Jump to content

eWOF in Wellington


Recommended Posts

Galvanic corrosion happens through DC cabling as well. If you have a galvanic isolator, then the shorepower connection wont make any difference. If you dont, I'd leave the ac ground and DC neg disconnected. However, be warned this is not compliant, and could possibly void your insurance if you had a fire.

I'm not an inspector, if you have an ewof, as a layman that's all that can be expected, and all the marinas ask for.

Its concerning though, that inspectors are signing off unsafe installs....

Link to post
Share on other sites

Completely agree about stray dc current being the biggest culprit.

I had a alloy prop shrink in size by about 2 inches over 6 months. Eventually found that someone had joined in a new bilge pump 3 inched off the pump, so the join was always wet...

 

So should I be nervous about the battery charger? It’s a pro mariner pro sport 20a triple charger, which is designed to be left running continuously apparently...

Link to post
Share on other sites

Galvanic corrosion happens through DC cabling as well. If you have a galvanic isolator, then the shorepower connection wont make any difference. If you dont, I'd leave the ac ground and DC neg disconnected. However, be warned this is not compliant, and could possibly void your insurance if you had a fire.

I'm not an inspector, if you have an ewof, as a layman that's all that can be expected, and all the marinas ask for.

Its concerning though, that inspectors are signing off unsafe installs....

It’s not just signing it off, this was a new install, done by one of the certified inspectors.

Brief was do what’s required for ewof to tun a dehumidifier and charger continously

Link to post
Share on other sites

Bilge pumps in a wet bilge are the cause of the largest percentage of stray current corrosion that I've seen. Often an internal issue in the pump, not a wiring problem.

All batt chargers can fail, but I've only seen 2 of those with issues. They were charging voltage problems , not safety.

Link to post
Share on other sites

Thanks for that island time, Am I right in undersanding in your opinion the battery charger is not a real risk in terms of adding to galvanic corrosion risk?

 

Have sorted the bilge now, no wires sitting in it, and found all the leaks so it’s dry, (ironically it’s raining here, and the house still leaks, bucket in the lounge room, but the boats dry!)

Link to post
Share on other sites

I've not actually measured the galvanic voltage with one of those on and off, without a galvanic isolator, so I dont know, sorry.

Most marine sparkies of any competence (including me :-) )will have the appropriate silver/silver chloride half cell so they can measure the galvanic protection in each case, to ensure its within specifications.

Link to post
Share on other sites

Interesting the comments on the DC not earthed to engine talk. I was going to make a comment on Matts earlier diagram showing the negative of battery banks going to a Bus Bar, when in fact, the Negative should go directly to the Engine Block and the termination point should be at the Starter itself, because that draws the greatest Current. The ALT Neg should also terminate at the starter. The DC neg Bus bar should also terminate at the Starter.
      The engine is earthed, no matter what someone says. If it wasn't, the Starter and ALT would not work. Nor any of the senders for the engine gauges would be working either.
The following is a slightly nerdy answer, but if you read it, it will make sense of the why for you.
   Why the need for a single common ground? Well this is how a "stray" voltage is created. In fact, you engine and electrical system is a circuit absolutely no different to a circuit in your TV or any electronic device. An electronic circuit in a basic description, is the manipulation of an electrical current to do work. Manipulating the Voltages in a circuit, means creating many very small currents from the main supply current. This is simply done via a resistance. A resistance in any circuit causes a Voltage difference to be created across it. That voltage can then be used to do something.
The the case of the Engine/electrical system, the resistances are the lengths of wires, the poor conductor of the engine Cast iron engine block and Salt Water.
If a conductor, lets say a sensor, is connected to the engine block at one end and the Neg from the battery is connected at the other end, what is called a "Voltage Potential" is created due to the engine block not being a fantastic conductor. Now lets consider that there could be many potential sensor connections and lets say the Battery is connected at a different point to the starter etc. Now we have all sorts of stray currents between conductors.
Taking all Earths back to one common point eliminates the various multiple currents flowing in the Engine Block.
In audio, these stray currents are called Earth Loops and result in unpleasant 50Hz hums heard from the speakers.
 

