Smart chargers and galvanic isolators

webcraft

webcraft

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I am in n the process of fitting a rudimentary shorepower system (consumer unit plus sockets) to the new boat. The system includes a CTEKM200 charger.

I am fairly convinced that a galvanic isolator would be an affordable and sensible precaution, as the boat will be left unattended plugged into shorepower for extensive periods. However, I read somewhere that GIs may not work with devices with switch-mode power supplies. Which the charger probably has?

All Greek to me - any thoughts?

- W
 
webcraft said:
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I am in n the process of fitting a rudimentary shorepower system (consumer unit plus sockets) to the new boat. The system includes a CTEKM200 charger.

I am fairly convinced that a galvanic isolator would be an affordable and sensible precaution, as the boat will be left unattended plugged into shorepower for extensive periods. However, I read somewhere that GIs may not work with devices with switch-mode power supplies. Which the charger probably has?

All Greek to me - any thoughts?

- W
Click to expand...

Providing you keep the shore power ground/earth cable isolated from the rest of the boat there is no need to fit a GI.
 
Is the CTEK charger double insulated? square-within a square symbol?
It may have no earth connection at all.
But I don't see how a GI would affect a switch mode charger anyway.

A GI is a good idea. Bringing shore earth aboard and leaving it floating can be a bad idea.
 
You’re right lw, the M200 has 2 core flex L + N with no earth.

Switch mode power supplies have no preference as to whether a galvanic isolator is in line with your vessels earth connection, or not. I’d put one in irrespective and make a substantial Earth to DC negative bond from the earth bar in your consumer unit. For the price of the bits to do it, it’s worth bonding in my opinion especially as you put more and more mains electrical equipment on board. It’s also a requirement in some countries.
 
webcraft said:
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I am in n the process of fitting a rudimentary shorepower system (consumer unit plus sockets) to the new boat. The system includes a CTEKM200 charger.

I am fairly convinced that a galvanic isolator would be an affordable and sensible precaution, as the boat will be left unattended plugged into shorepower for extensive periods. However, I read somewhere that GIs may not work with devices with switch-mode power supplies. Which the charger probably has?

All Greek to me - any thoughts?

- W
Click to expand...

If you fit a shorepower system following the requirements of the latest editions of standard ISO 13297, (the International Standard for AC systems in Small Craft), you should bond the shorepower earth to the DC negative ( unless you have fully isolated DC system) , metal hulls and the anodes etc. Early editions of ISO 13297 ( Pre 2012 ??) did not require this bonding to the DC system provided there was an RCD protecting the whole vessel. Something of an anomaly when compared with, for example, caravans

If you do bond the earth to the DC system and anodes etc a Galvanic Isolator is next to essential if you leave the shorepower plugged in. It is not needed if your earth is not bonded in this way.

You are correct that switch mode power supplies can affect the operation of a GI , but only if there is a connection to the earth, ( One device may on its own may not cause a problem but the cumulative effect of several may do so.)
A non earthed, two wire, doubly insulated device such as a CTek charger should cause any problem,b
I would follow the requirements of the latest versions of ISO 13297, as no doubt Paul and Mathew would as professional marine engineers, Bonding the earth to the DC system and fitting a galvanic isolator.


There has been much debate in the past about the merits, or otherwise, of bonding the earth to the DC system and I guess this post will prompt the debates again.
 
lw395 said:
Is the CTEK charger double insulated? square-within a square symbol?
It may have no earth connection at all.
But I don't see how a GI would affect a switch mode charger anyway.

A GI is a good idea. Bringing shore earth aboard and leaving it floating can be a bad idea.
Click to expand...

It's the other way round that can be the problem. Switch mode devices may dump unwanted electrical noise into the earth. The resulting small current flowing to earth ( probably will need the cumulative effect of more than one though) can turn the GI to "conducting mode", like ac AC system fault would, rendering it useless for its primary purpose as an isolator of current from galvanic sources.
 
VicS said:
It's the other way round that can be the problem. Switch mode devices may dump unwanted electrical noise into the earth. The resulting small current flowing to earth ( probably will need the cumulative effect of more than one though) can turn the GI to "conducting mode", like ac AC system fault would, rendering it useless for its primary purpose as an isolator of current from galvanic sources.
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Has anyone ever measured that happening? It sounds quite dubious to me.
 
PaulRainbow said:
Providing you keep the shore power ground/earth cable isolated from the rest of the boat there is no need to fit a GI.
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My boat electrics are separate from each other, but during the summer I had to use a 'smart' charger to top the batteries up. This for some reason completely 'dissolved' the anode on my outboard, so I'm assuming that the type of shore earth linked up to my charger via the boats 12 volt negative supply to the engine. My next little project is to install a 'master' switch on the negative supply to the engine for when using the charger or just disconnect the negative cable for the duration plus turn off the engine positive supply.
 
If you have mains coming aboard then there is a possibility of earth currents from the bond between mains earth and battery negative. A galvanic isolator or isolating transformer is a good idea.
 
lw395 said:
Has anyone ever measured that happening? It sounds quite dubious to me.
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I cannot answer the question but it's theoretically possible. You will find some discussion on the Yandiina marine electronics website and a clear explanation by Chris Gibson on his Smartguauge website.

Chris Gibson takes the discussion much further and into the limits of my comfort zone but well worth reading.

Another piece of equipment that could affect the correct operation of a GI is a simple "polarity" indicator. If one is fitted, and is in permanent use, its earth connection should be to the shore side of the GI so that the current from it does not pass through the GI.
 
I tried to keep it simple in post #2, perhaps too simple ?

