Did you have your mains battery charger on?

By main isolator do you mean that the shorepower wasn't connected? Or do you mean that the 12V was turned off?

 

[RadiumRob]

12v supply was off at the on-board isolator; the shore power was on.

As far as I know battery charger (Sterling PRO digital) is on when shore power is connected. Not 100% on this though. New boat, full of mysteries...

Rob

 

[dt4134]

There's a fair chance that the AC leakage is caused by something connecting the mains Neutral to the mains Earth, especially as they are just lit faintly. Turn each AC item off in turn and see if the warning lights go out. That includes the battery charger.

 

[VicS]

Today I fitted a Safeshore galvanic isolator ...................... Should I be worried about it?

Thanks in advance,

Rob

.

Presumably thats 0.5 mA discahrge ?

Did the 0.5mA only show when the shorepower was plugged in, or did it still show when unplugged?

What happens if you turn off the shorepower isolator.

You say the battery isolator was off but wre there any "always on" circuits still connected?


If the BM1 was registering 0.5mA at the negative battery terminal there must somewhere somehow be a complete circuit to the positive terminal. Any idea how that would come about?


Now if the BM was showing a discharge and that was flowing out via the GI and shorepower earth it indicates that the GI is conducting.... That would be bad news because it would not then be offering the protection it should.
But the current flow would have to return somehow ... via the water?? ... to something from which there is a path to battery positive
Corrosion ( electrolysis) would then occur at the the point of return from the water.

However the current is so small that the corrosion would be very small.

I calculate that it would be the equivalent of a loss of zinc from an anode of about 5.5 g per year. However, loss of the equivalant amount of metal from a skin fitting spread over a number of years could be very significant.

Not an urgent problem perhaps but one that should not go unsolved for a number of years.

 

[rustybarge]

Hi rad,
The idea of an isolation transformer is that you do not Connect the shore earth to your boat, that's why it's called an isolation transformer.......be aware it can mean mains earth leakage fuse will not trip properly because earth is only through the hull & water.

Normal transformers step up or down the voltage......isolation is just 1/1 ratio.

 

[VicS]

12v supply was off at the on-board isolator; the shore power was on.

As far as I know battery charger (Sterling PRO digital) is on when shore power is connected. Not 100% on this though. New boat, full of mysteries...

Rob

If the battery charger was on then the battery monitor should have been showing the charge current

 

[RadiumRob]

Hi rad,
The idea of an isolation transformer is that you do not Connect the shore earth to your boat, that's why it's called an isolation transformer.......be aware it can mean mains earth leakage fuse will not trip properly because earth is only through the hull & water.

Normal transformers step up or down the voltage......isolation is just 1/1 ratio.

I have a galvanic isolator, not an isolation transformer. I think the two are subtly different, and the galvanic isolated has a wired earth.

Rgds

Rob

 

[nigelmercier]

Hi rad,
The idea of an isolation transformer is that you do not Connect the shore earth to your boat, that's why it's called an isolation transformer...

Whoosh!

 

[VicS]

I have a galvanic isolator, not an isolation transformer. I think the two are subtly different, and the galvanic isolated has a wired earth.

Rgds

Rob

Yes an isolation transformer completely isolates the boat's electrical system from the pontoon supply. There should even be no connection between the the pontoon earth and any part of the boat.
An onboard "earth" system has to be created and bonded to one of the transformer output terminals to create a "neutral"

A galvanic isolator can be used, when there is no isolation transformer, to block current flowing in the shorepower earth connection from very low voltage sources, such as dissimilar metals, which causes galvanic corrosion.
It will however allow current from higher voltage sources to pass. By doing that is maintains the safety aspects of the earth.

For better explanation see the MAINS ELECTRICITY section of Tony Brooks' TB training website

 

[RadiumRob]

Response from supplier:

Thanks for your input so far. If anyone is interested, here is the supplier's explanation and recommendation:

"...The leds will begin to trigger at around 1.8 volts & are fully illuminated at 2.4volts. At this point the isolator will begin to conduct . The 1.6 volts you are measuring is indeed some form of low level A.C. leakage which may cause the leds to glow slightly. The source of the a.c. may be from a neighbouring vessel as you appear to have isolated your own boat effectively. It may also be a low level leak from the shore power ( not uncommon!) but the most likely cause is an interference pulse from a switched mode supply within an appliance even on a neighbours boat. I attach an explanatory letter to this email). It is worth temporarily unplugging your neighbouring vessels whilst monitoring the leds to locate the source. Either way the isolator will still work effectively under these conditions: Should the voltage increase & the leds become fully illuminated then further investigation would be necassary..."

 

[VicS]

Thanks for your input so far. If anyone is interested, here is the supplier's explanation and recommendation:

"...The leds will begin to trigger at around 1.8 volts & are fully illuminated at 2.4volts. At this point the isolator will begin to conduct . The 1.6 volts you are measuring is indeed some form of low level A.C. leakage which may cause the leds to glow slightly. The source of the a.c. may be from a neighbouring vessel as you appear to have isolated your own boat effectively. It may also be a low level leak from the shore power ( not uncommon!) but the most likely cause is an interference pulse from a switched mode supply within an appliance even on a neighbours boat. I attach an explanatory letter to this email). It is worth temporarily unplugging your neighbouring vessels whilst monitoring the leds to locate the source. Either way the isolator will still work effectively under these conditions: Should the voltage increase & the leds become fully illuminated then further investigation would be necassary..."

Thanks for passing that on.

Any explanation for the 0.5mA reading on the battery monitor ?

 

[RadiumRob]

Thanks for passing that on.

