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Airlink BT3240


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Hi,

 

Was wondering if anyone had experience good or bad of the Airlink BT3240 transformer my boat is in for blacking and has some signs of electrolysis, so looking for a better way to protect the hull. The boat spends most of the time in a marina plugged in.

 

There is a galvanic isolator,

 

Thanks

 

Pete

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Have you tested the galvanic isolator to see if it is working properly? If it is working as it should, then you don't need an isolation transformer. What make/model of galvanic isolator do you have?

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I do have an isolation transformer, but not an Airlink one.

Advantages,

  • Doesn't have the failure modes that a galvanic isolator can have.
  • Will redefine neutral to boat earth, so can fix incorrectly wired shore leads, or bollards. Also generators and inverters with non neutral-earth bonded outputs, if that is a concern.

Disadvantages,

  • Hummmmmmmmmmm. Makes a little bit of noise.
  • Uses a tiny bit of power in internal losses. Some as heat, some as hummmmmmmmmmm.
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I won't be back on the boat until Friday so not sure, it is just a mysterious box with no indicators on it.

 

I did a test using the diode setting on my multimeter (after disconnecting) and assuming I did it correctely it indicated it was working.

 

Peter

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I have had an Airlink industrial transformer since 2006, from the days before they made the boat ones. As it's a toroidal transformer the hum is very slight and I can't hear it.

Only downside with Airlink is the softstart which does destroy itself after a while. I ran for 10 years without softstart before I got round to fitting something like THIS into the supply.

The only thing I would change is I would get one with primary taps as I tend to see variable voltages, between 220v and 250v, in different locations and it would enable me to set the voltage on the boat.

 

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31 minutes ago, baldlimey said:

I won't be back on the boat until Friday so not sure, it is just a mysterious box with no indicators on it.

 

I did a test using the diode setting on my multimeter (after disconnecting) and assuming I did it correctely it indicated it was working.

 

Peter

 

If the voltage on one side of the galvanic isolator is high enough they will conduct and thus be useless.  That is even if they test OK on a meter. This is why there was a change from two diodes in series to three or more. It is also why it is best to always get one with some kind of indicator on it. Reasons why the voltage may be high are legion and without testing the  whole mains system it is difficult to give the reason.

 

Also, a mains faults on adjacent boats can cause corrosion on your hull as electrons flow in and out of your steel but a GI or IT will tend to lessen it.

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39 minutes ago, baldlimey said:

Thanks Tony

I'm not sure what you mean by too higher voltage  any clues what I may be looking for or how to test?

Thanks

Peter

 

The GI is in effect a special type of "switch" in the earth wire as it comes into the boat. It is normally switched off until a fault puts mains voltage on the earth cable. Then it turns on, so a massive current can flow down the earth  wire and blow the fuse or trip the circuit breaker. The next question is what is this special switch and how does it work. Typically, IG's use some diodes in series that cause about a 0.7V volt drop so if you put two in series you get A 1.4v and with three in series it is 2.1V. So as long as the voltage on the earth wire is less than 1.4V or 2.1V the voltage will be dropped so no current can flow. Because diodes work with DC and the mains is AC two strings of diodes are needed pointing in opposite directions this means whichever way any mains fault current is flowing the GI will still allow it to flow and blow the fuse.

 

Now a bit more about the whole AC system.  If a live (DC) or line (AC) cable shorts to the metal of the hull the whole hull will become live and in the case of the mains it presents a real danger of electrocuting people stepping on or off the boat or in the water close by. To prevent this the hull of the boat should be bonded to the earth wire coming into the boat, so the fuse is allowed to blow.

 

That seems simple enough, but it connects your hull to the mains earth cable, but the hull is also connected to the mains earth system via the water and soil etc. Yes, canal water will act as a conductor, be it one with more resistance than the copper earth wire. Somewhere the neutral (blue) wire will be deliberately connected to the ground. This may be at the local sub station or where the mains connect to the marina's system. Because of the way things work it is common for there to be a small voltage in the earth cable and as it is bonded to your hull it presents this electrical pathway: earth wire > hull > water > ground > back to the ground connection. It is this circuit that is broken by the GI unless the voltage is higher than the diodes "turn on"/volt drop voltage. If it is then it will turn on and conduct, allowing electrons leaving the hull to carry molecules of "steel" with them, hence the pitting. Just to complicate things if you use equipment with switched mode power supplies on the boat it is possible for the radio suppression in them to dump the interference to the earth cable as a voltage so that acts back towards the mains input and could make the diodes conduct.

 

I understand things like electric railways, heavy industrial machinery etc. can, under suitable circumstances, raise the voltage on that green and yellow earth cable causing the GI to conduct. With an IT that is correctly wired this can not happen.

