Yet another electrics query..

phanakapan

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We have suddenly lost our domestic electrics. The batteries all seem fine, the engine and Eberspacher are wired directly in to them and both start ok.There is 12 volts plus going to all the switches in the panel for lights, pumps, fridge,radar vhf etcetc, but as soon as we try to switch anything on the voltage practically disappears and nothing works.
As you can tell from my language I know nothing whatsoever about electrics, and probably I've given far too little information here for any sort of diagnosis whatsoever, but if you have any ideas for a complete and utter novice I'd be grateful...
 

cliff

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Sounds like you have a very bad connection somewhere between the switch panel and the batteries.

You can read "12v" at the panel but as soon as you try to draw any power through the panel the voltage at the panel will drop dramatically and what ever you switched on will not work.

Check all the connections (including any fuse) in the power feed from the panel back to the batteries.
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cliff

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[ QUOTE ]
Also the earth return . . .

[/ QUOTE ]Thank you! forgot about the return lead on the neg bus - same applies - could be a very bad (high resistance) connection there /forums/images/graemlins/grin.gif

One way to check would be to run a temporary lead from Batt + to the power in on the panel and see if the problem was cured, if not run a temp lead from Batt - to the -ve bus in the panel to see if the fault is in the return (don't like the term "earth return")
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phanakapan

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Thanks guys, I'll start there.

It's funny, I am up for tackling most jobs on a boat, I've serviced/winterised engines, stripped winches, mended heads- but I'm irrationally scared and mystified by electrics. I don't understand the language and I always think I'm going to get a shock/blow something up! I wish there was a course similar to the diesel engine maintenance one, or a book that assumes the initial knowledge of a 5 year old!

Regards, Philippa
 

RobBrown

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There's also a two day marine electrics course run by Tony Brooks @ TVU Reading. I did the equivalent diesel etc maintenance course with him last year and it was excellent. I have yet to do the electric course, but hope to sometime over the winter.

site link:
http://www.tb-training.co.uk/

No connection except happy customer!
 

chas

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Do you have a wiring diagram for your boat? I see you have a M33 - judging from my experience on a similar boat, Mr Moody made exceptionally Good Boats but his electrics were Not Brilliant! It is also possible that previous owners have installed and unistalled various bits and pieces. At the risk of teaching Grandmothers, you get a large bit of paper and put all the lights, pumps and other electrical things around the edge, then trace the wiring and put all the switches, connections etc, right back to the panel(s). Then the connections from the panels to the batteries and so on. By doing this, I retrieved several yards of unused wire and all sorts of bits and pieces from equipment that was no longer present. It also helps in fault finding.
 
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[ QUOTE ]
Mr Moody made exceptionally Good Boats

[/ QUOTE ]Exceedingly, surely? /forums/images/graemlins/wink.gif
 

pampas

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I assume that you have a fuse between the battery and the domestics. if so replace it as it sounds as if the fuse has blown and is allowing a small amount of current to pass enough to measure voltage at the appliance but will not pass enough current to run it. Seen several ships put into port as their emergency generators will not power the main board,yet everthing on the main switch board appears ok. Just a thought.
 

cliff

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[ QUOTE ]
I assume that you have a fuse between the battery and the domestics. if so replace it as it sounds as if the fuse has blown and is allowing a small amount of current to pass enough to measure voltage at the appliance but will not pass enough current to run it.

[/ QUOTE ]Can you explain how you can deduce a blown fuse and not a bad connection somewhere in the power feed (or -ve return) line? I agree it sounds like a poor connection somewhere but I am puzzled as to how you can diagnose the fuse (if fitted) as being the culprit from the info given.

I had a similar problem last season and traced the feed line - turned out to be the connection between the feed line and the +ve bus.
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DaveS

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I think the point at issue is the fundamental difference between (a) guessing a part that may be faulty and changing that, then if the guess was wrong thinking of another possible failure candidate and changing that, etc. and (b) systematically tracing the fault using a meter until it is unambiguously located, then fixing it.
 

pampas

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I have had quite a bit of practical experience in the electrical field, and was suggesting to some one, with a problem a very important component to check if this item is included in the system. A meter on a voltage range will not find the type of fault that I described I also did not suggest that interchanging of compoments was nessecary other than the fuse, I respectfully suggest that you reread my post AGAIN.
 

DaveS

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[ QUOTE ]
A meter on a voltage range will not find the type of fault that I described

[/ QUOTE ]

Really? Going back to the OP's fault description, he obviously has a high resistance fault somewhere, in that as soon as he tries to draw current the voltage collapses. You describe a similar situation. In either case, with load switched on, a few minutes spent intelligently poking about with a voltmeter (and maybe a length of wire to extend your reach) should establish where the "missing" voltage has gone. Find that and you have located the problem.
 
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