Any explanation for the 0.5mA reading on the battery monitor ?

Vic - not yet. I will take another look at this at the weekend.

Rgds

Rob

 

[rustybarge]

Rad,

Go to : Van der Valk in build, page18.....in Motor boat sect. Page 2

This enormous new aluminium boat will be using a isolation transformer....it's the only way of stopping current leakage.

 

[claudio]

Thanks for your input so far. If anyone is interested, here is the supplier's explanation and recommendation:

"...The leds will begin to trigger at around 1.8 volts & are fully illuminated at 2.4volts. At this point the isolator will begin to conduct . The 1.6 volts you are measuring is indeed some form of low level A.C. leakage which may cause the leds to glow slightly. The source of the a.c. may be from a neighbouring vessel as you appear to have isolated your own boat effectively. It may also be a low level leak from the shore power ( not uncommon!) but the most likely cause is an interference pulse from a switched mode supply within an appliance even on a neighbours boat. I attach an explanatory letter to this email). It is worth temporarily unplugging your neighbouring vessels whilst monitoring the leds to locate the source. Either way the isolator will still work effectively under these conditions: Should the voltage increase & the leds become fully illuminated then further investigation would be necassary..."

Nice feature having the LEDs but also show that it cannot function with modern technology that requires RFI suppression.

So basically saying that the GI is a defunct piece of kit because anybody can set it into conduction by using standard battery chargers or electronic equipment.

What are you supposed to do, go round the marina and unplug everybody ?

The only sure way of isolation is to use an isolation transformer and wire it correctly. The shore earth goes to the transformer chassis and nowhere else. The chassis is to be insulated from all metal parts on the boat.

 

[dt4134]

Thanks for your input so far. If anyone is interested, here is the supplier's explanation and recommendation:

"...The leds will begin to trigger at around 1.8 volts & are fully illuminated at 2.4volts. At this point the isolator will begin to conduct . The 1.6 volts you are measuring is indeed some form of low level A.C. leakage which may cause the leds to glow slightly. The source of the a.c. may be from a neighbouring vessel as you appear to have isolated your own boat effectively. It may also be a low level leak from the shore power ( not uncommon!) but the most likely cause is an interference pulse from a switched mode supply within an appliance even on a neighbours boat. I attach an explanatory letter to this email). It is worth temporarily unplugging your neighbouring vessels whilst monitoring the leds to locate the source. Either way the isolator will still work effectively under these conditions: Should the voltage increase & the leds become fully illuminated then further investigation would be necassary..."

That's interesting.

I had a problem with my Sterling battery charger, which I assumed was caused by it somehow connecting the Neutral and Earth, but from the above may have been caused by switched mode power supply.

Anyway, I established that the battery charger did completely isolate the mains from the 12V, so that was my main worry crossed out.

What I decided to do, was to fit the GI between the mains Earth and the 12V GND and leave the 240/230V circuitry with a direct connection for the earth. VicS has a diagram he wheels out from time to time that shows that arrangement.

The monitoring GI LEDs no longer light so I'm happy that there is no galvanic current flowing. In other words, the original problem was caused by the battery charger, not galvanic voltages or neighbouring boats.

 

[RadiumRob]

Nice feature having the LEDs but also show that it cannot function with modern technology that requires RFI suppression.

So basically saying that the GI is a defunct piece of kit because anybody can set it into conduction by using standard battery chargers or electronic equipment.

What are you supposed to do, go round the marina and unplug everybody ?

The only sure way of isolation is to use an isolation transformer and wire it correctly. The shore earth goes to the transformer chassis and nowhere else. The chassis is to be insulated from all metal parts on the boat.

I don't think the GI is pushed into conduction because the voltage is too low for that. The 1.6V I measured was using the diode test facility with my 9V multimeter. The LEDs are barely lit, apparently they light fully when the isolator is conducting.

 

[VicS]

That's interesting.

I had a problem with my Sterling battery charger, which I assumed was caused by it somehow connecting the Neutral and Earth, but from the above may have been caused by switched mode power supply.

Anyway, I established that the battery charger did completely isolate the mains from the 12V, so that was my main worry crossed out.

What I decided to do, was to fit the GI between the mains Earth and the 12V GND and leave the 240/230V circuitry with a direct connection for the earth. VicS has a diagram he wheels out from time to time that shows that arrangement.

The monitoring GI LEDs no longer light so I'm happy that there is no galvanic current flowing. In other words, the original problem was caused by the battery charger, not galvanic voltages or neighbouring boats.

This one ??

There is a bit about the possible problems with switch mode power supplies on the Smartgauge website. On the second page of this article http://www.smartgauge.co.uk/galv_tran.html

I'd like to see it explained how the problem can be caused by switch mode powersupplies on a neighbouring boat ( not saying that I dont believe it, just that I'd like to see the explanation)

 

[dt4134]

This one ??

That's the one. Thanks.

Certainly the switch mode power supply issues are an argument for using an arrangement like Fig. 2.

I've only thought of one case so far that might weigh against Fig 2 but haven't really investigated it yet (I am thinking in the context of my own boat but I have pretty typical kit on board). There could be a problem with galvanic current causing corrosion through the immersion heater element in the calorifier. I've yet to check it out fully to see exactly what the Earth is connected to. The water does form a conducting path to the engine block via the heating coil, but it is fresh water albeit not de-ionised. And of course the engine block is connected to the 12V system, so it is a sort of bypass circuit to the GI. I need to think about it more.

 

[mhouse]

The Sterling charger caused the same problem last year for me also. I found out the -ve terminal had moved and was touching the metal charger case. The anode wear during this fault was excessive.