 

So a "too high" voltage depends on the number of diodes in the GI. How to test is outside my competence and as I have no idea about your abilities I can not encourage you to test because it might involve breaking into the neutral cable.

 

Hopefully another member more rooted in mains work will be able to explain how to test to see if the GI is conducting or not. If I were to fit a GI to my boat it would always have an indication of some sort.

 

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Thank you very much Tony for that detailed answer, if anyone fancies chipping in on how to test, if I say my knowledge is minimal that is probably over egging the pudding.

 

Pete

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This details how to rest a GI, but ignores the fact that many GI's use a capacitor to pass high frequency AC harmonics.

 

This capacitor needs to be discharged before using the multimeter to test on the diode test setting. To discharge the capacitor simply put a wire across the GI input and output terminals BEFORE using the multimeter.

 

https://galvanic-isolator.co.uk/how-to-test-a-galvanic-isolator/

Edited by cuthound
Clarification
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7 minutes ago, cuthound said:

This details how to rest a GI, but ignores the fact that many GI's use a capacitor to pass high frequency AC harmonics.

 

This capacitor needs to be discharged before using the multimeter to test on the diode test setting. To discharge the capacitor simply put a wire across the GI input and output terminals BEFORE using the multimeter.

 

https://galvanic-isolator.co.uk/how-to-test-a-galvanic-isolator/

 

I think that is just the standard diode test to see if they are open circuit or shorted. I think the OP wanted to know how to test the voltage on the AC earth cable either side of the GI in case it is high enough to force conduction during normal operation.

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14 minutes ago, Tony Brooks said:

 

I think that is just the standard diode test to see if they are open circuit or shorted. I think the OP wanted to know how to test the voltage on the AC earth cable either side of the GI in case it is high enough to force conduction during normal operation.

 

Ah, in that case one simply sets the multimeter to DC volts and measures across the input and output terminals.

The reading should give the voltage dropped across the diodes. If it is zero then the diodes are not conducting.

 

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2 hours ago, cuthound said:

 

Ah, in that case one simply sets the multimeter to DC volts and measures across the input and output terminals.

The reading should give the voltage dropped across the diodes. If it is zero then the diodes are not conducting.

 

 

I don't quite understand this. With the shoreline unplugged which it should be before any test is performed, then where does the voltage that is being measured across the GI terminals/diodes come from? The DC volts setting on a multimeter doesn't put a voltage into a circuit does it? 

 

Sorry if I'm being thick.

Edited by blackrose
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10 minutes ago, blackrose said:

 

I don't quite understand this. With the shoreline unplugged which it should be before any test is performed, then where does the voltage that is being measured across the GI terminals/diodes come from? The DC volts setting on a multimeter doesn't put a voltage into a circuit does it? 

 

Sorry if I'm being thick.

 

No you are not. Whilst I agree to "normal" GI testing the shoreline should be isolated the OP was asking how to check any voltage that may be on the earth cable in case it is high enough to open the diodes. I don't know how to do that. It might be AC volts between earth and neutral on a live circuit where it should read zero, but I can't be sure and I am not sure it would be wise to encourage all comers to mess with live mains circuits.

 

If the OP fits his IT then it is a non-issue

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On my old GI which had 2 pairs of diodes and went into conduction at 2.4v, the manufacturer recommended testing with a 9v battery across the terminals which would force the diodes into circuit. However that GI had a led status monitor which would illuminate. I thought the equivalent test on a multimeter was the diode test but could be wrong 

 

If I had an unknown GI I'd just swap it for something better or get an IT 

Edited by blackrose
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45 minutes ago, blackrose said:

 

I don't quite understand this. With the shoreline unplugged which it should be before any test is performed, then where does the voltage that is being measured across the GI terminals/diodes come from? The DC volts setting on a multimeter doesn't put a voltage into a circuit does it? 

 

Sorry if I'm being thick.

 

The test to see if the diodes are conducting by measuring voltage drop across them had to be done with the shoreline plugged in. 

 

It can be done after tests to prove the diodes are not open or short circuit, which are done with the shoreline unplugged has been completed.

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54 minutes ago, cuthound said:

 

The test to see if the diodes are conducting by measuring voltage drop across them had to be done with the shoreline plugged in. 

 

 

But if there was a substantial voltage leak to earth wouldn't that be hazardous?

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11 hours ago, blackrose said:

 

But if there was a substantial voltage leak to earth wouldn't that be hazardous?

 

Only if you touch the connections! If the diodes are conducting it will only be a couple of volts. However you are not confident working on electrics and aware of the precautions necessary then you should not work on them.

 

If there was a mains fault, then the protection should have operated. The test is to see if the earth voltage is enough to turn the diodes on and cause galvanic corrosion, not to see if the mains protection is working.

Edited by cuthound
Clarification
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