Boat Fault Finding - Marine Electrical Problems

The reason why relays are so common on cars is because with the advent of "steering stalk" switches, the switches are not large enough to carry the current required. In the old days with stator tubes right up through the steering column we used a horn relay because the cables up the tube (including trafficator wiring) were not large enough to carry the horn current, especially with twin windtone horns.

Now, ask yourself where we would mount such a relay for boat use. If it is going to be close to the switches we will still need cable capable of carrying the full current the length of the boat, if you add the cost of the relay, the slightly more complicated and thus slightly more unreliable wiring to the cost of a low current switch, we might just as well have used a decent switch in the first place and saved on about 4 connections. This gives a more reliable system that is easier to fault find.

If we mount the relays close to the light or horn we then need a single high current conductor run the full length of the boat, plus (for each item) a low current one. This implies two fuses or more and again more complicated wiring and fault finding, One might just as well use suitably rated cables and switches in the first place and do away with complications.

FWIW, I do use relays when appropriate, but it is not appropriate (in my view) to use them for the items you list. As an example, I want to switch my domestic water pump from both the kitchen and the toilet compartment as per the landing light at home. Suitable single gang, two way, switches rated at 12/24v DC are not available and as the pump switch might be operated with the pump under maximum load, the non-self quenching characteristic of DC current could lead to arching and burning of switch contacts rated at AC (the only ones easily available). In this case I use a pair of normal AC two way light switches, but use them to control a DC rated relay that switches the pump current.

So it is not a case of not using relays, but of only using them when the added complications of wiring is offset by a gain in reliability.

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If these are bi-coil gauges with three terminal on the back, I think two are transposed.

One is a live feed, one is a negative connection for one coil in the gauge, and the other is another connection for another coil, but this time running to the sender unit.
(Info and diagram on www.reading-college.ac.uk/marine )

You need to change the two coil wires over. If you are lucky they will be marked something like - or neg and S (for sender). As long as you do not touch the live (+) terminal I do not think that you can do much harm.

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I think you have either loosened a terminal or are suffering from a coincidental fault.

First tug/push/wiggle all the terminals on the starter circuit to see if you can find any loose ones, also try to start it and feel for any heat - indicating a bad terminal.

Make sure your battery terminals are both clean and tight.

The thing you describe as clicking is a starter solenoid off something like a mini or any other older car. If you carefully bridge the two large terminal studs with an old, large, screwdriver - be firm and positive, try to ignore the sparks - there will be a good chance that the starter will work. If it does, change the solenoid. Make sure you do not touch any other metal with the screwdriver, otherwise you could have a short circuit and fire.

If bridging the terminals does not make the starter run, I fear you may have a faulty starter, but as I do not know the starter type (axial, co-axial, or pre-engage) I can not give much more advice.

In the event of needing to change the solenoid, an insulated return version may be difficult to come by. Any modern unit will be satisfactory as long as you mount it on wood, to insulate it from the hull, and fit a negative wire onto a mounting bolt/screw.

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We don't want to be endlessly running the engine just to charge the domestic batteries and there is shore power available at our regular mooring so one option would be to use a (say) 40A charger to provide both charge and domestic supplies while we're moored there. Security concerns say that shore power will be disconnected when we're not on board and there'll only be a 12V alarm system left powered-up. Assuming the bulk charging will be done either from the mains charger or from the alternator(s) if we're cruising, we'd like to connect a third source, e.g. solar, to provide a float charge while the boat's unattended.

First question is: the three charging sources seem to require separate controllers which the Adverc website indicates might end up confusing each other. Is there anything available to tie all these together so we can avoid this happening, e.g a single box which can control all three raw sources or some kind of automatic switch-over unit?

The next question is: if this disconnects the solar panel, what happens to the energy it's collecting, i.e. does it need some kind of 'dump' load and if so how might we provide that?

I think you are right to consider solar power because of the burglar alarm.

Have you considered a well specified, mains, three stage charger that can be left on for 100% of the time you are away?

The easiest way to control the three sources, especially in view of your intended use, would be a great big three way, manual, switch. However there are automated units available, but I have no experience with them - my motto being KIS. You need to talk to some of the marine suppliers who advertise in the magazines.

I have asked my fellow electronics lecturers about leaving the solar panels without load, they appear to be of the opinion that they are just like batteries,. They just stop producing electricity because they can no longer push electrons around the circuit against an infinite resistance. They probably get a bit hotter because the energy is not being converted to current. I can not confirm this view.

