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Old 02-04-2010, 14:19   #46
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If money/weight/space were no problem, I'd own an isolation/boosting transformer. I have a problem with at least one of those criteria, so I live with my galvanic isolator (no capacitor) and fault isolation breaker(s).

I feel safe on my boat.
Yes you are almost as safe as without the GI. But without the capacitor, your boat is not protected like you think it is, maybe even not at all. And if that is the case, why bother with it at all when it still decreased your safety a bit without any other positive feature?

cheers,
Nick.
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Old 02-04-2010, 14:32   #47
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Nick, how could you 48 hours ago I set my mind on fitting a GI this Spring. Okay so GI is another $150 but I was resigned to the cost on the grounds of safety.

Now I read about isolation transformers and its going to cost £600 ($1000) its a huge great box and god only knows were it is going to fit. Additionally I now need to work out how big an IT I need by adding up all the amps we might use, batery charger, heater, kettle
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Hi Pete,

Good to see the difference I make ;-) After you install the IT (more abbreviations, isolation transformer this time) you will for ever sail without galvanic corrosion troubles and completely safe. It's like being on the safe side of a gun: no need to take cover.

You don't need to calculate at all. Just check your shore power cord and/or the outlet you stick it in and/or the main breaker value that it connects to aboard. Being a Brit I think you will have a 230V 16A shore power setup, so the Victron 3.6kW is what you need. If you turn on too much stuff concurrently, a breaker will flip. The transformer is fully protected against over current and over temperature: you can't hurt it with your heaters, chargers and kettles ;-)

Also: let no one tell you that you need more power on your boat. We have 3.6kW shore power which is more than enough for us. Right now, under a scorching tropical sun but in a nice air conditioned boat, I am using 1760W with the 18kBTU A/C and battery charger and my computer with 24" LCD screen running (plus some gadget chargers, cat fountain etc).
Dealing with cold is easier (electric heating is 100% efficient while cooling is just 70% efficient).

ciao!
Nick.
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Old 02-04-2010, 14:38   #48
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Hi Pete,

cat fountain

??? This is getting interesting.
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Old 02-04-2010, 14:40   #49
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I think that what you call the "dreaded open circuit fault of a galvanic isolator" is when one or more diodes have failed. This just shows that this isn't something that almost never happens. Diodes blow easily and quick (think of alternator diodes blowing the instant the battery switch is turned).
Although, 90+% of diodes fail short, not open. In the case of GI, safety is not sacrificed......I know, 90% isn't a good enough statistic....
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Old 02-04-2010, 14:42   #50
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??? This is getting interesting.
HA! Ha!...is was thinking the same thing..

Dont forget my question..... Nick
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Old 02-04-2010, 14:52   #51
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Yes you are almost as safe as without the GI. But without the capacitor, your boat is not protected like you think it is, maybe even not at all. And if that is the case, why bother with it at all when it still decreased your safety a bit without any other positive feature?

cheers,
Nick.
Diodes only, no capacitor, stop current flow, both AC & DC until, as you stated, 1.2v potential is crossed (or .6v * qty. of diodes in series). That's my goal. Since I don't spend much time in marinas connected to their power and ~95% of my shore power comes from my own dock, fed by my own power installation, I feel/know this is good enough galvanic protection for my situation. Yes, a leaking AC water pump">raw water pump motor could break down the diodes, but my main FI breaker will blow first/also. So galvanic corrosion from shore power is stopped and I feel the FI breaker protects the human factor. Of course, this doesn't stop the 'same boat' galvanic corrosion, hence I change my zincs religiously every 6 months regardless of noticeable corrosion.

Again, I agree the ultimate is an IT. It's just not a cost I can justify in my situation. That may change if/when I ever get to live long term on the boat (yes, Nick, I'm jealous!).
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Old 02-04-2010, 15:00   #52
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Nick...could you so eloquently describe the bonding issue...that's still and elusive one for me with conflicting thoughts...it does pertain to this thread as it is also galvanic in nature.