If a shore power installation has the shore power earth bonded to the vessels anode bonding circuit (usually via the DC negative, but not exclusively) then there is a direct electrical path between your anodes and anything else in the marina that is connect to the shore power ground. In this installation a galvanic isolator is an absolute essential (not wanting to get involved in discussions of isolating transformers as they are irrelevant to this thread)

If there is no such bonding connection and no electrical path between the anode and shore power ground, there is no need to fit a GI.

There is a requirement for various builds to have the bonding circuit, such as new builds. There are millions of production boats out there with no bonding circuit or GI, built before there was a regulation to have one.

If the OP is fitting a couple of sockets for a battery charger, he might well decide that a RCD and a MCB would be sufficient and that he does not feel the need to fit the bonding circuit and GI. He's under no obligation to do so.

To answer Vics comment regarding professional installers, such as myself and Mathew, there are very few regs that we are obliged to comply with regarding low voltage DC installations. Same applies to 240v installations, we don't have to work to 17th/18th editions. But an installation that would not comply, were it required to do so, would likely be a poor installation.
 
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I have just fitted a small (2 RCD) consumer unit with the battery charger on one RCD and a couple of double sockets on the other. The only connection between the boat's earth and the mains earth that could possibly happen is via the CTEK charger, and as someone has said this does not have an earth connection in the mains lead then I don't see how this could happen.

In that case, I guess I don't need a galvanic isolator?

If for some reason I wanted to bond the shorepower earth to the boat earth I assume I would take a wire from the earth bus bar in the consumer unit to an engine earth somewhere? Not sure why I would want to do that though, it seems sensible to keep the shorepower system completely separate.

- W
 
VicS said:
I cannot answer the question but it's theoretically possible. You will find some discussion on the Yandiina marine electronics website and a clear explanation by Chris Gibson on his Smartguauge website.

Chris Gibson takes the discussion much further and into the limits of my comfort zone but well worth reading.

Another piece of equipment that could affect the correct operation of a GI is a simple "polarity" indicator. If one is fitted, and is in permanent use, its earth connection should be to the shore side of the GI so that the current from it does not pass through the GI.
Click to expand...

Had a quick look at the Smartgauge website. It's a bit focussed on Narrowboats. Personally I think a steel hull needs something to ensure there's a limited potential difference between the guardrail on your left hand and the shore ladder on your right as you board or alight. That something is usually a GI.
On a plastic boat, a minimal system where anything permanent is double insulated and not connected to any earth on its mains side seems simplest and safest.

I've seen inside a fair few SMPS and put them through CE,(and US and other) testing. For putting current on the earth wire (if they even have one) these things are not likely to be your worst problem. A big fat transformer on the other hand, I'd be wary of.
 
webcraft said:
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I have just fitted a small (2 RCD) consumer unit with the battery charger on one RCD and a couple of double sockets on the other. The only connection between the boat's earth and the mains earth that could possibly happen is via the CTEK charger, and as someone has said this does not have an earth connection in the mains lead then I don't see how this could happen.

In that case, I guess I don't need a galvanic isolator?

If for some reason I wanted to bond the shorepower earth to the boat earth I assume I would take a wire from the earth bus bar in the consumer unit to an engine earth somewhere? Not sure why I would want to do that though, it seems sensible to keep the shorepower system completely separate.

- W
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I assume you mean a consumer unit ( such as a garage consumer unit) with an RCD and two mcbs ?

You are correct in guessing that if the shorepower earth is not bonded to the boat's earth you do not need a GI as It would serve no useful purpose but your installation would not conform to the latest standards. You are free to make that choice. It would not be wise choice though without an RCD.
 
webcraft said:
If for some reason I wanted to bond the shorepower earth to the boat earth I assume I would take a wire from the earth bus bar in the consumer unit to an engine earth somewhere? Not sure why I would want to do that though
Click to expand...

If you want to comply with the ISO, the essential thing is to connect the shorepower PE to some point that has a good electrical path to ground, that is the sea. Could be engine block negative, provided there is connectivity to the prop. If no path to sea, the whole operation is pointless.
 
My electrics are bonded (newish boat) but I never leave the shorepower connected when I'm not at the boat. Despite this, I did fit a galvanic isolator as I only lift the boat once every 2 years and I wanted some reassurance that the saildrive anode would last that long. From a safety point of view, I believe all boats should be bonded.
 
BabaYaga said:
If you want to comply with the ISO, the essential thing is to connect the shorepower PE to some point that has a good electrical path to ground, that is the sea. Could be engine block negative, provided there is connectivity to the prop. If no path to sea, the whole operation is pointless.
Click to expand...

You misunderstand the purpose of the bonding circuit. It is not to connect anything to "ground". It is to protect persons not on the boat from electric shock in the event of a fault that allows the hull or a metal component on the vessel to "leak" 240v into the water. This would cause anyone in the water near the boat to receive an electric shock as the fault may not trip the RCD. If the shore power ground is bonded to the hull (metal boats) or the anode bonding circuit (non-conductive hulls) then any fault that could allow 240v into the water is guaranteed to trip the RCD.
 
VicS said:
You are correct in guessing that if the shorepower earth is not bonded to the boat's earth you do not need a GI as It would serve no useful purpose but your installation would not conform to the latest standards. You are free to make that choice. It would not be wise choice though without an RCD.
Click to expand...

I said this way back in post #2 and again (in more detail) in post #11 :confused:
 
lw395 said:
Had a quick look at the Smartgauge website. It's a bit focussed on Narrowboats. Personally I think a steel hull needs something to ensure there's a limited potential difference between the guardrail on your left hand and the shore ladder on your right as you board or alight. That something is usually a GI.
Click to expand...

How does that work ?
 
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