It all depends how your switch is wired. It could be wired as a charging change over switch or as a load change over switch. There are diagrams on www.reading-college.ac.uk/marine  under electrical notes.

I do not like these switches because if they fail to make before they break, and you switch them with the engine running you are likely to destroy your alternator.

My preferred method is two master switches (one engine battery and one domestic) plus a split charge relay - see site above.

Normally the two battery negatives are linked with heavy cable - starter cable is fine - and the positives switched.

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I use my boats for cruising and therefore wanted the system to be less reliant on a shore line.

I have therefore increased to 4 x 110AH leisure batteries and fitted a Phoenix Combi inverter/charger and a split charge relay from the alternator.

Now, my question is regarding the good old fridge. I have 240v/12v/gas fridge which is currently only connected to the 240v. It would be far easier to wire it to 12v rather than connect the gas which due to the positioning etc would be a little awkward. Also I'm far more comfortable wiring than doing gas. Obviously I don't want the fridge draining everything so I was thinking that I might put in a dedicated battery with another split charge relay so that it could discharge itself without affecting everything else. Would this be a good solution or am I coming at it sideways? Or overcomplicating things? Would this battery be up and down too much and harm it and therefore the others when they were all connected via the relays?

Just for interest I've attached the wiring diagram I drew for the system. I've learnt as I went along by asking questions and researching etc. and am really quite pleased with what I've managed to achieve. The only other thing I am worried about is 240v leakage which I have read about. What should I have to ensure that the inverter in particular is safe when operating and unlikely to electrocute anyone!

Once again I would like to thank you for your advice I've managed to find on net. It has been most useful and has helped someone with a mere basic knowledge now have almost completed a project of which I am very proud.

Thank you for all that. You will now find our Electrical Course notes on the website.

I am almost certain that your fridge is an Electrolux unit and that it is only supposed to use 12 volts whilst driving to a site in the caravan. In this mode it does not need a thermostat, so one is not fitted to the 12v heater coil.

As an absorption fridge it is not very efficient, so draws something in the order of 6 to 8 amps the whole time it is turned on. I think you will draw your own conclusions.

If you can not continue to run it on gas, then practically you have two choices. Even if you run it off 240 volts, the loading on the batteries is likely to be the same or worse, except it should have a 240v thermostat so may only work draw current for 50% of the time.

1. A 12v compressor fridge. This will cost £300 plus and if its any distance from the batteries will require getting on for £150 for the cables.
2. A domestic 240v fridge plus inverter. As you have the inverter already I think this is the way for you to go. The only things I would be concerned about are:
a. Can the inverter cope with the fridge starting surge (probably yes for your inverter)
b. How high is the inverter "stand by" current when its turned on, but the fridge is turned off.

As far as using another split charge relay and separate battery, you really need to do the calculations to find out how low you would discharge it. These are in the electrical notes mentioned above. I am happily running a TV, waterpump, lights and 12v compressor fridge on a cruising boat with a 60 amp alternator and 2 x 110ah domestic batteries.

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By far the easiest way out of your problem - assuming it really is the alternator and not the wiring - is to get another ACR. If yours is the one with the big plastic end cover, then I think any ACR that looks the same should fit. (There is an issue about machine sensed or battery sensed, but battery sensed were quiet rare).

I think they will be readily available as exchange units from most Motor Factors or Vehicle Electrical Specialists, but I am also sure there will be available from a car breakers - just look for one that looks the same.

The mounting bracket at the opposite end to the pulley has a sliding, metal, mounting bush in it for the bolt. As long as you support the alloy bracket with a bit of tube or something, you should be able to tap it to move it to suit your engine mounting brackets.

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I currently have 5 batteries a 110Ah heavy duty starter battery (new) and 4 x 110Ah leisure batteries connected together for the domestic power. I also have a Victron inverter/charger for the 240v side and a Honda 2300w petrol gennie as back up. The engine has 2 alternators one for the starter battery and one (I think 35amp) for the domestic battery bank. On the load side I have the normal lights and water pumps, a microwave, an electric kettle and a washing machine.!

My questions are, could I reduce the domestics to 90Ah units ? & could I mix 2 x110Ah and 2 x 90Ah units together ? Is it worth getting a battery management unit in addition to the Victron ?