Your a venerable book of knowledge my friend and greatly valued.
Bonding is more complicated. There are two different approaches that both make as much sense: bond everything metal and bond nothing. So there you go... US boats often have 100% bonding and EU boats often have 0% bonding. I think both systems are fine which would make the EU setup more elegant again because it eliminates a lot of stuff like wiring and weight.

On a boat, you generally have 4 grounds: DC ground, AC ground, SSB ground and bonding. Best is to keep all four apart imo but others do not agree with that.

Bonding: everything or just underwater metals? If we're talking about just underwater metals, we are dealing with just one thing: galvanic protection for these metals. What you do is electrically connect all these metals and connect a zinc anode to just one of them. The anode will protect all the connected metals. That's it. We have zincs on prop and propshaft and two bronze plates under the masts for lightning protection that double as grounding plates for the bonding system. Those are probably protected by my zincs on the propshaft but maybe not. I check them when I clean them and they still look okay: I can still read the stamped-in lettering. I added 3 bronze keelcoolers for refrigeration, and two bronze seacocks. I connected these to my bonding system except for one seacock. I see no difference with that one seacock so as time passes I am proving it doesn't really matter. There are no other under water metals except for the lead keel which is bonded too (but always painted).

I would always add zinc to propshaft and prop, no matter what else I have.

Lightning: it is proven that my plates under the masts work. The wiring must go straight down between mast and plate without any bends. We had two strikes big enough to evaporate everything at the mastheads and all the charge was safely routed to ground via these plates. If they wouldn't have been there, the lightning might have holed us or it might have traveled through the interior with great danger to any occupants.
I am happy that my SSB ground isn't connected to that ground!

(I just switched on the water heater.... shore power consumption went up to 2700W so still 900W below the 3.6kW).

I will add something about shore power capacity here, something I forgot to mention. Surges are not important, the components incl. IT can deal with them and fuses survive them too (they are too short to blow the fuses or breakers).
Also, I have a Victron Quattro inverter/charger. It has a feature called "Power Assist". This means that whenever it detects that I use more power than available from shore or genset even after it reduced battery charging to zero, it will add power by taking it from the batteries. For this purpose, it keeps it's inverter synchronized to the incoming power from shore or genset so that it can do this in a flash. It can add 3kW of power that way for a total of 6.6kW when I am at shore power or 9kW when I am on generator.
I can also adjust this feature to kick in at different power levels, like 2kW from shore. Handy when you blow a fuse ashore otherwise.

ciao!
Nick.
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Old 02-04-2010, 15:04   #53
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Since I don't spend much time in marinas connected to their power and ~95% of my shore power comes from my own dock, fed by my own power installation, I feel/know this is good enough galvanic protection for my situation.
Aha, you're cheating!! ;-)

Of course, when you have the shore power under your own control, and make sure it's good now & then, you're perfectly fine.

ciao!
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Old 02-04-2010, 15:11   #54
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Also, I have a Victron Quattro inverter/charger. It has a feature called "Power Assist". This means that whenever it detects that I use more power than available from shore or genset even after it reduced battery charging to zero, it will add power by taking it from the batteries. For this purpose, it keeps it's inverter synchronized to the incoming power from shore or genset so that it can do this in a flash. It can add 3kW of power that way for a total of 6.6kW when I am at shore power or 9kW when I am on generator.
I can also adjust this feature to kick in at different power levels, like 2kW from shore. Handy when you blow a fuse ashore otherwise.
Ah, that's how you live on 3.6kw....good stuff. I have (2) 16k btu AC units, each pulls ~57A (120v) inrush (measured with Fluke inrush meter). With your setup, I could have gotten by with a much smaller genset, but instead, I have 7.6kw (more $$ & weight). Running demand is ~3.2kw aggregate for both AC units.
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Old 02-04-2010, 15:24   #55
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??? This is getting interesting.
You don't have a cat fountain? How can you go without one??!! ;-)

We have three ships cats and they like their water fresh fresh. If it's not to their liking, they will claw it in an attempt to make it suitable... which isn't really something our varnished floor appreciates.

