Mains charging a battery while afloat - basic question

[FairweatherDave]

So I have 2 batteries with a 1 2 Both switch and a small solar panel, however my electric consumption has gone up and I'm in the middle of sorting out my solar problems. But I have never charged a battery from the mains while afloat. My question is if I hook up to marina electricity for a mains battery charge with a smart car battery charger (C Tek) do I need to disconnect that battery from everything else in the boat and put on the crocodile clips? I am assuming for a single overnight charge I needn't worry about electrolysis and anodes? Advice much appreciated as always. I'm normally on a swinging mooring or at anchor so this is a new problem (and apologies for not doing the research beforehand )

 

[RupertW]

I would still be concerned about anodes assuming battery is grounded to the water although I admit I charged batteries from mains for years without a galvanic isolator.

Solar and alternator and domestic loads are fine to leave connected when charging - it’s just another charging source.

Ive never had anything but Halfords cheap car chargers but nver left them unattended for more than a couple of hours and kept an eye on the voltage.

I was going to get a decent charger when I redid the electrics and fitted mains throughout the boat a few yearsa ago but found that the new solar meant I hardly ever use the charger - maybe for a couple of hours a couple of times a year.

 

[VicS]

So I have 2 batteries with a 1 2 Both switch and a small solar panel, however my electric consumption has gone up and I'm in the middle of sorting out my solar problems. But I have never charged a battery from the mains while afloat. My question is if I hook up to marina electricity for a mains battery charge with a smart car battery charger (C Tek) do I need to disconnect that battery from everything else in the boat and put on the crocodile clips? I am assuming for a single overnight charge I needn't worry about electrolysis and anodes? Advice much appreciated as always. I'm normally on a swinging mooring or at anchor so this is a new problem (and apologies for not doing the research beforehand )

No
Because sparks igniting hydrogen is a possibility connect the charger to the battery then switch on the power. Switch off the power before disconnecting the battery.
(It is a very small possibility but a battery exploding in your face will really spoil your day and possibly the rest of your life.)
The usual recommendation with a vehicle is to connect the positive first then the negative to the "chassis" away from the battery, Disconnecting in the reverse order.

With a 1,2 both switch system I'd charge the battery not in service then switch over and charge the other.....

No problem with anodes etc using a temporary connection but a campsite hook up with circuit breaker and rcd would be a good idea if you are planning to connect like this frequently.

 

[VicS]

I would still be concerned about anodes assuming battery is grounded to the water although I admit I charged batteries from mains for years without a galvanic isolator.

Solar and alternator and domestic loads are fine to leave connected when charging - it’s just another charging source.

Ive never had anything but Halfords cheap car chargers but nver left them unattended for more than a couple of hours and kept an eye on the voltage.

I was going to get a decent charger when I redid the electrics and fitted mains throughout the boat a few yearsa ago but found that the new solar meant I hardly ever use the charger - maybe for a couple of hours a couple of times a year.

The problem with anodes only arises with a permanent shore power installation where the shore power earth is connected to the boats internal grounding point and the anodes are connected to it as well.
No connection between the shorepower earth and the anodes, which there won't be with a temporary shorepower connection, means no problem with the anodes

 

[RupertW]

The problem with anodes only arises with a permanent shore power installation where the shore power earth is connected to the boats internal grounding point and the anodes are connected to it as well.
No connection between the shorepower earth and the anodes, which there won't be with a temporary shorepower connection, means no problem with the anodes

Thanks for the explanation - that certainly applies to the setup I built but not to the basic extension lead connected to pontoon mains I used before. I need to think s bit more about connections of boat negative to the water and mains pontoon earth to the water.

 

[VicS]

Thanks for the explanation - that certainly applies to the setup I built but not to the basic extension lead connected to pontoon mains I used before. I need to think s bit more about connections of boat negative to the water and mains pontoon earth to the water.

With a permanent shorepower system it is important that a galvanic isolator is fitted in the incoming earth conductor, at least if the shorepower is likely to be connected for prolonged periods.

It is a requirement of the iso standard that there is a connection between the earthing system and the water.
This is commonly done via a connection to the anodes but this is wrong in my professional opinion. Some boat builders now fit an additional small anode , which is not part of the cathodic protection system, specifically to make this connection to the water.

 

[RupertW]

Edit. - thread drift

 

[VicS]

Yup I followed those rules when permanently fitting mains except for the small anode part as I just attached to engine Earth point. Interesting idea and wonder how you can ensure it’s the least resistance path.