Link to post
Share on other sites

Interesting the comments on the DC not earthed to engine talk. I was going to make a comment on Matts earlier diagram showing the negative of battery banks going to a Bus Bar, when in fact, the Negative should go directly to the Engine Block and the termination point should be at the Starter itself, because that draws the greatest Current. The ALT Neg should also terminate at the starter. The DC neg Bus bar should also terminate at the Starter.

The engine is earthed, no matter what someone says. If it wasn't, the Starter and ALT would not work. Nor any of the senders for the engine gauges would be working either.

The following is a slightly nerdy answer, but if you read it, it will make sense of the why for you.

Why the need for a single common ground? Well this is how a "stray" voltage is created. In fact, you engine and electrical system is a circuit absolutely no different to a circuit in your TV or any electronic device. An electronic circuit in a basic description, is the manipulation of an electrical current to do work. Manipulating the Voltages in a circuit, means creating many very small currents from the main supply current. This is simply done via a resistance. A resistance in any circuit causes a Voltage difference to be created across it. That voltage can then be used to do something.

The the case of the Engine/electrical system, the resistances are the lengths of wires, the poor conductor of the engine Cast iron engine block and Salt Water.

If a conductor, lets say a sensor, is connected to the engine block at one end and the Neg from the battery is connected at the other end, what is called a "Voltage Potential" is created due to the engine block not being a fantastic conductor. Now lets consider that there could be many potential sensor connections and lets say the Battery is connected at a different point to the starter etc. Now we have all sorts of stray currents between conductors.

Taking all Earths back to one common point eliminates the various multiple currents flowing in the Engine Block.

In audio, these stray currents are called Earth Loops and result in unpleasant 50Hz hums heard from the speakers.

 

Wheels, a small system having the engine block as common ground is good. In a larger system, the regs say you can't have more than 4 connections on a single terminal, and it's common to use a neg bus bar as the common point, and a single good sized (normally 35mm +) cable to the block. These systems normally have a ground plate, also connected to that bus bar. This is the system required by maritime nz, for any commercial vessel.
Link to post
Share on other sites

Yes you are correct. I was simply referring to that the circuit drawing you posted earlier did not show the Neg Buss Bar connected to the Engine block. It wasn't really important for the drawing to show and hence why I didn't comment. But when a couple of comments mentioned the engine, I thought perhaps I should comment after all. Certainly nothing you have said has been wrong.

Link to post
Share on other sites

If you want to run shunts multiple loads  etc battery neg direct to block isn't practical.

You need a neg bus.

In fact, I have three, one on either side of the shunts, one for house loads.

Clarification: the neg bus on battery side of shunt could have been a terminal

but I put it in before I decided I wanted shunts. It links the two series banks,

parallelling them port/strbd. Yep, I know , not ideal.

 

Oops on the single common ground though.

Alt, starter, block all go to neg bus bar.

Will check on pd between them.

Also will do AgCl half cell test.

Thanks for the hurry up.

Link to post
Share on other sites

 

If you want to run shunts multiple loads  etc battery neg direct to block isn't practical.

You should only have three Neg cables going to the engine. One from Engine start and one from House bank and one back to Neg Bus. Engine start does not need a shunt. You only need a shunt on the House bank which is also the Neg Bus line. The shunt should be close to the Battery as possible/ practical, and no other loads should ever be between it and the Battery terminal.

Link to post
Share on other sites

You should only have three Neg cables going to the engine. One from Engine start and one from House bank and one back to Neg Bus. Engine start does not need a shunt. You only need a shunt on the House bank which is also the Neg Bus line. The shunt should be close to the Battery as possible/ practical, and no other loads should ever be between it and the Battery terminal.

I think I have only one 35/50mm2. load side of shunts. But it does go a terminal and split into three, to alt, block & starter.

I better check. I have forgotten already and it was only 5yr ago.

So I could have PD between those three depending on resistance of each connection?

Thus stray current in engine block?

Link to post
Share on other sites

The marina does not give a damn, they just want an EWOF.  You have to have an inspector willing to sign off one if these. They are just an ebox with a polarity light and ground cable, fixed to the boat as I understand it. EAL have an inspector who will do this.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...