The main reason is that I think the existing batteries have been discharged a few times below the "safe" level and are tired and secondly I have the chance to buy some Bosch batteries at a discount price but only for a couple more weeks. I would buy 4 the 110Ah units but cannot get the terminal configuration to fit my battery box whereas the 90Ah units ate available "left" or "right" handed.

1. I hope you're wrong about the domestic alternator only being a 35 amp unit. This would be fine for an engine battery, but not for your domestic ones.

2. The Victron is no help whilst away from a shore line.

First you must do a power audit - details of how on www.reading-college.ac.uk/marine  in course notes. This will require you to calculate the amperage drawn by all your electrical equipment and an estimate of how long you use it for per day.

Divide battery powered equipment wattages by 12 and inverter powered equipment wattages by 10. Multiply inverter powered equipment amperes (if given) by 20 to get amps for the power audit.

If 30% of your battery capacity is less figure found in the power audit either fit an advanced alternator controller and recalculate using 48% or install higher capacity batteries.

You then need to decide upon a "nearly worst case" time you will run your engine for in a day - the "day could be two days if you tie up for a couple of days in each town.

Then (and this is only a rough guide) multiply half the alternators rated output by the time you get in the above paragraph. If this gives a figure in amp hours that is less than that given in the power audit, you need a larger alternator.

If the charging current after about 10 mins running is more than about 20% of the capacity of the battery bank, fit more batteries. This will maximise battery life. 5 X 110 ah batteries allow about 100 amp input, and as this would probably cause problems for an ordinary V belt, this will probably not be an issue.

Only after you have done all this can you get an answer to your questions.

It is probably not good practice to mix battery capacities, but may well work - it all depends how much cheaper they are - and do Bosch supply deep cycle batteries? Please do not use engine batteries for the domestics unless they are so cheap you can throw them after a couple of years if you need to.

If you change from 110ah to 90ah you will be loosing 80ah capacity, which is nearly another battery. As the batteries will only deliver about 30% of their rated capacity and you have a lot of high current devices I could not advise changing to 90 ah.

90 Ah will be fine for the engine.

I would always advocate an advanced alternator controller because :
1. It will charge your batteries to about 98% fully charged as opposed to 80% with a standard regulator.
2. It will convert your (probably) machine sensed alternator to battery sensed (if you do not understand some electrical notes should be on the above website by the end of April).
3. The higher state of charge will minimise sulphation, although this is less of a problem for liveaboards where the batteries are always charging or discharging.

My notes name the make that I feel makes the optimum product.

Sorry about the technical stuff and maths, but if you do not do it, how can you know what you dealing with?

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I do not like going against a BSS inspector - but he is wrong.

Fuses in fuse boxes protect the wiring NOT THE APPLIANCE. If an appliance needs its own protection it will be fitted with its own fuse like TVs, radios and inverters it will have its own fuse.

Just because a Wylex fuse is marked 15 amps does not mean its fused at 15 amps - that depends upon the size of fuse wire fitted - did the inspector measure this? (rhetorical questions) The 15 amps is the maximum rating.

In a perfect world you would ensure the fuses blew if the current flow exceeded the capacity of the cable, but as I have no idea about the size of cables used in your boat I can not advise, however the most likley size for much of it is 28/0.30 with a cross section of 2 sq mm. This is rated at 17.5 amps, so this and anything thicker will be adequately protected by your fuses.

There is a lot more to fusing than meets the eye, especially when looking at motors and inverters. These should all be cabled for 20% more current than stated on the label or measured once running - they take a lot more for a split second when starting.

At present I am putting our Boater's Electrical course notes on the website ( www.reading-college.ac.uk/marine ) and I hope to have
them on by the end of April. These should make the whole thing clearer for you.

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I have a query with regard to a problem we have with the boat electrics which I was hoping you might be able to suggest a way forward.

When we bought the boat about 7/8 years ago she was already about 4 years old and fitted with 4 x 6 volt batteries to give us a 24 volt system. I think the batteries were original and within the first year we started having problems with the electrics, but generally more during the winter (fairly obvious really with lights being on more often). These 4 batteries were replaced with 2 x 12 volt 110 amp hr. ones connected in series.