You probably can't
Perhaps the answer is to leave the flexible shaft coupling un-bridged and make the connection between anode and shaft via an "electro-elimninator" or similar then the only connection between the earth system and the water will be the specifically fitted small anode

 

[PaulRainbow]

With a permanent shorepower system it is important that a galvanic isolator is fitted in the incoming earth conductor, at least if the shorepower is likely to be connected for prolonged periods.

Length of time connected to shore power is irrelevant, i've seen systems where an anode could be eroded in a very, very short time. The defining factor for whether or not a galvanic isolator should be fitted is whether or not the incoming Earth conductor is connected to the vessels anode circuit. If it is, it needs a GI.

It is a requirement of the iso standard that there is a connection between the earthing system and the water.

This only applies to new builds. It's been a requirement for some time, but there are still many, many boats out there without such a connection.

This is commonly done via a connection to the anodes but this is wrong in my professional opinion.

"Professional opinion" ?

What profession are you in ?

Where would you suggest an anode be fitted on a vessel with a non-conductive hull, with no ground plane ?

Some boat builders now fit an additional small anode , which is not part of the cathodic protection system, specifically to make this connection to the water.

Who does this and why do they do it ?

 

[PaulRainbow]

Edit. - thread drift

Hi Rupert, long time no "see".

RupertW said:

Yup I followed those rules when permanently fitting mains except for the small anode part as I just attached to engine Earth point.

Fitting to the engine Earth point only works if the engine is connected to the water. This may be the case via the shaft/prop, but i wouldn't recommend that.

If a standard hull mounted anode is fitted this is ideal, it's what a great many new production boat builders do.

 

[roaringgirl]

Surely getting your anodes eaten is only a problem if there's current running to earth?

 

[PaulRainbow]

Surely getting your anodes eaten is only a problem if there's current running to earth?

How do you mean ?

 

[Tranona]

Who does this and why do they do it ?

Bavaria do as on my 33. No other anodes except on the saildrive.

 

[roaringgirl]

How do you mean ?

If the anode is attached to mains earth, so what? It's only if there's current in the earth circuit that the anode is going to be involved in something other than the normal sacrificing of material to protect the metals in contact with the water.

 

[VicS]

Surely getting your anodes eaten is only a problem if there's current running to earth?

Not to earth necessarily..
A common example is between the anode(s) on one boat and the steel hull of another. One half of the circuit is through the water, the other half of the circuit is via the shore power earth conductors. The current t which flows between the two will cause rapid corrosion of the anodes. It can be halted, however, with a "galvanic isolator".
A galvanic isolator is a device which blocks current from very low voltages sources , such as dissimilar metals, but allows current to flow from higher voltage sources eg the AC mains. This means it does not interfere with the normal protective function of the earth in an AC mains system

 

[mattnj]

Are all the problems (that you are arguing about) solved with a GI? If so why would anyone NOT put one one....15min job and what £50?

 

[VicS]

Are all the problems (that you are arguing about) solved with a GI? If so why would anyone NOT put one one....15min job and what £50?

It should solve problems arising purely from "galvanic" or "dissimilar metal" sources but a GI could fail ... for example due to a high current fault to earth in the AC system .. they are now required to "fail safe" but safe means maintaining the integrity of the AC system earth connection, not maintaining the protection against galvanic corrosion.
It must also be remembered that a GI wont prevent electrolysis caused by leakage from the 12 volt DC system.

The only reasons not to fit one are if the boat is never left with the shorepower connected or if only a temporary hook-up, like that mentioned earlier in the thread, is used with no connection between the anodes and the earth conductor.

 

[FairweatherDave]

Thanks all for the advice, it is really appreciated and reassuring, and point taken about the hydrogen risk and sparks - a bit of revision is always a good thing!

 

[PaulRainbow]

Bavaria do as on my 33. No other anodes except on the saildrive.

Exactly. The reason that they fit the "button" anode is to make the AC Earth connection to the water, as there is no other conductor on the boat that can do this.

They do not fit it to avoid using the main hull anode, as suggested in post #6

 

[PaulRainbow]

If the anode is attached to mains earth, so what? It's only if there's current in the earth circuit that the anode is going to be involved in something other than the normal sacrificing of material to protect the metals in contact with the water.

That's correct. If a GI (or isolation transformer) is fitted there won't be any current flowing ashore and if there is any Earth leakage from the system to the water the RCD should trip.