Re: [Amel Yacht Owners] Upgrading all electronics

Bill Kinney <greatketch@...>
 

Kent,

It’s not simple…

Connecting the charger safety ground can be done to either the AC safety ground wire, or the bonding wires, assuming the bonding wires are big enough to take full current from the AC system.  Since those two systems are interconnected, they are are pretty much the same.  

There is no “DC Ground” as you seem to think of it  There is only a DC negative.  The reason for this is that 24Volts is not going to kill you, although, DC current running around on you boat can cause havoc as you well know!

Stray DC current certainly is the culprit in electrolytic damage. “Stray” AC current isn’t so much a corrosion issue as it is a serious safety problem.  The issue when connected to  shorepower is DC currents that flow over the AC Safety Ground wire when plugged into shore power. In this case every boat in the marina is grounded to the same point on shore.  Any problem on any boat can result in DC currents flowing between boats, through the water and back on the ground wire.

Now it gets more complex… electrolytic and galvanic corrosion are not exactly the same, although people frequently use the terms interchangeably.

Electrolytic corrosion is caused by imposed electrical currents.  Galvanic corrosion is caused by an electrical current generated by the presence of dissimilar metals in an electrolyte. No external voltage source is needed. Galvanic voltages are low, usually less that 1 volt and are blocked completely by a galvanic isolator (hence the name…)  Stray currents can be up to 24 volts.  If they are greater than about 1 volt the galvanic isolator does not work.

One other difference.  The isolator blocks galvanic action between different boats.  It will not protect you from electrolytic corrosion caused by stray current generated by your OWN boat that do not flow through the AC safety ground wire.  And an isolator does nothing at all when not in a marina.



On Aug 10, 2016, at 14:06, Kent Robertson karkauai@... [amelyachtowners] <amelyachtowners@...> wrote:


Well crap, I guess I still don't understand it all.  So IF the charger has an AC only ground , it should be connected to the bonding system.  What about the DC ground (I assume a charger would have a DC ground too)?  I'm not talking about the DC output negative, I'm talking about something that would become hot with DC if there was an internal short on the output side. Is that run back to the battery negative?  If the safety concern is that either AC or DC current could shock you if the case became "hot", how could you separate the two?

Stray DC current is supposed to be the culprit most of the time in electrolytic damage.  Low current leakage that isn't enough to trip the breaker, but enough that over time it destroys your underwater metals.  Stray AC current can do it, too, particularly when on faulty shore power without a galvanic isolator.  Do I at least understand that correctly?

Sigh,
Kent, "Rusty", "Patch"
SM 243
Kristy



On Aug 10, 2016, at 1:49 PM, Bill Kinney greatketch@... [amelyachtowners] <amelyachtowners@...> wrote:

 

Kent,


It is not as simple as saying it is "OK as long as you  don't connect the ground [of the charger] to the bonding system

You can not, and should not, remove all connections between the bonding system and the AC safety ground.  Those connections are there by Amel design—not by accident and are shown on Amel’s electrical drawings.  See Olivier’s comments on this matter.  Because of the connections between them, the bonding circuit and AC safety ground circuits really are all part of the same system, in normal operation carrying almost no current, but equalizing voltages.

Because there are always going to be connections between the AC safety ground and the bonding system, ANY connection between the DC negative and the AC safety ground is the same as connecting the DC negative to the bonding system. This should NOT be done--anywhere--on an Amel.  

The apparent problem with some battery chargers is that they make such a connection between DC negative and AC safety ground internally.  These are the kinds we need to avoid.  On a proper marine battery chargers this connection would not be part of the design.  It would be bad practice on any boat to have multiple connections between DC negative and AC safety ground scattered around the boat and always bad to have the charger case be part of the DC negative circuit. I am pretty sure that such a piece of equipment would not be considered ABYC compliant.

An important point to remember is that the AC Safety ground—in normal operation—should not carry any current at all.  It is only there to drain off hazardous voltages caused by short circuits to equipment cases.  Almost always, when this happens the current draw is enough to trip the circuit breaker, shutting down the faulty circuit.

Recommending that the case of a battery charger (or inverter, or any piece of equipment connected to AC line voltage) should not be grounded should not be done lightly.  Most of the time, that ground is an important safety issue.  If there was an internal short the case of the charger could become “hot” at full line voltage.  If the case is not grounded that condition can continue until the next thing to touch it (You?) carries 220 volts to ground. 

Bill Kinney
SM #160, Harmonie
Highlands, NJ
“Ships and men rot in port."





On Aug 10, 2016, at 08:50, Kent Robertson karkauai@... [amelyachtowners] <amelyachtowners@...> wrote:


 I'm looking for a new charger now, too.  My Charles 60 A charger doesn't have an equalization cycle.  So far I've only been looking at chargers recommended by Amel owners on this forum, and for a 75-80A 24V charger with equalization mode only the Victron Skylla-i meets my needs.  I'm also looking at MasterVolt but a few owners have had bad experiences.

I think any good marine charger is OK as long as you  don't connect the ground to the bonding system.

I think ideally we want a charger with separate AC and DC grounds.  That way you could connect the AC ground to the boat's AC ground, and the DC ground to the battery negative.  Unfortunately they all seem to have a common ground that ABYC standard wants you to connect to the boat's "earth".

Are you just dropping a lead into the water and measuring between that lead and the bonding system?

It sounds like there is a fault in you charger.  But if it isn't connected to your bonding system, there is another connection to your bonding system that is carrying current to the water.  It could be on either the AC or DC circuit.
I'd be interested in what you find if you disconnect the AC and DC wires from the charger and measure resistance between each wire and the bonding system with the circuit breaker off, and again with CB on.  That should help you determine where to look for the connection.

On my boat I was never able to completely eliminate all connections to ground.  Your 220V air conditioner water pump, for example, is connected to the bonding system.  My generator case is also connected to the bonding system. (Read Olivier's earlier comments on this.)
I purchased a silver/silver chloride reference electrode to monitor hull potential and do that once a month, and every time I drop anchor or tie up to a marina dock.
Let us know what you find.
Kent
SM243
Kristy



On Aug 10, 2016, at 4:49 AM, rossienio@... [amelyachtowners] <amelyachtowners@...> wrote:

 

Hi Kent,

 the Sterling ProCharge N is only charger, it was  installed  time ago, without ground connection, but I have seen the problem only now, touching the mooring wet of salt water, while the boat is connected  to  the shore power of the Marina and with the C.B. on.
I can see the voltage leak with the tester on AC (2V) and DC (2.5V) connecting metallic parts of the boat with sea water.
Now the generator (Fischer Panda) is totally isolated, with all wires ( in and out ) disconnected so I' using now only solar panels.
I am going to do all the measures suggested by Olivier, but I think that the Sterling is not suitable for our boats.
Could  you give me some indication about Battery Charger  suitable to boats with the electrical system isolated, like Amel?
I also istalled an alternator-to-battery charger Sterling, do you think that it too could not be ok  for the Amels?
Here I'm not able to find an Amel-savvy electrician. 
Good wind






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