The way we use the boat is that my in-laws go away on the boat during the summer months, April to end September usually. When they finish cruising for the day they will probably watch TV and have a shower in the morning and they did not suffer the problems we had. We have the boat out at other times of the year and usually over the Christmas period. We cruise for the day and will have a shower in the evening. We found that when we came to switch the TV on (a 10" CRT colour portable) it would quite often not switch on unless I started the engine. So we then switched the TV on before we had a shower but the found that the TV would switch off part way through the evening especially if the water pump was run.

In trying to resolve the problem I found a duff inverter which was drawing current even when nothing was running off it. This has now been taken out. We have also replaced the CRT TV with an LCD one. The TV runs from a 24 volt to 12 volt converter and I have replaced the wiring between the converter and the TV with thicker material (as suggested by the boatyard). Last summer we had an Adverc fitted. Despite this we still have problems when we went cruising last September and more so over the Christmas period. We can cruise for 5/6 or 7 hours and if we have a shower in the evening we have problems with the TV. We still put it in before we have a shower and part way through the evening if the water pump is run or a light is switched on the picture goes off on the TV although the sound stays on. If we change the channel over the picture comes back on. We have also noticed that if we have had the lights on for most of the night, had the TV on and also had a shower, the water pump sounds very strained in the morning.

Here is a list of the electrical items we have on board:
12v radio/cassette 16w/channel. (which we rarely use)
TV 12v LCD 3.2amps
saloon lights (4) 24v 20 watts
table light 24v 20 watts
water pumps (2) one is rated at 1.8 amps the other 3.5 amps is used as a spare and is not connected.
shower pump out 24v 6.5 amps
lights over dinette, bedroom and engine room (3) 24v 21watts.
small lights over bed (2) 24v 21/6 watts.
Fluorescent lights in galley and bathroom (2 with 2 tubes in each) F13w/w
I've not included the tunnel lamp or the horn. We run the fridge off gas.

Do you agree with the following calculation based on a typical 'winter days use':

Does this seem reasonable and do you think that our battery bank of 2  12v x 110amp hr batteries connected in series should cope with this ?

Were you aware that all inverters draw a small current if left on with no load. In my view they need their own on/off switch - depending upon model allow about 1 amp = 24 AH per day.

Now lets look at the battery question. I assume your calculations are correct.

You now have an Adverc, so at we can assume them being 98% charged at the beginning of the evening as long as you have cruised enough during the day. We know that at 50% discharged the voltage and the life of the batteries drop. We do not know how sulphated the batteries are or how well they hold their charge, especially as the indications are that they have been too deeply discharged in the past.

98% - 50% = 48%.
48% of 110 AH = 52 Ah

So with good batteries, fully charged you have just 10AH spare. With the inverter in circuit you probably had a deficit of 14 AH, so you were discharging your batteries too deeply, shortening their life.

I think the 24 to 12 volt converter may be more inefficient than an inverter - how hot does it get in use. If it warms up its drawing current itself and probably dumps it to earth - not very efficient!

It looks to me as if your batteries are at or very close to the end of their life (I make them about 6/7 years old by your figures and suspect their life was up a couple of years ago, so you have done well). Get them tested at a battery specialist (yellow pages). I also think that you are cutting the capacity very close. If it was a 12v volt boat I would advise putting another battery in the bank, but two more is a bit expensive.

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It appears (http://www.cruzpro.com/vah30.html#HEADINGA) that there are four connections to make from the meter. One goes to the positive terminal of the battery. Two go to the high resistance circuit of the shunt (one +ve, one -ve). So far so good. The fourth goes to a "ground" - I assume that is "earth" - terminal on the shunt. The other terminal on the shunt is connected to the negative terminal of the battery. And finally the "ground" terminal of the shunt is connected to the "ground bus". The diagram shows the "power bus" as being connected to the battery +ve. My system does not have an earth  as such, so what do I do?

I am not surprised you are a bit confused - given conventional split charge, boat wiring I do not think the diagram from the manufacturer will work.

My understanding is that these gauges require both the load current AND charging current to pass through them, and as drawn I think that one of those will not.

Look at your battery banks. You should see a heavy cable (often starter cable size) joining the domestic bank negative to the engine bank negative. This is needed to allow the charging circuit for the domestic batteries to find its way back to alternator negative.

You should also see another heavy cable running from domestic negative to inside the boat. This leads to some form of "multiway"
connector inside, or close to, the fuse/circuit breaker box - this is the negative (or ground) bus.

The above wire only carries load current, the inter-bank cable carries the charging current.

