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firecrestphil
Oct-18-2005 @ 1:48 PM                           Permalink
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Well, blow me down. After many months and much money spent trying to sort out our electrics, it turns out that the engine on our boat is positively earthed, whilst the the rest of the boat system is negatively earthed.I don't really understand the implications of this, but people who know have all gone " sharp intake of breath " in the way garage men do when they are about to tell you the cost of a job. It is going to cost me, of course, but at least everything else might start working properly at last!

They said" Don't buy a wooden one, whatever you do."

woodwose
Oct-18-2005 @ 6:41 PM                           Permalink
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Mardles sometimes
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Phil

Is this actually a problem?

I could understand it being a problem in a car with a metal body, but if your boat is GRP or wood then the electrical fittings in the boat can't have an "earth". They all need two wires.

Is your engine diesel or petrol?

Nigel

woodwose
Oct-18-2005 @ 7:59 PM                           Permalink
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Mardles sometimes
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Phil

Giving this more thought, there is a possible situation where a fault that caused a connection between a wire supplying -12V (to some domestic fitting) and the engine block could bypass the fuse. This would result in a short circuit of the battery and that would be a serious fire risk.
However, this could easily be corrected.

What actually isn't working?

Nigel
Ludham

roya
Oct-18-2005 @ 8:08 PM                           Permalink
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hi Phil
yep im with nigel on this
an alternator puts out d c at 12 or 24 volts on an engine.
now we know that d c only works one way
so i cant see the prob.
if all the red or brown live wires are
connected to the+
and the blue or black are connected to the -
it should all work.
sounds like crossed wires some where.


roya

Stranger
Oct-18-2005 @ 8:11 PM                           Permalink
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hi phil you dont say what the actual problem is m8 is it a streight wiring set up from the batterys or has someone been playing with diodes to prevent the current flowing the wrong way

have a nice day all the best Dave

Bounty
Oct-18-2005 @ 10:59 PM                           Permalink
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It's not a problem assuming the engine is designed to be positive earth. It will mean the your starter and alternator will have to be positive earth also. I have no doubt that this will add substantially to the cost of either item.

billmaxted
Oct-19-2005 @ 12:27 PM                           Permalink
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Must admit that I was not quite sure why there should be a problem. I have had a boat on the hire fleet which has always been positive earthed. The one complication is that it is the positive terminals on the batteries that are interlinked common so there is more chance of a dud one pulling them both down.

Quite normal in thses circumstances for the domestic wiring to be conventional black return and red from the fuses.

Not sure about the last point my starter and alternator are identical to all my others. It's where to other ends of the connections end up which is different.

"I should let go of the quant... Too late... We'll try and get back to you!!!"  Bill...

firecrestphil
Oct-19-2005 @ 1:35 PM                           Permalink
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And I think therein lies the rub, Bill. Apart from the off chance of an explosion, I am on my sixth battery in the last year and I have been under the impression my solar panel is no good. I have checked and there is no drain from elsewhere.I've fitted shore power so the only thing using the batteries is a water pump and the occasional light, and yet the batteries ( 2x 110 )drain over two days, including the engine battery which is not seperate. So I'm having the engine and domestic batteries isolated and the engine re-wired to make the whole thing negative. And then I'll see what happens!  Smile

They said" Don't buy a wooden one, whatever you do."

billmaxted
Oct-19-2005 @ 1:44 PM                           Permalink
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Oh Dear, Well I hope the batteries were under warrentee. where are you based?

"I should let go of the quant... Too late... We'll try and get back to you!!!"  Bill...

fendoff
Oct-19-2005 @ 2:15 PM                           Permalink
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Hi
If the batteries are being drained it must be a serious wiring problem or is it to do with electrolysis and the cathodic protection of the boat. If the propeller and shaft are wrongly bonded to the engine and electrics this can cause batteries to drain but something is corroding badly to make this happen ! The fitting of shore power and bonding can give problems as well. Definitely time to get advice from a marine electrician.

fendoff

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