After a year or so of research I found the solution: a cat fountain! There are several models to choose from and this is the one we have:

There's a little fountain pump in there that uses 12V AC (yes, I had hoped for DC). It came with an overheating wall-wart transformer so I installed a decent toroidal transformer instead. Water is continuously circulated and filtered and flows over the dome, coming up from the center. Perfect for a boat.

For a house I might select a different one, like this:

But that would spill water on a boat obviously. The grass is a nice optional feature, I would like that if I were a cat ;-)

Another gadget that is on it's charger is the vacuum robot... can't imagine living on a boat without one ;-)

ciao!
Nick.
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Old 02-04-2010, 15:38   #56
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Ah, that's how you live on 3.6kw....good stuff. I have (2) 16k btu AC units, each pulls ~57A (120v) inrush (measured with Fluke inrush meter). With your setup, I could have gotten by with a much smaller genset, but instead, I have 7.6kw (more $$ & weight). Running demand is ~3.2kw aggregate for both AC units.
hmmm... it's nice to have the power assist mode available but it only activates when I want to play with it; I can do without.

As I wrote before, you do not have to take inrush current into account for the IT nor for the shore power connection. You can run both 16kBTU A/C units from a single 3.6kW shore power feed just fine. Trouble only comes up with gensets and inverters.

Some more tricks to deal with surges:

- go to 240V (for US 120V boats). Surges are less at the higher voltage.
- replace the start capacitor in the device with a special soft-start one.

The first one makes more difference than I thought before I added 240V. So much so, that I didn't need the 2nd option, which is much easier to do and very (very!) effective.

cheers,
Nick.
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Old 02-04-2010, 15:39   #57
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Anodes on propshaft and adjacent to...

Have you considered placing anodes on the propshaft and on the hull adjacent to the propeller and evaluated the electrical systems used in your immediate vicinity?

I have a similar problem on Boracay, not as noticeable though, and have thought that it could have been caused by 1) anodes on propshaft falling off (don't ask), 2) insufficient hull anode protection adjacent to the propeller, 3) not using an appropriate primer system on the propeller, 4) the length of time the propeller had been exposed to adverse circumstances and/or 5) the possibility of stray current corrosion.

I tried getting voltage readings from the area around my boat using a zinc anode on the end of a wire. The results were interesting, but not conclusive.

Like you I fear a new propeller is in my future.
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Old 02-04-2010, 16:02   #58
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- go to 240V (for US 120V boats). Surges are less at the higher voltage.
- replace the start capacitor in the device with a special soft-start one.

The first one makes more difference than I thought before I added 240V. So much so, that I didn't need the 2nd option, which is much easier to do and very (very!) effective.
Some choices the PO made...like 120v ACs. Hard to throw away working systems. But, when the time comes they die, I'll make some changes.

Thanks for all the info....enlightening! I didn't know about Victron.
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Old 02-04-2010, 16:10   #59
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You don't have a cat fountain? How can you go without one??!! ;-)
Nick.
So you have a $1000 victron 3.6kw inverter to stop the cat getting fried with AC if there is a short circuit in its water bowl, sheeesh

Still good thread and for DH wind stopped its now lashing down with rain again. Tomorrows spring deck scrub is likely to be cancelled.

Pete
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Old 02-04-2010, 16:31   #60
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Some choices the PO made...like 120v ACs. Hard to throw away working systems. But, when the time comes they die, I'll make some changes.

Thanks for all the info....enlightening! I didn't know about Victron.
There is equipment that makes the change easy without any work needed on the 120V part of the installation. The wonder-unit is called an auto-transformer and is cheap and easy.

I have a thread on the complete project: From My Design to My Installation: New AC Power System

ciao!
Nick.
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