I think this may have to be wired as described below, but you MUST CHECK WITH THE MANUFACTURER.

Assuming the domestic master switch is in the positive lead.

Disconnect ALL cables from the switched side of the master switch (I think there will be two- but there may be more).

Connect these to one side of the shunt.

Make up a heavy lead to connect the other side of the shunt to the master switch.

Meter (F) to small shunt terminal closest to the master switch

Meter (E) to other small terminal

(Once fitted, if the ammeter is reading the wrong way round, reverse these wires)

Meter (A) to any suitable negative connection point.

Meter (C) from any domestic positive connection via a 1 amp fuse.

Meter (D) - if you want to use it - from any fo these, tunnel light switch, ignition switch, its own switch.

Meter (G) - a voltmeter connection, to the engine battery positive.

Meter (H) - another voltmeter connection, to the bowthuster, winch, or fridge battery positive.

I state that it is your responsibility to ensure that my advice is correct.

Whilst you are on the the manufacturer you might ask them how the meter allows for internal, self discharge of the battery. I am not too worried about this if you are an inland boater, but if you go to sea, you need to ensure that the meter has/can take account of self discharge, otherwise it will be telling you that your batteries are 3/4 charged, yet they may only be 1/2 charged.

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Please make sure that you put a subject on your emails. Luckily I had a look through my spam bin and found yours.

First of all visit the www.TB-Training.co.uk website and study the charging system section of the Electrical Course Notes. That should give you some idea of what split charging systems are all about.

Without checking the boat I would say that during normal use the engine and domestic switch should be turned on and the link switch off.

I would expect the link switch would only be used when the engine battery was flat and it would then form a sort of "Jump lead" circuit so the engine started from the domestic battery. This will not be good for the domestic batteries, but will do little harm now and again.

Unfortunately the term "split charge system" has no definition, so the above assumes some form of automatic battery "linking" system when the alternator is charging - either a split charge diode or split charge relay system. This, however may not be so. That link switch may be the means of charge splitting, so you need to do a test.

Set the switches as outlined above and measure the voltage across both battery banks (expect over 12v on each). Start the engine and give it a bit of a rev to make sure the alternator has energised and remeasure each battery bank voltage. Both should have risen and be virtually identical. If so you have some form of "automatic" charge splitter in use.If not, turn the link switch on. You should then find both banks give the same voltage reading. If this is the case the link switch should be turned off as soon as the engine is stopped for the day and on as soon as it is started in the morning.

Please be aware that master switches in the negative side of the batteries may cause a fire under certain conditions IF YOU HAVE ANY EQUIPMENT THAT REQUIRES A PERMANENT FEED - typically a car radio, automatic bilge pump or security system. If nothing is permanently fed I am sure it will be OK.

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We are having electrical power problems. The boat has a 240v , 24v and 12v systems with a 240 v fridge and other 240v and 12v power points. Apart form the fridge and seldom the TV the 240v circuit is not used much but the service batteries are loosing their charge faster than the engine alternator can replace the charge. The result is a dead 240v circuit and failure of the Ebersbacher heating system.

I have been told by a fellow boater that I should consider replacing the 6v service batteries with 4 x 12v as the residual charge would last longer. It's also possible that the old Hawker batteries are finished.

Questions.

Apart from a voltmeter and hydrometer how can I check if the batteries are gone. They seem to hold the charge must better from the landline.
1) Can I just replace the 4 x 6v batteries with 4 x 12v.
2) Do I need to consider the charge rate of the Victron inverter /charger / Genset / Alternator
3) Do I need to uprate any fuses. I have a 16amp fuse box between the landline / genset and the 240v circuit.

The voltmeter states a charging rate of between 12 and 14 volts for the main engine, genset and landline individually. I have two alternators. 1 for the engine / batteries and 1 dedicated to the bow thruster.

This is probably just a battery issue as I believe the Hawker 6v may be original, but if I can increase the storage by uprating to 4 x 12v I would like to do so.

The life you get put of batteries will very much depend upon how you use them, how you maintain them, and type. I think the Hawker batteries are deep cycle batteries and this is why they may be 15 years old especially if you often have a landline and charger connected to them. If you want similar life out of any new batteries make sure they are good quality deep cycle ones. The engine starter, generator starter and possibly the bow thruster batteries should be starter types.

