jebro

electrical problem?

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Hi everyone,

I'm new here, this is my first post and i really like this forum.

I discovered this issue when i was mucking about with my multi meter after reading stuff about batteries and isolators and so forth.

I wasn't sure if my isolator was actually working so i put multi meter across battery terminals and got 12.60Volts, i then unscrewed green knob and put black multi meter lead on other side of isolator and still got 12.60Volts. I then put black lead on hull of boat and got 12.60Volts. i put black lead on steering arm of motor and got 12.60Volts.

I disconnected cables on positive side of battery and still the same outcome. I tried disconnecting the outboard neg cable in an attempt to try and find which cable is the issue. same result, disconnected the accessories cable and still got same result

Can anybody explain what is happening. I think i have a issue somewhere but cant figure it out. I thought it might have been a worn cable but cant find anything with the wiring.

Isolator is ok

Thanks in advance for any advice or comments

 

 

boat 1 .JPG

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Hi Jebro, where does the other smaller black negative cable go ? 

That might be the issue ? 

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hi mate,

the small black cable runs to the center console. the small red one runs there too, power for lights, sounder

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Hi Jebro

When testing was the red lead from the multimeter always on the positive of the battery? If so that would explain always getting 12.6V as the multimeter is only picking up the potential difference between the two points you are testing.

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ok, i think i understand a little better now

thanks for your help

 

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Try keeping the black lead on negative of the battery and moving the red lead to different places to see what voltage you get.

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ok, i will try that, thank you very much for your help.

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No worries mate hopefully that gives you the results your after

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Jebro, in your original post you said you disconnected cables on the positive side,, I don't know which ones, but when you are testing the isolator I'd be disconnecting the smaller red and black you said goes to the centre console. Because they appear to bypass the isolator. 

It's very possible with these smaller cables that supply the centre console, that they are powering accessories that allow the reading on your multimeter to happen. 

 

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@T_Bert83 is correct that the voltmeter is measuring potential difference.  To my understanding, you cannot get a potential difference reading from your multimeter unless there is a circuit path from positive and negative back to the SAME battery.

So in your case, if you have switched off the isolator (negative in your case),  you must have another connection to the  hull from the negative somewhere. I suspect the small black lead that you said goes to the console is connected to a device that is "earthed" to the hull (maybe through the mounting screws and that is providing another path back to the negative terminal of the battery through the hull.

So your boat is negative earthed through that small black lead...and if one side of your tester is connected to the positive of the battery, anywhere you touch the hull will give you a voltage reading.

It's simple to test. Disconnect the small black lead at the battery and repeat the hull touch test you did... I am sure you will see zero reading on your multimeter.

PS - If you want to test my statement that you need a path back to the same battery, do a simple test with the multi meter and any 2 batteries (AA, AAA, 6V etc). Put the multimeter on positive of one battery and negative of another battery and you will not see a potential difference on the meter as there is no connection, no path back to the same battery.

PPS - I always fit the isolator on my positive circuit and leave the negative circuit connected. There is some debate on this, but most of it leads to isolating the positive.

Cheers Zoran

 

Edited by zmk1962
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Its effing hard to analyse a problem without being there to do our own tests.... 

Zoran is spot on...

 

 

but he is being ..................................................   'gentle'............  

"to my understanding..."                                  He knows damned well  he is correct........    and he is!!

 

 

Edited by dmck

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@dmck hahaha. Thanks for the vote of confidence.  I prefer subtle and there is always someone smarter to learn from. Just speaking from experience. 

cheers Zoran 

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thanks to everyone who had comments and advice. the knowledge you guys have is fantastic. i'm glad i found this forum.

thanks again.

cheers

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13 hours ago, jebro said:

thanks to everyone who had comments and advice. the knowledge you guys have is fantastic. i'm glad i found this forum.

thanks again.

cheers

Welcome to fishraider  @jebro 

Our community is full of people that are a wealth of information on all subjects fishing, boating and pretty much anything else!

Use the search engine to research as there are 1000's of threads and posts here. 

Look forward to your contributions :) 

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