You give no data on the amp hour capacity of either your hawker batteries or the 12v ones the boater proposed that you used, so I can not pass any comment upon getting a capacity increase by changing to 12v batteries. As an exceedingly rough guide if the batteries will fit into the same space they have a similar capacity. more space = more capacity.

Inverters do not charge batteries - they change low voltage dc into 220v ac. However I suspect that your inverter may have a battery charger built in.

Of course you have to CONSIDER the charging voltage from all charging equipment. If it is too low the batteries will never be charged and if it is too high you will ruin your batteries. However without far more information about rated capacity from all charging sources, the charging current, and battery condition I can not pass comment on you particular system. If the batteries are in a poor state (probable internal short circuits) they will draw a high current from whatever source and this will depress the charging voltage. As the batteries charge up and the current falls, the voltage will gradually rise to a little above 14 volts. As you say you do get to 14 volts I suspect your charging system is OK, but I am very worried about the 12v reading. I would like to know the terminal voltage on each battery first thing in the morning and also after being left in a charged state and not used for a week. I suspect the terminal voltage will be below 12v in both cases and if so it indicates faulty batteries.

I think you will find that the charger in the inverter has a much more sophisticated charging process than the engine alternator. However if you mean that when on the land line the batteries do not go flat I am not surprised - they are being charged all then time.

As for testing the batteries I trust the hydrometer, but difference in reading between any two cells in a battery of more than 0.3 (I say 0.5) sg indicates a faulty cell - do not try to test if you have just topped the batteries up.

Other indications of a faulty cell are coloured electrolyte, one cell needing far more topping up than the others and one cell bubbling more than the others when on charge.

When battery cases swell it is a fair indication that they are getting towards the end of their life.

You could fully charge the battery and then put a known load on it and time the discharge. If the time x load (amps) is significantly lower than the ah capacity the battery may well be faulty.

Most reputable battery retailers now have sophisticated electronic battery testers.

All the above is no use unless you do your power/energy audit and charging calculations. You give me no idea indication that you have done them so I would suggest that before you part with any money you go to my website and look in either set of course notes. Both tell you how to calculate your theoretical battery and charging system needs - then you will start working from knowledge, rather than towpath expertise. While there look in the electrical notes and find out how to calculate the total battery capacity for batteries connected in series (like each pair of your six volts) and in parallel (like the two 6v pairs.

There is little point in increasing the storage capacity of your battery bank unless you find it marginal or deficient. If we are talking Hawker batteries to do so is likely to be expensive, but as long as the charging systems you employ can cover your discharges with up to 40% spare you will do no harm.

Be careful about changing batteries because it is all too easy to get batteries you can not lift easily. This may well be why you have 4 six volt ones rather than two 12 volt ones.

You can replace the 4 x 6v batteries for 12v ones as long as you get the connections right. However I suspect you may not get the results you think you will.

I have no idea what causes you to ask about fusing the mains circuit because it should have little to do with batteries and charging. If you only have a fuse on the mains circuit I must advise that you fit a suitable RCD PDQ and also make sure the mains system is earthed as per the BMEA codes. Fuses protect cables - nothing else, so if your mains wiring is rated at above 16 amps then you can increase the rating if you wish, but I still do not understand how this fits in with the rest of the question. 16 amps at 220 volts = 3500 watts. 3500 watts at 12v = nearly 300 amps so if you are concerned that the fuse is "throttling" the charging you need not worry. I doubt the charger draws much more than abut 5 amps from the mains and probably closer to 3.

If you want more help come back, but I do need to see your energy\power audit, battery capacity and charging time figures.

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First of all how did you measure this? If you measured between battery negative and the hull with the master switch off you would find a voltage because the electricity from any permanent feed equipment could not get back to the battery through the open master switch.

I really need a complete wiring diagram of your boat to answer this and if you had one I suspect you would have found the answer by now.

The most likely cause is a bit of incompetent "add on " wiring, a car radio, bilge pump or any other item that is allowed to bypass the master switch, or wet/damp/submerged connections.

Putting master switches in the negative side of a boat's circuit is dangerous and can lead to fires under certain conditions if you have any equipment with that requires a permanent feed.

I would immediately CHANGE your master switch(es) to the positive side.

Who said the 12v is causing the pitting? Before it can do that it has to leave the hull and then get back into it.

If you have a land line without an isolation transformer or galvanic isolator that is far more likely to be the cause.

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